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Do you think this would be practical overall? It would gain a lot of pushing power and speed but I feel like I would see more people oversizing drive components if it was worth doing. I'm sure I can make everything fit, but figured I should ask before I buy any components. Thanks! [Logan, Utah]
A: Mark J. You are wise to note that oversize drive motors are not commonly encountered. If big motors gain an edge in pushing power, why isn't everyone using them? If speed is a sure path to victory, why are chunky brushless drive motors so rare?
Pushing Power - See Ask Aaron: Optimizing Drivetrains.
Q: Hey, Oversized ant drive guy here again, good call on the traction, I hadn't considered it. However, I have thought of one more point.
Since spinning weapons get more bite the faster they charge at something, would it be practical in that way to increase drive speed? Most of my successful robots have essentially been fast glass cannons that rely on outmaneuvering and ending the fight without taking damage. In this way, would it be wise to have an oversize drive to allow for faster retreats and a hit and run style strategy? Or perhaps just the antweight size brushless drive options?
I've mostly used the repeat brushed mk2's, but do have a set of mk3 mini brushless motors on hand. The brushless seem to not perform as well, but it might be due to them being paired to some of the very first brushless drive esc's that were released.
Thanks as always for the knowledgeable perspectives!
A: Brushless motors are only as good as the controller firmware and setup. Trying to control them with ESCs not perfectly matched to their requirements will yield very poor results. I like brushed drive motors because they're stupid simple to set up.
As mentioned in the post above, acceleration force is also traction limited. All torque above the physical traction limit will simply set the wheels free-spinning without adding to acceleration. More power won't give you as much improved performance as you think, and the effect on robot control can be catastrophic. The Tentacle Drivetrain Calculator takes this traction limit into account when modeling robot performance, so let's use it to compare the performance of two ants powered by normal and oversized motors.
The robots are two-wheel drive with 2" diameter wheels and 3S LiPo batteries. The only difference is that one is powered by the familiar Repeat Drive Brushed Mk2 ant motors while the other is powered by the more-than-twice as powerful Repeat Compact Brushed motors. Both are modeled for a 6-foot sprint across the arena floor:
For the six-foot sprint, the 115% power increase results in:
I'm trying to figure out how to set up the electronics for fairly cheap and it sounds like a good start is a dual brushed ESC with two high ratio n20's but n20 motors say they are rated for 6v so is the 7.4v-8.4v of a 2s too much for them? I know there are better motors but I don't feel comfortable buying multiple $20 motors without a bit more understanding and I'm pretty sure a BEC can't provide enough current for running a whole bot.
I already have a Flysky controller and receiver, so I only need a power switch, esc, and motors. I thought that the most economical solution would be a Fingertech switch ($7), Repeat Electronics 'Budget Ant DESC' ($15), but then got stuck at the motors since the cheapest reliable motors I saw were $20 a pop which felt like a lot since I'd probably need three for the drive and hammer, can I just buy a few pairs of cheap n20's for $5 each and not have to worry about them failing immediately?
And for the hammer I'm going to canibalize a cheap servo that I already have, then throw some extra mosfets on it to run a snail cam that can safely charge and discharge the hammer; so I don't need an esc for the weapon motor.
A: Mark J. So, for your first 'bot you've decided to build a plastic ant shuffler with a pair of the cheapest N20 motors you can find on a mild voltage boost dragging around a cam-and-spring hammer weapon controlled by a cannibalized cheap servo board with extra MOSFETs. I wonder why you're feeling overwhelmed?
You've already rejected my standard advice on what a first robot should be, ignored my detailed list of reasons for that advice, and dismissed my opinion on cheap robot parts. I wonder what value you might place on my advice to the questions you now ask, particularly if I tell you something else you don't want to hear. Let's find out...
A: Mark J. Just to make things complicated, the NHRL has a 'cube rule' for dimensions:
A: Mark J. What is it that is done to arrange words into a beautiful sonnet? There is no one thing done to enable precision control and pushing power on a two-wheeled 'bot -- there is a long list, and you have to get everything on that list right. Here is part of that list:
A: Mark J. See Frequently Asked Questions #2. Read the rest of the FAQ while you're there.
A: Mark J. The axle has torque, the wheel has pushing force.
Example:
Example:
The ratio of the pulleys is the same as the ratio of the wheel diameters. Here is an example calculation for 2.5" diameter rear wheels and 1.5" diameter front wheels with a 30 tooth pulley on the rear:
Teeth on Front Sprocket = 30 Teeth × 1.5" ÷ 2.5" = 30 Teeth × 0.6 = 18 Teeth
A: Mark J. The top pole is an extension of the non-spinning weapon axle. The images below show 'Megabyte' with and without the weapon shell mounted.
A: Mark J. Prescient of you, Icey. I was just about to post the question below when your shufflebot animation arrived. If you're going to continue working with gif animation you'll want to know about Ezgif.com. Using this site I was able to edit your animation (remove excess frames, increase use of transparency, crop, shrink, change the frame rate, and gif optimize) to reduce its size from 105K down to 18K. You can also add text and rotate the gif. Very handy.
I've worked on this robot for nearly 2 months now prototyping and testing the shuffler drive to work well. One of the main things I'd love to work more on is the shufflers, and specifically trying to improve the linear drive speed. While it's not slow, it's nowhere near the top speed of many other robots (including some other shuffler robots). Most of the dimensions currently present are either just assumed to be reasonable values or found through some testing.
I've done my best to work on figuring out the mechanics and math behind the cam system, including trying to find resources online, but it's been frustrating since there appears to be very little available for what I'm attempting to optimize here (lateral speed of the foot, primarily), since the slotted single cam mechanism appears to be used for very different applications in industry. Searching through the Ask Aaron archives yields extremely little regarding shuffler information so I thought I might as well ask if you had any sort of knowledge to start more work off of. I am currently using Repeat Compacts for the drive running at 4S, but I may look towards better motors in the future.
Thanks for your help. Your site has assisted me an extraordinary amount over the past couple of months while I am learning more about combat robotics.
Ryan D.
'Faraday' appears to be a near-perfect copy of Monkfish and their 'pinned slot' shuffle variant which decreases the wasteful 'lift' phase of the cycle and extends the lateral motion, but other builders have further improved on this design. Take a look at at the article Experimentation in Shufflers by Absolute Chaos Robotics for an up-to-date review of shuffle design evolution. This short video of Jamison Go explaining a few points on the Silent X shuffledrive may give you some ideas.
it's been fully printed out, and in testing, I give it the throttle and..... it flips over
I reverse, trying to flip over again, and it doesn't. why is this the case?
A: Mark J. I'm having a hard time imagining that your fully assembled 'bot with that heavy direct-drive weapon hanging out in front is flipping over at all. Perhaps the center of gravity is so high that it is causing trouble.
I have previously directed you to Section 2.2.7 of the RioBotz Combot Tutorial for their formula to optimize weight distribution for best traction for a two-wheeled 'bot while keeping the nose down. That should apply in either direction. Some thoughts:
Reply: Thanks for the advice! Turns out it's the screwheads, they are just long enough to keep us from flipping back over. Our competition is this weekend, but after that I'll definitely try some of those suggestions! Unfortunately, magnets are a no-go with the non-metallic floor arenas that are popular here.
A: Mark J. I don't believe that double-hinged wedges as sometimes seen on multiple competitors are intended to directly win 'the ground game'. I believe their purpose is to allow specific wedgelet designs to glide more easily over imperfections in the arena floor while still presenting a ground game to match their opponents. The technique may be particularly useful on invertible 'bots.
A: Mark J. Mathematically:
While we're on the subject, was Run Away! the last combat robot to use car-steering?
A: Mark J. Realtively few combat robots have used automotive-style 'pivot steering', but many fans are surprised to hear that Combat Robot Hall of Fame members 'KillerHurtz' and 'The Judge v1.0' had steered front wheels. Stability in a straight-line and the ability to hold a smooth turn radius remain good reasons to consider the design, although the development of solid-state gyro controllers has brought similar control to skid-steer 'bots.
A: Mark J. When you have built and competed with your wedge you will better understand:
A: Mark J. I can think of several more embarrassing ways to lose a match, but I won't list them here. From the manufacturer's website:
Q: Also, sorry for my recent posts not being very Ask-Aaron-Mission-Statement-ey™. I got a "little" (put "little" in a slanted font) carried away, but I'll do better from now on.
A: Not a problem. I enjoy your posts, Icey. I also enjoy popcorn, but when there is so much popcorn that I can't find the TV remote I have to sweep the popcorn into the special popcorn room.
Q: But I do have one favor to ask before I go. Could you please change all mentions of the word {something incomprehendibly random} on this and my previous post to something incomprehendibly random? : )
A: I told my fave AI to globally replace {something incomprehensibly random} with {something incomprehensibly random} but it apparently found all of runamok.tech to be {something incomprehensibly random} and I had to restore the site from a backup tape I keep down in Deep 13. Unfortunately I can no longer remember what word I was replacing with {something incomprehensibly random} as it was replaced by {something incomprehensibly random}. Sorry.
A: Mark J. I don't have anything specifically from Team Drillzilla, but there are multiple shufflebot resources on the web.
A: Mark J. UHMW polyethylene takes wood screw threads well and loses very little strength if you take care when re-inserting the screws and don't over-tighten. Assuming that you drilled a proper pilot hole (~3/32") into the UHMW for the #6 wood screws and the 1/2" length is long enough to bite well into the plastic support you can reset the screws dozens of times and the mounting will remain strong.
If the plastic the screws thread into is worryingly thin you can switch to machine screws with a small 'rivnut' (pictured) inserted from the back side and never worry.
A: Mark J. Section 2.4.3 of the venerable RioBotz Combat Tutorial sets out the 30-30-25-15 Rule as general guidance for allocating weight:
A: Mark J. Trot over to your local Ace Hardware store and buy a length of K&S 1/2 inch OD brass tubing. The wall thickness is 0.014" which makes the inner diameter 0.500 - 0.014 - 0.014 = 0.472 inch.
Cut the tube to length, press the bearing into place, insert into your UHMW chassis hole, and remember to measure next time.
Hope you could settle an argument for me.
Suppose you had a lead screw you wanted to power with some sort of motor for a lifter mechanism in a robot. What would the optimal configuration be for the layout to maximise the force transmitted to the lead screw? In this scenario, there are 2 options (See attached image):
All the best. [Manchester, England]
A: Mark J. Pleased to help, Manchester. Just to clarify,
The 'other party' is correct that the advantage of one sprocket is cancelled by the the disadvantage of the other sprocket in Option 2 -- but if I'm being picky (and I am picky when a pint hangs in the balance) Option 1 and Option 2 do not transmit the same overall force.
A: Mark J. From T.i. Robotics Designing Around the Gyroscopic Effect:
One thing I noticed at the event was that my driving was a little subpar, I was able to survive but I struggled to stay aggressive, I wasn't comfortable enough with my own robot to be able to confidently get hits, even in fights I was winning. I spent quite a bit of time driving the thing around but was still struggling to control it properly.
My question for you is, do you have any tips for getting more comfortable in driving? Obviously I understand that nothing beats actual time in the box but I would like to know if there is a good way for me to prepare and familiarize myself with my own robot better.
Thanks! [Worcester, Massachusetts]
P.S. -- I've been working on a new custom bot which (if parts come in on time) I'm hoping to have built by around mid December, giving me time to prepare for the NHRL January New Bots event. The thing is essentially a custom Peter Bar kit running brushed drive and 2 ar500 weapon bars.
A: Mark J. Welcome back, Team Stamina.
A common answer: "They aren't. Their robots are set up better than yours."
Thank you
A: Mark J. Most of the equations used by the 'Team Tentacle Drivetrain Calculator' to calculate drivetrain performance may be found in our Ask Aaron: Optimizing Drivetrains page.
For equations not discussed on the 'Optimizing Drivetrains' page you can right-click on the Drivetrain Calculator window, select 'View page source', and scroll down thru the code to view the equations as written in javascript. Example code:
motorAmps = motorTorque / document.forms[0].Kt.value;
totalAmps = document.forms[0].MotorsPerSide.value * 2 * motorAmps;
imax = document.forms[0].stall.value;
ah3min = totalAmps * (document.forms[0].PctPeak.value / 100) * (3 / 60);
ah5min = totalAmps * (document.forms[0].PctPeak.value / 100) * (5 / 60);
Oh, and say "Hi" to Mike the Tiger for me.
A: Mark J. 'Team Small Robots' has an excellent and entirely complete five-part video on using the very popular -- and free for personal use -- Fusion 360 CAD software to design a combat robot: How to Use Fusion 360 to Design a Combat Robot.
A: Mark J. From Frequently Asked Questions #8:
A: Mark J. Threaded inserts in hard plastics are OK but in soft plastics like HDPE or UHMW polyethylene they are - as you have discovered - sub-optimal. The grip obtained in a soft plastic by heat-set, self-tapping, or press-in inserts just won't handle high-load impacts -- the plastic has too much flex.
I have three options for you:
A: Mark J. 'Beta' does not lose matches against vertical spinners because of the 'Ugly / Mullet' armor -- they lose in spite of switching out their impressive wedge for the specialized armor. From the 'Beta - Fighting Robot' Facebook page:
A: Mark J. "Optimal" is hard to define. Some weapon types work best with a specific number of wheels, and some wheel lay-outs work better in some weight ranges. Some considerations:
My question is what sort of motor should I use to power the weapon and what mounting orientation should that motor have? I've already chosen a mounting position and a motor in the example photo. If you think that the motor and mounting positioning I've already chosen will work well then I'll keep going in this direction but any advice on how to mount it securely as possible would still be appreciated. Thanks so much in advance. [Lexington, Kentucky]
A: Mark J. Calculating the required torque for this type of 'flipper' is a bit complicated as the geometry of the mechanism is dragging your opponent's tire(s) sideways while lifting the mass and tilting itself backwards. Assuming that this is an antweight, some back-of-envelope calculations indicate that a motor with 128 in-oz of torque could perform the task without bogging down. Your selected motor delivers twice that torque so should be fine from a power standpoint.
The motor position as shown in the render seems fine, although you do not show how you plan to transfer power to the weapon shaft. Perhaps by a timing belt? The weapon shaft itself will be exposed to high loads from impact and should be supported on bearings where it passes through the front and rear of the chassis. The gearmotor itself is somewhat isolated from heavy impact and may be mounted to the chassis with the goBILDA mounting plate.
The Bad News: Scroll down the page to the Pop a Sick Wheelie post. Your design will flip the weapon over to the back of the 'bot as soon as you apply forward drive power. Adding springy trailing arms to prevent a flip-over will prevent a full flip but will still allow the weapon to lift a bit on acceleration and make it very tough to 'get under' your opponent.
More Bad News: Have you considered how much time you will spend blipping the weapon motor to rotate the fork into just the right position for an attack? You're going to be busy enough driving the 'bot to worry about such details. I don't think your design is workable.
Regarding 'Orienting a Fork', I believe I might be able to offer some first-hand input to this sort of design - I ran 'Grapple Turnover' (image at right) at Beetleweight over in the UK - it's not a super competitive sort of design, unfortunately, but it is fun to try and use. As you point out, blipping the weapon to the right position for an attack is a pain, but it's a little less of a pain than you'd imagine, particularly if Lexington intends on running a single point of contact at the front - single point of contact is pretty much the ideal, and it's where I'm moving to with the Grapple Turnover redesign.
As you point out in your answer, a belt is pretty much the ideal here for torque transfer. On Grapple Turnover I ran an 8mm shoulder bolt as the weapon deadshaft, cantilevered through about 20mm of HDPE (note, I'm of the understanding that UK HDPE is comparable to US UHMW and US HDPE is garbage, so I guess read UHMWPE where I write HDPE). If I were to do it again, I'd probably add some sort of aluminium insert to prevent the hole rounding out. Oilite bushings work well for keeping the weapon turning and are a bit more robust than ball bearings for the sorts of loads this kind of weapon can take when tackling spinners.
Something to prevent wheelies is a must, as you note.
My main concern looking at the render is there is a lack of width (shocking, I know). You need the robot to be REALLY wide to make sure you're always winning the leverage battle when trying to turn over an awkward shaped opponent. Outriggers are good for this - Grapple Turnover was about 600mm wide with its outriggers on, and worked a lot better than when I tried it without them.
I'm not sure if any of this helps - hopefully it does! Horizontal lifters are tough and uncompetitive, but they are workable and they're good fun once you get the geometry right. I've been toying with the idea of bevel gears and greedy snake mechanisms for a sort of 'grab and twist motion' for the sake of weapon effectiveness (a losing battle!), but that's for the future.
As a final aside, Lexington may enjoy checking out Daniel Kerrison's 'Agitator' - a 150g bot that originated (to my knowledge) the concept. [Oxford, England]
A: Mark J. Thank you, Oxford! It's always a plus to hear from builders that have direct experience with an unusual robot design. I appreciate the breadth of your comments and I'm sure Lexington will benefit.
A: Mark J. Magnet downforce adds virtual weight to the drive wheels but does not add corresponding mass, so there are multiple inputs involved in simulating the effect on performance. I have a spreadsheet that I use to modify calculator input values to simulate downforce before entering them into the calculator, but it's a little clunky:
The in-calculator 'Help button' has been updated with this description:
Magnet downforce will improve pushing power and acceleration, but will cause greater current consumption by the drive motors and require greater ESC and battery capacity. The calculator will show the changes in performance and capacity.
Team Tentacle Drivetrain Calculator: Brushless
Looking for help with magnet selection? See the Magnetic Downforce Calculator.
JavaScript debugging is not my long suit, so I called in Rodger the Web Gerbil and he found it in a flash. Rodger is refusing to divulge the details, but from the wry smile on his face I'm assuming I simply failed to properly define a passed variable. Rodger got his cracker and we have a working tool -- case closed.
A: Mark J. The Team Da Vinci Robotics Understanding Pneumatics page provides a detailed overview of combat robot pneumatic systems that may be useful to your project. I will reprint their disclaimer warning here for emphasis:
Also, about what angle and other geometric considerations should we go with to deflect and control horizontal spinners? We are likely to use an 1/8 or 1/4 in welded wedge made from either grade 5 titanium or ar400 because we found out the hard way that bending Ti is hard. [Urbana, Illinois]
A: Mark J. As you have specifically mentioned combating horizontal spinners I will assume that you either have a different wedge configuration for vertical spinners or do not consider them to be a problem. My comments will apply to designs intended to deflect and control horizontals.
Wedge mounting options are problematic:
Yes, bending grade 5 titanium is a pain. Cold bending AR400 should be done transverse to the rolling direction with a minimum radius of three times the plate thickness.
Don't forget to pre-heat your AR400 before welding to reduce embrittlement in the weld area. Pre-heating to 200 F will suffice for thin plate.
A: Mark J. You've performed an entirely correct static analysis of the force holding the nose of the robot down. However, calculation of the forces that go into countering that force to raise the nose off the ground when the robot is in motion requires dynamic analysis. It is technically not the torque at the rear wheels that determines if the robot will 'wheelie' but rather the traction-limited acceleration that torque can produce. The formula to determine the required acceleration (g) at which the force holding the nose of the robot down is exactly offset is very simple:
Example In your diagram the distance of the center of mass ahead of the rear axle ("L") is roughly twice as great as the height of the center of mass above the floor ("H") which makes the required acceleration:
The requred acceleration exceeds practical levels -- the nose of the robot will not rise.
NOTE 2 Yes, magnet wheels on a steel arena floor combined with gobs of drive power can give you acceleration well above 1.0 g, but magnets are beyond the scope of this question.
A more detailed examination of wheelie physics is available at PHYSCLIPS.
A: Mark J. Since you didn't tell me anything about your current wedge I'm unable to suggest specific improvements. In general, playing the 'lowest wedge' game can be frustrating.
A: Mark J. If you're accessing the Ask Aaron main page or one of the archives from a laptop/desktop computer, over in the left margin of the screen is a lovely set of eleven colorful icons. Mobile devices may not display those icons in the archives, but will display a full set just below the page header in the
A: Mark J. No Your wedge will most frequently engage unpowered sections of your opponent that you will want to slide upward into your spinner as freely as possible. Leave your wedge smooth and slick and rely on your bot's forward speed to propel the target up the wedge and into your weapon.
A hard and slick wedge is also a better defense against spinner weapons; you don't want their weapon to get a grip on your wedge.
A: Mark J. This may help: Traction Magnet Calculator.
A: Mark J. The 'rule of thumb' for best pushing power without lifting the nose of a two-wheeled robot is to place about 65% of the weight of the 'bot on the wheels with the rest on the front contact point with the arena. Measure the weight on the front of your 'bot and move components forward to get ~1/3 of the weight on the nose. Test to confirm that the front stays down on acceleration.
A more complete engineering explanation involving the height of the robot's center of gravity and the coefficient of friction between the tires and the arena surface can be found on page 46 of the RioBotz Combat Tutorial.
Another concern of mine is that, according to my calculations, my 'bot's top speed will be just over 1mph, which seems a bit slow. Is it possible to be competitive with this speed?
Finally, my last question is regarding batteries. If two different brands of lipo batteries have the same specs, is there any difference in performance (e.g. Galaxy vs. NanoTech)?
Thanks. [Isolated from Competition in New England]
A: Mark J. Building a wedge for your first 'bot is a fine plan. Your questions, by the numbers:
1) Two-wheeled antweight wedges can be quite competitive. Wedgebots based on the FingerTech Viper kit have done quite well. A few notes:
2) At 1 MPH everyone's going to be quicker than Gaston. A whole lot quicker. An adequate ant speed is around 4 MPH, reaching that speed in about 4 feet. Many ants are MUCH quicker.
3) For the purposes of a simple ant wedge you need not worry about differences between LiPoly brands or flavors. Select something with a connector compatible with your charger and robot wiring harness. A 300 mAh pack should be adequate for Gaston.
A: Mark J. The Servo City motors you have selected are sized correctly for 3-pound 'beetleweight' robots. They are very heavy for an antweight (over 3-ounces each) and offer no performance advantages over commonly used ant motors.
The FingerTech motors I recommended are commonly used in antweight robots for good reasons:
Your new design presents new problems. The smaller wheels mean that Gaston will be completely stuck when (not if) flipped over onto its back. The forward placement of the wheels also creates the possibility of Gaston being stuck upright balanced on the rear panel (this WILL happen). Switching to the smaller gearmotors will save you 4 ounces of weight -- put that to use.
I was recently watching Terra Engineering (creator of Triple Crown bot)'s youtube channel and saw an anti-vert module he made for a vertical spinner like Endgame. I can't wrap my mind around how it works or what it may do and was wondering if you had any thoughts.
Thanks, Neil! [Tukwila, Washington]
A: Mark J. I have great respect for Todd Mendenhall of Terra Engineering. Todd is a world-class engineer who dominated multiple combat robotics venues in the 2000's. His 'Panzer' robot series has gained full membership in the Combat Robot Hall of Fame.
Todd has been out of competition for a couple of decades and has re-entered the arena on what he freely admits is an experimental basis. A number of the features on 'Triple Crown' are exotic, conjectural, and un-tested. His 'anti-vert' module (video) is all that.
Q: Bonus question if you have time: his robot also uses wire rope isolators which seem novel - any idea of ways those could be put to use in a 250 pound bot?
A: Terra Engineering had a bunch of those wire rope isolators in their shop. I've got a box of them as well. They decided to see what use they might be, in spite of known problems with their use in combat robots:
Reply: Mark J. Thank you, Team Geronimo. I'll keep your extensive and detailed comparison of spinner types on file, but I want to share your "Main Takeaway of Combat Robot Designs" today because:
- Team Geronimo
A: Mark J. I have known builders who took their heavyweight robots up onto the roofs of their homes and threw them off onto concrete driveways -- repeatedly and at all angles. While this may or may not be effective at uncovering weakness, it is not a common practice as most builders like to show up at an event with a pretty robot. Anything with enough impact energy to properly test is gonna leave a mark, and by the time you hit your 'bot from all possible angles you're not gonna have much of a robot left.
Get your robot out and fight. Creating a great robot is an iterative process: build, fight, evaluate, improve, repeat. Take a look at Jamison Go's blog post on the evolution of his Hall of Fame beetle 'Silent Spring' for some of his tips on testing and improvement.
I'll leave you with a quote from Team Juggerbot:
A: Mark J. Who wants dibs on the name "Antisocial Distancing"?
Update: The name has been claimed. Absolute Chaos Robotics has taken "Antisocial Distancing" as the name for their new hobbyweight.
A: Mark J. Not a dumb question at all. An option popular with small robot builders is FingerTech NutStrip.
See also: How to use NutStrip.
A: Mark J. They left out a few arrows.
Mouse-over or 'tap' the image to see if my version makes more sense to you...
The force of the disk being rapidly brought up to speed in one direction understandably causes the rest of the bot to counter-rotate, but for reasons I don't yet grasp it will sometimes also causes it to tilt on another axis at the same time. This has the undesirable effect of causing the blade to strike the ground and send myself flying.
You can see it near the start of this video (recommend setting to 0.25x playback speed) with another good example at 62 seconds.
What would be behind this undesirable tilt, and what could be done to combat it? [Newark, Delaware]
A: Mark J. It looks like 'Someone Else's Problem' turned out to be your problem after all.
For those unfamiliar with spinner gyroscopic forces:
My theory is easy to test. Add an ounce or two of lead weight to the top of the weapon axle support and try it out in a safe test box. The weight will both raise the front mass center and apply extra weight to the weapon skid. If this reduces the problem we're on the right track.
A solution? Aside from a complete re-design, you could try an R/C gyro to reduce the counter-rotation at weapon spin-up. You could also dial back on the weapon speed.
Q: I'm so used to thinking about gyroscopic forces in combat robots that I completely forgot to think about centrifugal forces as a possible issue. This also helps to explain seeing the nose rise when spinning while right side up, while it looks like the rear rises when spinning up while inverted.
Your assumptions about the mass placement are pretty spot on. The center of mass of the front half (front end of pink line) is indeed lower than the center of mass of the back half (not pictured, but level with the axles).
In my similarly designed 3lb bot I have a BLHeli_32 ESC that I have recently adjusted the settings to limit the disk acceleration in hopes of combating these issues, but I have not had much chance to test it yet. My older 1lb ESC does not have this acceleration damping capability, so it looks like I may need to look into upgrading to a newer ESC to slow down the spin-up on my 1lb as well.
Luckily as a short term solution my receiver already includes a gyro, so I guess I need to look into using that with my current transmitter based mixing and dealing with shutting it off if I go inverted.
As a long term solution, it sounds like I may benefit from actually moving the wheels back and farther behind the center of mass? (in order to put more weight on the front and decrease the rise)
A: Yes, your render confirms my assumptions and tells the story. It looks like you have about 75% of the robot's weight on the wheels, which is likely too much for stability of the weapon. Some experimentation with weighting the nose on your current chassis should supply guidance on how much rearward wheel displacement is needed.
Thanks in advance for any pointers and advice! [Schaumburg, Illinois]
A: Mark J. What you are proposing for your weapon is not a hubmotor. A hubmotor is embedded inside the device it is powering, like the vertical spinner weapon on 'Algos', or the simple Fingertech clamping drum weapon. Your design hangs a large spinning mass off the far end of the weapon motor, where a weapon impact will act with a large lever advantage on the bearing tube support at the base of the motor. This effectively guarantees structural failure of the weapon motor. Reconsider
A conical washer nut is tempting for the reasons you mention, but if does start to loosen it has progressively less locking force to prevent further loosening. Add a drop of threadlocking fluid (Loctite) for extra security. If you need to service the weapon during an event a fresh drop of threadlocker won't have time to properly set, so keep some of the nyloc nuts as supplied with the motor handy in your spares, along with some conventional 12mm washers. Don't use threadlocker with nyloc nuts -- Loctite destroys the nylon.
I'll also point out that you are relying on compression by the retaining nut to both hold the weapon drumette in place and prevent it from rotating relative to the motor. Better design would have the drumette located to the top of the motor with hardened pins, or have the motor shaft and drumette keyed to prevent rotation even if the nut is a bit loose -- but 'iffy' design of this type is common in insect class 'bots. Keep your fingers crossed and check tightness before every match.
A: Setting a bearing so close to an existing bushing requires very close tolerances to avoid binding -- even a couple thousandths of an inch can cause trouble. You will also gain little additional strength from a second support immediately adjacent to the first. A more effective solution would be to shock-mount the gearmotors themselves. I wouldn't bother with a second support bearing.
A: A vertical thwack can have a heavy weapon hanging out the front -- if it is counter-weighted by mass behind the axle line. You may note that 'Starchild' has the drive motors mounted as far forward in the chassis as possible, leaving room behind the motors for batteries and electronics to partially offset the weapon weight. Think of it as a seesaw at the playground; some weight on one side helps lift the weight on the other. Assuming that you are planning to use the prototypical large diameter wheels on your thwack, there is plenty of room to shift some weight well to the rear. Move those drive motors all the way to the front of the chassis and extend rearward to get the center of mass closer to the axle line. Moving the weapon motor back into the chassis and belt-driving the spinner would certainly help as well.
I think you can make this work, but if you'd be more comfortable with a conventional vert spinner I certainly won't try to talk you out of it.
A: Mark J. The RBCRT is a fine document to study after you've built a couple of robots and want to invoke engineering principles to refine weak elements in your designs. Unless you have a strong engineering bent it is not where you should start. Read some build logs, view Robert Cowan's YouTube videos, drop in on some events for the weight class you plan to build and talk with successful builders.
Response: Thanks! This is really helpful advice.
A: Mark J. Maybe something like this?
A: Mark J. They might call it 'braced', but I'd call it 'trapped'. Two options:
A: Mark J. You may be surprised, Kansas City. I know multiple veteran teams that DO use hard endstops and DO manually cut power at the ends of travel. More parts equals more failure points, and a failed limit switch can disable a weapon just as effectively as having your opponent rip it off. Simple is good.
I asked the teams you mentioned for details on their weapon arms and got these responses:
Zachary Lytle writes: "[Skorpios] is far less complicated than you might expect. We believe the fewer things you have in the robot to break the better. So the arm is just clutched and it's Diana's job to turn the motor off before it fries."
A: Mark J. Those are questions I can't answer. Your choice of materials depends on your skills, your experience, and your resources:
I've gone everywhere from antweight clamps like 'King Googly' to overengineered monstrosities like 'Saturn' and most recently, an antweight version of 'Black and Blue' (render attached). Alas, after I get the CAD complete I still find myself dissatisfied, leading to a redesign from the ground up, then disliking something about that, and the whole process keeps happening. I don't know if other people have a similar problem. Is there any advice you can give on what I should do? What am I doing wrong? [Aurora, Illinois]
A: Mark J. Yes, other people have similar problems. It's called procrastination, but putting a title on it won't solve the issue. 'Psychology Today' has a list of 11 Ways to Overcome Procrastination that you might like to read thru. The one that may best fit your description is #11:
Perfectionism is an all-or-nothing mentality: Something is either perfect, or it is a failure. People with perfectionistic tendencies tend to wait until things are perfect in order to proceed—so, if it's not perfect, you cannot be finished. Or if it is not the perfect time, you believe you can't start. This all-or-nothing mentality can hold you back from starting or completing tasks.
Instead, focus on being better than perfect. This means to still strive for excellence, creating excellence, or setting yourself up with excellent conditions, but at the same time, you focus on getting the job done. #DoneIsBetterThanPerfect
A: Mark J. It would have helped if you had mentioned the 'one site' that you found so that I could avoid the work of duplicating your effort.
Back to your question Many builders maintain 'build logs' of their robots with many pictures and a discussion of the design elements. A couple to get you started:
Thanks for keeping the site going, our team has been following your infinite wisdom for some time now.
A: Mark J. Thanks for not putting "infinite wisdom" in quotes to mark it as ironic.
There's a difference between building a 'bot to do generally well and building a 'bot to win a specific tournament. For example, you mentioned Norwalk Havoc which has a number of unusual rules and conditions that would need to be taken into account:
Q: Hi Mark. Question following on from the recent one from Akron, Ohio. You mentioned a anti-backout lip on a dustpan. Would this count as a pin if the other robot couldn't escape due to the lip? The dustpan can't really "disengage" as it were.
A: Exactly what counts as a 'pin' is something of a situational judgment. Ultimately the decision on what is and is not a 'pin' resides with the event organizer, but in genneral a 'pin' is described as one 'bot actively restricting the motion of another.
For my antweight, I'm planning to use a 6061 or 7075 aluminum (cost/weight considerations) mounted to a 3D Printed nylon base wedge. I'd like to get some clarification on what would be a good starting points for µb for this calculation for 6061/7075? Is there a good way to figure out the µb for a given material without using approximations? On the same note, lapping and polishing the aluminum to say a mirror polish would help reduce µb right? [Arlington, Virginia]
A: Mark J. I'm glad to see that you've been studying the RioBotz tutorial, but there are a few odd things about the RBT you should know:
The rule they neglected to include is: Your wedge should be at least as hard as the impactor striking it.
I saw camber was discussed in relation to Donald Hutson's designs in the archive, but haven't seen anything on toe in/toe out. [Arlington, Virginia]
A: Mark J. A crossover question! I know a bit about automotive suspension design from my involvement with vintage British race cars: my hobby car.
Combat robots do not turn like cars.
A: Mark J. Talk to the printers on the Facebook Robot Combat group. The group is your best source for up-to-date information on 3D printers for use in combat robotics. Factors like price, bed size, and the ability to print specific filament types are common discussion topics. Printers given high marks by the group include, in no particular order:
A: Mark J. Another school assignment, Brighton?
See Next Post Down!
You're welcome to use the Ask Aaron archives for your homework, but I'm not going to write essays for every schoolboy in southern England.
A: Mark J. What's going on? Scan down the page and read the last few questions. I'm seeing a theme here...
The short answers to your questions are:
what is the best type of wheels for a small robot and which material is best? [Brighton, England]
A: You've given me very little information about your robot. You mention that it is 'small', has two motors, is 4-wheel drive, and requires 0.2 Nm (28 in-oz) of torque per wheel. That is not enough information to answer to your questions. The Hamburger is Bad.
Once you have determined your actual torque, speed, and voltage requirements you can look thru gearmotors at on-line robot suppliers in your country -- like 'Robotshop'. A quick search there found a 12V 970RPM Econ Metal Gearmotor that may meet your requirements and budget.
About wheels and tires: There is no single 'best' wheel/tire type. How 'small' is your robot? What type of surface does the arena floor have? How important is traction versus durability? Will the wheels be exposed to direct weapon impacts or are the wheels protected by armor?
There are dozens of posts on wheel and tire selection in the Ask Aaron Materials and Components archive, and for very small robots there are additional posts in the Ants, Beetles, and Fairies archive. Search there for guidance on wheel/tire selection.
A: Mark J. I can't teach you Mechanical Engineering in a few paragraphs, Edgware -- but I do have a collection of on-line tools and Excel spreadsheets here at runamok.tech that can help with your design calculations:
What weapons are most effective in robot combat? The answer may surprise you: What Weapons Win?
A: Mark J. There is no single 'right' wheel radius for a robot of a given weight. For a specific motor and weight, the correct drive train will be a function of wheel radius and gear ratio: larger wheels require greater gear reduction, smaller wheels require less gear reduction. See the post immediately below for links to equations and tools to select the correct combination of motor, gearing, and wheel radius.
A: Mark J. I've got a whole webpage on that topic, Brighton: Optimizing Combat Robot Drivetrains.
Once you have the theory down you can automate the selection of drive motors and gear ratios with the on-line Tentacle Drivetrain Calculator.
If you have trouble with the Tentacle Calculator, I have a step-by-step Example Drivetrain Analysis.
Thanks for your help. [Cambridge Massachusetts]
A: Mark J. Massive wheels... Tiny drum... But you only asked about the ESC, so let's talk about that.
Yes, you can run all the motors from a single 4-in-1 quadcopter ESC, and the motors don't even need to all be alike. I know of several small 'bots running two drive motors and a dissimilar weapon motor from a single compact quad ESC.
NOTE Quadcopter ESCs in general do not use the common 'PWM' receiver output protocol with one three-wire connector per radio channel. The specific ESC you are considering uses the 'DShot' serial protocol, so you will need a receiver with that type of output. Check the requirements of any quad ESC before you proceed.
Update - I asked some builders familiar with Quad ESCs about your choice. It seems the APD f-series ESCs may not be programmable for reverse operation. Another builder suggested the Racerstar ReachUP 100A, but I don't have confirmation on usability.
Q: I give up. How does it work? [Multiple Requests]
A: It's called a Killough Platform -- similar to an omni-wheel in action, but different in structure. The two wheels in each of three cradles are connected by gears to each other and to a drive motor which can rotate the wheels while they remain oriented at 90 degrees to each other. One of the pair of wheels is always in contact with the floor as they rotate and 'walk' the platform along. The wheels remain free to spin on their own axles and roll sideways to comply with motion imparted by the other two cradles. You can see the action clearly in this video.
A: Mark J. Builder Tommy Wong calls 'Droopy' a gyro walker, but it doesn't work on the same principle as vertical gyro walkers like 'Wrecks'. It's more accurate to call it a torque reaction walker that gets help from a small gyro effect.
When you apply power to a horizontal spinner weapon, the weapon motor apples torque to the spin the weapon in one direction, but it also applies torque in the opposite direction that attempts to spin the robot chassis in the other direction. By increasing and decreasing weapon motor torque you can get the robot to rotate back and forth, but it won't move forward.
Droopy's name gives you a clue about how it turns that torque rotation into forward motion. A perfectly horizontal spinner does not lift the leading wheel when turning like a vertical spinner does, but Droopy's counter-rotating weapon disks each angle down just a bit toward the outer edges of the 'bot. That little bit of 'droop' creates enough gyroscopic force when the 'bot turns to transfer weight off the leading skid and force the 'bot to pivot around the skid more distant from the advancing
side.
My original description had the weapon spin direction backward. Here's the correction Tommy gave me:
I am designing a 12 lb hobby weight battle bot with 2 wheel drive. The arena is 8X8 ft and I am trying to find torque calculations for the wheel to spin. Please help. [Louisiana State University]
A: Mark J. My visitor log shows that you found appropriate pages here at RunAmok.tech about 30 seconds after you sent in your question -- but you missed the page that gives you the theory to write up for your class project:
A: Mark J. As you didn't provide details on the weight class or the design of your proposed weapon, I can't directly comment on the suitability of your fabrication process. The hamburger is bad.
I will say that I see combat robot builders using 3-D printers to produce components that would be much better fabricated by other means. There is a well-known saying often credited to Abraham Maslow that I will paraphrase here:
A: Mark J. Chassis magnets can be more trouble than they are worth, getting you stuck to kickplates, uprights, and even your opponent. Magnet wheels can drive you right out of awkward situations like those, but the neodymium ring magnets themselves are fragile, particularly in larger sizes.
Team Dark Forces has an interesting solution for larger 'bots. Their lightweight spinner 'Dark Ripper' has 2.5" wheels constructed by making a triple-layer sandwich of three ring magnets between four steel washers. Claimed downforce is 50 pounds per wheel. The slightly larger diameter washers protect the brittle magnets and focus the magnetic flux for greater attractive force. The recesses also provide a place for any magnetic swarf the wheels pick up to slide out of the way. I'd suggest bonding the entire 'sandwich' together with epoxy or Goop to keep it in one piece if a magnet does break.
A: Mark J. Don't block -- deflect. Have you seen any of the Team Dark Forces 'bots fight? Builder Russ Barrow is fond of protecting his vert spinner weapons with wide, curved plows that will deflect attacking horizontal weapons up and over the weapon supports. Granted going 'full Russ' requires some radical design commitment, but adding a couple of wide armor 'ramps' up the sides of your support horns will perform a similar function.
Q: I know what you're talking about in the answer with the defensive wedges on the support horns, but do you have any advice on how to attach them to the robot? I could just use 1 NutStrip and screw the wedge onto the bot, but I am skeptical that only a few screws won't fall off or shear.
A: You're wise to worry about shearing fasteners. Machine screws are made of material and temper to optimize tensile strength -- not resistance to shear forces. Take a look at this video from Robert Cowan for details. You can use Robert's hardened pin technique, or you can 'slot and tab' (see illustration) the panels to take some of the shear load off the screws.
Q: Does UHMW plastic have the same "wedginess" capability as a metal like steel or titanium? I want to use UHMW for my insect bot's wedgelets as titanium/steel is a pain to machine. I only have access to small hand tools.
A: If UHMW was a good wedge material you'd see it being widely used in this type of application -- but it isn't. UHMW has many useful attributes but it is very soft. A hard (and possibly sharp) metal weapon impactor will dig in and 'grab' the soft surface rather than slide up the wedge and deflect. Not what you want.
Now, you could screw mount a nice wide UHMW wedge to either side of your weapon support structure and 'clad' the impact surface with a strip of hardened steel or titanium. The UHMW would be light, energy absorbing, and easy to mount -- while the hard metal strip would be efficient at delecting weapon impacts.
A: Mark J. The correct usage of tread locking compounds like Loctite is to apply a small drop to the clean screw/bolt threads before you spin on the nut and tighten (video). Anaerobic threadlockers like Loctite cure when confined in the absence of air between close fitting metal surfaces. Applying a drop to an assembled screw and nut does not provide these conditions. Properly applied, blue Loctite produces a fair bond in 20 minutes and a full cure in about a day.
A: Mark J. A combat robot is a complex assembly of components and systems that all have to work together to be successful. Forcing new builders to add an active weapon (lifter, flipper, spinner, crusher...) is a disservice to both new builders and the combat robot community. It creates a barrier to participation that practically guarantees frustration and failure for novice builders.
If your first robot must have an active weapon, concentrate on the basics and build a robot that does not rely on its active weapon to be effective. Start with a strong, capable chassis with a wedge and enough weight allowance left over to add a small active weapon system. The weapon can be whatever you're comfortable bulding. A simple electric lifter would be a good choice, but don't allow the active weapon to compromise your strong drive train and wedge. Your active system is secondary and entirely expendable.
Drivetrain, radio set-up, general construction practice, and weapon/chassis balance are all much more important than the type of weapon you choose. There are plenty of examples of winning robots with ineffective weapons, and there are many more examples of losing robots with awesome weaponry. If you get the basics right you're going to have an above average robot no matter what weapon it carries.
A: Mark J. It's not your imagination. I won't comment on 'Hypno-Disc' directly (see FAQ #37) but I will direct you to the Hypno-Disc website where you may notice some differences between their front and rear tires starting in Series 5.
You may also find this post in this archive interesting.
A: Mark J. You're not giving me much to go on, Florida. The snail cam is a reasonable mechanism to compress and release spring force, and it is fairly simple to calculate the energy stored in the compressed spring, but translating stored energy into 'impact force' is complex, requires many assumptions, and varies with the characteristics of the object being impacted.
Here's a link to a good article at wired.com: How Do You Estimate Impact Force?
A: Mark J. Brushed Permanent Magnet Direct Current (PMDC) motors produce their maximum torque at stall, with torque falling away linearly with increasing RPM. At no-load free-running RPM the torque usable torque has dropped to zero -- if there was any available torque the RPM would continue to climb.
From a standing start your robot will accelerate more and more slowly as the speed climbs and torque diminishes. With greater speed comes greater friction and aero drag. When the total drag climbs to the point that it matches the available torque from your drivetrain, acceleration stops: you're at top speed.
Actual top speed should be 85% or more of calculated speed. Getting to only 57% of calculated top speed would indicate that you either have a great deal of drag in your drivetrain or you have insufficient gear reduction and are 'bogging' the motors. Check for free-running in your drivetrain before adjusting gear ratio.
I've written a guide to help determine optimum gear ratios for combat robots. It goes thru the math and then points you to my version of the Tentacle Torque-Amp calculator to let you compare the effects of gearing changes on acceleration and top speed within an arena of given size: Combat Robot Drive Train - Optimum Grear Ratio Selection.
I've also written up a walk-thru of a drivetrain optimization for a combat robot: Example Drivetrain Analysis using the Tentacle Torque Calculator.
As always, thanks! [Social Media]
A: Mark J. The mechanism in question is often referred to as a single motor clamp lifter. Powered rotation of a spur gear (shown with a red dot) drives a clamping arm attached to a second spur gear downward until on object stops it's motion and prevents further rotation of its gear. Continued rotation of the powered spur gear will then rotate the entire gearbox and attached lifting platform around the axis of the powered gear. Reversing the rotation of the powered gear will lower the platform and release the clamp. Note The clamping force is created by weight on the lifting platform. As the lift angle increases there is less weight pressing down on the platform: clamping force becomes essentially zero when the lifter is vertical. In practice, there may be additional gears involved to provide additional gear reduction in order to gain the substantial torque needed for the lift. The animation has been reduced to only the critical components.
Note The clamping force is created by weight on the lifting platform. As the lift angle increases there is less weight pressing down on the platform: clamping force becomes essentially zero when the lifter is vertical.
What notes must you play while performing a concerto?
A: Mark J. Can you name a Mecanum-wheeled combat robot with a winning record? The closest I can come is superheavyweight 'Alcoholic Stepfather' with a 5 win / 5 loss record. They managed to get pretty good traction, but their custom wheels cost $1000 each and were regularly destroyed in combat.
The problems associated with Mecanum wheels go far beyond traction. Here's what the Stepfather team had to say about them in a 2015 Reddit post:
Advantages: great orientation control (keeps our uberstrong front end pointing at the opponent). But the biggest advantage is they look really cool when you can get them to work well. That is really why we used them.
I know this design is one that's probably better suited to show off than to be competitive, but it's one that I enjoy and would like to put my own spin on... whenever I get around to doing so. [Joliet, Illinois]
A: Mark J. 'LOLCano V' (fight video) is not a unique design. It's a eggbeater variant of a "full-body drum spinner" (FBDS) of which there are several well-known examples:
Q: In that "Actual" pic of "LOLcano" it looks like the wheels don't even touch the ground. Am I seeing that right? [Wellesley, Massachusetts]
A: Mark J. No wheels are shown in either the 'Rendered' or 'Actual' pics of 'LOLcano V'. Large diameter wheels mount to the hexagonal section hubs you can see in the 'actual' pic, and square guards then mount to the shaft outside the wheels. I've added a photo labeled 'Complete' below the 'Actual' photo that shows shows the whole robot with wheels and guards.
A: Mark J. Many designs qualify as a 'clamping' collar, and some are better than others for both torque transmission and axial shock. Holding 'well enough' depends on the specific application, information you have elected to withhold. I can comment that clamping collars are generally preferable to set screw collars.
Q: If I were to machine my own clamping-style shaft collar and shaft, would there be any benefit to including a Morse taper on the mating surfaces?
A: Adding a matching shaft and collar taper will greatly improve axial shock resistance in one direction -- and entirely screw up resistance in the other direction. Unless the shock loading direction is completely predictable (and nothing in combat robotics is completely predictable) I would strongly avoid any taper.
I'm assuming that you're asking about shaft collars because your application requires axial adjustment along the shaft. If not, a simple machined groove and snap-in circlip are the standard and preferred solution.
A: Mark J. That would be Gene Burbeck's beetleweight 'One Fierce Low Ryda' (build log). The 'bot fought at the 2008 Motorama event where it did quite well, winning 6 of 8 fights.
The huge friction-driven horizontal weapon blade ran on a live spinning shaft that stuck out the bottom of the robot, where it was fitted with a 'cupped drive nub' of traction material. When the weapon was parallel to the arena floor the shaft rested on the floor like the point of a spinning top. Tilting the robot chassis with servos attached to the un-powered rear wheels changed the contact point of the nub and caused it to drag the robot in a corresponding direction. Greater tilt equals greater speed.
Gene's 'WackerDrive' is pretty much the only possibly competitive design that hasn't shown up on the BattleBots reboot. If you're looking for an unusual design to impress the competitor selection committee I'd say it's definitely worth a shot.
It seems like people have had success with the DYS BE1806 and AX-2810Q, but simply based on the motor characteristics on HobbyKing I don't know what makes them better than others. I know that a lower Kv means higher torque, but how do you know that the Kv is low enough to drive your bot?
A: Mark J. You won't find drive train tools analogous to the
Tentacle Torque Calculator for brushless motors because brushless performance depends as much on the controller firmware as on the motor. All the possible combinations are staggering in number and largely theoretical in practice. The way brushless drive is done is to go for overkill and not worry all that much about the details. See this previous discussion in the Ask Aaron archives: Brushed vs. Brushless Drive.
There's a "rule of thumb" for brushless motors circulating out on the builder forums that appears to work well for drive motor selection. The rule states that a set of brushless drive motors together weighing between 2% and 3% of the total weight of the robot will have more than enough power and adequate 'thermal mass' to survive. By that rule a pair of DYS-BE1806s is about right for a beetle and twin AX-2810Qs is overkill (which might be just right for a Melty).
What makes a motor better than others? Somebody used it successfully on their robot and word got out. Brushless meltybrain spinner? You're on your own. Best luck.
A: Mark J. The saying goes, "You can't have your cake and eat it too." You can't have a razor-edged paint-scraping wedge and still not get stuck on a raised floor seam. The best design for getting under wedges is actually something other than a wedge.
A wide single piece dragging wedge will ride along the highest part of the floor it contacts, which leaves the rest of the wedge spaced above the arena surface. Multiple hinged 'wedge killer' forks have a good chance of riding down in a lower section of the arena floor and slipping under a wide wedge.
Get to know the arena you fight in. Learn where the bad floor spots are and make a habit of running across the floor seams at an angle where you can. If you're still getting stuck too often, feather that sharp leading edge just a little.
A: Mark J. I'm not sure what 'attachment' you mean. The D2 robot kit comes with a big titanium plow similar to the one commonly used by 'Original Sin', and I don't recall OS ever using wheel protection of any sort.
The D2 uses big foam tires that can absorb a lot of abuse and are inexpensive to replace. I think you're best advised to leave the wheels open as designed.
Q: i am the d2 guy and i mean that spinners keep getting on the wedge, to the top of my robot and shredding my wheels. this original sin attachment has a blocker to keep horizontals off the top.
A: Ahh... you're talking about Original Sin's "bar spinner trap" (pictured). Team 'Late Night Racing' built the trap specifically to counter Last Rites' huge bar spinner by forcing it to repeatedly impact the hard steel trap and possibly break. It has had mixed success in that role.
A similar design could certainly keep horizontal spinners from climbing your plow, but your driving has to be spot-on to keep that spinner away from the hard edges on the exposed ends of the trap. Don't use it against vert spinners.
A: Mark J. Scroll down four posts to Columbus' question about active weapons at BattleBots. Another 'Tombstone' clone wouldn't get your design accepted for BattleBots, but hanging a bar spinner or two off the side of a 'bot got these teams 'in'. Valid combat reasons? You can circle your opponent with a weapon pointed at them and veer inward to 'strafe'.
A: Mark J. Odd things happen when you ship your 'bot. Very odd things...
I should mention that reversing the direction of ring rotation may or may not reverse the direction of travel -- bristlebots are funny like that. You should also know that you don't so much 'drive' a bristlebot as make some general suggestions. You'll probably want to change your team motto to
A: Mark J. Hal Rucker has a different paradigm for combat robot design than most builders. There is always an emphasis on survivability above destructive mayhem. The weapon may not do a lot of damage, but it's gonna get multiple shots at you. Here's what Hal said on Reddit about the key design elements of 'Marvin':
In a 4WD setup where the four motors independently drive the four wheels, does a forward leaning center of gravity (weapon and wedge being at the front, like in the case of a vertical spinner) usually cause the front motors to experience such higher loads that they would consistently fail earlier than the rear ones? If so, would a slightly more aggressive rear gear ratio/wheel diameter combo help mitigate this issue? Thanks.
A: Mark J. There is a fair bit of confusion among builders about how the weight on a driven wheel affects the motor driving that wheel. The Ask Aaron Optimizing Combat Robot Drive Train Guide gives a step-by-step process to select the 'ideal' gearing for a drive motor based on the weight carried by the wheel it powers, but in your case different wheels carry differing weights. What to do?
Simply shifting the weight of a robot toward the front wheels of a four-motor four-wheel-drive chassis does not place significantly greater load on the front motors while the robot is freely moving; both the front and rear motors will contribute equally to the acceleration and movement of the the 'bot. The difference in load comes when the robot is pushing hard against a resisting/immovable object and the wheels break traction and start spinning freely. The point at which that traction break takes place is a function of weight carried by the wheels. Here's an example:
Following the steps in the Optimizing Combat Robot Drive Train Guide for this bot's specific drive train, we calculate that:
Select wheels and gearing based on the more heavily loaded end of the robot to make their breakaway current sustainable for those motors. Keep gearing and wheels for all motors the same for balanced torque at all wheels. The front motors will have greater loading, but if you have failure issues with them you should reduce gearing at both ends of the 'bot.
What do you think? Is there anything else the original 'Wrecks' had that made it better than season 2 'Wrecks', or is there something significant about season 2 'Wrecks' that makes it superior to its predecessor? [Newton, Illinois]
A: Mark J. The reduced maneuverability for season 2 'Wrecks' had very little to do with the changes to the pivoting 'leg'. Gyroscopic precession walkers operate on physics principles that are in conflict with the optimum performance of their spinner weapon. Trying to strike the best compromise between weapon power and robot maneuverability is a challenge. A reader from Ontario, Canada pointed this out to me when they wrote in to comment on this post:
I've spent some (too much) time trying to figure out gyroscopes myself for future bots and I'm not an expert but I figured I can still help with the info I somewhat understand.
The 'Hyperphysics' site explanation on spinning top physics is probably one of the most complete sources for this info that isn't completely indecipherable."
I am looking into the prospect of making the front and back wall of my robot out of aluminum (6061) but I don't really have a solid idea of how strong it is in the world of combat robots. I know this is not a lot of info to work off of, but do you think that a 1/4 inch aluminum plate reinforced by nutstrip would hold up somewhat well as a front wall/armor? Ideally most of the hits would be taken by the wedge, but I've quickly learned that things don't always go exactly as planned... [Anacortes, Washington]
A: Mark J. A first-round draw against any of Russ Barrow's 'bots is a tough break -- initiation by fire. Glad to hear you weren't discouraged.
I'd be fine with 1/4" 6061 alloy for front and rear panels in a beetleweight, but I'm not a fan of relying entirely on nutstrip to hold the corners together. Machine screws are made of material and temper to optimize tensile strength -- not resistance to shear forces. Take a look at this video from Robert Cowan for details. You can use Robert's hardened pin technique, or you can 'slot and tab' (see illustration) the panels to take some of the shear load off the screws. That will greatly reduce the number of pieces you'll need to pick up after a match.
A: Mark J. Given your selection of tools, I think the jigsaw is your best option. Several tips:
A: Mark J. The Tentacle Drivetrain Calculator is a tremendously useful combat robot design tool, but you need to understand what it's actually telling you about the drive train design. Among other things, the calculator estimates the amount of torque needed to 'break traction' and spin the drive wheels of the robot based upon the weight pressing down on the wheels. If the drive train cannot provide at least that much torque the drive motors may 'stall' under heavy pushing loads, which will both reduce pushing power and risk damage to the motors. The calculator will warn you of this condition.
For calculation of pushing force and stall conditions you do not need to worry about your opponent weighing you down.
Thanks. [Jakarta, Indonesia]
A: Mark J. Some things have changed since 2009, and some have not. Are you planning to build a 'bot with a 3D printed chassis and brushless drive motors? The RioBotz tutorial may not provide adequate guidance to build a 250 pound class heavyweight to compete at Discovery BattleBots, but it should do very nicely for an Indonesian combat event.
There is no comprehensive guide more current than the RioBotz tutorial, but for clear and detailed information on a variety of combat robot topics I can recommend the 'Robert Cowan YouTube Channel' as mentioned on my Team Run Amok page:
There once were a great many combat robot build logs out on the 'net. A new builder could learn from the experiences of other builders and find answers to questions they didn't even know they had. Now there are very few builders that even maintain websites, and fewer still who are willing to share their build secrets.
Fortunately, builder Robert Cowan has taken on the task of providing well produced videos of the intimate details of building a combat robot, as well as other tech projects he undertakes. His YouTube channel page is here. You might want to start with his video series on his antweight robot 'Sgt. Cuddles'.
For bristlebots, is there a preferred orientation for which way the offset weight spins? The small hexbug toys have the weight spinning perpendicular to the direction of travel, while 'Clean Sweeper' has the weights spinning parallel to the direction of travel. Does it matter or will it be terrible regardless? [Manchester, England]
A: Mark J. I'm happy to hear that 'the cheerleader' is doing her job... kinda.
There are so many variables in the design of a bristlebot that it becomes difficult to sort out the best vibrator motor axis. I've seen working bristlebots with every possible orientation of the vibratory axis, and with adjustments to the bristle design they all worked pretty well. A pair of Italian scientists have even claimed to have worked out vibration frequencies that will get your bristlebot to reliably back up -- in theory.
If you plan to use your rotary weapon array as the vibration source it makes sense to orient the weapon axis in a useable direction -- as 'Clean Sweeper' has chosen with their dual vertical bar spinners. If you're using dedicated vibration motors you may have other considerations:
A: Mark J.
You've told me absolutely nothing about your robot or your weapon, but you want me to recommend motors. It this the type of engineering they teach at ITT Kanpur?
The idea behind the robot is essentially to make a fusion between 'Clean Sweeper' and 'Wrecks'. The robot has two weapons (either a pair of 6" Diablo Sawblades or a pair of Fingertech Bars) connected by a singular axle. The weapons would rest a distance off the ground to prevent them from hitting the floor when the robot tips too far over, and would use an angle limiter to keep the servo from tipping too far (at most, I'd say 22.5 degrees left or right is the aim for the maximum angle). A weapon motor will be connected by a 1/8" urethane belt, and the robot will move by using a servo. The servo has a stick connected to it, and will pull up or push down against the ground to make it move. In theory, the servo goes up, the directional stick goes up, tipping the robot to the right and forcing the robot to turn right. The servo goes down, the directional stick goes down, tipping the robot to the left and forcing the robot to go left.
Thanks, and have a good one! [Newton, Illinois]
A: Mark J. Is that you, Champaign? Your server address has drifted about 70 miles to the south.
The 6" sawblades weigh about 5 oz each, so I'm guessing that this is a beetleweight. As long as you realize that this isn't going to be a competitive robot, you're generally on the right track. Take a look at this video of a small non-combat gyro walker that uses a servo to actuate walking same way your design does.
I've spent some (too much) time trying to figure out gyroscopes myself for future bots and I'm not an expert but I figured I can still help with the info I somewhat understand.
The 'Hyperphyics' site explanation on spinning top physics is probably one of the most complete sources for this info that isn't completely indecipherable.
Thanks for the excellent resource! [Ontario, Canada]
A: Mark J. I've always believed that the best way to learn about something is to try to explain it to someone else. The other half of that process is to have someone tell you when you've made a mistake. Thank you for the correction!
The Hyperphysics website is my go-to source for understandable explanations of physics concepts -- you'll find it referenced multiple times in the Ask Aaron Archives. I'm a bit embarrassed that I didn't take the time to check there for the math. In my defense, I believe it preferable to have 'too much' of something and be able to throttle back than to have too little with no option to recover.
Thanks again for the correction and the hyperphysics reference.
The only way to avoid the transmission desaster, (which in my opinion turned roboteers away from this concept in the first place) is to implement a solution where the motor is inside the Hub and get´s turned around with it. 360° of course would be the optimum. So no wires attached or a 180° solution which I had in mind at first.
Then I found some wireless charging station plans, using coils, but I skiped that because of weight.
In the end it really struck me when I took apart a Drill motor. Brushes! I drew a quick sketch outlining the concept:
On the Topplate of the enclosure, there are two copper rings. One is connected to the positive terminal and the second one to the negative terminal. Up too four brushes share each copper trace (splitting the amps and working as a backup) and join together on the respective motor connection. I presume something between 15-20mm² in diameter on the brushes and Wire. Maybe i can find some carbon brushes used in Makita motors or else.
The rest stays the same as before. A ballbearing on the top enclosure and a aluminim ring in the lower part with (nylon?) V-pulley rolls. Which will function as an absorber on the lower part of the axis. Encoders on the Top and on the wheel will do the position control for the ESC´s to do the adjustments.
This became a hell of a journey and sadly not many people are excited to join in. Luckily I found some in my hometown who even have the lathe so machining parts might start next year.
Any suggestions or recommendations? I know that open traces for 140A (stall torque) and upwards are a bit messy though. As soon as we have the first prototype we will check radio interference and counter measures.
With kind regards [Niedersachsen, Germany]
A: Mark J. I'm pleased to find that you're continuing development of your swerve drive, Niedersachsen. It's more than a bit too complex for my personal taste, but it will certainly be an accomplishment to get it operational.
I strongly recommend that you use carbon brushes. A web search for "benefits of carbon motor brushes" should convince you of their merits at high current levels: self-lubricating, self-cleaning, reduced radio interference, and they don't weld themselves to the copper slip rings.
Replacement 'carbon brush assemblies' for electric drills are widely available; they include brushes, brush holders, and tension springs in a handy little package. Should do nicely.
Can you give any insight on what they do for that bot that makes it so much more successful than others? And if someone were to look into making one what your best advice for them would be? [Grove City, Pennsylvania]
A: Mark J. The primary audiences for 'Ask Aaron' are and always have been 1) new builders, and 2) builders frustrated by their lack of success.
I'm going to paraphrase 'Ask Aaron FAQ #28' and paste in 'ring spinner' everywhere it originally said 'flame weapon':
Q: Would it be a good idea to make a 'bot with a ring spinner that would destroy the competition?
How does insert ring spinner name here's weapon work?
A: You can search the archive for ring spinner to find our many previous posts on ring spinners. Briefly:
A: Mark J. There is a great deal of information on combat robot armor in the RioBotz Combat Tutorial. Start with Section 3.9.6: 'Minimum Weight Traditional Armor'.
First I will explain the idea then I hope for some enlightenment from your side and maybe a pointing finger towards some builders who already did this and obviously better. The idea is to have a bot capable of strafing around the opponent with accuracy. Hitting the weak spots like wheels with accuracy. Pushing from the side and avoiding deadly spinners. The trade off would be less armor. Obviously this system would require a second smaller motor, rotating the Hub of the drive. It would also require more A/h on the battery side and would contain many small parts and if build wrong it would scatter as the above mentioned scrapheap across the arena. The drive has to be located inside the bot.
In the picture (not to scale or anything) we see the main Hub. The motor (blue) is fixed to a circle; it drives the wheels (fixed to the circle of the Hub) with a timer belt. Above the motor is a second circle (the top of the hub) with a shaft for the wires and pressed into the ball bearings of the upper enclosure. On one side of the lower circle is half of a gear. This lets the Hub turn 180°. With the right adjustment of the controller software this would amount in 360° of turn radius and would make the build way more easy. Also there are two blocks on the lower circle (left hand picture) they will prevent the Hub from over turning from i.e. impact. Also a Sensor measures the position of the Hub in total for readjustment.
On the Lower enclosure there will be steel Balls (a poor-mans ball bearing because a BB of this size is expensive and heavy) with the lower circle of the Hub resting on top. Distance rolls on the sides keep the Hub from hitting the wall of the enclosure and turning smoothly. Outside of the enclosure is a smaller motor driving the Hub through a hole. It has, just like a servo, some sensor/potentiometer attached. It's all in an enclosure so I can swap the whole thing fast if damage because it's too complicated for repairs inside the bot.
Thanks for all you do for the community and I always enjoy learning from you. The German guy [Niedersachsen, Germany]
A: Mark J. Good to hear back from you, Niedersachsen. I enjoy your ideas and I very much love your sketches! Please don't apologize for your English -- es ist viel besser als mein Deutsch.
Your concept is very well thought out, and I will assume that you enjoyed the exercise. I am pleased to report that the concept is entirely workable and that I can point an enlightening finger to design resources. All you need are the magic key words -- Google: swerve drive.
Swerve drive is widely used in the non-combat First Robotics Competition (FRC) but has seen very little exposure in combat. Here are a few links to get you started:
Reply: Thank you Mark! What a simple word can do. Swerve would've never crossed my mind. This opened up a whole new world of info. Thanks! The bevel gear option was on the table in an older version but I expected it to be a weak spot when hit. On the other hand I made a trade off with the cable which gets stressed out by turning. So I only did a 180° turn radius and planned for some stopping blocks. If I would try the 360° option I maybe have to add some brake based on relays or something like that. Just to protect the drive from impact.
It's really obvious now why this drive hasn't been done so often in combat robotics. But I will start the modeling in CAD now. You gave my Odyssey a good push forward. Thanks again from Lower Saxony!
Response: I've got another search term for you. You might find some worthwhile information in a search for crab drive. 'Crab' uses the same drive modules as 'swerve' but simplifies the control requirements by linking directional control of some or all modules together. Linking all four isn't very interesting -- but linking the front modules as one unit and the back modules as a second unit gives a lot of maneuverability and still allows use of standard R/C gear for control.
A: Mark J. The layouts of precessional walkers 'Wrecks 2' (heavyweight) and 'Gyrobot' (antweight) are essentially identical. The differences are more a function of their relative sizes than an engineering choice. For example, Gyrobot can get away with a direct-drive weapon because of its small scale, whereas the larger Wrecks must use a chain drive. Placement of batteries and electronics in the base versus alongside the weapon are also scale related. The choice of design would depend on how large a robot you are building.
now, here i want my suggestion. cases are Motors..
now,re caps.. I'm interested using 775's but would using 555's will do for me.?? & brushed ESC for a good price & i don't mind them used.. [Bangladesh]
A: Mark J. From what I've seen of robot combat in your region, six RS-555 motors geared down to 300 RPM in a featherweight would be entirely competitive with other robots. The small arenas combined with a builder preference for slow speeds don't require much power.
The
Tentacle Drivetrain Calculator
is handy for these design calculations. It says that a 30 pound robot with six 300 RPM 555 series gearmotors @ 12 volts with 6" diameter wheels will have a calculated top speed a little better than 4 MPH, reaching that speed in about 3 feet with a maximum current draw of just 3.5 amps per motor when pushing hard.
Not sure what ESCs might be available to you in Bangladesh. Given your budget you might be interested in the inexpensive Australian BotBitz controllers.
Q: as my design is pretty compact & we have size limitations out there.. i have at most 11 inches for all three wheels. so,do you think it'd be fast enough with 3.5 inch wheels.??
A: Here's a table showing performance with different wheel sizes. The 3.5" wheels are slow -- not even walking speed. If you were to drop down to four motors and wheels, you'd have room for larger wheels for greater speed. Four of your 555 gearmotors with 5" wheels gives a 3.6 MPH calculated top speed reached in about 3 feet with only 4.3 amps of current per motor at max push. That sounds like a good solution.
I'm not certain what your battery options are, but these motors will handle a bit of overvolting. Running 14.8 volts (4 LiPo cells) with four motors would boost your speed to 4.4 MPH and keep your acceleration brisk. Max current remains at 4.3 amps per motor because your max torque is traction limited.
What are some of the advantages and drawbacks of multi-motors setups for HW Horizontal weapons? [New York, New York]
A: Mark J. Good engineering practice calls for a design solution to be as simple as possible. Abandoning the traditional single-motor solution to a spinner weapon adds to system complexity and increases the number of potential failure points in an already highly stressed system. If you're going to do that you'd better have very good reasons.
One common reason for resorting to multi-motor weapon drives is satisfying dimensional restrictions imposed by the robot design. The current incarnation of 'Son of Whyachi' abandoned the motors used in previous versions because they were too tall to fit into the desired very low profile of the robot chassis. Team Whyachi's final weapon design relies on a circle of eight(!) 'Mini Magmotors' driving a central spur gear. The ring of small motors allowed the height of the robot to be reduced by several critical inches.
A: Mark J. The RobotShop calculator is for hobby and utility robots that glide along smooth floors and up gentle ramps, not combat wedges that push full-throttle against opponents that push back equally hard. I'd suggest evaluating drive motor performance with a tool intended for combat robots.
The Team Tentacle Torque Amp-Hour Calculator says that a 60 kg robot with pair of typical 175 watt electric scooter motors geared as you suggest would take a leisurely 3 seconds and more than 20 feet to accelerate to 7 mph. Pushing hard against an opponent on a typical arena surface would bog down the motors near stall and rise total current consumption toward 60 amps for the pair: that's 1400 watts of drain on the battery and way too much current for those motors to handle.
1) Is there a way to determine the gearing ratio on a robot with a chain or belt-driven drive with front and rear wheels of different sizes? For instance, the rear wheels are 3", and the front wheels are 4". The rear has, say, a 1.75" sprocket, the motor itself has a 2" sprocket, and the front has a 3" sprocket. These aren't real numbers, they're just random numbers to be used as an example.
2) Is there a way to determine the speed of a shufflebot? I ask because the calculator does calculations for wheels, and IDK if there's a way to calculate for shufflebots.
Thanks again! [Jacksonville, Illinois]
A: Mark J. By the numbers...
If you want an estimate from the Tentacle calculator of how fast it would be going if it wasn't hopping, double the offset distance for a lobe on the shufflepod cam and enter that value as the 'wheel' diameter. But seriously...
I'm designing a 'Breaker Box' style rammer bot for 15# competition. I was curious about different types of drive motors. There are several variations that will allow the full pushing force, but I imagine a higher torque motor would win in a pushing match. In my area, Leopard and Castle Creation 540 size motors attached to Banebots gearboxes are most common. I was curious if you can use an outrunner with the same or similar bolt pattern, hooked up to a Banebots gearbox, as a drive motor. I know AmpFlow motors are all the rage in the higher weight classes, would one be suitable here?
I was also wondering how to maximize grip on the area floor. I have cut treads in tire and clean my wheels religiously with mixed results. Do lower shore hardness wheels offer better grip, ex green banebots vs black banebots or Colsons? Has anyone had success with adding "grip" to the tire? I was thinking studs like Riobots did, low grit sandpaper, two sided tape or something that can be sprayed on that adds grip.
Your insight and experience is much appreciated. [Pittsburgh, Pennsylvania]
A: Mark J. You're asking about very popular design topics. A search of this archive yields 127 hits for 'traction' and 128 hits for 'pushing'. The Ask Aaron Robot Motors and Controllers archive has dozens of posts about using brushless motors for robot drive systems.
Here are some quick topic highlights -- search thru the archives for details:
A: Mark J. The
Team Tentacle Torque/Amp-Hour calculator
was designed for brushed motors and assumes an inverse linear relationship between motor speed and torque. Common hobby brushless motors do not have that speed/torque relationship, and the entire concept of brushless 'stall torque' doesn't really make sense. To further complicate the issue, the torque curve of a brushless motor is highly dependent on motor controller firmware and on the specific user-adjustable firmware settings. The Tentacle calculator is nearly useless for designing a brushless drive train.
See what successful bots in your weight class are using for brushless drive motors, gearboxes, ESCs, and (importantly) controller firmware/settings. In general you'll find motors with high Kv constants, high reduction ratio gearboxes, and controllers flashed with SimonK or maybe BLHeli firmware. Brushless is a whole lot more complex than brushed drive, and I'd strongly recommend that you start with a proven combination. Experiment after you have a working drive train.
So here's where I'm at. I recently built a brand new hobbyweight. Spent months on the design, meticulously selected components, machined every part, and promptly went 0-2 in my first competition.
The flaw lay in a very poor hardware choice. The output shafts for my drive gearboxes have a 3mm hole. I designed wheel hubs to slip over the shaft and used an M3 alloy bolt to lock the shafts to the hubs. Bad idea. About a minute into each fight, both bolts sheared and turned my bot into a very expensive paper weight. I didn't take any major hits, and I believe that the bolts sheared solely from the torque of the motors turning the wheels back and forth.
I am now wondering if a 3mm hardened pin will be sufficient to lock the hubs to the shafts. The ones I have in mind have a 1600lb shear rating. I emailed McMaster-Carr to try and get a shear rating for the bolts so I could compare, but they said that they don't test shear on their bolts. I am wondering if the pins would hold up, or if I should completely redesign the hub?
I'm running 12 volt Johnson RS-550 motors (40:1 reduction). Also attached is my CAD of the hub and gearbox.
As always, I appreciate your input very much! [Albany, Oregon]
A: Mark J. That's what's so great about combat robotics; you learn all sorts of unexpected things that you wouldn't run across in a normal lifespan. Sometimes it's fun, sometimes it's painful.
Bolts are designed for optimal tensile strength at the expense of shear resistance. Make that 3mm bolt out of alloy instead of steel, add in the leverage advantage of a (perhaps) 50mm radius wheel on the outer surface of a 2.5mm radius shaft, and then try to abruptly reverse the momentum of a 12-pound robot moving along at 9 MPH, and presto -- shear failure.
If those shafts are as small as they appear you don't just need new hubs, you need new gearboxes. For a hobbyweight, I'd look for minimum 8mm diameter steel shafts with no cross-drilled holes.
Q: So it sounds like a hardened pin isn't going to be my simple solution. I don't know of any other offset gearboxes that I could switch to and fit inside the robot in the same way. I'm trying to avoid redesigning the whole bot and have a couple ideas. I could try to modify the gearboxes and install a larger shaft, but I'm sure that is easier said than done. My other idea seems a little more appealing (for the moment).
I was thinking I could press fit a square hub (red in the picture) made out of a somewhat flexible plastic onto the existing shaft. This would take the cross-drilled hole out of the equation and add some flexibility. Is this a viable solution, or recipe for disaster?
A: I'm concerned that the gearbox weaknesses run deeper than the shaft -- why would there be combat-quality components up to but not including the output shaft? I suspect that you're going to chase a series of weak points thru the entire structure of those boxes, ruining your combat success for as long as you keep them.
I realize that you've invested effort and heart into your current design, but there are reasons your competition does not use those gearboxes. Cut your losses and start fresh.
A: Mark J. A better idea is to design your robot with components spec'd to handle the current loads -- with some to spare. You really don't want to be a sitting duck for 15 seconds while your breaker resets.
Additional Problem Auto reset breakers are not designed for the physical shock loads combat robots experience. A sharp impact will trip the breaker well below its current rating, which makes them worse than useless.
A: Mark J.
I really ought to put this in the Frequently Asked Questions...
A: Mark J. There is a simpler and more workable solution. A heading hold gyro of the type used in R/C helicopters will detect an unwanted rotation of your 'bot and signal the drive motors to compensate for the rotation. The gyro is lightweight, inexpensive, uses your existing drive train, is simple to implement, and has the advantage of operating when the robot is moving rather than locking you in place 'til the weapon is up to speed.
What material did they use (I'd assume S7 steel, but I didn't know)? Other than less weight, is their any other advantage to having a thinner flywheel? Are there any notable disadvantages? [Champaign, Illinois]
A: Mark J. 'Wrecks' relies on gyroscopic precession generated by its vertical spinner (made of AR400 steel) for it's 'walking' motion. A larger diameter weapon has a greater mass moment of inertia (MoI) and generates greater precession force at the same RPM. Cutting the flywheel width in half allows for a 40% increase in diameter at the same mass, and doubles the MoI.
Advantage
1) 'Double Dutch' is quite an unusual machine, both in shape and its idea of using two counter rotating blades as weaponry. My first question about Double Dutch is simply this: does using two counter rotating blades generate more force than, say, using two blades rotating in the same direction? I'd assume that the answer would be no, but hey: that's why I came to ask you!
A: Mark J. A major problem with a horizontal spinner is that striking your opponent sends them off in one direction and sends your 'bot off in the other direction, wasting about half of the impact force (see Newton's Third Law). If you can manage to hit both sides of an opponent more-or-less at the same time you can transfer more of the impact energy to your opponent and less into sending both 'bots sliding across the arena... in theory. In practice it may well just 'spit' the opponent out like a watermelon seed and shove itself backwards.
A second 'benefit' is that the gyroscopic forces from the counter-rotating blades cancel each other out. There's no danger of odd 'gyro dance' effects if the 'bot is kicked up off horizontal. This is less of a problem with horizontal spinners than with verticals, but it's still a bonus.
2) I recall builder Kevin Lung mentioning in a reddit post that 'Double Dutch' was capable of omni-directional drive. Is this true, and if it is, how given that it uses normal, non-omni wheels?
A: Take a close look at the photo of 'Double Dutch'. Notice how the wheels aren't all pointing in the same direction? If you drive those wheels independently in the same way you drive omniwheels you can get a sideways 'strafing' motion as well as conventional motion. It requires lots of power to spin/slip the wheels in this manner, but it can kinda work.
3) I noticed that 'Sawblaze' uses a flamethrower alongside its powerful saw. Does this fire actually help the saw cut through the opponent, or is it more or less for special effects?
A: Fire pretty.
4) What exact purpose do the curved bits of 'Bronco' serve? I'd assume they're built to keep vertical drums at bay, but if they are, aren't there simpler ways to deflect vertical drums?
A: Yes they are; no there aren't.
A: Exactly how bristlebots work is far more complex than their simple construction would lead you to believe. Simplified explanation: an imbalanced rotating mass jiggles the robot up/down fore/aft and - if you get the speed right - the loading and unloading of the brush bristles contacting the floor produces a net vector in a direction perpendicular to the axis of motor rotation. Motion is slow and with very little force. Place an independently controlled motor/brush on each side of the 'bot and you can get it to turn. Reverse the motor rotation and maybe it will back up -- or maybe not. Like I said, it's a complex and inefficient system.
6) Why aren't Horizontal Crushers, like 'Kan-Opener' and 'Tough as Nails', as popular as Vertical Crushers, like 'Mohawk', 'Spectre', and 'Petunia'?
A: More moving parts are required for a horizontal crusher, plus top armor is usually thinner than side armor. The real question: given their generally poor performance, why do builders consider any type of crusher viable?
A: Mark J. In my opinion, based on results at King of Bots, 'Spectre'.
Q: What makes 'Spectre' so good? I thought that crushers were fairly ineffective in modern age combat robotics but 'Spectre' was able to take out more conventional and tested designs.
A: It isn't the weapon that makes a robot effective. The following advisory appears at the top of the Ask Aaron Robot Weapons archive:
Drivetrain, radio set-up, general construction practice, and weapon/chassis balance are all much more important than the type of weapon you choose. There are plenty of examples of winning robots with ineffective weapons, and there are many more examples of losing robots with awesome weaponry. If you get the basics right you're going to have an above average robot no matter what weapon it carries.
A: Mark J. In general I'm gonna say that so little clearance is going to bite you.
A: Mark J. Are you using the washer to locate a hub that's free to float inward toward the gearbox? If so your nylon washer is likely OK, but I'm a little worried about arena swarf getting embedded in/under the soft washer and causing friction/binding.
I'd rather see a real thrust bearing. Whichever you use, I'd suggest a generous coating of light grease to help keep debris out.
Q: Forgot to mention that the hub is the Banebots clamp type so it can't freely float on the axle. I wanted to stick the washer between the gearbox face and hub to eliminate both any empty space and ensure my offsets are identical for both gearbox/wheel sets. Still ok in this case?
A: Your nylon washer will most likely be fine. Leave off the grease since it's not under load.
My personal preference, since it's functioning as a spacer that takes no axial force, would be a short length of 1/2" inner diameter aluminum tubing to slide over the shaft and rest against the inner race of the gearbox bearing. You can snug that up as tight as you like with no chance of binding, a drop of Loctite will keep it on the shaft during wheel changes ["Where did that %#@*&! washer go?"] and there's nothing to rub on the gearbox face.
However, I have other concerns about taking a wedge to a competition. I plan on participating in the U.S. antweight category (1lb/454g) and I worry mainly about how fun it would be for other teams to compete against a wedgebot. I watch other competitions and when a robot does not have a weapon capable of damaging the enemy robot it seems that the intention is to either flip the opponent, or hope they self-destruct on the wedge.
My question is if you recommend that a builder first build a wedgebot, do you also recommend that be the first bot they take to competition? I hope to assuage my concerns that bringing a wedgebot to competition is something that is frowned upon, or detracts from the experience for other competitors. [Gainesville, Georgia]
A: Mark J. It's very considerate of you to express concern over the experience of the other builders, but let me dispel those concerns:
A: Mark J. It will make more sense if I answer your questions in a different order than you asked them:
A: Mark J. Hydraulic systems are in general much heavier than comparable pneumatic systems.
A: Mark J. I know of no guide at the level of the RioBotz combat manual for combat robot wheel hub design. My general advice is to study successful designs in combat applications similar to your use and modify those to your purpose. You may find this MAE Wheel Hub Design Guide of some use, but it is not specific to combat robotics.
I'll suggest that you consider what benefits you might reasonably expect to gain from machining your own hubs and casting your own wheels, and carefully consider other options. There may be more fruitful areas in which to expend your efforts.
A: Mark J. Torque determines acceleration and front end lift, but because you've provided only RPM I can't tell you 'how quick' your robot might be. Smaller wheels will increase effective torque and acceleration, not reduce.
Placement of the center of gravity relative to the drive wheels determines how much acceleration you can have without lifting the nose of the 'bot. There is a complete explanation of acceleration and lift - with an illustration - on page 46 of the RioBotz Combat Tutorial.
A: Mark J. When you see a Hal Rucker robot with some unusual component that you don't understand, the correct question is not "Why is he doing that?" The correct question is 'Why am I not doing that?"
The metal cylinders with olive-green inserts that sit between the gearboxes and axle shafts on 'DUCK!' are not universal joints. They are 'flexible plumb shaft couplers' consisting of pairs of multi-jawed hubs with a squishy synthetic rubber 'spider' sandwiched between them. The couplers serve multiple functions:
'DUCK!' had a rear wheel sheared off by a devastating weapon strike in its BattleBots debut, but I'm willing to bet that the associated gearbox lived to fight another day. Hal Rucker knows what he's doing -- pay close attention.
A: Mark J. That's easy...
Pros They look cool.
Cons Everything else.
Tracks are heavy, vulnerable to attack, complex, unreliable, reduce turning agility, and most importantly have no traction advantage on the smooth hard surfaces where combat robots fight. 'Bite Force' (pictured) had experimental magnetic tracks at the 2015 ABC BattleBots tournament where the 'look' was important in getting accepted to compete on the show, but they were more trouble than they were worth and were replaced with wheels for the 2016 season. If you need a robot to fight on sand or in mud, consider treads -- otherwise avoid them.
A: Mark J. It's been nearly 24 years since the first Robot Wars, and some of the most creative minds on the planet have spent that time designing, evaluating, and refining the state of the art in robotic combat. It would be incredibly egotistical of me to suggest that they missed something, or neglected to recognize a promising solution that was tried and failed because of execution. Yep, that would be boastful vanity...
A: Mark J. Previously answered. See this archived post for a clean explanation.
A: Mark J. Combat arenas are not very smooth surfaces. A wide blade will set up on top of the highest part of the arena floor it rests on. Think of a straight edge resting on an irregular surface -- there will be gaps underneath most of the length of the edge.
A hinged narrow wedgelete approaching that broad wedge will stand a good chance of riding in one of those low gap areas and sliding under. At worst it can be no higher.
A: Mark J. You don't have that quite right. 'Wrecks' is a 'precessional walker' -- its legs aren't powered at all, but the weapon still makes it walk. See this post farther down in this archive for a description of the principle.
A: Mark J. 'Tazbot' was very successful... at getting a good share of the air time on the original BattleBots TV series. Only a small percentage of the actual tournament fights made it onto the televised shows, but Taz was fun to watch so it got a lot of TV time. However, it was only an average combatant.
Official record:
Like 'Vlad the Impaler' - which you asked about in your last post - Taz last fought more than fifteen years ago. Combat robots have changed a great deal since then. Even the most successful 'bots of that era would be poor models for success in current competition. Pick newer 'bots to wonder about.
A: Mark J. Two things:
Q: So I saw overdrive S1 had some technology in it's wheels. What does this do? Thanks! [M]
A: Series 1 'OverDrive' was powered by direct-drive electric bicycle brushless hub motors, which place the entire driveline into the wheel. This greatly simplifies robot design and speeds construction, but also limits the ability of the builder to optimize the drive system.
Although the motors were placed in the smallest practical wheels, the drive provided considerably less torque than conventional combat robot drive systems. For series 2, a completely new version of 'Overdrive' wisely reverted to conventional drive motors.
My idea is to make a featherweight full-body spinner similar in shape to that of 'Ziggo' (the idea was that it would be themed around a land mine) or the only FBS that was a featherweight I could recall off of the top of my head: 'Badger' (from Australia).
There are five things I came here to ask, which I will lay out for you below:
I know that that's a lot of info, and some of the info is missing because an exact size hasn't been chosen yet, but I hope you can help me out! As always, if there's anything else you would recommend I am always happy to hear your advice! Thanks again for the advice and all of your help! [Champaign, Illinois]
A: Mark J. New question length record - 847 words I think I can answer your questions more concisely.
The featherweight FBS that you should 'recall off the top of your head' and emulate should be:
Tetanus / Triggo - Team Brain Damage owns the featherweight class in the northeast US. Full-body spinner 'Tetanus' went 21-2 with five titles before being updated with a stronger shell, renamed 'Triggo', and adding on a 20-6 record and three more titles to date.
A: Without full motor performance specifications I have no way to calculate the performance of your platform when powered by your proposed drive train.
With complete motor and drive train specifications, the
Tentacle Drivetrain Calculator
can provide a very good estimate of performance on flat terrain. For example, a pair of 200 watt motors with a no-load speed of 3500 RPM and a stall torque of 0.55 N·m driving a 160 kg platform via 8" diameter wheels thru a 7:1 reduction has a calculated top speed of 19 km/hr, but acceleration is so poor that it would require a run of hundreds of meters and several minutes to achieve that speed. Further, the platform would lack the capacity to climb even a very slight incline. A total of 400 watts motor power is MUCH less than you will need to achieve reasonable performance, and your motor controller may need to be upgraded as well.
'Ask Aaron' specializes in questions about combat robots, which have very different requirements from the platform you are building. We are not a free engineering service. I think you will do better to find a general robotics forum to supply advice for your project.
BTW I have asked you several questions over the last few years and your answers have been spot on. I truly appreciate the time you take to offer us advice. [Albany, Oregon]
A: Mark J. Thanks, Albany. I got a lot of help from some very generous people when I started to build combat robots, and I'm just trying to pay back my debt to the community.
You and I have previously discussed the merits of non-circular shafts and matching hubs for small shafts, as well as clamping collars and the problems with set screws. Readers can catch up on that post in the Ask Aaron 'Ants, Beetles, and Fairies' archive (link).
I'm not prepared to say that an interference 'press-fit' is categorically the 'best' method for attaching a hub to a small motor shaft. Press fitting is something of a black art, particularly then using dissimilar materials like steel into aluminum. You can try an on-line calculator to assess the torque capacity of a specific press-fit junction but, as you point out, combat robots place odd and unpredictable loads on structures.
I'm willing to say that I'd much rather go into combat with a correctly press-fit pulley than with a set-screw pulley. The only down-side I see is the difficulty of pulley replacement in the pits if you do have a failure at an event. Having spare complete motor/pulley assemblies in your kit would be the solution.
I've used a lot of press-fit gears on small motor shafts over the years and never had a failure. Make up a hub and do some testing.
A: Mark J. 'Tombstone' is likely the simplest 'bot at the BattleBots reboot and it has the best record at those events -- but the producers of the show only accept complex robots with big weapons that generate a lot of destruction for the cameras. Truly simple robots aren't allowed to compete, so this can't really be considered 'open' competition.
The 250-pound version of 'Tombstone' does very well against the artificially complex robots at the new BattleBots: a 91% match win rate! However, Ray Billings' other bar-spinner robots don't have the same success rate against more competitive 'real world' combat robots.
Why not as good? Because simple robots are tougher competition than complex showboat 'bots. Which heavyweight robot has the best record against 'Last Rites'? That would be an even simpler robot: the fearsome wedgebot 'Original Sin'.
Simple 'bots win
A: Mark J. There is a lot of space between 'good idea' and 'totally dumb'. People build combat robots for all sorts of reasons:
I have evidence that simple robots win. In 2006 and again in 2016 I sifted thru the results of robot combat tournaments and compared the results obtained by robots with different categories of weapons. You can read the results here. The results may surprize you.
Build what you like, but if your idea of a 'simple robot' is to take a deceptively complex robot of a design that rarely wins and mount it on top of another style of robot that nullifies the only advantage the weapon has, you're asking for advice at the wrong place.
Now press the cheerleader button; it'll make you feel better:
A: Mark J. The heavyweight version of 'Brutality' was thrown together on short notice, largely from spares for the earlier middleweight 'bot of the same name. Paul Ventimiglia was with Team Demolition at the time, and the 'bot was later campaigned by Paul for WPI Robotics. Aptyx Designs is a more recent team created by Paul for the BattleBots reboot.
Brutality's drive motors are short MagMotors connected to Team Whyachi parallel-shaft gearboxes powering the front wheels. A long chain runs back on each side to drive the rears.
The weapon is powered by two AME D-Pack motors driving a right-angle Team Whyachi M3R2 gearbox up to a final stage spur gear at the blade. Similar in size and performance to the AmpFlow E30-400 motor, the inexpensive AME D-Pack was widely used for weapon power until supplies dried up several years ago.
'Thank-you' to Paul for quickly returning my message and verifying what I gleaned from the photo -- he's pretty busy right now.
A rather confusing request, at least in my mind, but I will do my best to explain it. I have 2 Banebots 540 drive motors connected to an ESC -- currently it is a Mamba Monster, but I am very open to suggestions.
A: Mark J. The Mamba Monster is a bulky and complex single-channel controller intended for brushless motors but with a 'brushed mode'. If you want independent control of two motors you will need either:
Q: Using the Spektrum DX6e and subsequent receiver, I want each gimble to power the drive motors forward and reverse. Probably very easy.
A: It is very easy, if I correctly understand what you want. I believe you're asking for 'tank steer'.
Q: Would you need a v-tail mixer with this setup or an alternate?
A: No, but few robot drivers set their transmitter up in 'tank steer' mode you are requesting. Read our guide to Transmitter Programming for Combat Robots for alternative control setups. If you do decide to use a 'mix' setup, your DX6e transmitter has built-in mixing capability -- no external mixer is required for most control choices. If your controls are not behaving as you expect, our Transmitter Set-up Troubleshooting Guide can help.
Q: Then I want to power a Leopard 3650 3450kv weapon motor using an ESC. Currently it's a Mamba Max Pro, previously a eRC 85A. Again looking for suggestions.
A: Same problem here as with the drive ESCs. You haven't even told me what type of weapon you want to build -- spinner, lifter, hammer? With so little info I can't tell you if that motor is adequate for your weapon, and I can't recommend a weapon ESC. If you're building a spinner weapon, you'll want to read the Ask Aaron Spinner Weapon FAQ before you do any additional weapon design.
Q: I would like the weapon motor controlled by the "G" switch with 0 being no rpm, 1 being about half way, and 2 being max rpm. Is this possible? If so, how would one bind and where would the leads plug into the receiver?
A: Yes, and this is also easy. Follow the instructions for 'Channel Input Configuration' on page 17 of your transmitter manual to assign Switch G to port 6 (aux) on the receiver and plug the weapon ESC into that receiver port. You will bind the receiver in 'preset' failsafe mode with the gimbals centered and Switch G in the 'off' position.
Q: Many Thanks.
P.S. How would you like your site cited in a paper? Just curious because you are the best website for the topic and much of my knowledge is from your site. I just want to give credit where due. :-) [New Castle, Pennsylvania]
A: Thanks for asking. In general a source is not asked if it wants to be cited. If you are referencing specific info from 'Ask Aaron' in a paper it is correct practice to cite your source. If you simply want to list 'Ask Aaron' in a general bibliography for your paper, the choice is yours.
A: Given the components you've selected and the gear ratios you're looking at I'm gonna guess that you're coming at this from an R/C car background. The requirements of a combat robot are a great deal different than R/C cars.
Take a look at the screen shot from the Team Tentacle calculator at right. I've input the drivetrain details you've provided.
Your brushless Leopard motor has similar problems driving your weapon. Popping your weapon specs into the Run Amok Spinner Spreadsheet with a 3-cell LiPoly battery and 3:1 gear reduction, the 80 amp max motor will pull an average current in excess of 400 amps for the first two seconds of spinup, and will still be pulling 200+ amps when it hits 85% of full zero-drag speed. With the aerodynamic resistance of a 5" beater, the motor will likely never drop under 150 amps at cruise. It will suffer the same incandescent fate as your drive motors at their original gearing. Not * gonna * work.
Sub-lightweight 'bots typically use much lower 'kv' outrunner motors to provide more torque so that they might survive at reasonable timing belt pulley reductions. The Leopard motor might survive life with your beater bar if it had about a 6:1 reduction, but so large a reduction is not easy to accomplish on a weapon. Reconsider your weapon motor choice.
Q: Just one more question... Can you give a little more step-by-step direction to assigning the RPM on the "G" switch?
A: I don't have a DX6e here in my workshop to poke at; I'm working entirely from the Spektrum DX6e manual. I can't do better than the step-by-step instructions for 'Channel Input Configuration' on page 17.
I believe that receiver channel 6 is assigned to Switch D by default. You can just leave it there if you like.
A: Mark J. Two answers:
Many Thanks! [New Castle, Pennsylvania]
A: Mark J. Yes there is a calculator, but the variables used by the calculator are a little different. It will tell you how fast you can rotate without wheel lift, and if you know the weapon MOI you don't need the spinner spreadsheet. All the design factors are explained on the calculator page. So... where is this calculator? If your question starts with 'Is there a calculator...' your first stop should be the 'Combat Robot Design Tools from Team Run Amok' page:
After walking you thru the math, the page offers a simple javascript calculator that will model the stability of specific robot designs to let you know how serious the gyro effect will be on your planned robot. If you're designing a big drum or vertical disk/bar spinner you'll want to make use of this calculator to avoid unpleasant surprises in the behavior of the finished robot.
The unit is an Australian made twin motor machine, with both motors run as one rear drive and front wheel control arm steering. I will pick it up tomorrow and don't know the spec of the motors/gearing yet, other than it is 24vdc with a single Curtis controller and has a brake and regenerative charging. I'll remove the brake to make room for an encoder, and because I don't want it on there..
My plan is to run it in reverse with dual controllers giving skid/dynamic steering through the motors, and letting the steering rack trail like castors for now, and possibly fitting a motor/actuator to the steering rack at a later date for added control.
The robot will carry quite a payload as it will be used for selective spraying and will have a 50-80L tank on board, along with associated controls and array. I will aim for 200kg but allow for 300kg absolute max, more likely 250kg max (size of a medium quad bike).
The robot will need to travel over open pastures, and I'd say the 20 deg inclines would be the max when loaded but will attempt to make it negotiate as steep as possible land as it can handle without rolling over.
It's on about 330mm OD tires/wheels right now, but I'd like to run 400-450mm tractor style tires at the front and would like a nice strong 4-5km hour continuous working speed, with possibly a bit faster for moving it around between jobs.
I'm quite keen on a 36-48vdc system for increased efficiency between battery charges, and will run as large a battery bank as my weight/space limits will allow, and I may even go with Lithium batteries as they are much lighter (and dearer).
My questions would be:
Please let me know you thoughts, and thanks in advance for your advice. [New South Wales, Australia]
A: Mark J. I don't think I can be much help to you. 'Ask Aaron' has a collection of design tools for weight-restricted robots that operate for three minutes at a time across flat smooth surfaces, pushing at full capacity against immoveable opponents, all the while balancing on the edge of thermal failure while their opponent is unleashing kinetic energy attacks entirely capable of ripping them to scrap. Typical longevity of our drivetrains is measured in minutes. None of these things apply to your robot project.
I do have a few comments that may help.
A: Mark J. 'Heavyweight' covers a wide range of weapon and motor sizes. A 20 HP motor spinning up a huge bar spinner will have different requirements than a 4 HP motor spinning up a compact diskette. There are also considerations other than belt width. See this guide to belt selection for a starting point. I'd advise finding a comparable weapon on a successful robot and finding the belt solution they use. The hamburger is bad.
Q: Hey, it's me again (apologies for not sending this with my last message. I remembered this just as I had hit send. (-3-) Anyways, I heard about the "toothless" drum spinner that used Colsons instead of an actual drum. I was wondering this: if a row of Colsons were combined with a sloped wedge or plow and the robot was given good torque, would it be able to throw robots easier?
A: Several things:
Q: I have returned (again)! First off, I wanted to apologize for the bad Hamburger I gave you yesterday. At least you won't get salmonellae from it. Second, I was cleaning out some old files and found my old collection of questions I asked several months back, along with a few I never asked. I didn't intend on sending you another message 24 hours afterwards (I didn't want to annoy you because I feel like my constant questions can be a bit annoying sometimes), but I wanted to give these questions before I forgot. OKAY, so, here we go:
A: In Sewer Snake's standard configuration the black 'rear hinge' fork is primarily offensive while the red 'front hinge' fork is almost entirely used to self-right or otherwise get the 'bot out of awkward positions. Together, they make great use of a single electric lifting system.
A: Multiple benefits:
Search this archive for 'Bombshell' to find an earlier post discussing other facets of this design choice.
A: Career competition record for 'S.L.A.M.' (1999 - 2000): 1 win/3 losses. The one robot it beat had a 0 win/2 loss record. I think that says enough. Emulate successful robots -- or you can always click the
button.
A: I don't think I understand the question.
A: Do not angle your horizontal spinner. An angled spinner will strike downward on the leading side of the spinner arc, and a hit on that side will throw your 'bot upward. Keep it flat.
A: See my earlier answer about drumbeaters. Call them anything you like -- if the weapon energy storage numbers work and they're strong, they're viable.
A: No one material is 'best' for all parts of a robot, but not everything has to be 'machined'. I'd bolt on a few flat steel armor plates and impactors.
A: It looks entirely classic US style to me -- nearly identical to Team Run Amok's The Gap. I'm not sure what you mean by 'not as stiff'. You will want a clevis mount to locate the bottom of your cylinder -- you cannot just leave it hinged on one end and unattached on the other. The disadvantage to the design is the height of the structure; see similar but more compact design examples at the Team Da Vinci 'Understanding Pneumatics' page.
Anyway my question, between all my coworkers plans to build very destructive robots, I would like to try to win my battles by a bit more control. Taking inspiration from 2 Robots I liked, being Dr Inferno Jr and Tazbot. The idea is to combine a base with good protection from wedges and deflection for spinners with a turret mounted arm to control and work as a srimech. For it to work I think grip is very important. Any advice on which tires provide best grip? I was thinking of using polyurethane wheels from a palletloader that i have but I do not know if they provide good grip in a normal arena. [Zuid-Holland, Netherlands]
A: Mark J. You've failed to mention what flooring you will have in your "normal arena". It matters. What I would recommend for a steel floor would be different from a painted wood surface, which would be different from a dusty concrete floor. My choice also varies with the size of the wheel you want to use. Traction is also highly dependent on the percentage of your robot's weight that is supported by your driven wheels.
Search for "traction" in the Ask Aaron Materials and Components archive and you'll find many posts about tire compounds and traction tricks. You'll also want to read the Ask Aaron guide on Optimizing Robot Drivetrains for tips on getting motor power efficiently to the ground.
Q: The first idea was combining the simple forks from panic attack with a reversible shuffling to gain a small weight advantage, but looking for shuffling robot I only find a lot of a guy with a cardboard robothead, so I let that one go.
A: If you search for 'shufflebot combat robot' you'll get results more relevant than 'cardboard robothead guy', but don't build a shufflebot -- Simple Robots Win.
It might be a bit risky to put such components into the ring but that is where the epoxys come in. Plus any excess weight will be put into making the ring thicker. The design is an outterrunner with about 80% of its mass spinning as a weapon, it can be flipped and continue running.
Basically it can run like Ringmaster but other than using epoxy to protect everything mechanically the design should be simpler. [Zuid-Holland, Netherlands]
A: Mark J. I can't find a question in there, so I'll give general feedback on the design elements you've given:
A: Mark J. It's not so much 'absorb' as 'deflect'. A flat-hard surface offers nothing for a spinning weapon to grab onto or bite into. The inclined angle transfers some of the force of the glancing impact downward to the arena surface and some into popping the attacking weapon up and back. Little of a weapon impact is left to transfer to the body of the robot. Make your wedge smooth, thick, hard, and tough -- then mount it very firmly at a shallow angle.
A: Mark J. It means that you shouldn't take the builder-entered robot 'strategy' descriptions in the Builders Database seriously.
'Foiled!' and 'Foiled Again!' are antweight horizontal spinners from team 'Bad Robit' in Massachusetts. Their spinning weapons incorporate airfoil cross-sections in an attempt to gain ground effect aerodynamic downforce to press them down to the arena floor.
Robots with increased 'apparent weight' - either from magnetic or aerodynamic force - may have better traction and be more difficult to lift. This makes them more stable, but "make wedges useless' is only wishful thinking.
How can I best determine the maximum ratio between spinner and body weight on the Robot? I have a concept and it does involve more than 50% of the robot mass to be actually spinning and I am concerned it will reduce handling by too much.
- Alex [Noord-Brabant, Netherlands]
A: Mark J. The archives have become so large that it can be a challenge to find a specific topic therein, but I do appreciate your effort.
A: Mark J. 'Ask Aaron' has developed and assembled a collection of combat robot design tools and FAQs to assist builders in answering questions like the ones you ask. We develop the tools, you use them to answer your questions.
When you put your motor and robot specifications into the calculator you will find that your robot will be horribly slow (about 1 MPH) and the motors will stall under hard pushing (very, very bad). You should look for gearmotors with at very least twice that torque and four times that speed.
Incidentally, I don't accept robot questions from builders competing in India due to
safety concerns
and the reluctance of Indian builders to search the Ask Aaron archives for answers to their questions. I answered your question only because it was the first Indian inquiry of the New Year. Next time, check the archives -- your questions have been answered multiple times there.
Everything made of plywood (except the vertical disk and wedge on the front) will be made of UHMW when I build the real thing. The robot as of Right now has a top speed of 4.5 mph and the disk has a maximum speed of 20,000 RPM and 800 joules of energy storage. The outer walls and weapon supports are made of 3/8 inch UHMW and the top and bottom are made of 3/16 inch UHMW. Thanks! [Nashville, Tennessee]
A: Mark J. It's a fine idea to build a mock-up using inexpensive and easy to work with materials. Even cardboard is useful to get a better idea of how the design elements relate to each other.
I like your overall design, but I can make a few suggestions:
[Wheel location] is a problem I was worried about and plan on fixing when I build my real robot. I'm actually a bit cramped on space surprisingly so that's why the wheels are in the very back. I think I can still shrink all dimensions by at least 1/4 inch.
A: Cramped? Have you never seen the inside of an insect-class robot? Seriously, you could fit another whole robot in there. You've got to play 3D jigsaw puzzle with the components for maximum packing efficiency. Pull out that oversized Arduino board and battery, slide the drive motors up close to the weapon motor, tip the battery and board on their sides, put them behind the drive motors, and saw the back two inches off the 'bot.
Q: I agree with you that bite at 20k RPM is going to be terrible. I only have it that high in case I have a spinner on spinner match. For normal use, I plan on running it at 12k RPM.
A: Spinner-on-spinner fights are dependent on tip speed, not pure RPM. Your 3" diameter disk will have as much tip speed at 8000 RPM as a 1.5" drum has at 16,000 RPM. A drum weapon that has climbed your wedge isn't going to be able to 'launch' you anyway -- unless your wedge is hinged. Gear the disk down and be kind to your weapon motor.
Q: My logic behind the tall weapon supports is that when I get flipped over, I can slide on them and hit an arena wall or my opponent at a low speed and flip myself back over.
A: From the photo it looks like the wheels are off the ground when inverted. Either way, while you're crawling along 'at low speed' your opponent is gonna be all over you. Using the weapon/floor contact to 'pop' right back upright is popular for good reason.
Q: The reason I have it hinge mounted is because the robot slides on it's weapon supports when it's driving. I plan on having a small insert on the front of the wedge to decrease contact area and of course bending the sides for a more Algos like wedge.
A: Sliding along on the weapon mount puts the full weight of your weapon and wedge on it and allows the mass forward of that point to lever weight off the wheels. You're already struggling to get weight on the wheels, so I think it's an error to let this type of construction add to your troubles. That hinged wedge will also be prone to 'bounce' when it hits an arena irregularity, giving an opponent's wedge a shot at slipping underneath. Poor design.
A:
The experts in fan-downforce are the builders of line-follower and maze-runner robots. The photo at right shows the underside of a line-following 'bot with fan downforce. There is a post farther down in this archive with some links to useful info -- search for 'suckbot'.
General pusher tips
A: Mark J. The FingerTech pulleys and wheel hubs have threaded holes with set-screws that tighten down onto the support shaft to lock them in place. The belt turns the pulley, the pulley turns the shaft, the shaft turns the wheel hub. FingerTech blade weapon hubs have a similar design with screws that pull two sections of the hub together and clamp the shaft in place.
If your design has the weapon rotating on a non-moving 'dead shaft' you can align the pulley/shaft/weapon assembly and drill crosswise thru the pulley into the weapon, fixing the pulley in place with screws into or thru the weapon rotor. FingerTech offers a pre-bored 30 tooth timing pulley designed for this purpose and used on their beetleweight beater-bar weapon.
A: Mark J. Thank you for consulting the FAQ! Upsizing a design by any substantial degree will cause structural problems due to the 'scale factor'. Let's run the numbers for your antweight to hobbyweight plan. You're upsizing by a weight factor of 12:
See this Wikipedia article for a more complete explanation of the engineering effects of the square-cube law.
A: Mark J. I like to position the wheels so they touch the ground, but that's just a personal quirk.
Have a look at section 2.7.7 of the RioBotz Combat Tutorial for the math to calculate placement of the wheels relative to the robot's center of mass to get optimum traction without risk of nose lift.
Caution The way you have the impactors arrayed on your drum will cause trouble. The drum may be in 'static' balance but will be out of 'dynamic' balance. Move the impactors to holes 1 and 4 on one side of the drum, and to holes 2 and 3 on the other side.
A: Cutting that much weight from the rear will shift the center of gravity so far forward that your wheels will have very little traction -- so little that not only acceleration but also turning maneuvers will be severely compromised. The RioBotz tutorial section referenced above explicitly warns against this type of wheel placement.
Q: I currently have .3" thick UHMW, for everything, but .5" thick for the parts surrounding the weapon. Is that overkill?
A: Not by much. The successful 'Saifu' antweight kits run 0.25" UHMW for a similar chassis structure and 0.063" for wheel guards. Note how the impactors are arranged on the drum to maintain dynamic balance.
A: Mark J. I know that I suggested that you build an insect-class robot, Champaign -- but let's compare your desired design to your résumé.
A: Mark J. I'm disappointed in you, Champaign. I thought my advice plus the brickbats thrown from the Facebook Combat Robotics group had steered you away from building a heavy robot. You even posted a 'thank you' on Facebook to the people who convinced you "how stupid you were being". Now you're back to asking about wheels that weigh "only 5 pounds each". Shame on you!
1) Is there a type of wedge or plow shape that's good at deflecting both horizontal and vertical spinner attacks?
A: A concave scoop with a radius a little greater than the spinner you're facing is effective against verts, but all you can really do for horizontal spinners is keep the angle shallow and the surface hard. Design to do two things at once and you end up doing neither well. A shallow dome section like Team Dark Forces uses might be a reasonable compromise.
2) What is considered the "average" size for each weight class? I know that ants and beetles at Peoria could be no bigger than 12" in any dimension, but Battlebots robots can be no bigger than 8 feet in any dimension. Deciding on the exact size of my robot is probably the hardest part of designing a robot (for me thus far)!
A: The 'net wisdom' is to simply make the robot as compact as possible - regardless of weight class. The theory being that a smaller 'bot can have thicker armor and still make weight. That's a good place to start, if you want to be 'average'.
3) This is more of a question about a weapon: How does the thinner end of Cobalt's blade store more energy than the wide end?
A: You shouldn't think about 'ends' storing energy. The weapon is one piece and it's the entire weapon that stores kinetic energy. When you try to stop either 'end' you're trying to stop the whole weapon and the full stored energy is in play.
4) What is a good angle to have leading wedges? My CADs all have varying angles for their leading wedges, ranging from as low as a 17 degree angle to as high as a 50 degree angle! I am also aware that I need to keep them above the upsweep angle. Also, how far should leading wedges stick out?
A: "Good" depends on what you're trying to do with the wedge. Shallow for defense, steep to ram. I like scoops. Don't worry about the upsweep angle.
How far? I've heard that Abraham Lincoln was once asked how long a man's legs should be. He answered, "Long enough to reach the ground." The same applies to wedges.
5) For heavier robots, when would it be deemed necessary to use welding instead of bolts? I intend to (whenever I get the experience) build a heavyweight using only bolts. I also know that the cost of bolts is weight which I've gotta take into account for.
A: There you go with heavy robots. It's never 'necessary' to weld but it is sometimes 'convenient'. Best is one solid piece, but that's often 'impractical'.
6) Against a metal floor, how much traction would plastic have? I found a set of plastic training weights that I could use as wheels (because they're only 5 pounds each!). If not, how helpful would scoring the wheels be? If that's not a viable alternative, would bolting on a bicycle tire to said training weights be a viable alternative for traction?
A: There are lots of different plastics. You can find tables of the coefficients of friction for one material on another. Higher numbers equal greater traction. Rubber on steel runs around 0.6 to 0.8, and structural plastics run from about 0.1 to 0.5 -- but that's not the whole story. A nice thick layer of soft rubber can conform to the surface and get better grip, while a thin sheet of rubber stretched over hard plastic can't do that. 'Scoring' the wheel surface is next to useless on a smooth arena. See what works for other builders as a starting point.
7) Why aren't there many robots made with Magnesium parts? I know the Ringmaster had Magnesium parts, but why isn't it discussed as much as other materials? (Aluminum, Steel, etc.)
A: Magnesium has applications, but exposed surfaces of combat robots aren't their strength. Strong, stiff and very light, magnesium is also brittle, soft and under some conditions flammable! Look up 'magnesium flare'.
Now, stop thinking about heavy robots and build an insect class 'bot. I'm going to ignore future questions from you about heavy robots.
A: Mark J. Suggest you watch some videos of Indian Robowars. A typical Indian combat robot is very slow -- about walking pace. Indian builders favor a 300 RPM drive wheel speed, but for the life of me I don't know why they like slow robots.
A: Mark J. I can post formulas and diagrams about gyroscopic forces that go on for pages, and in fact I have: search the Ask Aaron 'Robot Design' and 'Robot Weapons' archives for 'gyroscopic'. If you really want to understand gyro forces I strongly recommend that you purchase a small toy gyroscope and play around with it.
Any time you apply a force to change the direction that the axis of a spinning mass is pointing, gyroscopic resistance will attempt to redirect that force at a right angle to the original force direction.
Q: I've seen several Antweights ('Odium' from Bot Brawl 2017, 'Debacle' from TeamVelocity's YouTube Channel, and a green spinner in the Team Velocity video of the rumble at NG Conference 2017) that get thrown onto their backsides and manage to drive on their back ends. Is the force being made from the spinner essentially acting as a front-mounted propeller?
A: Horizontal spinners standing on their tails are stabilized by the gyroscopic forces of their weapons, not an aerodynamic 'propeller' effect. Think of it as a very slow gyro dance and then go back to my answer to your first question.
A: Mark J. 'Crazy Susan' fought at one event, lost two matches in a row, and never fought again. It wasn't effective. Hal builds robots for his own reasons, and those reasons may or may not include winning. Don't forget his designs, just don't build one with expectations of success.
A: Mark J. I wish that I could give a clear definition of 'walker', but there is no agreement on a standard rule set. Events that offer a walker weight bonus all encourage builders to contact them with their specific design details prior to building so that the organizers can think about whether or not it qualifies as a true walker. It seems that event organizers can't define a walker well enough to put it into a 'no loopholes' written rule. Here's an overview:
Design 2 A smaller but wider drum that uses outriggers that cover each side of both wheels. While it wouldn't protect the wheels 100%, it would help. I doodled designs with and without wheels.
Design 3 Similar in dimensions to Design 2, but only with outriggers on the inside. This would leave the wheels wide open, but would save weight. These would most likely be oval-ish in shape.
Design 5 Have a small, rectangular area that sticks out the back, similar to the first design, only having a metal bar in the back. The idea behind this is to keep people from hitting the side where the drum is spinning down.
Design 6 Use a long rod with an axe or hammer on it: make both an overhead thwackbot and a full-body drum spinner!
Design 7 Utilize an oddball design like 'Infernal Contraption' or 'The Phreak' to power the drum and put all of the electronics in each wheel. Of course, this would probably be the worst because it would over complicate things a LOT more than necessary (although it might get kudos for creativity).
Design 8 Use one, triangular piece for each outrigger similar to the beetleweight 'Tumbleweed' (Motorama 2006) but with the outriggers sticking out only on one side.
Design 9 Have a tail or spear similar to 'Stinger' as an outrigger, again acting as both a thwackbot and a full-body drum spinner
Design 10 Have a plow in the back similar to 'Demon Duck' acting as a plow and an outrigger
Design 11 Have a very skinny drum and make it similar to 'Heavy Metal' in concept but, you know, lose the metal wheels.
Design 12 Use a cage similar to that of 'Nuts' but with it being connected in the back. The front would not be connected like the back, and instead the bars would roll around the front of the wheels.
Thanks yet again for sharing your knowledge! :D [Champaign, Illinois]
A: Mark J. This one's simple: none of your concepts are competitive. I like your imagination and variations on the concept, but you're basing your designs on a novelty robot from fifteen years ago that was unsuccessful at the time. Why do you believe you can take that design and make it successful against modern robots? Experienced builders won't touch that layout and I suggest that you - as a novice builder - leave it alone as well.
I should point out that 'several people' will tell you that your designs are awesome and that you should totally build any one of them. If I were competing against you I would think it would be awesome for you to build one as well because the video of my 'bot tearing yours to shreds would grant me YouTube immortality. Don't be a chump.
Q: Hey. I wanted to apologize if I seem to be "invading" the forum with my random questions. Probably the BIGGEST problem and the reason why I haven't really gotten a bot built yet is that I find it difficult to tap into my own mind: I have this awesome design in my head, but when I go into Fusion 360 and go to make it, I go blank. Completely blank. It's part of the reason I ask you so many questions (and why I got the Riobotz book): by reading what specifically does or doesn't work or what shouldn't be attempted, it has helped me make better choices in my designs. So, I also guess I gotta say thanks again for answering all of my questions and apologies for somewhat "invading" the forum.
A: No apology needed. Answering questions like yours is why 'Ask Aaron' exists, and I hope that I'm being some help to you. I don't sugar-coat bad news about proposed designs, but that's not an indication that I'm running short on patience or interest.
You're also not even close to invading 'Ask Aaron'. Others have made much greater demands of us, and they were welcomed. I received so many questions from a builder in Texas last year that I gave him his own section in the Ask Aaron Archives -- take a look: The Texas Archive.
One warning: there is a fatal flaw in a couple of your design variations. A 'no body' design like 'Barber-Ous' requires a rigid trailing 'outrigger' to counter the motor torque when accelerating forward. A "wedge with angled sides up front rather than any outriggers" will simply flop back over the top of the robot when you accelerate - like a 'reaction hammer' style robot - and render itself useless.
Q: I was reflecting on your point about the wedge flopping over and serving no purpose. It was then that I got this idea: what if the wedge was intentionally placed in the rear, but had a folded lip? What I mean by that is that it would have pieces of metal welded to the wedge to stop opponents from coming up from behind and hitting the drum in its weakest spot as well as act as an alternative weapon! Even driving inverted wouldn't be an issue: I could ram into somebody with enough speed with the ramp (might work under certain circumstances) OR (more dangerous, but a bit more entertaining) hit them with the drum, now spinning downwards!
A: I don't think you understand the purpose of the 'outriggers' in your design. In order to move, the drive motors require a lever contacting the arena surface to the rear of the robot's direction of travel. Without that lever to counteract the drive motor torque, the tubular chassis would simply spin and the robot would not move forward. If you are using the proposed wedge as your only outrigger it will always flip over to the rear of the robot as you accelerate, regardless of the direction of travel. It is not possible to "ram into somebody" with the ramp as it will always be in the rear.
Watch 'The Master' in this fight against 'Blade Runner' and pay attention to what happens with its hammer weapon when he accelerates and decelerates. A 'Barber-Ous' themed design is not viable in modern robot combat.
Important You requested that I not use the drawing you sent -- but you may have noticed that there are no current robots running similar designs. There is a very good reason: your weapon is unstable. Take a look at the post about polhode motion here in the archives and watch 'Secto' in this video. Your design is not identical but it has the same instability! Also the fastening method you propose for the impactors puts a huge shear load on the bolts, which is very poor engineering practice. The bolts will fail. I'd strongly suggest starting over on the weapon design.
A: Mark J. Is the hamburger bad?
What does that mean? The whole body is a ring shape inside with the drum rolling on top of it?
Okay, I get that.
"...The challenge would be to implement at each wheel an independent braking system that would allow the chassis to spin up without moving the bot around. After reaching full speed, the braking system would release, and the robot would be driven by slightly accelerating or braking each wheel motor."
Um... What?
A: Mark J. The RioBotz Combat Tutorial was written in Portuguese and loses a bit in translation. The descriptions are also a bit brief in places. To be fair, 'Ask Aaron' probably doesn't translate well into Portuguese.
Congratulations on breaking through 6000 questions, the community warmly thanks you from here in western Pennsylvania. [New Castle, PA]
A: Mark J. Thank you, New Castle. I hope 'Ask Aaron' continues as a useful resource for you and the other builders on the Allegheny Plateau.
Shock absorption is a too-frequently overlooked aspect of armor mounting. In combat robotics, layered armor has proven inferior to single-piece armor with rubber shock mounts. The photos at right show the front armor pods and rubber shock mounts used on BattleBots competitor 'Overhaul'. Properly sized mounts will be quite firm -- they will barely flex under the best pressure you can exert on the panel by hand.
A web search for 'vibration isolators' will find items similar to those used by 'Overhaul' in a wide range of sizes. This is reactive armor, not ablative armor. Torque them down snug, without play or slop.
If you really want to try a layered armor, a sheet of solid 'Buna-N' rubber between metal layers would be a good choice. Try about 3/16" rubber thickness for a 15 lb robot.
A: Mark J. First, don't use that machine shop again. A just-passable machine shop will hit a critical bore to ± 0.03mm, and your guys are off by ten times that much. I'd reject it and ask them to try again, but that may not be an option for you. Solutions:
First, I would like to know what some of the cheapest, but EFFICIENT, motors, batteries, power supplies, tires, etc, are for an antweight. I'm hoping to have my first ant to be a drum spinner, but that'll have to depend on how much money I have. [Champaign, Illinois]
A: Mark J. We all hope to make amazing machines, but 'first combat robot' and 'drum spinner' do not go together. You may be surprised to learn what weapon types are most successful. See also this post farther down the page.
I'm not willing to provide a shopping list -- see Frequently Asked Questions #4 and #16.
Q: Second, I'd like to know if a particular metal would work or not for an antweight: it was a thin panel from the school's old fountain, but I managed to save it from being scrapped. I don't know exactly what it is, but I can provide you with a pic if need be.
A: I don't do psychic metal identification. There are hundreds of metal alloys and useful/useless ones look the same in photos. Common metal identification methods.
Q: Third, what kinds of printers can be used to make 3D printed robots? I know a lot of people in the antweight category 3D print, but I didn't know if my school's 3D printer would be able to print parts off: I'm assuming the 3D printers used by roboteers either prints things off in HDPE or UHMW, which is why I was asking if you knew any printers that would be best for this.
A: Mark J. Robot parts are rarely printed in HDPE or UHMW. I suggest that you join the Facebook 'Combat Robotics' group.
Q: Also, while on the topic of plastic, if one were to make a 250-pound robot with 100% plastic armor, how thick must said person make it so that it can be as strong as the armor of, say, Minotaur's, and is it really worth the time, money, and weight?
A: By the time you are ready to build a heavyweight robot you will know the answers to those questions. See Frequently Asked Questions #17.
Q: ALSO also, and this is off topic, do you happen to know where I can find a picture of two of 'The Bishop' from the Robot Wars that was unaired in 1997?
A: No photos. A web search for -- "Robot Wars" "The Bishop" -- will turn up a very poor video of the only match Stephen Gaudio ever won with the 'bot. I believe the robot was taken from the event and thrown off the Oakland Bay bridge. See Frequently Asked Questions #32.
Note - none of the US Robot Wars (1994 to 1997) were 'aired'.
Q: Alright, I have a pic of the metal (and also a pic of another part of the fountain I found as well!) I asked about in my previous question. The one on the left was the one originally in question. I was unable to do any of the main tests in the helpful link provided (due to the lack of tools with my only tools being a soldering iron and some Allen Wrenches), but I was able to find out the following:
A: I understand how enthusiasm leads new builders to plunge past multiple prompts in the 'submit a question' process to 'Read the FAQ'. Don't worry -- if I didn't want to answer your questions I simply wouldn't do it. Nobody has a gun to my head.
About those metals: the link to the metal identification tests was there largely to convince you of the difficulty of the process. I guess you didn't believe me when I said that I really can't identify metal from a picture. Although that is generally true, given the history of the pieces and their apparent use I can take a guess.
Summary - there are lighter, tougher, harder, and stronger materials available for combat robots. Your opponents will be built from them.
Now the real question: how would you go about building something similar to it anyway without feeling bad the entire time, and trying to win some fights? [Buffalo, New York]
A: Mark J. This really doesn't fit in with the Ask Aaron mission statement.
There are two broad groups of combat robot builders: those who build to win tournaments, and those who build to impress other builders with their cool designs and machine skills. I have no issue with 'cool bot' builders, but Team Run Amok builds to win. If you wanna be cool you're gonna have do it without our help.
Short answers:
A) Anything that would be accepted for ABC Battlebots.
B) I'd rather shoot myself.
1) I'm very new to this, could you double check my gearbox choice (or even motor choice if necessary)?
2) I will be using A123 LiFe batteries (3.2v, 1100 mah 30 amp discharge). If my calculations are correct (which I doubt) 1 of these batteries should be able to power the weapon and drive for 25.714 minutes.
How many batteries do you think I need? Thanks for the help. [Hicksville, New York]
A: Mark J. I can't see all your input fields in the image you sent from the
Team Tentacle Torque Calculator
, but it's clear that you have not entered the correct values for the RS-395 motor. Let's start over with the correct values:
The 20:1 ratio P60 gearboxes with the 2.375" wheels give the best performance from the RS-395 motors in a moderate size arena: around 5.5 MPH, reaching that speed in about 6.5 feet. That's ample speed and power to push around a big spinner weapon. The 26:1 gearboxes would be a little easier on the motors, but the 20:1 should be fine.
The RS-395 motors run well between 12 and 15 volts -- you'll need four LiFe cells wired in series to provide 12.8 volts. The drivetrain will use about half of the capacity of the 1100 mah cells in a 5 minute match.
Your weapon motor is a powerful choice for a hobbyweight. It operates in the 22 to 30 volt range, so you will want a separate battery to operate your weapon. That battery will require between 7 and 9 LiFe cells wired in series. You have not given me enough information about your weapon to calculate the battery capacity (mah) needed. Heavier, longer blades will use more battery power to spin up, and the reduction ratio between your weapon motor and blade will also impact current usage. Example, courtesy of the Team Run Amok Excel Spinner Spreadsheet:
So, you'd need one four-cell LiFe battery to run your drivetrain and one 7 to 9 cell LiFe battery to power your weapon. Combined, they should run your 'bot in combat for about 10 minutes on a full charge.
Are you sure you wouldn't like to build a nice wedge robot instead?
Q: Thanks for the quick response. My weapon's current plan is a 5 pound 12 inch diameter 1/2 inch thick S7 steel asymmetrical "disc", shaped somewhat like a teardrop. The thickness is to avoid vertical spinners from breaking the blade. None of this is set in stone but the 12 inch diameter, and somewhat the weight.
My fights will only be 3 minutes long. The bot does strategically not need to be fast - in fact it should be as slow as reasonable to save weight and power consumption. The 26:1 gearboxes look best to me to that effect.
I hope to have as little power left over after a fight as reasonable, perhaps only enough to last 4 minutes in total. That being said, I still think I can squeeze 12 LiFe A123-18650 batteries into my bot, in 2 groups of 4 and (with slight design alterations) 2 groups of 2. But of course the fewer needed, the better.
Funny you should mention wedgebots, as I eventually hope to build a bot to take down Original Sin! Anyway, do you have any blade alteration or battery number suggestions? Thank you.
A: A 12" diameter, 1/2" thick steel disk weighs more than 16 pounds, so your 'teardrop' design must have a LOT of material cut away from the full disk. A simple steel blade 12" long, 1/2" thick, and 2.875" wide weighs 5 pounds. A 5-pound weapon is heavy for a hobbyweight, so be careful with your weight calculations.
The number of cells I'm suggesting for your batteries are not there for current capacity, but simply to obtain the voltage needed for your two motor systems running at differing voltages. You can't run your drive motors at 30 volts, and running your weapon motor at 15 volts would drop it's power output from 1000 watts to 250 watts. 'Tombstone' has this same problem and solves it the same way that I suggest you do: two battery packs with differing voltages.
I'm a bit concerned about the ability of the cells you have selected to provide the start-up amperage needed by your monster weapon motor. The motor is rated 40 amps continuous, but can briefly draw as much as 140 amps under starting load and will draw over 70 amps for as much as two seconds while staining to pull that heavy weapon up to speed. Given that your cells are rated for 30 amps continuous draw, pulling more than twice that current may damage the weapon battery. You may want to reconsider your LiFe cell choice.
Q: Thanks for the advice. I'm happy to lock in 4 1100 mAh batteries (the yellow ones) for the drive power with 26:1 gearboxes, if you think that's not too many.
A: My earlier explanation was not sufficiently clear. A battery pack for a specific application must supply three things:
We have also calculated that the peak current draw of the drivetrain is about 10 amps, so your 30 amp continuous output cells also have that well covered.
That leaves voltage. To get adequate performance from your chosen drive motors you need a battery pack that will supply 12 to 15 volts. Each of your cells produces 3.2 volts:
Q: Now for the weapon power. Apparently the bigger A123s (green) are back in stock. They have a very slightly lower voltage (3.2V) but a higher amperage(50A), plus a maximum impulse discharge of 120A.
However, as I understand it, the same number (7-9) of these green batteries would be needed for the weapon motor's voltage as of the yellow batteries. Since the greens weigh more and are slightly bigger, this is less ideal. LiPos are not allowed at my upcoming event. Is there another battery you recommend instead?
Not using 100% of my motor's capability seems ok to me, as it might help prevent breakage (I think). Obviously I want to use as much as possible, but I'm okay with using less. Perhaps not filling up the voltage requirement completely but satisfying the corresponding Amp requirement would do the trick. The green A123s might be better at that. I currently have 1-1.5 pounds to spare for batteries, and the fewer cells I can reasonably use the better. What do you think?
A: Your problem is that your weapon motor is, as I mentioned before, a powerful choice for a hobbyweight. It requires both high voltage and a high peak current capacity. Having a big weapon motor and not running it at full voltage is a serious waste of power. Power varies with the square of voltage, so dropping a couple of cells cuts your power by almost half:
If you ask around the on-line forums, someone is going to suggest that you build a 9-cell battery pack to power the weapon and 'tap' the pack at 4-cells to power the drivetrain. This is possible, but I cannot recommend it. You'll be drawing more mower from some of the cells than others, and the draw from that big weapon motor may 'brown out' the drive and electronics. Proceed on that path at your own risk.
I think I'd go find a more reasonably sized weapon motor that would run well at four or five cells, downsize the weapon rotor, and run the whole bot off a single battery pack.
A: Mark J. There have been several questions about 'scale factor' and the 'square-cube law' recently. Take a look at this post from 'Urbana' in our Weapons archive and this post from Buzzards Bay in our Design archive.
Given this interest, I've summarized the earlier posts and added it to Frequently Asked Questions #17.
A: Mark J. I generally assume that builders writing in to 'Ask Aaron' are interested in combat robots that will win matches, but an increasing segment of builders are interested in impressing audiences and other builders with 'show-off' designs. While our focus remains on supporting simple and effective designs, I also recognize that one man's crazy is another man's awesome.
The recent long series' of questions about... unusual... weaponry and design has found a place in this archive and I'll keep trying to set reasonable expectations for any design thrown at me.
A: Mark J. It's a common error for new builders to assume that a given combat robot performs well largely because of the design. The robots you mention are successful for many reasons. They are:
As with every response, your time is greatly appreciated! [Champaign, Illinois]
Strike 2 You should know quite well how I feel about complex combat robots. I've made that clear in answering your prior questions.
Strike 3 There is no YouTube channel for 'AltaPowerDog'. Please be more careful with your spelling.
Q: I would like to chime in the horizontal clamper question. There IS a channel called AltaPowederDog (he won a competition with a cardboard bot).
Anyways,I came across a video of Japanese sumo and those bot are fast! Can you explain how they are so fast? [Perth, Australia]
A: Mark J. I've heard of 'Australian Rules Football', so I suppose there may be an 'Australian Rules Baseball' as well. Perhaps three strikes aren't enough in that league?
Here are a few more YouTube channels that do not exist:
Japanese Sumo: We have discussed the incredible quickness of autonomous sumo bots multiple times here at Ask Aaron. We've posted videos, we've discussed suitable motors, and we've calculated required downforce levels. You ignored the plea appearing directly above the box into which you typed your question:
I'm going to provide you with a correctly spelled and formatted link that will transport you directly to one of several archived Ask Aaron posts which discusses how sumo bots achieve their quickness. By clicking on the link you agree to be nice to some total stranger who asks you for something they could do on their own but who would rather inconvenience you. Here you go: Sumo Magnetic Downforce.
P.S. - A cardboard bot? Big deal. Team Run Amok once won a competition with a yam, four nails, and a girl in a mouse suit -- but you'll need to buy me a beer to hear that story.
A: Mark J. There's a theme to your questions. New builders often have some difficulty recognizing that there are two broad groups of combat robot builders: people who build to win tournaments, and people who build for other reasons -- usually to impress other builders by showing off their cool designs. Your questions are (almost) all about goofy 'show-off' designs that fit into the latter category. I have no issue with 'cool bot' builders, but Team Run Amok builds to win. If you wanna be cool you gotta do it on your own.
I kept my answers short so that I could get back to you quickly. Feel free to ask for more info on specific questions...
1b) Do face spinners cause issues in driving depending on the way they spin? Would it be possible to have it spin in a way that makes it easier to drive forwards?
1c) Why are face spinners never seen in heavyweight competitions nowadays? Are they ineffective? Do they not upscale well? Is there a way to make them effective in the heavyweight categories?
Face spinners are a lazy builder's way to add some sort of active weapon. Hit one edge you throw your opponent in the air, hit the other edge and throw yourself in the air. Whichever way you spin them they aren't viable. Inefficient, unpredictable, and nearly useless; the biggest 'do' is just don't.
The 'Polar Vortex' electric lifter design is awesome. It takes all the impact load off the lift mechanism but keeps full lift functionality. As a flipper it would be really dumb: blunting flipper efficiency by adding unnecessary mass to the flip, and flipping your own robot with each use. Awful combination.
3b) How heavy would you be able to go before it became nearly impossible to make?
3c) Would a brushbot qualify for a weight advantage, if given?
Brushbot: no reverse, slow, pitiful pushing power, and no weight bonus under common rules because the propulsion is derived from rotary motion. Pick something else.
4.5) If not, would a design like Aftershock work with a massive drum spinner?
A gyroscopic precession 'walker' could technically 'work' with any style of vertical spinner -- but tilting it back and forth to 'walk' would require a lot of space under the drum and leave one end of your drum high off the arena floor when walking. Add to that all the disadvantages of the slow and forward-only precession and it's clear that it wouldn't be competitive.
In a wheeled robot like 'Aftershock' a 'massive' vertical spinner can cause problems with maneuverability. Check your specific wheeled design with the gyroscopic effect calculator to see if might be unstable.
I don't know and I don't care -- but I believe you now hold the record for most questions in a single 'ask'.
Read our Spinner Weapon FAQ to learn what design elements make a spinner weapon effective. Once you understand the energy storage principle of a spinner you'll be able to answer your own question about miter saws.
Friction drive saves weight and complexity so I'd really like to tell you that it's a viable option for combat robot drive trains -- but it isn't. You might get away with friction drive for a spinner weapon, but you don't want to deal with the slippage and bearing side-loading for your mobility drive.
Search "Barber-ous" in the Ask Aaron Robot Weapons archive for my notes on concentric drum spinners.
Do not underestimate the impact of size and scale on weapon effectiveness, and do not underestimate Dale Hetherington's engineering skills. The miracle of 'Warrior' is that Team Whyachi got the 'Spin Kinetic Force' weapon to work at all. There are multiple posts about Warrior SKF in the Ask Aaron Robot Weapons archive.
10b) What do you think would need to be changed to make Pussycat competitive today?
10c) How well do you think Pussycat would perform with a bigger flywheel in the bot's center with a more compact body?
Once in a great while a perfect combination of oddball design elements can come together to create a beautiful and unique creation that performs above all expectations. Such a thing was 'Pussycat'.
Pussycat was difficult to fight because it responded to attacks differently than did other robots. It was difficult to get far enough 'under' to flip, and it rolled and spun away from pushybots. That worked well in events where effective spinners were rare, but in current competition it would be torn to bits. It was awesome in its time, but trying to 'improve' it by upgrading the weapon would be a error; change any single element and the design degrades into just another odd conglomeration.
If you want to get one of the limited number of slots at ABC BattleBots you need to propose an unusual design. Team Fast Electric Robots decided that a spinner on a lifter arm might impress the selection committee and get them on TV. The design got them a tournament slot, but it didn't go well.
The small spinner weapon had too little mass to rack up points in the damage-heavy BattleBots scoring system. The lifter itself is very effective -- note how 'Whiplash' (aka 'Splatter') won a semi-final at Robogames '17 with the spinner disabled -- but without a damaging weapon their TV career was doomed. Do not split your weight allowance between two weapons!
12b) How difficult would said bot be to drive upside down, and is 45 degrees way to steep?
Cambered wheels, as favored by Donald Hutson, have no substantial benefits and several design drawbacks. Donald uses them as a trademark and designs around their drawbacks, but I can't advise that you do the same. Keep the wheels upright.
I know that this was a huge load of questions, but your response to any and all questions is greatly appreciated!
Thank you! [Champaign, Illinois]
A great deal of very clever engineering talent has spent much of the last 25 years designing and testing combat robot variations. If the design elements you're asking about had benefits outweighing their drawbacks, you'd see them on successful robots. If you want to win, keep it simple.
Q: Hello! I have returned with another large load of questions! Some of them will be questions I already asked revisited, some will be additional questions, and some will be brand spanking new. I know some of these questions are kinda dumb, but it's actually late where I'm typing this, I'm tired, and wanna go to bed, but I also had to ask you these questions before I forgot. I would write several more, but I'm not really feeling in the mood to do so. As always, your response to any of these questions is HIGHLY appreciated. This is really the only place I can ask these questions without people acting like I'm asking them to give a limb and a left kidney.
Thanks! [Champaign, Illinois]
Personal thoughts: when my 'bot is upside-down I really wish it had a self-righting mechanism. Sometimes I remember that I built one in. Then I'm happy.
If I was lying face-down on the floor, would you try to turn me over by lifting me up to my feet and then lying me down onto my back? It's easier to just roll me over to the side. Same thing with a 'bot: take the easiest path. Sometimes you may have a lifting arm or flipper oriented the 'wrong' way, but since it's already there it may be a simple matter to go ahead and modify it to self-right. Do what makes sense for your robot.
Wider wheelbases slow down the turning rate of the robot. A wider 'bot also has more area to armor and more area for your opponent to attack. Keep it reasonable.
European flippers often have relatively short-throw, big diameter rams fixed to the chassis with the weapon arm floating on top. This design is useful in flippers designed to toss opponents out of the ring, which is a common winning tactic in the type of arenas used in Europe.
North American arenas usually have very little (if any) space around the arena into which an opponent may be tossed for the win. American flippers are designed around longer-throw rams with pivot mounts at both ends to control a toss high into the air for maximum damage to their opponents.
Different arenas -- different tactics.
No. At the time those robots were competing spinner weapons did not have the high energy storage levels seen in current competition. Those designs are not structurally strong enough to survive the impacts seen today.
I see little advantage in using cone-shaped ends on a drum weapon. The design would store less rotational energy than a conventional drum of the same mass and it would be more difficult to build. The tapered ends may be an attempt to defend against horizontal spinners, but I'd like to see that work in practice before recommending the design.
You asked about 'face spinner' weapons in your last set of questions. The same problems that I listed for face spinners apply to these designs as well. The design is only useful if you have a weapon motor too bulky to mount in a conventional manner and you want to add a spinner weapon as kinda an... 'Afterthought'. I don't think that name is coincidental.
Entirely a 'show-off' design. Only relatively low kinetic energy spinners can be slowed and sped-up quickly enough to achieve 'melty brain' translational drift control. Not competitive in any weight class.
7.5) What about Spin Kinetic Flippers?
Too mechanically complex to be reliable, and why bother when other designs are effective? Builder Dale Hetherington has been working on flywheel flippers for more than a decade and has some interesting sub-light designs, if you really want to try one. Start with T-Boner, then browse his other robots.
Which is better: aluminum or steel? Depends on the application. Same for plastics.
For a multibot? I don't like multibots in general. See my answer to the next question.
About 300. It's like going bowling with a basket full of ping-pong balls; you can't hit a bowling pin with enough of the balls to knock it down.
Incidentally, 'Cone Army' does not exist. It was 'entered' in the 2017 Motorama event as a 'Superheavyweight' which was the event code used to purchase a parking pass. Actual weight classes for the event topped out at 30 pound feathers and sportsmen.
Update - Wedge Industries wrote in to tell the full story of 'Cone Army':
I remain hopeful that one day the cones shall get the opportunity to fight the good fight and ascend to RoboValhalla, but until that day comes, Cone has to keep his day job protecting the citizens of Upper Saucon Valley from road hazards.
- Alex H., Wedge Industries
See my answer to question #3 above. Front-hinge flippers are very good at low-arc ejections, while rear-hinge flippers give you height.
The torque reaction when spinning up an FBS is hard enough to control with conventional wheels. Ditto controlling the ricochet when you hit something. With omni-wheels the thing would be a hockey puck.
You don't. Physics is a harsh mistress.
Some builders believe that combat robots are like 'Rock, Paper, Scissors" -- that every design dominates some other designs and is in turn dominated by another design. 'Huge' has vert drum weapons pretty well covered, but picture 'Huge' against a big horizontal spinner...
The current crop of successful robots look the way they do because they are the best solutions to the design challenge given the available technology and metallurgy. The oddball stuff is either just for fun or simply outdated. I'll say it again: if you want to win - keep it simple.
A: Mark J. We discuss general LiPoly mounting considerations in the Ask Aaron LiPoly FAQ. Actual mounting technique varies with the size of the battery, but you're correct that zip-tie mounting is to be avoided! Hard case lithium batteries are worth considering, but the selection of hard case batteries is poor compared to LiPoly soft-packs.
My favorite mounting technique at the moment is to make a fabric sleave to hold the battery. Tabs on the sack can be bolted to the chassis and the fabric distributes loading on the battery over a large area.
A: Mark J. The Tentacle Drivetrain Calculator
shows that two of those motors in a 20 kg robot would exceed both their torque and amperage ratings by a factor of three under combat conditions. In addition the robot would be very slow, crawling along at less than walking speed. The motors are not suitable for your purpose.
A: Mark J. There isn't a simple answer to your question. Successful combat robots span a broad range of speed and acceleration parameters due to variation in weaponry, arena size, attack strategy, and driver preference.
How well do you think its design would hold up in different weight classes? If I were to go with a drum, say, 3" x 3" x 3" for a 30-pound robot with this design, how well do you think it would perform? Any tips or advice other than to "not make it, test it, or use it the way these people did" on building a similar design?
Your help would be greatly appreciated! [Urbana, Illinois]
A: Mark J. I'll admit to being a fan of Indian robots. There is a beauty to the re-purposing of scrap items into a functional machine, and there is a keen sense of suspense in their battles. Your pic of 'Angar' is particularly appealing: short-coupled, large worn tires and wheels, exposed motor -- almost steampunk and kinda Road Warrior.
You've no doubt noticed the VERY slow pace of Indian robot combat. The competitors will ease toward each other and carefully position themselves, then one machine will dart forward a few inches to make contact. This persists even in combat with wireless robots -- 'Angar is an 'old school' Indian robot trailing a cable to a control box that also provides electrical power. This style of combat is not going to work for you in fast and aggressive western robot combat, and that presents some problems with the design:
Response: Hello! This response is composed of two parts, so sit tight:
First, I read your response to my question regarding Angar. I see the issues with things such as drivetrain and whatnot. However, I do have a few questions about your response:
Second, I mentioned Infernal Contraption a moment ago. I was wondering if you would have any tips on building an axlebot that is also a large drum spinner (as in Yeti-sized big). I do know the pros and cons of these designs, but I would like to know what you think!
Thank you for all of your help! [Urbana, Illinois]
Volley: Mark J. An assumption I make about all questions that come into 'Ask Aaron' is that they are from builders who have a primary interest in building winning robots. I have discovered that this is not always the case. I have no quarrel with builders who have other ambitions, but our design philosophy is centered on building simple and effective combat robots that win matches. If your primary goal is to be unique and odd with effectiveness secondary, I'm likely not the best target for your questions. This has come up previously. That said, I'll offer what help I can:
I'm not a fan of the drum-axlebot concept for reasons given above -- but search the Ask Aaron Robot Weapons archive for "Barber-ous" to find a post about the concentric drum axlebot. You may harvest some ideas that might be applied to your line of thought.
A: Mark J. The practice is not effective. Simply scaling up dimensions quickly runs into a problem with the Square-Cube Law.
Consider what happens when you double the dimensions of an object: the volume and weight of the object increase by a factor of eight (height x width x depth = 2 x 2 x 2 = 23 = 8) while the cross-sectional area and strength of structural components only increase by a factor of four (height x width = 2 x 2 = 22 = 4). As a real-world example, ants can get by with tiny, hair-fine legs -- but elephants require legs as thick as tree trunks to support their mass.
You also run into trouble with the power of larger motors growing faster than their surface area, leaving the motor with too little surface area to effectively dissipate its generated heat.
A: Mark J. Thanks for the props, Scott. Several places in these archives you will find the following advice:
There are exceptions -- foam 'servo' tape is useful to hold very small electronics, Zip ties are useful to bundle wires out of the way, and the proper adhesive can bond structural components if properly used. So how do you secure your 89 gram ESC? I'd use automotive hose clamps looped thru the CF (picture below). They're heavier than other options, but they sure aren't gonna break!
Take your pick. Either will work.
A: Mark J. 'Bombshell' was designed to accept multiple modules in the central weapon bay. The outer drive pods have the drive wheels on one end set in conventional position toward the outside edge of the 'bot, while the other end has the drive wheels set well inboard -- actually encroaching on the weapon bay. This offers advantages depending on the weapon module used.
With the lifter it'd be run wide side forward. As far as handling, it actually drove quite well. We had plenty of drive power to turn when we wanted to, so one of the major bonuses of the odd layout was that the narrow side helped the bot track straight under acceleration.
A: Mark J. Since we're talking about a design concept unrelated to a particular event I think we can avoid the mystery and let the readers know that we're discussing 'Razer'.
This drivetrain design is well known to builders but has limited utility. The omniwheels on the rear of Razer were of greatest importance in close quarters, allowing 'bot to pivot around the forward-set front wheels and bring the crushing weapon into play even when the opponent was already in contact. This specific type of 'maneuverability' would not be of use to a rambot, which requires rock-steady straight-line running ability. Although potentially useful for a spinner weapon, it would be difficult to place the front wheels far enough forward to make this a useful tactic for currently popular spinner styles.
A: Mark J. Spinner defense is best accomplished with perfectly smooth, hard, gently curved surfaces on the outside of the robot. No sharp edges to give spinners a place to 'bite', no soft materials for sharp spinner teeth to dig into -- so absolutely no wood blocks!
You'll want to make your wedges out of harder material than aluminum. A hard, curved scoop is the preferred shape for spinner defense. Keep it between you and your opponent, and watch that they don't get to your wheels. Practice your driving until you can do this without even thinking about it.
Q: Hi it's the wood block guy and I read your previous message sent to me (I know not to use a wood block now I just wanted you to know it's me) but anyway I wanted to know if this same design/strategy would work against drums, eggbeaters, and vertical discs/bars.
A: This type of scoop-bot is known as a 'spinner killer'. It is very effective against vertical spinners, assuming that the curve radius of the scoop is at least a little larger than the radius of the opponent's spinner weapon. Be very careful with the vertical edges of the scoop when facing a horizontal spinner: pay attention to the direction the weapon spins and keep the edge of your scoop away from the incoming weapon strike.
Q: The wood block guy (yes again!) and I was thinking about an interchangeable weapon so that it it would look similar to Tornado form Robot Wars (a spike on each corner with one large one in the middle for the front). Would it be an effective weapon against any specific type of bot or should I just not bother and focus mainly on the wedge/scoop?
I have a little driving practice with the Battlebots Hexbugs however I'm not sure if that helps (you said to practice driving in a previous question).
A: Spikes are very useful against robots armored with:
Every robot drives a bit differently and it is crucial to finish your 'bot well before the tournament so that you can practice and adjust the response of the robot to your liking.
Another question is can you tell at what rpm I should rotate my drum and what diameter and material I should go for my drum? Can you suggest some motor alternative to A28-400 ampflow motor for rotating the drum as it's too costly.
P.S My current drum is about 13 kg with 18cm diameter and 4800 rpm rotated by E30-400 ampflow motor. I am going for 120 lbs category [Tamil Nadu, India]
A: Although I very much wish to support the technical aspects of robot construction in the energetic and expanding Indian subcontinent, I am also greatly worried that I may be contributing to an extremely dangerous situation for both builders and spectators. This has brought me to a painful decision:
I will point you to the Ask Aaron Spinner Weapon FAQ for guidance in the design of drum weapons and weapon motor selection. I will not, however, make specific recommendations.
I can also warn you that the construction of a reliable custom gearbox is well beyond the ability of the average robot builder. You may find some useful information on multi-stage chain and sprocket drivetrains elsewhere in this archive.
Q: Hi Mark, I am the Indian guy who asked the question. I think you are still under the wrong impression that arena used in our competitions are unsafe. Now most of the places in India use polycarbonate sheet walls for the arena. The good teams don't participate in the competitions whose arena are not safe for fighting due to obvious safety reasons. The sheets in the image are 10mm thick.
A: I follow Indian robot combat closely. I'm one of the moderators for the 'Combat Robotics India' Facebook group and I review the arena construction details of all the events that post there. I also scour YouTube for video from recent Indian combat events.
I can agree that Indian robot combat arenas have improved in the last few years, but there are still MANY events run with completely inadequate containment. The current Indian standard for a 'safe' arena for 120 pound robots would not be viewed as adequate for 12 pound robots in the US or Europe. Your current drum weapon - as described in your post - stores more than 10,000 joules of energy. On a 120 pound robot that's more than enough to breach 10mm polycarbonate walls, let alone the more common Indian arena containment.
I receive many requests from Indian builders who are interested in building more and more powerful weaponry for their robots even though the arenas barely contain the current weaponry. I have no way of knowing if the question comes from a 'good' team that will compete in a 'safe' arena, or what their workshop and testing safety practices might be. I don't want to be involved in a death or maiming resulting from design assistance I might provide.
I believe I understand Indian combat safety quite well. If you want information on making events safer I'll be glad to assist. If you want information on more powerful robots for your current arenas the answer is 'no'.
A: Mark J. Top-ranked combat robots like 'Algos' do not have design features present just to look cool and waste weight allowance. In this case, the turned-down wedge end caps serve two important purposes:
So I have my ideas pretty much all drawn out. But it's just that, just ideas. The problem I have is convincing my parental figure (my mother, my father (who funnily enough introduced me to Robot Wars) passed away 13 years and 2 days ago on writing this message) into doing this, as she seems a little pessimistic with it all.
She has two concerns that kind of stand out, understandably;
One more question: Would a decent scooter motor work? Say, a 750 watt motor ran at 24/36 volts? Or would that lead me to "The Burger is Bad"?
If you've answered these questions before, then I deeply apologise. But I thank you for the time you take for reading this question in the first place.
Oh, and Merry Christmas and a Happy New Year when it comes around! [Sheffield, England]
A: Mark J. Hello, Sheffield. Thank you for your kind holiday wishes.
Your component selection questions are all very reasonable and address problems encountered by all combat robot builders. They are also difficult to answer, particularly with the limited information you've provided about your design.
Take a look at Frequently Asked Questions for advice on drive motor and ESC selection. A great many heavyweight robots have been powered by the motors from salvaged electric wheelchairs ('invalid chair' is the Briticism, I think). These are easy to mount, have an integrated gearbox, and often come with suitable wheels.
Many successful combat robots have bolted steel tube chassis. If the chassis members follow good structural design guidelines and use gusset plates to reinforce the joints, the chassis strength can equal that of a welded chassis. Bolted construction also makes on-site repairs a good deal simpler.
Also, arc welding is something of an art -- there are lots of ways to do it wrong and only one way to get it right. It takes many hours of practice and guidance to become good enough at it to reliably make welds that will hold up to combat stresses. I would much prefer to have a novice bolted joint than a novice welded joint holding my robot together.
Mark J. I generally don't accept 'guest commentary' from builders, but I received a note from Rob at 'ARC Robotics UK' offering support in response to the question from 'Sheffield'. Since I'm 4900 miles away, I thought it might be useful to port some advice from a more local source:
In terms of approaching your mother, think through it. How much is it going to cost? What tools will you need? Do you have any help/teammates? What could you do to negate some of the cost? Are there local resources that you could tap into (for example, a school's DT lab)?
-Rob [North Walsham, England]
A: Mark J. Family robot fight -- awesome!
A slipping belt drive is the standard weapon drive in larger robots like yours. A standard 'V-belt' set a little loose works nicely. Include some tension adjustment in your design to fine-tune the amount of slippage and you'll be fine.
A pair of 'hacked' generic 18 volt cordless drill motors are adequate to give your 'bot enough speed and push for a family fight. There are many guides on hacking drill motors on-line. Keep your wheel size small -- no more than 10 cm diameter -- to keep your motor loading reasonable.
A two-wheel drive 'bot won't have a huge pushing potential, but keep your weapon spinning and you'll earn some respect.
A: Mark J. If you're asking someone for a favor, the correct form is:
You didn't mention what weight class you're considering, but there are some serious problems with these designs:
1) I've learned that construction sites will lay a crisscross surfacing weld on their heavy machinery scoops, such as an excavator bucket. They do this to increase the surface hardness and to lengthen the life span of the component. I was wondering how well an anti spinner scoop could hold up if I were to put on a layer of weld and grind the surface flush. Would this make for a stronger anti spinner scoop, or would it not do anything?
A: Mark J. That's an imprecise, labor intensive, and unpredictable method of hardening a steel surface. Suggest you read up on the wide array of more standard hardening techniques. I think you'll get better results.
2) I've noticed that many builders when they weld will only do one pass. How come builders don't do multipass welds? [Oregon]
A: Multipass welds are only needed in very specific situations. There's a good discussion on when to use multipass at the Miller Welding Forum.
A: Mark J. I have no experience with either of those software packages. You'll need to get your CAD advice elsewhere.
A: Mark J. See this post farther down in this archive. The post is for teeth on chain sprockets, but the same formula works for gears.
3 minutes later:
Q: what do we need to make a combat robot ? [Pulau Pinang, Malaysia]
57 minutes later:
Q: what do we need to make a combat robot ? [Pulau Pinang, Malaysia]
A: Mark J. An engineering mindset, mechanical experience, and the ability to read all the way to the end of a sentence. While you're developing those skills, read the Frequently Asked Questions.
My plan is to increase the down force by a vacuum or downward thrust system to take advantage of my powerful drive and grippy wheels, but at the moment I'm unsure of the design to use. I've looked into possible several options, but don't know which would be most suitable. Perhaps a large ducted fan, with an open base to suck in as much air as possible, or a vacuum pump with a flexible skirt to conform to the floor? Maybe the ducted fan with the flexible skirt? I just don't know. My goal is to add at LEAST 10 lbs of additional downforce, but that is the absolute bare minimum and I want as much as I can use. I really don't know how far I can go with this, but if Terrorhurtz could use this technology to climb a wall...
INFO: I've equipped it with 6 Fingertech sumo wheels, 4 Banebots P60 38:1 gearboxes hooked up to 550 motors running at 14.8v, and a massive Breaker Box-style scoop. The matches take place on a smooth plywood ring 10ft in diameter, and are 6 minutes total if the entire 3 3-minute matches last their full length (not often). I've never come close to draining the battery after a fight, and should have plenty of power to spare for a vacuum downforce system. [Ontario, Canada]
There are a couple of discussions about 'suckbots' on the Pololu forum and blog:
I don't have a tool to help determine how powerful a fan is needed to meet your goals -- I think this is probably a 'trial and error' project. Let me know how this works out for you.
I read that 'beta' uses a gearing system and then cams to keep the load on the motor right so that its always in its maximum power band. Neat stuff! My question is, etc. How would you begin to calculate such a thing? I'm guessing you calculate the weight of the hammer at the end of the head after gearing as the load to start with, but what would the load be once it is in motion so you could figure out the cams?
Not looking to build one I just thought it was a neat question. [Dublin, Ohio]
A: Mark J. I've vowed to avoid calculus in the answers I give here at 'Ask Aaron'. I'm severely tempted to break that vow for this question given that the answer involves a system of non-linear equations, but I think I can provide an approximation that's plenty close enough for combat robot purposes while leaving a trail of crumbs for the 'Sons of Newton' to follow if they so desire.
Calculating the acceleration of a directly-geared electric hammer weapon is essentially the same as for a spinner weapon, the difference being that the spinner has unlimited rotation and can build energy over an extended time period while the hammer is restricted to (typically) 180 degrees of rotation.
In 2010 I took apart the Team Run Amok Excel Spinner Spreadsheet and re-wrote sections of the code to calculate and graph the energy storage of a hammer weapon of known configuration powered by PMDC motor with a fixed gear reduction thru a default rotation of 180 degrees: the Run Amok Hammer Spreadsheet.The hammer spreadsheet guides the user to find motor gearing that places the motor power peak at the mid-point of the swing in order to optimize the power output. The spreadsheet accounts for gravity, but does not account for the rotational inertia of the motor armature because that information is rarely available. I took this opportunity to clean it up a little from the previous beta release 0.9 (no pun intended) and now call it version 1.2.
The calculations are relatively simple because the torque output of a PMDC motor is linear. Now you come along and want an explanation of how to design snail cams that make the applied torque non-linear and extend the period during which the motor operates near peak power. If I were still teaching at university I'd ask you to see me during my office hours and then keep my office door locked and the lights out for a week in hopes that you'd give up. Unfortunately, I no longer have that luxury.
The overall concept is to start with a high gear reduction to allow the motor to quickly spin up close to 50% of its no-load RPM -- the point at which max power output is achieved. Gearing reduction is then decreased as the snail cam rotates to keep the motor near that same RPM thru the rest of the hammer swing.
Take a look at this discussion about axe mechanisms on the Australian Robowars forum. The whole exchange is worth reading, but note the post where 'kkeerroo' discusses his approach to 'snail cam' design:
You can use the hammer spreadsheet to aid you in finding a solution similar to that used by 'kkeerroo':
This 'four stage' approximation will provide a good practical solution given the multiple unknowns and unattended variables. Calculus will give you a more accurate theoretical answer, but the real-world result will be much the same.
Note: all this fancy machining and extra moving parts are extra pretty and quite fascinating, but due to the torque characteristics of a PMDC motor the impact on energy storage by the hammer is not all that impressive -- about a 20% theoretical increase over an optimum fixed reduction ratio. It is much easier to use a more powerful motor to start with and save yourself the grief.
Comment: Thanks for the answer to my 'beta' question! Also, on your tools page you don't have your hammer calculator spreadsheet!
Reply: Mark J. You're welcome. I haven't advertised the hammer spreadsheet for a couple of reasons:
Please let me know what you think! -Blockhead Robotics [Illinois]
A: Mark J. I recommend caution in building to compete at BattleBots. The competition lives and dies on television ratings and the ratings weren't good this year. It's unclear if the show will be back for a third season, and if it is renewed you still have to gain approval from the show producers in order to compete. I know of several established and competitive teams that failed to gain acceptance to this year's tournament. Don't get your hopes up.
Back to your questions:
A: Mark J. Fairyweights (150 grams), antweights (1 pound), kilobots (2.2 pounds), beetleweights (3 pounds), mantisweights (6 pounds); aren't there enough insect weight classes? Who decided we needed a 4 pound class???
You haven't given me much about your design or what rules the event will run, but in general I like a large footprint on insect 'bots. Team Run Amok's successful six-wheel drive beetleweight lifter 'Zpatula' is 12" wide by almost 16" long!
Conventional design theory says that a smaller robot is better because the armor can be thicker with less area to cover. This is true, but the larger footprint allows for much greater turning torque, plus the larger 'bot will react less to weapon impacts. Judges also generally respond better to a larger robot; the size differential works in your favor.
Go bigger and dominate the small arena.
Beetle, wedge. Front steel wedge (1/16) at 35 degrees. 4 drive motors (970 rpm servocity econ motors). 2.875" Banebots wheels outside if it matters. Aluminum base. My question refers specifically to the base plate to relative dimensions. Do you think an overall size of 8" wide x 9" long with 1/8" aluminum is better than 1/4" aluminum with dimensions of 6" wide by 9" long?
Thanks [Pennsylvania]
A: Mark J. I don't have much to add to the previous answer. I like large footprints for insect class 'bots for the reasons given.
You haven't given me enough structural detail about your chassis for me to comment on the adequacy of the baseplate thickness, but as a general comment 1/4" unspecified aluminum alloy is a very thick baseplate for a beetle.
See also: The Hamburger is Bad.
A: Mark J. Seems like a good idea, doesn't it? Many builders have tried to use magnets to increase traction or fight gyroscopic lift, but over and over it's been proven that chassis downforce magnets are much more trouble than they are worth in combat robots.
The Total Insanity Gyroscopic Force Calculator can help adjust robot design to better cope with the weapon gyro forces.
In episode 5 of Robot Wars (2016) there was a 2-wheeled vertical spinning bot called 'Infernal Contraption'. Due to the weapon's placement being so close to its high-torque drive system it would easily invert itself by just driving forward (a la any overhead thwackbot).
Is there a rule of thumb or formula I could use to ensure that I can maintain good torque in my drive system without ending up flopping around like a Magikarp-out-of-water?
Thanks! David R. [Livermore, CA]
A: Mark J. Getting a 'bot to do the whole torque-reaction overhead hammer thing requires some deliberate design work to set the center of mass close enough to the drive axle and eliminating rear overhang. The chance of doing this inadvertently is vanishingly small, but getting the center of mass 'just right' does require some planning.
Have a look at section 2.7.7 of the RioBotz Combat Tutorial for the math on where the center of mass should be placed in a two-wheel 'bot to get optimum traction without risk of nose lift.
I like the 'Magikarp out of water' analogy. I'll save the image and use it to adorn unworkable or needlessly awkward solutions. Watch for it.
A: Mark J. 'K2' is a lightweight combat robot from Team Velocity that last fought at RoboGames 2015. Overall record: 38 wins, 12 losses. Currently ranked #3 among lightweights.
The chassis layout if 'K2' is similar to the lightweight version of the BattleKit but there are design and material differences:
A: Mark J. It's bad on many levels.
First - you can't have 250 simultaneous users on 2.4 GHz spread spectrum R/C. The bandwidth tops out around 80 users - depending on the specific system. Whether it's a good idea or not, it just won't work.
Second - ABC BattleBots is all about violent destruction. They aren't going to accept an entry that would fight like termites nibbling at a log.
Assuming you could overcome those deficits I think you're still sunk.
I have read through the archives dozens of times and, due to the weight class, my teammates and I decided to create a bot quite similar to Breaker Box. Problem is, everyone on the team is worried that due to the passiveness of the bot (see: Stinger losing to Mega Tento) it will lose in a judge's decision. Our arenas are quite small, and 99% of the people show up with a drumbot, eggbeater, or some other variation of it, so we need something that will be able to continuously be ready for a fast attack.
I guess the main question is, do you think that a Breaker Box type robot is still the best option, due to American rules favoring damage over everything else?
Thank you for all that you do! [Ohio]
I don't recall you mentioning what weight class you're building. You may want to study Breaker Box's beetleweight sibling 'Wallop'.
Comment: Sorry for the lack of information about the Breaker Box design-it's for a 15 lb. bot. Thanks for the advice on the B.B. vs. regular competitions, it makes sense. I guess we're just a little nervous is all, since it seems every competition we go to has a drum or egg beater as a winner.
Response: You're welcome! Some builders like to think of robot weapon selection as a game like 'rock-paper-scissors'. If your opponent is going to play 'scissors' with a drum spinner, playing 'scissors' back with another drum gives you no advantage. Play a spinner-killer 'rock' and you're taking it to them.
Comment: On a side note, we did have a 4 bar lifter our first year, but it was quite sad. Yes, I know, our site is quite outdated and sad - we are overhauling it sometime in the fall.
We are already working on CAD models for the new design. I will send you photos as we progress, as well as any questions we may have.
Thanks again!
Response: Looking forward to your updates.
Also, im working on a bot for any robotic compition and its mainly going to be a middle weight with a spinner, are there any other suggestions?
Thanks, Sean. [Georgia]
A: Mark J. The cost of a 250 pound BattleBots competitor varies a great deal depending on how much of the machining and general metalwork you can do yourself and how much you have to 'farm out' to professional fabricators. I'd estimate that a horizontal spinner with a full set of spare parts might average $30,000 -- 'Tombstone' maybe a bit less, 'Son of Whyachi' quite a bit more.
My suggestion for a first robot is to build a lighter weightclass. You will make a lot of mistakes with your first 'bot and those mistakes are much cheaper in a lighter weight class. Read thru the Frequently Asked Questions for more first robot tips, and read 'What Weapons Win' for some guidance in weapon selection.
A: Mark J. No one from New York would list their location as 'N.Y,USA'. Your question came in from an IP server in Bangalore, India. I have good reason to reject questions from builders competing in India. Your shallow lie is an attempt to endanger others for your personal gain. You disrespect me and dishonor yourself, Kuthi.
I noticed that 'Complete Control' uses a large worm gear to drive its lifting forks. This gives them significant speed reduction in a compact package. This got me thinking about how almost all the combat robots I have seen use some combination of chains, pinion gears, and planetary gearboxes for all their speed reduction needs. Do you happen to know of any other combat robots that use bevel gears, worm gears, or other less-typical speed reduction methods to drive a mechanism? [Madison Heights, Michigan]
A: Mark J. There are generally good reasons for the selection of the common drive mechanisms found in combat robots. One of the primary design considerations in drivetrain selection is:
...with basically no space between the bearing, 1/4" shaft collar, and wheel.
I would file a small weak point just after the shaft collar, so that if struck by a weapon strong enough to break the axle it would tend to snap off after the shaft collar and not bind up the rest of the drive, the shaft collar would stop the shaft from working out of its bearing and falling into the robot.
Is this a terrible idea? I could put a cheap 5mm titanium rod or something through the hex to reinforce it. I just figured it would be best for the wheels to tear off and sacrifice themselves rather than take other things with them. [Dublin, Ohio]
A: Mark J. I understand how nice it is to build with VEX components. They all fit together and assemble without trouble, they all come from a single source, and they are reasonably priced -- but they really aren't designed to withstand full-on featherweight robot combat.
We've come to a few decisions on the material for our drivetrain. We're going for 22mm diameter Silver Steel axles, and duplex sprockets, along a similar drive train to yours, somewhat.
Now here's the question.
The 24v 750w DC motors that we're going to use has a much smaller shaft in length and diameter than that of the silver steel. We need to make it longer. Do we just hook up a sprocket to the motor then run that to an axle which in turn drives the other axles? Or is there a way to connect the thicker axle to the thinner one?
Any help would be much appreciated. [Sheffield, England]
A: Mark J. I strongly advise against attempting to extend/enlarge the motor shaft -- all sorts of problems and weaknesses result. Run a sprocket on the motor shaft to an idler axle, then duplex from there to the drive wheels. Take a look at this prior post.
Note: if I was bothered by combat robot questions I wouldn't carry on answering them. Keeps me sane. Kinda.
A: Mark J. There are good reasons why you can't find so large a pulley for so small a shaft-- it's poor engineering practice. You haven't told me what you're building, but I can't think of an application where this would be a good idea. I'd feel much better about this if you'd share your design with me; I might be able to head off a problem.
If you'd rather learn for yourself why this is probably a bad idea, your solution is on the right track. Rather than starting with something the right outside diameter and trying to bore a precise concentric hole thru the center, it's much easier to start with a piece of thick-wall tubing with an inner diameter matching your 5mm shaft. You can turn down the outer diameter on a lathe if needed to match the inner diameter of the pulley. Drill a hole for the set screw to pass thru and you're set.
Q: Just a note on pulleys and small-diameter motor shafts, I have actually seen pulleys that large for even smaller shafts (in Tamiya kits) but they're made more like spoked wheels. I don't know if that changes anything about it, though. [Illinois]
A: Such pulleys are made for low-power low-speed applications -- certainly not to attach to the shaft of a high-speed motor in a combat robot. I don't know what the builder from Corvallis is trying to make, but I can't think of a combat application where a 2" pulley on a 5mm motor shaft is a good idea.
Q: I am building a hobbyweight with a small (~2 lb.) vertical spinning bar sticking out of the front wedge. I recently attended an event in which a couple of the other competitors were running Turnigy brushless motors for their belt-driven weapons (both of them did well). I am basically just trying to replace my heavy brushed motor with a lighter brushless motor while keeping the belt drive. What should I attach to a brushless motor (5mm shaft) to spin that 2 pound bar on my hobbyweight? [Albany, Oregon]
A:
Your questions are streaming in from a couple different IP servers -- one reads Corvallis, one Albany. Confusion reigns.
I need more info:
Q: The steel bar is 5" x 3" x 1/2" (roughly, a couple of the corners are taken off a little bit). It is attached to a 3" pulley. I was running a Kawasaki 21.6V circular saw motor with a 7s lipo. I haven't yet selected which Turningy motor but was thinking something along the lines of the Turnigy XK3665-1200KV and running it with a 3s or 4s.
A: Hmmm... I have no clue about the power output of your circular saw motor, and I suspect you don't either. How did you decide on a 2" to 3" pulley ratio for the weapon?
The Turnigy XK3665-1200KV is an inrunner motor that would spin at close to 18,000 RPM on a 4-cell battery, but running it on 4 cells rather than its rated 7 cells reduces the output power by almost 70% [1 ÷ (7 ÷ 4)^2 = 33% of max power]. Pick a motor rated for the number of cells you want to use. For 4-cells something like the Turnigy Aerodrive SK3-3548-1050kv would be about right.
Your weapon bar is puny. At 8000 RPM (too fast) it stores less than 570 joules of energy. Consider adding thickness, increasing the diameter, or going to a full disk. Changing out the bar for a 6" diameter steel disk 1/2" thick bumps the 8000 RPM energy storage to nearly 1700 joules -- no longer puny.
Running a 1" diameter motor pulley to a 2" pulley on the weapon could work nicely for this set-up. Make sure the belt width is adequate to carry this amount of power.
Q: Thanks a lot for the advice. Looks like I'll be making some changes. Your answers to my previous questions have been spot on, by the way. One more thing; where can I find smooth pulleys for a 5mm shaft? I've looked all over and can only find timing belt pulleys that are that small.
A: Go ahead and use the timing pulleys and belt. A couple of tricks to get the needed slippage:
A: Mark J. Traction is simple, but traction 'myths' confuse many builders and create the poor performance you have noticed.
There are many posts in this archive about optimizing traction. Search here for "coefficient of friction".
Quick summary: you already understand 'weight on powered wheels', and the only other factor in the equation is the coefficient of friction between the tire material and the arena surface.
P.S: Loved watching Run Amok run through the competition in Robotica when I was younger.
A: Mark J. Thank you for your remembrance of 'Run Amok'. Those were good times.
The Bosch GPA 750 has a long and honored history in combat robotics. Fifteen years ago it was one of the 'go-to' motors, particularly in Europe. Favored at Robot Wars by competitors and the 'House Robots', the motors proved themselves adaptable and reliable. Team Run Amok used them for both drive and weapon power in 'Run Amok' and its Robot Wars variant 'Run Away'. But, that was all 15 years ago and robot combat has moved on.
Still, if run at 36 volts the performance in a 250 pound robot isn't bad. A pair of them geared 10:1 with 6" diameter wheels will push the 'bot to a top speed close to 11 MPH in 20 feet. Pushing torque is very good, breaking traction at a current draw less than 60 amps. Not so bad.
Now, gear reduction. If you were an experienced machinist you wouldn't need to ask me how to make a gearbox, so we'd best keep this simple. Take a look at a previous post in this archive on two-stage chain reduction drivetrains. 'Run Away' used a two-stage chain and sprocket drive to give a 12:1 reduction ratio, so it's certainly do-able without precision machining or great expense.
An alternative: the other 'go-to' motors back in the day were electric wheelchair motors, often scavenged from used wheelchairs. Some of these had power comparable to the Bosch GPA and had the advantage of being a simple bolt-up power unit. Overvolting a pair of wheelchair motors like the NPC T64s to 36 volts with 9" wheels can give speed close to 10 MPH in under 20 feet, breaking traction at less than 70 amps of current.
That gives you a couple of old-school options. Neither is 'state of the art', but either will get you out there fighting.
Q: In all honesty, I'm not an experienced machinist, but I have been drawing robots ever since the first Robot Wars appeared on British television. This included batteries, and funnily enough, drivetrains. But this robot is still going through it's design phase over and over, because there are always new ideas that pop up in my head, but the measurements are not final. But I have a couple more questions for you now, so please bear with me. I also understand that drawing robots and building robots are two completely different things, but it's better to get the experience than not do it at all, right?
A: Mark J. You have to dive in someplace, so let's go...
1) For the drive train itself, would pushbike sprockets work well enough for the drivetrain? Or would I have to go for a thicker material? My worries with such sprockets is that they're flimsy as all heck. Same goes with the axles too, what would be a decent thickness and material for a drive and/or idler axle?
A: I usually avoid giving specific material advice because there are so many possible variables in any given design that might invalidate my assumptions (see Frequently Asked Questions #17). I typically advise looking at designs similar to your own and seeing what has worked in real applications. However, in this case I have that similar design in my workshop.
'Run Amok' still has the dual-stage drivetrain used by 'Run Away' so I went down and took a photo and a few measurements:
2) Sticking with the drivetrain, to help with the spinning of the idler shaft and the wheel axles, would it be better to go with bushings first, just to start off with? Or would it be better to go with bearings? I know both sides of the argument have pluses and minuses, but I would love to get your input on it. And hopefully a way to mount them too, as I've been looking all over the internet to see how I can mount such pieces, and all I get redirected to is how to mount them into cars and the like. Addition to this part: I have checked one of the questions, but all it talks about is putting the axle into the bearing, and I would like to know how to put such bearings/bushings into an axle mount.
A: Run Amok uses bronze 'oilite' bushings for the drive axle and ball bearings for the idler. The axle bushings came with the assembly I scavenged from the junkyard, but I found it easier to locally source bearings for the idler assembly. Use what you find convenient.
The drive axle bushings are flanged and simply drop into mounting holes in the chassis. They are held in place by the wheels, which are attached by bolts that run thru holes in the live axle.
The idler axle is also 'live'. The bearings have extended flanges with bolt holes that are used to mount them to the chassis. The bearings also have extended inner races drilled and tapped for set screws that secure the axle to the bearing races. The idler sprockets are also secured to the axle with set screws that nest into drilled recesses in the axle.
For additional options on shaft mounting see section 4.2 of the RioBotz Combat Robot Tutorial.
3) Battery packs. I was initially planning on running both the Bosch motors with two 24v NiCad battery packs (one pack for each motor), but I can't seem to find such packs in the UK. And I know for a fact that buying drill battery packs are a pretty bad idea because some of the battery packs could be of low quality and or bad efficiency. But I've also heard about NiMh battery packs. But it's the same problem with the finding of such packs. Would the best way of getting such battery packs be to just bite the bullet and get 4 (2 spares) from the robotmarketplace along with a decent charger? I know for a fact that it might cost an arm and a leg due to shipping and such, but it's better than having to jerry rig battery packs. And is it possible to link both batteries to one speed controller, or would that make the ESC go boom?
A: NiCad and NiMh are old school, which is probably why you're having trouble finding them. The currently favored battery technology is Lithium Polymer (LiPo). Smaller, lighter, and less expensive than NiCad or NiMh, they are a bit trickier to look after but provide very high performance. Lots of Q&A about LiPo batteries in the Ask Aaron Radio and Electrical Archive.
If you're going to run a pair of Bosch GPA motors in a 250 pound robot I think you'll need to run them at 36 volts in order to provide enough power for adequate performance. At 36 volts I calculate that your 'bot will consume about 4 amp-hours of current in a three-minute match. You'll want at least a 20% capacity 'cushion' to avoid dangerously over-discharging the battery. A pair of LiPos like the Turnigy 5000mAh 5S 30C Lipo Pack wired in series will give you the required voltage and capacity to run both motors. You'll want two chargers specifically made for LiPo batteries -- one for each pack.
The two packs in series will feed into the single, dual channel ESC.
4) Speaking of ESCs... Now I'm no electronic whizz kid, but I have been looking at reviews of some of the speed controllers from other places on the internet. Two of them have caught my eye. The Vyper 120A DC Motor Controller and the Sabertooth Dual 2x32A 6V-24V Regenerative Motor Driver. Would either of these work for the 250lb robot we plan on making?
A: The Vyper ESC is overkill for your 'bot. It's a 'single channel' ESC so you'd need one for each motor, and at $249 each that's getting expensive. Each of your motors will consume no more than 60 amps at maximum pushing power so a 120 amp controller isn't needed.
The Sabertooth ESC is right out. It has only 32 amps continuous current capacity, will not operate at 36 volts, and has a reputation of just stopping at awkward times in combat. Avoid.
The favored ESC in your ballpark is the RageBridge2 from Equals Zero Designs. Operates at up to 40 volts, has true current limiting to keep it healthy, and can provide up to 75 amps for a full 30 seconds to each of two motors. Reasonably priced and combat proven.
Q: I may end up sending more questions your way. I've always loved robots, and I've always loved to know how they tick.
OH, and forgive me for my clumsiness, but me and my friend send our condolences for your loss of Aaron. Taken from the world way, way too soon.
A: Thank you. I miss Aaron every hour of every day. A large part of me left with him.
A: Mark J. I saw that you posted this same question in one of the forums along with a diagram (at right). The advice you received there was good: tap only the bottom piece and,
"...drill a larger hole in the top piece, so that the screw can pass through and tighten it down onto the bottom piece."
A: Mark J. There's a great deal of variance in the weight allowance given to the different systems in a combat robot. Different designs and weight classes require sometimes radical alteration of 'standard' guidelines. Very general parameters:
So I just saw the new Battlebots episode and it really inspired me to try and build my own bot. Do you have any general tips for a first time robot builder? I figure that it should be something small and simple, but I don't know where to go from here. Any help would be apprieciated.
Thanks [California]
A: Mark J. Sure. Start by reading the first eight entries on our Frequently Asked Questions page. They're aimed at the questions new builders most ask and/or most need to know. You'll want to read the rest of the FAQ, but the first eight are a good start.
You may also be interested in a combat robot kit for your first robot. I keep a fairly well updated list of currently available small combat robot kits.
Then there are 5600 more questions and answers about combat robot design, construction, control, and events here at 'Ask Aaron'. If you don't find answers to your questions here feel free to ask new ones.
A: Mark J. What exactly is holding it in place? If it has its own compartment, that's great. If it's just wedged in with other components, a good hit can shove it so hard into those other components it can crush them, or shove them into the battery to crush it. Go 'belt and suspenders' and secure EVERYTHING!
You can use zip-ties for hard-cased things like receivers and ESCs, but narrow ties will cut into a squishy LiPoly and/or crush the internal structure on hard impact. Wide straps for the battery, please.
Q: Hi lipo guy again ; ) can i use these Velco battery straps to strap my battery securely to my chassis?
A: I don't know how large your battery is or what mounting opportunities your chassis allows, but you're on the right track to use a 20mm wide strap that will spread the load out and not cut into your soft battery. You can pick up Velcro straps like these at office supply stores -- they're used to bundle computer cables and keep them tidy. The buckles aren't needed and they take up weight and space; just fasten the strap to the chassis and wrap around the battery.
Q: Hi lipo guy again, i use this battery and the space is very tight. i was just wondering, i also use 2 tiny esc and a minimixer from fingertech. can they puncture the batery? or im i ok with the strap only and the other electronic resting on it or near it
A: I like to tie down everything. The tinyESCs and mixer are small enough to mount with squares of foam mounting tape which takes very little room or weight. Good for receiver mounting, too.
Why are you running a mixer? Does your radio transmitter not have mixing options? You can save space and weight if you can switch to transmitter mixing.
If you don't mount everything will something be damaged by a big spinner hit? I can only say that I'm not willing to take that chance and I don't think you should either.
Q: so if i unederstand well, if everything is strapped, bolted, glued or smash so hard it become one with the chassis, i dont need any foam around the battery, just the strap wll do the job well?
A: No. Every component should be individually anchored to the chassis:
Q: can i replace the battery i showed u before with this NiMH battery? it is listed as 9gram on other website and since its my first robot.. im a little bit concerned about lipo fire..
A: You should be a little concerned about LiPo fires -- enough to take precautions. Unless a LiPo is crushed, cut, improperly charged, or otherwise abused they're fine.
The NiMH battery you found is a poor choice for your application:
So I've re-evaluated my options a bit since you helped me to realize that building a ring-spinner akin to 'The Ringmaster' isn't the best first robot to build. I did indeed do a google search of Hal Rucker. I then proceeded to cry. Yeah, he's good. Really good.
But in all seriousness, I've scaled back a bit. Instead of a lightweight single-tooth ring spinner, I think I want to see how well I do with a beetle first. I've also realized that I'm just as happy with a Single-Tooth FBS instead. What's that you say? A FBS is unlikely to do well in a beetle match because of the small arena size and less time to spin up?
I know . I'm not in it to win it. I just like Full-body spinners and want to get my feet wet and simply...have fun!
So I was wondering. Aside from the fact that a FBS wouldn't be the best idea, given the beetle arena size, do you think a SINGLE-TOOTH full-body spinner would work decently and provide a little extra bite? And...have there even BEEN any single-tooth fbs bots that you know of in the bigger circuits?
Thanks Mark, David R. [Livermore, CA]
A: Mark J. I looked up the competition results for every beetle FBS and ring spinner at a major event for the last decade. Let the dream crushing begin:
That totals 2 wins and 16 losses. What could be worse than these dismal records? Each of these 'bots fought at that single listed event and never appeared at a major tournament again. Their builders were apparently so discouraged with their performance that they completely gave up on them. Doesn't sound like much fun to me. Single-tooth or not, I really don't see a beetle FBS being viable. By all means build what you want to build, but remember that even nicely made lead balloons fly poorly.
On the topic of single-tooth FBS -- no, I can't think of a true single-tooth FBS that has competed in any major event in any weight class.
UPDATE I missed a few beetle FBS that had their weapons listed oddly at buildersdb.com. In general their records are more of the same, but in fairness there is one that did a bit better:
Beetle FBS 'S.S.O.D.' first appeared at the 2005 Motorama and had a typical beetle FBS result of 1 win and 2 losses. However, the builder kept working on the 'bot and it got better. Its final two events fell within my 'last decade' time frame, and it managed to win as many matches as it lost:
Q: So in your response to the "Crushed Dreams" guy's question about beetle weight FBS's, are those same crushing stats true for most weight classes? And why do you think all those bots were failures? [Kansas City, MO]
A: Mark J. As a class, shell spinners don't do terribly well, but there are certainly exceptions: Featherweight 'Triggo', lightweight 'Ziggo', and heavyweight 'Megabyte' are all mentioned in the Combat Robot Hall of Fame. I note that those three shell spinners have a common design element, can you spot it? Maybe it's just coincidence, maybe it's not.
As noted in an earlier post in the Ask Aaron Weapon Archive the force vector of the impact from an FBS tends to be nearly as large a problem for the FBS as for the opponent. In a small insect arena this is a particular problem. Larger arenas are better suited to robots that turn into high-velocity hockey pucks. Beetle FBS are doomed by tiny arenas.
A: Mark J. All-wheel drive provides superior traction and pushing power by placing all of the robot's weight on driven wheels. Powering each wheel with its own gearmotor is one method of powering all wheels, but there are situations where this is not practical:
A: Mark J. All of Team Plumb Crazy's heavyweight robots have weapon receivers that accept a variety of attachments. 'Stinger' has a robust front bar for a pivoting passive wedge/scoop, and an active lifter with a square tube receiver designed to quickly add or change between multiple forks and probes. I assume that the lifter receiver is sized to accept the bolt-on attachments that were available to their earlier robots as well as new attachments built for 'Stinger'.
A: Mark J. Ballast, or just run it light.
A: Mark J. Take another look at the weapon pulley in the 'Backlash' build report -- that's a sealed bearing at the hub. The loading at the hub of a high-energy spinning weapon far exceeds the capacity of a 'greased up shaft'. On a good hit it would spall and seize. You can (and a fair number of builders do) use oilite bronze bushings in place of ball/roller bearings to support weapon shafts. They have a bit more friction but can survive enormous shock loadings. Keep them well oiled.
Q: So if I wanted to use something like a needle roller bearing, I would put it on the dead shaft and then attach the weapon/pulley to the outside of the bearing? If so, what is the best attachment method? I know set screws aren't great but could they work for a 12 pounder?
A: Not a great idea to apply significant point force (like a set screw) to the outside race of a bearing. A needle bearing would typically be installed in the weapon/pulley as an interference press-fit with thrust bearings and spacers taking up any lateral motion on the shaft.
Alternately, flanged ball bearings can be simply inserted into the sides of the weapon/pulley assembly to be held in place by the structure supporting the dead shaft. Washers or tubular spacers can take up any excess clearance.
A: Mark J. Some of those components get hot in operation, and others don't like to be close to each other due to electromagnetic 'noise'. Space them out a bit. If they're so tightly packed that you're worried about room for wire the components are too close.
If you're not careful your wires can turn into a nasty tangle that can take up as much room as the other components combined (photo at right)! Give some thought to where each wire starts and where it ends in your component layout and shorten excessively long wires rather than just stuffing them into tight spaces. Do not shorten antenna wires!
A: Mark J. That kinda depends on your opponent. A 45 degree wedge is generally more of a defensive design than an offensive weapon. Shallower angles are more effective at getting under opponents, if the leading edge is sharp and low enough.
A search of this archive for 'best angle' and 'lowest wedge' will find several posts on this topic.
A: Mark J. I don't consider any of the weapons to be practical, so let's talk about the designs purely from a conceptual standpoint.
A: Mark J. I like people who want to be educated rather than just be handed an answer. It takes longer for me and for you, but the result is more rewarding. Here we go:
When you go out to buy a car, do you start by deciding how many cup holders the car should have? Unlikely, because the number of cup holders is not critical to meeting the needs you have for a new car. Likewise, when designing a combat robot you don't start with the number of wheels. Start with the specific type of attack you wish to use and the specific method by which you will execute that attack. Example:
Now you can design a chassis to support the weaponry required for that sort of attack. In this case:
Start with exactly what you want the machine to do and design toward that goal. The number of cup holders will become obvious at some point in the design process.
A: Mark J. You usually hinge a wedge to allow it to drop down and drag along the arena surface. In a two-wheel 'bot the wedge already drags along the arena floor -AND- it has the weight of the robot pressing it down. Bien supérieur! Bolt the wedge securely to the chassis.
A: Mark J. Worried about control versus traction? Start by reading the Run Amok Guide to Combat Robot Gyros.
With four-wheel drive a short wheelbase gives greater maneuverability and a longer wheelbase gives greater stability. I think an ideal balance comes with a wheelbase close to the wheel track -- a 'square' wheel arrangement.
Don't overlook a six-wheel configuration. If the center set of wheels are set just a fraction of an inch lower than the fronts and rears you get great maneuverability without sacrificing stability. Search this archive for "six wheel" to find several discussions of this design option.
P.S. i really love ur site, its the best out there and u gave me the inspiration the build bot thank u :) [Quebec, Canada]
A: Mark J. Thanks for the props, Quebec.
The video of antweight 'Pad Thai Doodle Ninja' self-righting is taken from an awful angle to actually see what's happening. I think you'll get a much better idea of the process by watching this video of 'BioHazard' self-righting. Getting a 4-bar lifter to flop back upright requires extensive pre-planning and a fair amount of tinkering. You'll notice small extension 'claws' on the back of PTDN's lifter that I'm sure were added to get the self-righting to work.
Charles Guan's 'Equals Zero' website has an archive for PTDN that includes the design requirements for getting a 4-bar to self-right:
"[Self-righting] is kind of tricky with 4-bar lifters. You really have to take into account the center of gravity of the bot, and the length and extension of the arm, in order to facilitate this. Generally, 4-bar lifter bots flop onto their backs and come to rest on the arm whenever it is then deployed, as the CG is too far forward, and no self-righting is possible. [The classic video of former Battlebots heavyweight Biohazard shows how a 4-bar can self right.]
Notice how [BioHazard's] center of gravity is far enough back that the bot hinges on its rear edge and does not come to rest on the arm. The arm's retraction then keeps the CG within the line drawn between the arm's contact point and the bot's rear edge, and it gathers enough momentum to push back over. Making it able to do this meant making the arm extend all the way back across the bot. Notice also how Biohazard had a ‘tang' at the very back of the arm, a part that sticks up – this aids in the maneuver by making the contact point with the ground further forward, so the ‘line' is longer.
This goal meant that I was continually watching the bot's center of gravity in autodesk Inventor, and also continually modifying the linkage to suit. The arm had to have a certain amount of extension to make sure the CG was in the right place, and that extension had to jive with everything else's placement."
A: Mark J. Aaron wrote a haiku that covers this:
Robot haiku:
The least you could do is re-word your assignment before you send it to me. Start your research here: Optimum Robot Drivetrain Gearing.
A: Mark J. I'm happy to answer specific questions about robot design, construction, and materials, but I'm not going to design your robot and spec the parts for you. See Frequently Asked Questions #4, #17, and #21.
A: Mark J. No.
A: Mark J. The smaller wheels must spin faster to provide the same ground speed, so they require less reduction. How much less? Let's have an example:
Teeth on Front Sprocket = (3" ÷ 4") × 28 Teeth = .75 × 28 Teeth = 21 Teeth
A: Mark J. I'm puzzled.
For the benefit of builders who are interested in robot design, allow me to clear up a couple things about this gyroscopic effect:
If you don't like those links, a Google search will find dozens more web pages and videos for you. I'll warn that the answers to your questions are not simple and that the math gets deep very quickly.
A: Mark J. Let me tell you a true story...
These days I'm out on the 'net wearing a robot on my head. You aren't pestering me.
The correct method to support a shaft bearing a heavy load is to support the shaft on each side of the load with a bearing. You've already seen the result of inadequate support -- a bent shaft.
It's effectively impossible to machine an adapter with sufficient precision to support the far end of a shaft without creating a binding issue. Knowing as little as I do about your drive, I can only recommend that you source a motor with a long enough shaft to use a bearing block for support on the far side of the pulley.
A: Mark J. Due to concerns for the safety of combat robot builders and spectators, I regret that I am unable to answer combat robot questions from the Indian subcontinent.
Click here.
A general comment: there are many workable approaches to designing a successful combat robot, but choosing the dimensions of the weapon bar as a starting point and backing into the rest of the design from there is unlikely to give a satisfactory result.
Q: I am sorry,Mark.But remember,Tibet is a part of China since Yuan Dynasty!!!!!!!!!!!!!!!!!!!! [Jiangsu, China]
A: Mark J. Tell that to the Dalai Lama.
Politically, the issue of Tibetan sovereignty is debatable -- but from a geophysical perspective the 'Autonomous Region of Tibet, China' is part of the Indian subcontinent. I could throw in Afghanistan as well but the map is already large enough.
A: Mark J. Two things:
A: Team Run Amok answers questions about combat robots. We have never entered 'roborace' events like those that are popular in India; no such competitions are held in the US.
A: Mark J. A couple tips:
There are certainly other ways to design your robot, but this method is simple and easy for a beginning builder to understand and follow.
A: Mark J. Fairyweights (150 grams), antweights (1 pound), kilobots (2.2 pounds), beetleweights (3 pounds), mantisweights (6 pounds); aren't there enough insect weight classes? Who decided we needed a 4 pound class???
You haven't given me much about your design or what rules the event will run, but in general I like a large footprint on insect 'bots. Team Run Amok's successful six-wheel drive beetleweight lifter 'Zpatula' is 12" wide by almost 16" long!
Conventional design theory says that a smaller robot is better because the armor can be thicker with less area to cover. This is true, but the larger footprint allows for much greater turning torque, plus the larger 'bot will react less to weapon impacts. Judges also generally respond better to a larger robot; the size differential works in your favor.
Go bigger and dominate the small arena.
A: Mark J. Click here.
I used the torque, acceleration and battery calculator to which you refer. Inputs were 250 pound robot using two T74 motors with AmpFlow dual ESC (160 amps per channel) turning 10 inch wheels. I am planning on using five in series Turnigy 7.5 aH 90C 7.4V hard case LiPoly batteries to run the motors at 37V... (read more)
A: Mark J. Click here.
A: Mark J. Click here.
A: Mark J. Too finicky. Builders commonly use a stronger solution called Nutstrip. It's strong, comes in assorted sizes, reinforces the flange, and is considerably less expensive than the nutplates you've found.
Q: Nutplate guy here...
Thanks for the info on nutstrip, that does look like a good standardized product. A couple points about nutplates though:
Thank you for keeping this site running, this is a wonderful service for the community.
A: It's good to keep a mental file of unusual hardware and fastener solutions in case a unique situation arises.
Q: To continue the 'how to put threads in thin materials' discussion... Rivnuts are pretty cool. This guy does a better explanation than I can. [West Chester, Pennsylvania]
A: Mark J. Another specialty fastener for unusual circumstances. Requires a special installation tool, can loosen and rotate in the hole, and can pull thru more easily than the other options. Not really 'combat rated', but can be installed 'blind' in hollow tubes.
A: A better question might be "Why did Team Plumb Crazy stop running two wheels per hub on their heavyweight robots?" The answer is that it didn't work all that well for them. They only did it in the first place because they found a source of really inexpensive narrow wheel-tires. In the end the extra weight and complexity involved simply wasn't a net gain. Their 2015 BattleBots entry 'Stinger' reverted to a conventional one wheel-per-hub.
A: Mark J. There are many different types of 'electric wheelchair motors' with greatly differing specifications. Without knowing the motor specifications and the details of your proposed drivetrain I'd just be guessing at how much current they might be able to draw in your application. Read Frequently Asked Questions #21 then read my answer to this question from Georgia.
Note: salvaged wheelchair motors were a viable choice for heavier weight classes 15 years ago. That's no longer true.
Q: Hey mark. I was trying to figure out what the highest amount of current draw is on the ampflow e30-400
A: If prevented from turning while full voltage is applied ('stalled'), the AmpFlow E30-400 motor can draw 266 amps at 24 volts ('stall current') -- assuming that your batteries can supply that much current.
A properly designed robot drivetrain will be geared to allow the available torque to exceed the traction available to the tires and spin free before approaching stall. As noted in the next question down this page, a typical drivetrain application for the E30-400 might have it drawing less than 100 amps, even when pushing against an immoveable object at full power.
Q: Hey. Mark. It's me [Nashville] again. I was just wondering if I needed an esc for my brushed weapon motor (e30-400) or if I could just hook it up to an rc power switch and a battery?
A: If you could find an R/C power switch with a 200+ amp inrush capacity -- sure. Unfortunately, R/C switches top out at about 20 amps. Read the Ask Aaron: Solenoid and Relay Guide for options.
Q: I am changing route and going with 2 a28-150 motors with ampflow speed reducers on them (both run with a single ampflow 160 esc. I'm goin to use 6 in wheels and the reducer's gear ratio is 8.3-1. For my weapon I am using a solenoid to start an e30-400 driving a 20lb vertical spinner(direct drive). Does these seem alright for a heavyweight? Also what batteries should i use to drive the whole system. Thanks in advance.
A: The drivetrain is fine -- assuming a good-sized arena to allow you to use the available speed.
You've told me very little about your weapon system, but there may be a few problems:
As for batteries:
A: Mark J. RioBotz has a very analytical approach to robot design -- they don't do anything without good reason. A rounded footprint requires a great deal of additional time and effort to create but does offer a couple of advantages:
A: Mark J. If we were in a room with a pad of sketch paper and a half-hour to spare I could fully wrap your head around gyroscopic precession and demonstrate how it can be used to 'waddle' a combat robot across the arena. Given the lack of interaction here at 'Ask Aaron' the process is considerably more difficult.
I think it's best if I try to explain the 'how' and we'll leave the 'why' for a day when we can discuss physics over tall glasses of red ale and you're buying. If you can't wait for that opportunity to learn 'why', you may be able to glean some value from these videos:
It's also worth taking a look at this webpage about the inventor of the walking gyro that features his explanation and design drawings.
Back to the 'how': It's easier to see what's happening in a smaller robot. Take a look at this video of Team Misfit's antweight 'Gyrobot'. The spinning weapon is mounted to a servo that tilts the weapon to the left and right relative to the robot chassis.
This video of a small non-combat gyro walker that uses a servo to tilt the whole robot left/right may give you a better view of the details of the walking motion.
It may help to purchase a small gyroscope and play with it for a bit to see what happens when it's axis is supported horizontally at first one side and then the other.
Combat robots that use gyroscopic precession for locomotion are uncommon -- for good reasons. They are extremely slow, difficult to control, can't back up, and are incapable of motion if the spinning weapon stops. The only real advantage to the design is that some event organizers will give it a 'walker' weight allowance that can be used to construct a more powerful weapon. Technically a precession system is not a 'true' walker, but you may get lucky.
A: Mark J. The answer depends on your robot design and which components you want to make rather than buy.
A: Mark J. I too have plans for the source code for the T.i. Combat Robotics 4-Bar Simulator but the location of said code is a bit of a mystery. Adam Wrigley believes the code is on a computer stored at his parent's home.
Adam has promised to look for it on his next visit. With the holidays approaching I'm hopeful that he may find himself in a position to conduct that search soon. I'll ask if he's willing to make the code public.
A: Mark J. I've lost track of how many times I've commented on this topic. I direct you to this post in the 'Robot Design' archive that responds to an earlier question from the 'Chinese Forum'. Substitute 'Toon Raider 2' for 'Touro Maximus' and you have my answer.
A: Mark J. 'Ask Aaron' is not a free engineering service -- see Frequently Asked Questions #17.
I advise that you look to other builders with similar designs and learn from their experience. Assuming that you're using Grade 5 titanium, you might wish to use the optional titanium wedge for the D2 beetleweight kit as a design reference. It has a thickness of .080".
Note that the D2 kit uses countersunk screws to secure the wedge. I would advise that you use the same -- don't give those spinners anything to grab onto.
Q: What information would one have to provide in order to avoid FAQ #17?
A: As stated in FAQ #17, 'Ask Aaron' is not a free engineering service. No amount of information you can supply will avoid that.
If in some other reality we were a free engineering service, calculation of material thickness for a specific component would require a full drawing of the part, exact specifications of the material to be used (alloy, temper...), and details of the magnitude and vector of the force to be applied to it. That last bit is pretty much impossible to provide in combat robotics.
That leads us to the advice we offer on material selection: "Look to see what other builders with similar designs are using and learn from their experience. If it breaks, make it stronger."
A: Mark J. We have often remarked here at 'Ask Aaron' that the weapon may be the least important system on a combat robot. A well designed, well built, well driven robot with reliable components can win matches regardless of the weapon choice. Most people refuse to believe this statement, but the evidence is on our side.
Q: And Mark,do you think british robot Gabriel's tactic of setting extremely high ground clearence to make flippers have no chance to get a good position to flip is a sounding design? That looks pretty interesting and beat some flippers.
A: If that's Gabriel's strategy, it doesn't always work very well (video). The actual strategy seems to be surviving long enough for their opponent to make a mistake and drive into the pit.
A 'reaction hammer' style weapon cannot deal out any real damage, and I expect the British teams to quickly develop 'anti-Gabriel' attachments to their weapons that will provide enough extra height to deal effectively with the big-wheel tactic.
A: Mark J. Click here.
A: Mark J. Scroll down this page a few posts to find recommendations on wedge attack strategy against Indian robots with 'wedge skids' that applies to drumbots. Additional discussion on driving strategy for various designs may be found in this archive.
A: Mark J. First, the 15 pound weight class is not one of the classes commonly contested at open combat tournaments. It is reserved for 'educational' robot tournaments put on by organizations like Bots IQ and the National Robotics League that have their own rules. Your first steps will be to determine which tournament your instructor wants you to enter and obtain a full set rules and competition info.
Once we know what set of rules you will be using we can further discuss the details of design and components. Very generally:
Q: Hello. Yes, the class is the BotsIQ. I also found the rules pdf. In this weight class what are some popular designs and what are commonly used materials/thicknesses? (I know vague different designs require different materials but I just want a rough idea because I doubt all use 3/8 lexan and 1/4 aluminum.) Would a flipper be competitive in this class or should a spinning weapon be on my agenda instead?
A: Go search 'YouTube' for 'BotsIQ'. It's all about eggbeater and drum spinners. There's very little room around the edges of most of the arenas for a flipper to score an 'Out of the Arena' (OOTA) knockout. Even if there was room, the eggbeaters are doing at least as good a job of tossing their opponents into the air as a flipper might.
I think you can see enough of the bots in the videos to get a good idea of the materials used. The 'bots take a lot of abuse, and chassis rails of 1/2" aircraft alloy aluminum are not uncommon.
The topic of wedge angle has been discussed many times here at Ask Aaron. As a start, try a search this archive for "best angle".
A: Mark J. Wheel centerlines for four-wheeled robots are typically kept aligned with no offset. I see no particular advantage or disadvantage to a small offset, provided that the chains are kept in perfect alignment.
A: Mark J. Wedges aren't built to a specific percentage of robot weight -- they're built to be strong enough to survive the abuse they will receive.
Take a look at successful wedge designs on robots of comparable weight and layout. Examine the material, thickness, design, and mounting technique. Use that as a basis for your own wedge and calculate weight accordingly.
As an example: a plate of mild steel 500 mm by 250 mm by 6 mm thick might be formed into a reasonable wedge for a 40 Kg Indian robot. That plate would weigh about 3.5 Kg. Add perhaps another 2.5 Kg for supports and mounts and you could have a durable wedge.
P.S. - From now on I think I want every question to start with "Respected sir". That's a lot better than what they call me on the forums.
My questions are:
Thank you, JC [San Diego]
A: Mark J. Your calculations are a bit off. The power output from the gearbox will be down by perhaps 25%, but since power is the product of torque and RPM, each of those values is reduced by only 13.4% (1 - square root of 0.75). I make calculated top speed with 5" wheels and a 10:1 reduction @ 18 volts to be right at 25 MPH.
The bad news that the 10:1 reduction ratio gives really awful acceleration. It would take nearly 9 seconds and 45 feet to reach your desired 15 MPH, badly bogging the motors and pulling a combined 100+ amps for a good part of that time. That stinks!
The picture isn't much better for the 20:1 gearboxes. Top speed there is only 12.5 MPH for the RS-775s with the 5" wheels. Acceleration still lacks: in a 24 foot arena you'll only get 11 MPH and it will take nearly 3 seconds to cross the arena. That still stinks. A pair of RS-775 motors @ 18 volts simply don't put out enough power to give the performance you're looking for in a 60 pound robot.
If you really want to use those gearboxes to get close to 15 MPH with reasonable acceleration you're going to need to substantially upgrade your motor selection. A pair of AmpFlow F30-150 motors @ 24 volts with 8" wheels mated to your 10:1 gearboxes will push a 60 pound 'bot to 14 MPH in a 24 foot arena and your 'bot will cross that arena in 1.6 seconds. That's pretty good, and the current consumption peaks at a very reasonable 37 amps per motor.
Those gearboxes may not turn out to be a bargain, even if they were free.
A: Mark J. Weight balancing a 'bot is not difficult. The goal is to get the correct percentage of the robot's weight on each of the driven wheels -- so how many driven wheels does your robot have?
How do you do this? That depends on where you are in your design/build process.
You want a link and an image? Go read section 2.7.7 of the RioBotz Combat Robot Tutorial.
A: Mark J. See Frequently Asked Questions #17, and be so kind as to read the rest of the FAQ while you are there.
See also The Hamburger is Bad.
A: Mark J. That's a perfectly reasonable assumption. The treads do place a lot of magnets in contact with the arena floor, but I don't know if Paul wanted magnets from the start or if he wanted treads for some other reason and the magnets were an afterthought.
I sent a PM to Paul Ventimiglia to get the answer straight from the builder and got a quick reply:
your conjecture is correct. The original design called for treads in order to provide a large magnet contact area with the arena floor. Paul planned to use many more magnets than actually ended up on the treads, but he had VERY little testing time and he justifiably feared that too many magnets could be far worse than too few. Total downforce is in the 50 to 75 pound range -- well short of the 'hundreds of pounds' he had hoped to have.
Paul also points out that the Bite Force treads are not designed for perfectly flat contact with the arena floor. The 'slider beds' supporting the treads along the bottom have just a little rise at the midpoint of their length to make the 'bot easier to turn. This does reduce the magnet contact area, but a robot that doesn't want to turn would be a real problem.
A: Mark J. Powerful magnets can create more problems than they solve. There have been successful clamping lifters - like 'Complete Control' - that did not use any magnetic force at all.
The preferred solution is to shift the robot's center of mass as far to the rear as possible and to push the front 'stabilizer' extensions well forward. 'Bite Force' has its rather heavy clamping mechanism mounted quite well forward and the stabilizer extensions ahead of its treads are actually hinged, offering poor anti-tip support.
A: Mark J. The reduction ratio is the ratio of the diameter of the larger (driven) to the diameter of the smaller (driving, connected to motor) pulley.
Example: A 6" diameter pulley attached to the axle being driven by a 2" pulley attached to the motor is a 6:2 reduction, which reduces to 3:1.
More help here - if you need it.
A: Mark J. There are a great many simple CAD programs, but I don't use any of them and cannot recommend one. This 'Instructable' on CAD for Robot Design makes a few recommendations.
A: Mark J. Not very much. 'Bite Force' has magnets in its tank treads to pull them tight down to the arena floor for added traction. The drive train does lose a bit of energy with each magnet it peels up off the floor at the trailing edge of the tread -- but it gains a bit of energy as each magnet is pulled down to the arena floor on the leading edge. A very small amount of energy is lost due to the moving magnets inducing a tiny electrical eddy current in the steel arena floor.
A: Mark J. Shock mounted components and armor are not new to combat robotics. In theory the concept is sound -- but the energy levels of heavyweight spinners are so great that I don't believe any practical shock absorption system can take enough of the 'sting' out of a good hit to be worth the effort. I guess we'll have to wait for some future match to find out.
A: Mark J. In US competition flame weapons must use a gaseous fuel with no added oxidizer. That type of flame is not much of a danger to enter semi-enclosed spaces thru small holes. Even an open mesh metal screen will stop such a flame. It will also not 'cling' to a surface and continue to burn like a flaming liquid fuel.
If you're really worried about the flames you can pack the cavity of the robot loosely with fiberglass insulation. The flame won't penetrate the insulation and the heat will be kept well away from vital components.
1. Is it better to have flat sides, hinged sides (as a wedge), or solid wedges for walls when facing vertical spinners?
2. What spinning weapon motors are typically used in middleweight and above robots? Not building one, just curious.
Thanks for keeping the site active and for all the advice. [Brooklyn, New York]
A: Mark J. Everybody thinks their questions are easy...
The best thing to do for your 'sides' is to keep them away from spinners and keep the well-armored 'front' pointed at it. But I'll assume you're referring to anything that isn't a 'top' or 'bottom' as a 'side'. Specifically against a vertical spinner:
Spinner weapon motors for large 'bots are currently in transition. Traditionally, large 'bots used one of the more powerful flavors of the AmpFlow brushed motors. Many builders are now experimenting with very powerful sensored brushless motors from various sources. I personally prefer a reliable brushed motor.
A: Mark J. You'd like me to tell you if an
Q: Hi mark . Sorry for incomplete info . I was thinking of these couplings . they also have other series but I am confused to chose . my motor is 330 rpm , 400 watts , stall torque 20 Nm after reduction , driving 20 cm dia wheels , supported by regular SKF ball bearings ID - 15mm , OD 36 mm . Using solenoid drive , the shaft will face many impulses due to immediate braking . If not from above couplings , can u suggest any other type of coupling or any other mode of power transmission along the axis of the shaft? .. Thanks .
A: You've got bigger problems than coupling selection. Your motors don't have enough torque to drive 20 cm wheels on a 60 kg robot. I suggest that you read our guide to Optimum Gearing for Combat Robots. Assuming that the drive wheels have 70% of the robot weight on them, the motors will stall just as they reach the maximum pushing force available to the drivetrain. Stalled motors do not last long in combat, and your robot will have very poor acceleration. If you want to use these motors I would STRONGLY suggest that you use a MAXIMUM 5" wheel diameter to prevent the motors from stalling, reduce current consumption, and improve performance of the robot.
With 5" wheels, the drivetrain torque is traction-limited to about 1.3 Kg-m -- well within the torque limit of the size 95 'Type S' coupling. The rubber 'spider' will absorb shock-loads and should prevent damage to the cast iron. Of the coupling types offered by this vendor the 'Type S' is the best choice for your application. They are a bit heavy, but if a lighter option is not available to you, they will do the job.
I am concerned about fastening the coupling to your motor and the drive shafts. The 'Type S' coupling appears to have a keyway in one photo. If your motor shaft and drive shaft also have keyways you're in good shape. If not, it's unclear how this coupling would be fastened to your shafts. Do not rely on set screws to secure a drive shaft -- that type of fastening is a very common failure point in robot combat.
The Huco Guide to Flexible Couplings (PDF) provides a nice overview of coupling types plus guidelines on selection and usage.
A: Mark J. The hamburger is bad. Are you driving a weapon? What are the dimensions of the weapon? What material is the weapon made of? What is the weight class of the robot? How is the shaft supported? Is it a live shaft or a dead shaft?
I can't teach a mechanical design class in a short answer. As stated in Frequently Asked Questions #4:
A: Mark J. Previously discussed. The formula for maximum possible pushing power is simple:
Note that there is nothing in there about the number of wheels. Once you get to four, all the weight of the robot (minus any dragging wedges) is on powered wheels -- there is no significant advantage to adding additional wheels. The only exceptions are in conditions not generally found in robot arenas: severe terrain, deep muck, and the like. Once you reach maximum pushing thrust, adding additional motor power or additional driven wheels will not increase that thrust.
There are valid reasons why you might want to build a robot with more than four wheels, but raw pushing power isn't one of them.
Q: To comment on what the motor guy said, are 4 wheels better than 2 only because it puts all the weight on the drive system and not the arena floor? [Trevose, Pennsylvania]
A: Mark J. Exactly right. A two-wheel drive 'bot will place at least some of it's weight on unpowered wheels or a skid/castor/wedge, and that is weight that does not contribute to traction and pushing power. A four-wheel robot will also have turning and stability characteristics that differ from a two-wheel robot, but all we're talking about here is pushing power.
A: Mark J. Yes - my advice is to build a much simpler robot.
A combat robot is a tool for defeating other robots.
Simple robots win. We don't build 'show-off' bots, but if that's your choice then best luck to you. Try a web search for "gripping mechanisms" to get started.
A: Mark J. A timing belt drive is fairly common on smaller robots, but is typically used to power a second wheel from a gearmotor hub. It is difficult to get adequate speed reduction from an ungeared motor to a drive wheel with a single-belt system, and multi-stage belt reduction systems have too many failure points to be reliable in combat.
Here are a couple of links to belt drive design and selection information for V-belts and timing belts.
A: Mark J. Vacuum 'bots are very common in the heavier sumo robot classes, but quite uncommon in the combat classes. It has been tried on multiple occasions, but usually with limited success. I recall a couple specific 'bots:
A: Mark J. I suppose I can give one more design secret away, but at least a couple teams are gonna be mad at me...
Team JACD has some prior experience with shuffledrive, and they learned a great deal about how it should be done. If you get the design just right a shuffler can deliver better grip than either wheels or treads on a smooth arena surface. The individual shuffle 'blades' actually strike downward as they come into contact with the floor, momentarily giving a greater apparent weight and traction boost. You can see the team go thru their design and show their shuffle mechanism in this video.
Personally, I think this falls into the 'too complex for the benefit' bin.
A: Mark J. What isn't there to like? Powerful, controllable, modular weaponry, and based on a proven design. I'm not usually a fan of treads, but Paul Ventimiglia did them right. Every other tread has a magnet that pulls the gripping surface down to the steel arena floor and aids traction. From the ease with which it pushed its opponent around the BattleBox, I'd say the magnets are VERY useful!
A: Mark J. Take a look at the mini-build logs for these Full Body Spinner (FBS) Beetles:
I've also seen direct-drive spinners in the insect weight classes, with the shell directly mounted to an outrunner brushless motor. Motor shafts are not designed to take that great an off-axis load, and I really can't recommend such a design.
Read the Ask Aaron Spinner Weapon FAQ for information on spinner weapon motor selection. Calculating the power requirements is not a simple task, but the tools to help you are available here at Ask Aaron.
General comments:
Q: Hi Aaron. I am building a powerful beetleweight pusher box. I am using 1/2 inch HDPE and 2 pdx16 gear motors. I have two questions for this design:
1. What battery should I buy for competition that will power these motors and may not need charging after every match.
2. There are controllers that use a trigger and wheel on the right to maneuver the robot. Is there a controller of the same design with the wheel on the left for an affordable price (not the 250+ reversible controllers) . Thank You. [Pittsburgh, Pennsylvania]
A: You're a very busy builder.
Pistol grip transmitters are used by VERY few robot drivers. Few of them have the capabilities needed for robots (channel mixing, failsafes...) and those that do are MUCH more expensive than an equivalent twin-stick transmitter. I suggest you read our guide on Combat Robot R/C Features before making a radio decision.
Q: Hi, me with my beetle spinner again. Bottom line should I direct drive the motor or try to use belts or chains to lower the rpm? I can hardly see how effective a 25,000 rpm weapon is given it cannot make solid strong contact with the opponent. I am only doing a fbs because a horizontal spinner over arching the body is in excess of 5.25 lbs. If you have a better solution please tell me.
The most challenging competition are 8 inch flywheels with several teeth spinning vertically. The school that host this event in our area produces a fleet of such bots and are unstoppable. Strong push bots have done well against them historically so I though one on steroids might do the trick. (BTW should I toss a wedge, scoop, or leave the front flat against this kind of opponent?) I also thought that that a powerful horizontal spinner or fbs (since none of either style have been effectively produced) might be whats needed to knock out their weapon.
Finally, would a lifter (like biohazard or t-minus) (pneumatic or electric) be effective in this weight class against almost entirely vertical spinners. Thank You so much for the aid in redesign and construction. :-)
A: I believe I already mentioned that I cannot recommend a direct drive FBS. You could use an oversize low RPM motor to get enough torque for a quick spin-up, and compensate for high RPM with a single-tooth shell design -- but the loading on the motor shaft is still a vulnerability. The point I'm making is that a FBS design is NOT easy to implement, and NOT something I can recommend for a novice builder.
Lifters have to get past a spinning weapon to access something to lift, and effective pneumatic components small enough for a beetle are non-existent. My advice is to keep your design simple. Scoop and dustpan designs have proven effective against vertical spinners.
Q: Hi me with my beetle fbs and scoop again. I came across a few questions while redesigning the bots.
FBS: What is the best material for teeth? I cannot afford steel for weight and titanium is too expensive. My school has 6061 aluminum that I currently plan on using that is 1/4 in thick. For this application what would be the best material and what thicknesses? I have about a pound to work with for 2 teeth. The teeth also now over hang the top and connect on the bottom but not on the inside. They are currently 4 inches tall and 3 inches long to connect to the bot (leaving 2 inches of air between teeth and bot).
Scoop: Again, best material but for the scoop? For this I thought about 12 inch pvc pipe in 1 foot sections. The material is cheep and if one scoop is destroyed in a match then I have 3 replacements waiting in line. You suggest titanium but again really expensive and I am not sure which grade of aluminum or titanium and how thick.
Also design note. If i made a scoop and had the base plate extend out to the edge and got flipped over, could I just use really larger (like 6 inch or so) wheels so on one side i have a scoop and on the other I have a wedge? If not, then how do I fight with a c going against vertical spinners (I don't want to give them free aggression points).
Thank You so much. Your input has been quite helpful. [Pittsburgh, Pennsylvania]
FBS: One pound of your three-pound robot is devoted to the impact teeth? That's a lot of weight, and they overhang the shell WAY too far. You haven't told me about your latest design revisions so I don't know how fast you decided to spin the shell, but the impact the teeth must survive will be at least as great as you could deliver swinging a claw hammer as hard as you can. Large, overhanging aluminum teeth mounted the way you describe will very likely shear right off with the first good hit.
Take a look at successful FBS designs and how their teeth are designed. If you're spinning the shell at 5000 RPM, the teeth only need to stick out about half an inch. For strength they should bolt directly thru the shell wall.
General recommendation: aluminum makes a lousy impact tooth, but a vertical strip of that 1/4" 6061 aluminum bolted thru the shell with 3/8" steel bolts would be an acceptable design. The exposed bolt heads would be the impactors with the aluminum serving to space them far enough out from the shell to be effective. About 5 bolts per tooth for your 4" tall shell, with nuts holding them on inside the shell.
Scoop: Not PVC! I'm sure those nasty vertical spinners you'll be fighting have hard and sharp steel teeth, and a plastic scoop is no match for that. The steel will dig in -- even with little bite -- and rip the plastic apart. You'll need to match the hardness of their teeth with your scoop. Steel is a good choice here. Make it as thick as your weight allowance permits. Spend some time looking around the tool section at a hardware store -- you may find something like the big curved chunk of steel that pictured beetleweight 'CoMotion' uses for its scoop.
Inversion: Yes, it's a good idea to be able to operate inverted -- but I don't understand how extending your baseplate gives you a wedge when your 'bot is upside-down. If you're mobile, charge back into the spinner and let then flip you back upright. You get aggression points for charging toward your opponent whether you do any damage or not.
Q: Hello again. On the teeth for the fbs I made them smaller in length (less overhang and material on body) and in with (1.5 in wide to 1 in) and now they weigh .383 lbs each compared to the .575 lbs they were. Long story short, the bot is just .25 lbs over weight.
Two quick questions for you now:
1. Is 1/4 in steel ok for a tooth design like that overhangs the body like we first talked about?
2. Is pvc an ok material for the body? I know you will recommend UHMW or a steel bowl but I don't know where to get a large tube of UHMW.
One question for the scoop. Do you know what is better or have a preference for the PK27 motor or the PD27M motor? Still looking for a powerful motor but adding the scoop will increase my weight by at least .75 lbs so I need lighter motors than the PDX16s. Thanks as always.
A: Mark J. I'm missing a great deal of information about your design for the spinner, which makes it very difficult to give advice on the selection of materials and the dimensions of impactors. I don't know how fast you plan to spin the shell or exactly what mounting method you have for the teeth. I'll do the best I can.
I'm also concerned that you think your 'bot is four ounces overweight and you're considering changing the tooth material from aluminum to heavier steel. A change to a more conventional tooth design could shave off that extra weight, and instead you're changing to a heavier material. There are very good reasons why no one uses a tooth design like you plan. Please reconsider your design.
There is a shortage of motors suitable for beetleweight robots at the moment. Although still listed at Robot Marketplace, both the PK27 and PD27M gearmotors are out of stock and do not have an expected restocking date. Unless you have another source I wouldn't count on being able to obtain these motors. Either motor is overkill for a beetle, but both spin rather slowly and would need to be matched to uncomfortably large diameter wheels to provide decent speed.
You might be interested in these Servo City Precision Gearmotors that are in stock and available to ship:
I really do need much more complete design details for your 'bots to be able to give more exact recommendations.
A: Mark J. The answer depends on how you define 'successful'.
Note: as we've said several times here at 'Ask Aaron', "The weapon may be the least important system on a combat robot." See this post for a full explanation. Success in combat robotics depends much more on the experience, skill, imagination, and resources available to the team than on the type of weapon.
A: Mark J. First, what do you expect to gain from 6-wheel drive? You'll not gain appreciable pushing power over four-wheel drive and it adds complexity in the drive train. Exposed chains are a weak point in a combat robot drive train -- you want as few of them as possible. I'd suggest sticking to four-wheel drive unless you have a very good reason to go to six. There is an advantage to six-wheel drive but it isn't traction.
A typical Indian combat arena seems to be about 6 meters square. Indian builders have a preference for slow robots -- perhaps from the old cable-control days?
A wedge is typically full-width, so in your case 60cm. Height depends on how tall your robot is. It should go at least to the top of the 'bot, and a little higher if the 'bot is very low profile -- you don't want your opponent to be able to just drive 'up and over' your wedge.
Angle for a simple wedge should be no steeper than 45 degrees. I'd suggest laying it down a bit more if possible to perhaps 30 degrees. 'Best' angle is not a single angle at all, but a curved 'scoop' as shown in the drawing. A scoop is MUCH more effective against the drumbots that are so popular in India.
A: Mark J. Sorry, but 'move 100+ [pounds?] easily' does not give me enough information to recommend a motor. The hamburger is bad. See this post for an explanation of the problem and a list of the information needed. There are also a great many posts about motor selection in the Motors & Controllers archive.
If you write back with complete information about your robot and the performance expectations you have, I may be able to make a motor recommendation.
Q: I'm expecting it to go at least 3 mph and be somewhat small and good for a battle bot competition in the USA not UK.
A: That doesn't really qualify as 'complete information' -- but I'll do what I can.
If you want to build a competitive combat robot for US competition you're going to need better than 3 MPH. You're also going to need enough power to accelerate to that speed quickly and provide good pushing power. Just how much speed and acceleration you need depends in part on your attack strategy; a ramming or wedge robot will need more speed and power than a robot carrying a large destructive weapon.
There's also the matter of how many motors your robot will use. Most have two drive motors: one on each side of the 'bot. Some have 4-wheel drive with four motors. A few have more.
Then there is the drivetrain. You can't just bolt a wheel directly to the shaft of a motor without gear reduction. The gear reduction ratio needed depends on the motor characteristics, the wheel diameter, and the weight of the robot. Since you're looking for a 'compact' solution, I'll assume you want a gearmotor that needs no external drivetrain components.
Using the
Tentacle Drivetrain Calculator
to model performance of a 100 pound robot with two motors:
Q: I am joining the new battlebot competition in the middle white class so most likely it will be 115 pounds and i will be using five motors in all four for the drive and one for the weapon. the weapon consists of a fly wheel and steel bars with padlocks used as hammers. My design is some what like Mauler's but my body will be square. The wheel diameter will most likely be 3-5" tall and 2-3"wide all of the armor will be steel. The wheels will be boxed in. All of the armor will be 1/8". 18v motor. This is all of the information i have for now.
A: You haven't done your research -- BattleBots has changed:
A: Mark J. A chain drive at a 20:1 reduction requires a two-stage reduction thru an 'idler shaft'. The idler shaft is supported by bearings and has sprockets of differing size fixed to the shaft. To get a 20:1 reduction, the 'first stage' from the motor to the idler might be a 5:1 reduction (9 tooth sprocket on the motor to a 45 tooth sprocket on the idler, for example) with the 'second stage' from the idler to the wheel a 4:1 reduction (maybe 10 tooth on the idler to 40 tooth on the drive wheel). The overall drive reduction is the product of the first and second stages (5:1 × 4:1 = 20:1).
The upper diagram shows a two-stage chain and sprocket reduction with two idler output sprockets driving two wheels on one side of the robot.
The lower diagram shows the two-stage chain reduction in a BattleKit Modular Drive Unit with the idler shaft in-line between the motor and wheel.
A: Mark J. External 220V - 10A AC power???
Q: Sorry Sir but I want to correct the previous question about AC supply in competition. I'm pretty sure about the rules. We can use either AC or DC supply. We wanted to use AC so that we can save the cost of Batteries as will be using Hydraulic pistons for our weapons that are quite costly and we have to outsource it. We will be using simple on off switches for driving (Wired Control). What we have planned is to convert AC to DC and all the motors will be DC so I Want to specifications of motors like Horse Power, Torque and rpm for the same above conditions stated in previous question? and the type of drive(four wheel or two wheel)?The robot will be 70*50 cm size and maximum height can be 1m. We want to use a heavy rotor, so motor must be powerful.
A: Mark J. Several problems:
Would you be so kind as to give me the contact information for the organizers of this event? I'd very much like to have a safety discussion with them.
A: Mark J. 'Ask Aaron' gets many questions from Indian builders about alternatives to Electronic Speed Controllers (ESC), drive motor selection, and ESC selection. I suggest you start by reading Frequently Asked Questions #21.
If you are looking for a very simple switch control box system that runs full voltage and current thru the long control wires and switches, you can use a pair of high-current Double-Pole Double-Throw (DPDT Center Off) toggle switches wired as 'H Bridges' (diagram at right) to control the right and left side motors in forward/off/reverse. There is some considerable power loss in running the primary robot power thru such long wires, but this has been commonly done for robot control in India.
Wheels of a different diameter will require re-calculation of the performance numbers.
The E30-150 motor at 24 volts can draw 125 amps of current when stalled, but your gear reduction will provide enough torque to break traction and spin the wheels long before the motor stalls. With 8" wheels and a 20:1 reduction, the Tentacle calculator estimates a maximum sustained current draw of 18.9 amps per motor. I like to add a little for unexpected conditions, so I'd suggest an ESC that can deliver a minimum 25 amps continuous current per channel.
Q: hloo sir, Pnumatic guy again..
1) So i can use Sabertooth 2 x 25 Dual 25A Motor Driver??
2) i read the whole solenoid sections last night. I think 4 40A relay switch for channel is good?? and i will use 2 30 Amp DPDT Switch for wired control. Any suggetions??
last questions according to our specification about bot: can we go for AME 226-series 12V 325 in-lb LH gearmotor(68A stall current) or RS775 12V(stall current 30A)? please suggest.
thanzz alot in advance sir. this askaaron site is heaven to me.
A: Mark J. I'm a bit confused -- are you planning on using an ESC, solenoids, or wired switches? You don't need all three!
1) The Sabertooth 2x25 ESC has sufficient current capacity to control a robot with the specifications given in your earlier post (75 pounds, E30-150 motors, 20:1 reduction, 8" wheels). You may wish to consider alternative ESCs, as some combat related problems have been identified with the Sabertooths. See recent posts in the MOTORS archive for some ESC recommendations.
2) You can get away with a 25 amp ESC, but switches and relays are another matter. Instantly switching high current DC loads with contacts can cause arcing and may even weld the contacts together! This is a particular problem when attempting to reverse a rapidly spinning motor. I wouldn't be comfortable using a switch or relay with a direct current rating any less than half the stall current of the motor being controlled -- and even then I'd be very cautious about reversing a spinning motor. In your case, that would be 65 amp DC ratings.
If you're using relays/solenoids to control the main current flow to the motors, the switches that activate the solenoids will only carry a small current -- typically about one amp.
I've been reluctant to provide a circuit diagram for a wire controlled solenoid drive 'bot because I didn't want to encourage builders to use this control method. However, I've decided that it's necessary to clarify the control issue. The diagram at right shows the two solenoids and single remote switch needed to control the drive motor(s) on one side of a 'bot. As noted above, the control switch has a very low current requirement since it only activates the coils in the solenoids.
Now, about those motors:
The 12 volt 30 amp RS-775 you mention has only about 90 watts of output power -- far too little for your robot.
The more powerful 18 volt 130 amp RS-775 has about 585 watts of output power and is more commonly used in combat robots. These are high speed/low torque motors that require a large reduction ratio. A 64:1 reduction would give you around 7 MPH top speed with 8" wheels, but acceleration would not be as good as the AmpFlow motors could provide. Peak pushing current is about 27 amps.
The AmpFlow motors are widely used for good reasons. If you want reliable speed and torque with easy drivetrain construction, the AmpFlows are well worth their price.
Comment: thanxx alot sir..
Drum weapons are common in India, and I need to stop their attack. I'm building a 35 Kg wedgebot with a pair of AmpFlow E30-150-G gearmotors for power. Many builders suggest that I use 4-wheel drive for better traction.
Output speed of the gearmotors is 650rpm @ 24v. I need 500 RPM after making the reduction for 4 wheels. What is the correct chain reduction ratio? What problems do I face in making this chain drive? [India]
A: Mark J. Why 500 RPM? I get many questions from Indian robot builders seeking a 500 RPM drivetrain output speed. I don't know how that number became the standard in Indian robotics, but there isn't a valid engineering reason for it. You've spent good money for your AmpFlow gearmotors and it would be a pity to handicap the performance of your robot by picking an arbitrary output RPM, particularly since it requires a needlessly complex chain reduction system to implement.
The
Team Tentacle Drivetrain Calculator
shows that a 35 Kg robot with two E30-150-G gearmotors and 4" diameter wheels would have excellent performance without additional gear reduction:
That seems ideal for a quick wedgebot in a small Indian combat arena.
A 4-wheel drive system to improve traction is a good plan. However, adding a chain reduction to drop the output speed to 500 RPM gives no increase in pushing power, costs weight, and adds new failure points to the design. Keep it simple! Mount a wheel and sprocket on the strong output shaft of the AmpFlow gearbox, mount a matching sprocket and wheel on a bearing supported live shaft, and run a short chain between them (see top photo at right).
With this design, even if all the chains fail you will still have partial drive power. Align the sprockets carefully and select the correct distance between axles to keep excess slack out of the chain. Simple is good!
If you're still interested in selecting the correct reduction ratio to drop your speed to 500 RPM, the question has been recently answered -- scroll down about five questions in this archive. The formula for calculating gear reduction to obtain a desired output RPM is:
Your chain and sprocket reduction would be: (650 ÷ 500) to 1 = 1.3 to 1. You could achieve this reduction with 20 tooth sprockets on the gearmotor output driving 26 tooth sprockets on the drive wheels -- as one example.
I've looked back at those recent questions and asked myself three new questions that I think may remove some of the confusion about motor power requirements and pushing force:
A: It takes very little power to overcome the initial rolling resistance of a wheeled vehicle on a smooth and level surface, so the real question is how quickly you want to accelerate and to how great a speed. The
Tentacle Drivetrain Calculator
will model the acceleration, pushing power, and speed of a robot of a given mass given the specific motors used, the number of motors, the gear reduction, the weight supported by the driven wheels, and the wheel diameter.
A: The maximum potential pushing force of a robot can be calculated from the weight bearing down on the drive wheels and the coefficient of friction between the tire material and the arena surface:
The effective coefficient of friction for a grippy rubber tire in a somewhat dirty robot combat arena is around 0.8, so unless your robot has at least [60/0.8 =] 75 pounds of force bearing down on the drive wheels, you aren't going to get 60 pounds of pushing force regardless of your motor power.
If you are willing to push very slowly, a very small amount of motor power can be geared down to provide the torque needed to maximize the pushing potential of the robot weight and traction conditions. More motor power will allow greater speed while maintaining the required drive torque, but will not increase your pushing force.
A: The answer depends on the characteristics of the object you want to push:
As described above, the maximum pushing force of a robot depends on the weight bearing down on the drive wheels and the coefficient of friction between the tire material and the arena surface. Once there is sufficient motor torque applied to achieve this maximum pushing force, additional motor power will only spin the wheels without providing additional pushing force.
For general info and advice on motor selection for your combat robot, see: Frequently Asked Questions #21.
A: Mark J. Depends on how far and how fast you want to push it, and how hard it's pushing back. I can't summarize a full kinematics course here, but I can simplify your question and provide what may be a useful real-world answer.
The Tentacle Drivetrain Calculator can estimate the pushing force and current drain for a combat robot under heavy pushing conditions based on:
Since you haven't given me most of that information and since you probably don't have good motor specifications, I'm going to have to make a series of blind guesses that may or may not yield a figure of any use to you.
Guessing:
Assuming that the robot is pushing at maximum capacity 70% of the match, the total current draw is around 6.175 Amp-Hours, so you'd need two of the batteries in series to provide 7.5 Amp-Hours of current at 24 volts.
If your motors are rated 1 horsepower at 12 volts, current drain doubles to 12.35 Amp-Hours (half the voltage requires double the current to provide the same wattage output), so you'd still need two batteries, but wired in parallel to provide 15 Amp-Hours of current at 12 volts.
If ANY of my guesses are wrong, the entire calculation is flawed and you're on your own.
Note: the amp-hour ratings for lead-acid batteries are based on a slow drain period (10 hours). They must be de-rated for rapid discharge, but the degree of de-rating depends on the specific battery type and manufacturer. Given that it's unlikely that your robot will be pushing at full-throttle for 70% of the match length, I think you'll be OK with two of the batteries.
A: Mark J. Hi, Anthony.. I've got a number of concerns about your design:
A: Mark J. Don't be a dummy -- read the FAQ! Start with #4 and #21.
A: Mark J. Chain and sprocket is the standard method to make a two-motor robot 4-wheel drive. Keep your sprockets well aligned, maintain proper tension on your chains and you should be fine.
Your E30-400 motors have a no-load speed of 5700 RPM at 24 volts. The formula for calculating gear reduction to obtain a desired output RPM is:
For the E30-400 motor, (5700 ÷ 400) : 1 = 14.25 : 1 gear reduction. You didn't mention what size wheels you plan to use, but that should give good performance in a 66-pound robot with wheels around 6" in diameter.
A: Mark J. Your pushing power is traction limited. If you require 100Kg pushing force from a 3 Kg robot, you will need a great deal of magnetic downforce. Assuming a coefficient of friction of 1.3, a magnetic downforce of 75 Kg, a wheel diameter of 10 cm, and two motors producing 4.14 Nm stall torque each -- you will need a gear reduction of 4:1.
Update: I recall from an earlier post that your two motors have a combined torque of 4.14 Nm stall torque -- so you'd need an 8:1 gear reduction to achieve 100 Kg of pushing force.
I saw the Combots V Breaker Box vs Sewer Snake fight and noticed that the plow could lift the forks easily. Also in the fight with Great Pumpkin it could get underneath easily but I think that may be partially due to the fact that when GP accelerates it's nose lifts up a bit making it easier to get under.
What do you say would a low wedge (somewhat like one on Original Sin) get under a plow or not?
Should I try interchangeable weapons or stick with the hinged plow?
Are there any specific advantages for the wedge over the plow (like flipping vertical spinners over, for eg. Terminal Velocity vs Pipe Wrench, which I think couldn't have been possible if PW used a plow instead of a wedge) and for the plow over the wedge so I can change my strategy against different bots?
A: Mark J. There is no advantage in design between a wedge and a scoop (plow) in a contest of who gets under whom. The difference comes in construction skill and attention to detail. Lowest edge wins, whether it's on a wedge or a scoop.
The advantage of a scoop is that the gentle curve allows it to better fit the radius of a vertical spinner/drum and prevent the weapon from obtaining 'bite' on the scoop surface. The curve is also useful in preventing an opponent from driving 'up and over' your 'bot.
You can get into trouble with a scoop if its radius is smaller than the radius of the vertical spinner weapon you face -- such as the large radius weapon on 'Terminal Velocity'. A change from a direct frontal attack to an angled attack in such situations can help to overcome that disadvantage.
In general, I'm not a big fan of interchangeable weaponry -- particularly if it's just swapping out a scoop for a wedge. The pits can get hectic between matches, and trying to squeeze in time for a weapon swap may result in some critical item being overlooked. Also, your 'quick change' fittings are unlikely to be as strong as more permanent mounts. I'd build a good, strong, shallow scoop and run with it.
A: Mark J. Where do you plan on fighting a superheavyweight combat robot in Ecuador? See Frequently Asked Questions #2, and read thru the rest of the FAQ while you're there.
Superheavyweight 'Ziggy' is a very complex combat robot with a great many custom made parts.
There are many posts about 'Ziggy' in the Weapon archive that may give you some insight into its design and construction.
A: Mark J. A few problems:
I really can't see the competition being a success. I recommend spending your time on a more reasonable challenge.
A: Mark J. I'm not sure exactly what your question is.
A two-wheel drive drumbot will typically have at least 70% of the total weight of the robot supported by the drive wheels. More weight on the drive wheels equals more traction, but also risks stability problems on acceleration. See comments on robot design and center of gravity at simplerobotics.org.
The RioBotz guys favor putting almost all the weight on the drive wheels and stabilizing the 'bot with castors -- see sections 2.7.4 and 2.7.7 of the RioBotz Combat Tutorial.
You can get more weight on the drive wheels by moving robot components (batteries, electronics, weapon motor...) toward the rear of the robot, or by moving the drive wheels forward.
A: Mark J. Relying on a strategy of attacking a vulnerable exposed side is not terribly workable. It's a rather long path to maneuver around to the side of your opponent, and all they have to do to counter is pivot. You might get lucky against your first opponent, but your second opponent will be waiting for that move.
I've seen a number of combat robots employing a wide range of fork-like wedge teeth. The design has been fairly common when used with an integrated lifter weapon ('Pack Raptors', 'Tazbot', 'Pipe Wench', 'Vlad the Impaler', 'Wendingo', 'Takatakatak'...). Individual long wedge fingers are not as strong as a solid wedge might be and are susceptible to impact damage. Solid plate wedges have proven more durable and more useful against a wide range of offensive weapons -- particularly spinners.
Dual-ended parallelogram-profile robots were also fairly popular back in the BattleBots era ('Bad Attitude') but are no longer seen in robot combat. The added weight and awkward design is not worth the protection against being inverted. If being inverted is a real concern, a single hinged wedge that can drop down into a new position if inverted is more effective. Do you really expect your low wedgebot to be flipped very often in a small arena?
If you're worried about sharp corners on your robot attracting spinner attack, round the corners off! Even a little work with a hand file can round off a sharp edge enough to be useful, but a gently curved surface is ideal. Very hard surfaces are also useful in preventing a spinner from digging into the surface and getting 'bite'. Best option is probably keeping your wedge between you and the spinner.
There is a lot of discussion about wedge material choice in the archive -- suggest you look there for ideas. A great deal depends on what materials are available to you in India. A tough titanium alloy is ideal, but resilient heat-treated steel alloys can be a good solution as well.
Q: hey mark ... the fork tooth guy ..... Now , if I make a hinged wedge which is invertible .... and I bend the edges of the wedge downwards ( for preventing side attacks ) like woloop or original sin.... then when the bot gets upside down .. then the portion bent down will be upwards ... will that be a good wedge?
A: I really wonder why you're so worried about being invertible. Small arena + low wedge robot = low chance of being flipped. The wedges on 'Wallop' and 'Original Sin' would be next to useless if flipped over. I'd suggest worrying more about building an effective robot and less about being flipped.
Q: Or else how about forks like skewer snake? are they invertible? are they vulnerable to spinners?
A: 'Sewer Snake' can self-right if inverted, so it doesn't worry about inverted operation. It also has an assortment of front attachments. When fighting horizontal spinners it has been known to replace the forks with a smooth conventional wedge -- a much better choice.
Q: hey mark .. fork tooth guy again .... sorry I am troubling a lot .... We have a lot of drum bots in India , so my primary concern would be getting under a drum bot .... now these things have the skates which support the heavy load of the drum .. so with a wide wedge it would be difficult to get under head on ... ( getting the wedge form the side would be tough manoeuvring ) .. can you suggest something to easily get under a drum if you go head on ... OR what should be the strategy against a drum bot? Can I have some other attachments against horizontal spinners using the same bot ? [India]
A: Mark J. Aha! Thank you for the explanation. I better understand what you're trying to accomplish. The 'spinner killers' in the US all use wide scoops or wedges, and these work well against drums too. Here's why:
A: Mark J. I could give you the full list of ways to reduce the output RPM, but I'd rather give you a single method that makes sense for your application. Offhand, I can't think of a reason why you'd want a specific 300 RPM output for a combat robot. You paid good money for the power and speed of the AmpFlow motors. My question to you: why do think you 'need' to reduce the RPM?
Reply to Mark: in india arena is so small so 700 rpm is difficult to control im not using speed controller (out of my fund) in such cases i would like to run those ampflow motors at 300rpm.
A: Overall, it would have been better to select gearmotors more closely suited to your requirements -- but you do have some options:
A: Mark J. I have no details on the 2014 Stem Tech Olympiad lightweight champion. Best I can do is the photo at left of the 'bot with its cover removed. The motors look like Castle Creations products, but I can't say which ones. If you're trying to duplicate the 'bot you'd better have serious machine shop skills and deep pockets.
A: Mark J. Please check at least the FAQ and the recent questions before submitting a new question.
A: Mark J. Your question reeks of a homework problem. Whether it is or is not, it isn't directly related to combat robots.
I'll put you on the right track: your free body diagram isn't working because the axial force is caused by the turning motion dragging the wheel sideways thru the turn. It's a sticky problem with a lot of unspecified variables (turn radius, weight on wheel, speed, coefficient of friction...) Figure out how far you're dragging the wheel sideways per unit time and you'll have a good start on the solution.
A: Mark J. 'Ask Aaron' is not a free engineering service, and we aren't going to design your robot for you. See FAQ #4, and read the rest of the FAQ while you're there.
For my robot i'm planning on using 2 motors driving 4 wheels with timing belts. These motors are originally designed for use on hydraulic power packs. The specs of the motor are 24v, 500W, 2800 rpm, Duty cycle: S2- 5min (I don't exactly know what this means but it was written on its spec sheet & I think it might be the 5min working duration), 2.6kg weight, 3.75Nm stall torque, 80A stall current, 4A no load current.
I'm thinking of applying a 4:1 reduction with 6 inch wheels (or would 5:1 be better?)
The plow would be made of tempered 4340 steel including the arms. The rest of the robot would be 6061-T6 aluminum. I'm thinking of using wiper motors for the arm articulation.
I'm using a custom made motor driver with dual channel & PWM so that it controls both the motors with 80A current carrying capacity (is it enough?).
The robot would be powered by NiCd cells & controlled with a 2.4ghz 6ch controller.
Are the drive motors which i chose good enough for this design? AmpFlow motors aren't a choice because they would completely blow my budget if I import them. One more thing that concerns me is that they're designed for hydraulic power packs. Can I still use them in the drive system or will it have any adverse effects?
And would the gear reduction suffice or should I consider a 5:1 reduction for Indian arenas?
Any comments which could make the robot better would be greatly appreciated!
Thank you!
P.S.- I tried using the Team Tentacle calculator but couldn't make out much maybe because I'm not that technically sound with motors. Sorry!
Thank you again! [India]
A: Mark J. The hydraulic power pack motors should be fine. An 'S2- 5 min' duty cycle indicates that the motors are designed for five minutes of full-power operation followed by a good cool-down period. That's pretty much what robot drive motors go thru, so you should be OK.
You'll need more than a 4:1 or 5:1 reduction with 6" wheels. Acceleration would be poor in a small arena with those ratios. For a small arena (3 or 4 meters across) you'll need 8:1 or 10:1 reduction to give the responsive control you're going to need.
Wiper motors are marginal on power for your plow lifting arms. A pair of very powerful wiper motors (http://www.robotmarketplace.com/products/AME-226-3003.html) would provide about 50 pounds of lift at the end of a one-foot pivot arm, but the stress on the gearbox would be considerable. More importantly, if you attach the plow arms directly to the wiper motor shafts you're going to transmit a very great amount of impact to those fairly small shafts, bearings, and gearbox housing. That's a guaranteed failure point. Consider a fixed (unpowered) spinner-killer plow for your first robot.
I'm worried about your 'custom made motor driver'. If the '80 amp current carrying capacity' is based on the simple power rating of the power chips, you're going to be in trouble. Those ratings are for instantaneous power surges at the rating temperature. As soon as the power chips start flowing power, their temperature rises and their power rating starts to drop. Read Chuck McManis' article on real-world power ratings for robot motor drivers for a full explanation.
For what it's worth, the Tentacle Calculator estimates that your motors will pull no more than 27 amps each with an 8:1 reduction ratio, or 54 amps each with a 4:1 reduction ratio.
Q: Thank you so much for your help regarding the motors!
Just one more question. I need just general advice whether I should stick with 6 inch wheels or should I swap them for 4 or 5 inch wheels. You know all the technical details much better than i do, so what would you choose if you were in my place? 6 inch wheels with a higher reduction ratio or 4(or 5) inch wheels with a lesser reduction ratio? And thanks! - Sage
A: Mark J. Wheel diameter is likely not a critical factor in your design. A 'Breaker Box' style robot would need to be invertible, so the wheels would need to be large enough to extend above and below the chassis/armor. In general, I recommend the smallest wheel that will meet the design needs of the robot. Smaller wheels are lighter, which allows for more weight to be used elsewhere in the design.
I am making a war bot first time and I am very interested in the wedge design. Can you please help me make an ultimate wedge bot - what are the essentials for a wedge design? I have searched online but one thing confuses me: if the bot has zero clearance it gets difficult for it to drive because of some back force it gets from wedge (scraping of the wedge to the ground) and if we keep some distance we cannot get under the opponent. How do I deal with this?
Also, if the wedge has zero clearance some weight is supported by the ground (because the wedge is touching the ground with a force) so we loose some grip too! I was just thinking about all this but couldn't get anywhere. Can you please help me out? [India]
A: Mark J. Yes, a zero-clearance wedge does cause a bit of drag and it does take some weight off the drive wheels, but neither of those things is a serious problem:
A: Mark J. That's a VERY small and cramped arena! About 4 meters across with two one-meter holes doesn't give much maneuvering space. I'm not sure how you're expected to get your opponent between you and one of the holes. I'd consider a 'dustpan' style robot to scoop up the opponent and sweep them toward a hole.
Your chosen AmpFlow E30-150G gearmotors are powerful enough to push a 55-pound 'bot with 4" wheels to about 6 MPH in just 2 feet, and you'll have more than enough torque to maximize your pushing power. A chain 4-wheel drive can put the entire weight of the robot on the drive wheels, which maximizes pushing power. However, four-wheel robots are not as maneuverable as two-wheel 'bots. In an arena this small maneuverability may be critical. I think I'd go with a 2-wheel robot.
A: Mark J. Blistering top speed does no good if you can't accelerate to that speed within the confines of the arena. Watch videos of recent robot fights and you'll see that the contenders are rarely more than a few feet away from each other. There simply isn't time or opportunity to back across the arena for a high-speed ramming run -- your opponent will follow and you'll lose aggression points for not constantly moving toward them.
Rule of thumb: gear for enough acceleration to reach top speed in about half the width of the arena.
A: Mark J. I can't recall Carlo ever saying anything that wasn't right -- at least at the time he said it. In 1999 combat robots were fairly unreliable contraptions. It was very common for wheels to come off, chain drives to fail, batteries to break loose from their mountings, and motor controllers to melt. None of those things ever happened to BioHazard because it was very well designed and constructed. Carlo's championships and win/loss record speak for themselves.
In current robot combat it isn't enough to just survive. The judging criteria have changed to place all the emphasis on aggression and damage, while more powerful weapons have made survivability more problematic.
Q: A robot weighing 25 kilograms is expected to move with a top speed of 3
meters/second. To produce such speed with a 10 cm diameter wheel the
motors should rotate with around 600 RPM. Suggest at least two motors
that can produce the required RPM and torque. Also suggest batteries to
power the robot for at-least 30 minutes and driver circuits (motor driver
IC) to drive the motor. [Delhi, India -- just west of Ghaziabad]
A: Mark J. Two absolutely identical questions submitted to Ask Aaron within a few hours of each other -- from two locations very close to a technical university. Questions that read very much like class assignments.
Why do you pay for an education and try to avoid learning? What do you expect to achieve by asking others to do your assignments for you? If you believe that I am so stupid that I would not recognize this as a class assignment, why would you trust my answers?
The worst part? All the tools you need to perform the calculations are available here on the Ask Aaron site and are discussed in multiple posts. If you had spent a few minutes reading you could have learned how to perform the required analysis and been done with your assignment.
You are embarrassments to your school and to your families.
A: Mark J. I assumed that 'Triton' was an implementation of 'melty brain' technology that allows a spinning 'thwackbot' to navigate - if slowly - in a controlled manner around a combat arena. That turns out to be incorrect.
A little research led to the discovery that Team Fatcats' three-wheel antweight hyper-spinner didn't actually have any real directional control at all -- it just spun, drifted randomly, and bounced off the arena walls. It did have a servo-controlled arm that could be lowered to drag on the floor and throw the whole robot off in some random direction if it wasn't being active enough -- but that hardly qualifies as 'controlled motion'.
I don't think many event organizers would allow such a system to compete. Not recommended.
A: Mark J. Your weapon is pretty much the LAST thing you should worry about. The really important things are the basics.
A: Mark J. BaneBots P60 gearboxes are modular. Your gearboxes have four 4:1 reduction stages housed inside a '4-stage' cylindrical ring gear. BanBots sells ring gears in 1, 2, 3, and 4-stage lengths. You can disassemble your gearboxes and reassemble them into one of the shorter housings while leaving out 1, 2, or 3 of the reduction stages. You'll end up with a 3-stage 64:1 gearbox, a 2-stage 16:1 gearbox, or a single-stage 4:1 gearbox. One of those ratios will likely be close to what you need.
Q: As I told you, I bought four BaneBots 256:1 gearmotors for locomotion in my 30 kilo robot. Since it is very slow I am planning to make an 18" wheel and make a dead wheel unit in that (see drawing). If I do this will I increase the speed? Is it reliable? [India]
A: Every gear reduction stage you put between the motor and the wheel steals power from the motor. You've already got 4 gear stages in your gearmotor, and you want to add another one? The chain reduction will sap still more power, add extra weight, and create a new mechanical system that can fail.
A simpler, stronger, lighter, and more reliable solution is to remove one gear reduction stage from the gearmotor. If you are unable to obtain the correct shorter housing, you may reduce the length of the current housing on a lathe. That will give you a 64:1 reduction, which will work well with about 7' wheels in a small arena.
A: Mark J. Sure. My billing rate for engineering and design services is $60/hour. Send me an advance for the first 10 hours and I'll get right on it.
Alternately, see Frequently Asked Questions #4 -- and read the rest of the FAQ while you're there.
A: Mark J. First, thank you for sending such complete information about your robot weapon. That makes it much easier for me to answer your questions.
Battery suggestions - Weapon: if you look a bit further down the page of the Run Amok Excel Spinner Spreadsheet that you apparently used to calculate your drum energy, just below the 'Results' box is another box labeled 'Battery'. This box reports that your weapon system might be expected to use perhaps 1.45 amp-hours of current in a typical 3 minute match. With a 9 amp-hour battery you have many times the power needed for your weapon.
Battery suggestions - Drive: to calculate the current consumption of the drive motors I need much more information about the motors -- their stall torque, stall amperage, gear reduction, RPM, and wheel diameter. With that info I can estimate their current consumption as well as the robot speed, acceleration, and pushing power. That said, I very seriously doubt that the motors will come anyplace close to completely draining a 9 amp-hour battery pack in a typical match.
Commonly, combat robots have a single battery pack that operates both the weapon and the drive system -- consider using only two 12 volt 9 amp-hour batteries for the whole robot rather than four. You may likely be able to reduce the size of the batteries even further, but I need that drive motor info to be able to tell you by how much.
A: Mark J. Often it is not big things that separate a successful robot from an average 'bot, but a number of small elements. If the basic design is sound and you stick with it you can identify and change the weak elements to improve the robot over time.
A change in gearing, a shift in weight distribution, a more efficient pneumatic system, stronger drive components, new armor materials, more secure equipment mounts, better battery technology, and refined R/C control set-ups are all things that could greatly improve robot performance and not even be visible to the audience. Persist and improve.
A: Mark J. A robot must be designed to meet the specific challenges it will face. You've told me a bit about the limitations placed on the robot, but nothing at all about the actual competition and your experience in this area. It's a lot like designing a race car; you'd build a much different car for a quarter-mile drag race than for an off-road endurance event.
Some of the things to consider:
A: Mark J. I went thru the math for this in a previous post. Search the archive for "brag about my spinner" to find the post with equations and a diagram.
The numbers from these simple equations overstate the real world performance of the weapon, since it is effectively impossible for a spinning weapon to transfer all of its energy directly into vertical acceleration of the opponent -- but they make for nice brag numbers.
Q: Thanks for referring me to the spinner brag equations. But I was really curious about getting a Force value out of it. Something you could apply to a finite element model or hand calc in order to determine the stress or displacement in your chassis or weapon mount.
A: Mark J. Unfortunately, joules of energy don't - in this case - convert directly to force. A heavy but slow moving object might just gently push your robot out of the way, while a fast moving lighter object with the same kinetic energy could deliver a damaging blow. Add to that the many different angles and places of potential impact and many possible values for inertia of the robot depending on the rotational axis imparted by the impact, and you'll get so great a range of theoretical force values (many highly improbable) that the analysis will be useless.
The 'classic' combat robot design advice is to build it strong, and if it breaks make it stronger.
A: Mark J. Lexan plastic (polycarbonate) gains its strength from its ability to flex on impact. Conventional use of bolts will restrict flexing and cause cracking and failure around the bolt hole. General rules:
A: Mark J. I'm not sure I understand the question. A vertical spinning weapon will exert a force that will attempt to lift one side of a turning robot. The more powerful the weapon, the stronger this gyroscopic force will be. It's not something you 'get', it just happens.
A: No -- very few combat robots have the capacity (or need) to change gearing between matches.
Q: So...Could Biohazard change its gearing? Because I saw Battlekits which designed upon it could change gearing
A: Gear changes for 'BioHazard' (or for the BattleKits which have similar but not identical drivetrains) would require partial disassembly of the drive modules and replacement of the motor and first stage sprockets. This is not a task that you would want to take on between matches.
A combat robot correctly geared for a given arena really has no need to change gearing during a tournament. The 'Robotica' competition was an exception, as the tournament took place in four different arenas with differing performance requirements. A few robots at Robotica changed their wheel size to change their effective gearing, while others simply modified their transmitter programming to dial back power and gain additional control for some challenges.
A: Mark J. I'm pleased to see Team Toad competing with a new heavyweight. 'Polar Vortex' is certainly recognizable as a Toad design, with large exposed wheels and a clean profile. The lifting action has the advantage of being simple and robust, but the lifter must generate enough force to lift both the opponent and a good portion of PV's own weight. Overall, a well designed and built robot -- typical for Team Toad.
A: Mark J. 'Axterminator' has beautiful design and construction, as you would expect from Carlo. The 'counter-rotating' reciprocating hammers would certainly have been interesting to watch, but the crankshaft/rod/chain/spring system proposed to drive the hammers would be heavy and complex enough to be troublesome.
As stated in the description, the dual-axe weapon system design was never completed and I'm not convinced that enough energy could be stored in the weapon to be competitive in current competition. Still, I would have loved to have seen it compete.
A: Mark J. The little rubber-topped cylinder at the front of KillerHurtz is a passive bumper to 'gently' stop the weapon arm if it fails to strike a target.
Right now my bot is working around a Viper chassis, currently in the card board mock-up phase (Image Here). The armor panels are what my questions are about (Also a critique of the overall design would also be nice, just in-case I'm missing a huge design flaw)
Right now, my motor shafts are sticking through the armor, I don't have a choice on that, they keep the robot from stable on its side. My issue is that another guy said if the sides take a hit, they'll bend and prevent the shaft from turning, but I'm also worried about damage to the shaft/motor if the bot hits the ground hard(Like most bots do), mainly because the motors are the older Gold sparks and not the tougher Sliver sparks. Should I:
A: Mark J. You're thinking about all the right things, Cobo.
A: Mark J. It's rare that any robot design element is all positive. Hinged skirts do get hung up on arena floor seams, and can cause serious problems for a robot design that relies on high-speed ramming attacks.
Biohazard's attack strategy did not rely on speed, so the problems caused by an occasional hang-up were more than offset by the defensive advantages they provided. Something that would be a mistake for one style of robot can be a strong asset for another.
A: Mark J. I'm not familiar with 4070 steel -- some molybdenum alloy. Not sure about its properties, but should work for an ant.
General hand tool method for cutting sheet steel is a hacksaw and a broad flat file. Cut a little outside your scribe marks and file to a clean, straight line. Plasma cutters are for sissies.
A: Mark J. I think you just answered your own question.
This question has been asked quite often by Indian robot builders. Search the archive for 'spinner killer'.
A: Mark J. Read our 'Frequently Asked Questions'. Write back if you have additional specific questions.
A: Mark J. Everything about combat robot design is a compromise, and finding the right balance is tough. Worse, the right balance will change depending on your opponent.
I don't believe that Frostbite 3.0 lost much mobility in converting it to an active weapon 'bot. Their four heavy motors were replaced by two lighter but more powerful motors, and a chain drive was added to retain 4-wheel drive. The Team Toad website doesn't seem to blame reduced mobility for their loss, just that they weren't quite quick enough in their turn.
Q: Then another question: Can using electromagnets to let your robot closer to the ground be a good idea? Complete Control used it in 5.0 but it seemed like a failure, making it being very sluggish.
A: Magnets have been tried on many robots over the years. Most commonly, permanent magnets have been used to increase traction and pushing power in arenas with steel floors. There have been many successful magnet-bots, most in the insect weight classes. A good example is beetleweight 'Wallop', which uses axially polarized magnets for wheels. Team Nightmare claims that 'Wallop' can drive upside-down on a steel surface or even straight up a steel wall.
Q: Thanks for clarifying magnet question,but what led to Complete Control's failure in using this technology to get lower ground clearence in 5.0? Wrath Jr. still got underneath it easily while itself could hardly move around the box,is it because of the design or control?
A: According to Derek Young's build journal Complete Control Version 4 (BattleBots 5.0) used powerful permanent magnets for "balance assist and wedge hold down." He blames his failure in the match to his lack of preparedness -- he worked on the robot for 36 hours straight before leaving for the event. That left little time for testing, adjustment, and driving practice. I think the magnets might have been useful if enough time had been available to get the set-up right.
Q: Sorry for another question about fights in old days: Did Killerhurtz vs Surgeon General fight in 4.0 prove car style steering is not suitable for arenas like Battlebox? Its anti spinner device in front worked very well in the begining, but it can't steer quick enough to face SG's blade again. then the side armour of it got torn off completely. Same thing happened in 3.0 as well, Hexadecimator could always get a quick turn to get underneath Killerhurtz and flip it over, while Killerhurtz's only successful hit was made after Hexy D thought it couldn't self-right anymore.
A: 'KillerHurtz' had a sophisticated turning system that included servo-controlled front wheels plus a differential steering system for the two drive motors -- so it wasn't really a car-style steering 'bot. It could not, however, pivot as quickly as a standard differential-steer 'bot.
Quite a few car-steer robots had been tried at BattleBots, and none did remotely as well as KillerHurtz. I think it's fair to say that differential steering had been proven to be the more effective method for the BattleBox long before KillerHurtz' loss to Hexy-D.
A: Mark J. You need a belt tensioner -- an adjustable pulley or wheel that presses against the belt between the drive pulleys to increase the belt tension. A trip to an automotive supplier or wrecking yard may provide a suitable tensioner.
Alternately, you may wish to use a toothed timing belt with matching pulleys that require little tension to operate without slippage.
A: Mark J. I love mousetrap cars! You can get some good help on design at the Doc Fizzix Mousetrap Car site.
Gear reduction is a method of changing the output characteristics of a mechanical power source. Your power source is the spring-loaded 'snapper bar' of the mouse trap. If you pull that snapper bar over and let it go it moves very forcefully back to its original position, but it only moves about half a revolution. You will want the wheels on your mousetrap car to revolve many revolutions, and you will want to reduce the force (torque) of the snapper bar to keep your wheels from spinning and wasting power. Gear reduction is used here to reduce the force (torque) of the bar and increase the number of revolutions the wheels will revolve under power.
You won't be using any actual 'gears' in your mousetrap car, but a string attached to the snapper bar and wrapped around the axle of the drive wheels. When the bar is released it will pull the string and cause the axle to revolve many times while the bar only moves thru half a revolution.
I hope this helps -- best luck with the project!
A: Mark J. I can't make design recommendations without knowing a great deal more about your skills and the competition you plan to enter:
A: Mark J. The E30-400 motor does not have the large mounting bolt holes found on some other AmpFlow motors. You haven't told me anything specific about your design, but I can offer some general suggestions.
The 'Ask Aaron' project was important to Aaron, and I have decided to continue the site in his memory. Thank you for the many kind messages of sympathy and support that have found their way to me.
- Mark Joerger, Team Run Amok
A: Mark J. here: your 29.9 Nm figure is the torque needed - at the axle - to break traction at the wheels. The
Team Tentacle Torque Calculator (as noted in the 'help' file of the program) gives the torque needed - at the motor shaft - prior to the torque multiplication of the gear reduction. The Tentacle figure is the number needed to check that the motor does not stall when the robot is pushing at full power. Divide your 29.9 Nm figure by the gear reduction (22) and you get 1.36 Nm.
For the record, here's the math:
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A: You aren't giving me enough information for me to recommend a motor. See: The Hamburger is Bad.
Q: Sorry Aaron for less info..
A: You still haven't told me how many motors (2 or 4) your robot will use, but let me guess that you'll use 4 motors and and give this a try...
The PL1103 gearmotor looks promising for your purpose. At 12 volts it has an ouput speed around 350 RPM, suits your budget, and with 75mm wheels they have enough power to propel your robot to about 3 MPH in just 4 feet. If you need more speed, I think they may be safely overvolted to 18 volts.
If you want to run two motors, a pair of RS-395 motors mated to the Banebots P-60 20:1 gearboxes would be a very durable and powerful option. It's a little outside your budget, but will give a top speed near 6 mph at 12 volts and is nearly indestructable in your weight class.
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Q: which mechanism is best for lifting the 5kg weight by using 12 to 24V? & it must be sutable to fit in 30cm*30cm*30cm [Poona, Maharashtra, India]
A: Mark J. here: since you aren't willing to read the before sending in your questions, let me reprint a relevant entry here:
Q: What design should I use for my [weapon/chassis/armor]? How [long/wide/thick] should it be? What materials are best? How do I add a self-righting mechanism? What type of [chassis/weapon/motors] will allow my robot to crush the opposition and never be beaten?
A: We're happy to answer specific questions about robot design, construction, and materials, but we're not going to design your robot for you.
Ask Aaron is not a free design and engineering service. If we were, we still wouldn't know what materials and components are available to you, what rules are in force at the competition you plan to enter, what tools you have, what your budget is, or what level of construction skill you possess. With such limited information, any answers we might provide would almost certainly be either useless or misleading to you.
Do your background work, develop a design that you believe might work for your purpose, and we will be pleased to evaluate your design and offer suggestions and alternatives.
I'm happy to provide free answers to specific questions about the design and construction of your combat robot. If you want me to design your robot for you, my labor rate is $45 an hour plus all the pizza and Mountain Dew I can consume. It will take about 30 hours of my time to sketch out a design and a parts list. I'd much rather have you design your own robot -- you'll learn more and have a lot more fun.
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and using 2 e30-400 ampflow motors for drive train with reduction ratio of 16:1 with 6 inches wheels. ist is good for 60kg robot?? plz suggest. thank you [Pune, MH, India]
A: Your lift motor is VERY heavy for the power it provides. In comparison, the economical and reliable AmpFlow E30-150 motor provides a full 1.0 horsepower with 51 kg-cm peak torque at a weight of just 1.6 kilos. You can overcome some of that deficiency by overvolting your industrial motor. A motor with a 10 hour work cycle at 12 volts should be well able to handle 24 volts for the length of a robot combat match. Doubling the voltage will give:
You didn't mention the planned length of your 'Sewer Snake' style lifter, which is critical in the calculations. Longer lifter arms require greater gear reduction.
Assuming that the lift arm is one foot long and that you do run the industrial lifter motor to 24 volts, your lifter will stall at about 75 pounds of lift -- not good if you're trying to lift an opponent almost twice that weight. I'd suggest increasing the lifter gear reduction to about 36:1 to get a good combination of lifting power and speed, and to prevent the lifter motor from bogging/stalling under maximum load. If you run the lifter motor at 12 volts, you'll need a higher reduction ratio due to the reduced torque -- maybe 70:1.
Your proposed drive train is under-geared. The
Tentacle Drivetrain Calculator shows your proposed robot accelerating to a top speed of just 6 MPH in a very short 5 feet. Dropping the gear reduction to 12:1 will boost speed to more than 8 MPH and still provide excellent acceleration, decreasing transit time across a 24 foot arena by 20%. Maximum current draw at 12:1 reduction with 6" wheels will be a very reasonable 42 amps per motor.
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A: Mark J. There are multiple posts in the archive about effective countermeasures to spinner drum weapons. Search there for 'spinner killer'. Your two best choices are a strong scoop or a faster spinning drum weapon.
Q: hi Aaron thank you for replying me. tell me the best design against this robots (video) in 60kg weight class. if i choose a design of Breaker Box. How many and which motors i have too use for driving and for lifting. Also tell me which material i have to use for wepon and for body.
A: Mark J. See #4.
I'm not going to design your robot for you. Many previous posts have discussed general design and material considerations for combat robots, and we have provided the tools needed to select drivetrain motors and the formulas needed for lifter calculations. Further, there are specific posts about the requirements for a 'Breaker Box' style lifting scoop. Dig thru the Ask Aaron archives and do your homework!
If you would like to submit a design plan to me, I would be pleased to evaluate the performance of the proposed design and suggest changes as appropriate.
And if we can construct then could you please enumerate the steps? [Rajasthan, India]
A: I recognize those rules -- you're building a robot for Battle of the Titans at the Mayoor school in Rajasthan. This is the third year for the event, and none of the event rules offer a substantial challenge to a team with basic electrical and mechanical design/construction skills. I can't teach those skills to you here.
I also cannot boil down the design and construction of a successful combat robot into a short list of steps. If I could, I wouldn't have needed to answer 4500 questions about combat robots over the last ten years.
For a start I suggest that you read thru the Ask Aaron FAQ for sources of information and help with basic robot design. The FAQ also has links to the searchable Ask Aaron archives, where you may find answers to specific questions on design and construction.
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The question is: if 'Motor 1' can produce enough torque to cause the wheels to slip, why does changing to 'Motor 2', with even more torque, improve my "Time to top speed"? I would have thought that there is an upper limit to the robot's acceleration that is set by when the wheels slip. [Atlanta, Georgia]
A: Mark J. here: the
Team Tentacle Torque Calculator
checks to make sure your drivetrain CAN spin the wheels IF its motion is impeded and the motor bogs down close to stall. If acceleration of the robot is unimpeded, the available torque at the driven axle in a typical robot will not reach the slippage level because motor power is freely converting into acceleration. Even a very powerful 'bot might spin the wheels for only the first few inches -- unless you're in a very slippery arena.
Torque will typically build up to the slippage level only when the robot's motion is impeded by contact with arena obstacles or your opponent. That is when you want the wheels to slip to keep the current draw of the motors at a reasonable level.
It is possible in theory to pack enough motor power into a combat robot to continuously spin the wheels under unimpeded acceleration, but in practice it does not occur. Adding more torque to that drivetrain would not improve acceleration.
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1. Should I use a dead axle or a live axle?
A: Sumo 'bots don't face the same challenges that full conbat robots encounter. If you were building a combat robot I'd suggest live axles to better distribute impact force across a wider base, and bushings on axles that take direct impact for their greater shatter resistance.
We don't compete in sumo, but I suspect that the choice is less critical there due to the lower energy impacts the robot will encounter. A lot of the decision will depend on your specific design, which you have not shared with me.
Q: sorry about that. My sumo robot is using a 150W dc motor and will be running at approximate speed of 2.5 m/s using a 20:1 gearbox. I am using 6 45mm diameter wheel. my strategy is to random broadside all my opposition all but the frontal section. I hope the information is enough.
A: To answer your questions I'm more interested in the details of your drivetrain: how much distance there is between the support bushing and the outer edge of the wheel, the diameter of the axles, whether the axle is supported on both sides of the wheel or only one, the width of your wheel hub if electing dead axles, etc.
I will say again that I don't believe the decisions on axle type and 'bushing vs. bearing' are critical to the success of your design. I'm more concerned that you concentrate on the structural soundness of the robot -- particularly wheel hubs and equipment mounts. Go with whichever design and components are convenient for a strong and simple design.
Note: I don't like your strategy. Your opponents are very unlikely to cooperate in allowing you to get into position to attack their sides or rear. You should expect them to keep their low-wedged front aspect pointed toward you. They can turn faster than you can outflank them.
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A: I don't understand what you think you will accomplish by using an R/C switch to shut down the speed controller. I suspect that you have misinterpreted the rule set.
Re-read the rule set and write back with a description of what you're trying to achieve.
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Q: Explanation: from my previous experience, the ESC that i use will "hang" under certain conditions (stall is one of them) which requires the power supply to be RESET for the ESC to resume its normal function. Since RETRY in combat robot is not allowed, i plan to include this remote switch so that i can reset the ESC through the transmitter.
I expect that you would suggest to solve the main problem which is the ESC. Actually i have switched to other ESC and so far this ESC has no similar problem but the bots still need to go through further test to confirm the ESC reliability. In the meantime, i want to experiment with the remote switch...but have concern over the amp capacity of the relay to be used.
A: You're correct -- I do strongly suggest that the problem be delt with at the source. I'd pull that ESC and make sure it never got into another of my combat machines! Reliability is the most important attribute of a combat robot, and taking time in the middle of a match to reset a balky speed controller is unacceptable in my book.
As to the capacity of the relay:
Q: This leads to another question: how do you prepare your battlebots before a tournament? Do you set a minimum training/driving hours required before you feel satisfied? What is the best training methods to train the driving skills? And how do you test the reliability of your battlebots? Did you do a mockup match to test how it will perform/will be affected during impact or flipped over? Did you add any special measure when installing the ESC and other electronics component to enhance the reliability? (ex; add cooling fan? using high-amp capacity wires, connectors & switches?)
A: Preparation starts with the initial design considerations. Simplify the design, anticipate failure points, and use proven components. Study failure points in other robots and learn from their errors. Tie down wires and hoses -- if they can break loose, they will. Your main battery pack is heavy and has no obvious mounting points, so take extra care to make sure its mounting can survive high impact loadings from ALL directions. Use wire suited to the current loading, and use the best connectors available. Crimp wire connectors are fine, but I solder them as well. Screw connectors are prime failure points -- limit their use and check them before EVERY match. Loctite threadlocker is your friend -- use it everywhere.
The drivability of combat robots varies greatly. Some feel very natural to drive right out of the shop and require little time for the driver to adapt. Other 'bots have poor responsiveness and present real challenges to the driver. An hour or two spent adjusting the transmitter settings can go a long way toward taming even the most difficult robot. There is no specific length of time I can recommend to practice -- just keep at it until you don't have to even think about what you're doing. I've previously listed some specific driving practice exercises that might come in handy.
How much 'durability' testing gets done on a robot varies by builder. I know of one builder who hauls every new 'bot onto the roof of his house and drives it off. I'm not exactly sure what that proves, but he has a good win/loss record. Certainly you'll want to drive a few simulated matches with some heavy pushing and ramming impacts into hard and heavy objects. Certainly those matches should include inverted operation (if possible) and self-righting (if equipped). It's also a good idea to practice replacement of key components so that you'll know what tools and techniques will be needed when you have to do it under time pressure in the pits.
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A: Search this archive for 'sumo' to find several previous posts on sumo design. Some of the posts reference external sources for more info. In particular, find a copy (check your local library) of Robot Sumo: The Official Guide by Pete Miles and read every word.
Note: Team Run Amok does not compete in robot sumo. Our information is gleaned from successful builders, but we have no first-hand knowledge.
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A: According to the team website (sung to the 'Spiderman' theme):
The 'Colsonbot' is a beetleweight full body spinner that uses a 6" diameter Colson wheel as a spinner shell.
Unfortunately, the center of mass for the shell is well above the center of thrust for the drivetrain, and the gyro forces from the spinning shell respond by tilting up 'on edge' and taking the 'bot off its wheels.
Two other Colson wheel based 'bots (Colson Bot and Agent Colson) have similar stability problems.
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A: The photo link you sent points to your own hard drive -- no way for me to access that.
Fortunately, I don't need a photo to answer your question. Touro's drive and weapon systems are covered in great detail in section 5.4 of the RioBotz Combat Tutorial -- recommended reading for any combat robot builder. Middleweight 'Touro' uses two AmpFlow S28-150 motors for drive and a single AmpFlow S28-400 for the weapon.
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A: Yes
Q: Please guide me how to do a hydrallic glove ?I just have the idea but dont know how to do it.
A: We do combat robots -- have no experience or expertise in hydraulic gloves. Best luck.
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A: We have discussed 'Warrior SKF' several times previously. Search the archive for multiple posts.
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A: Mark J. here: those are very weak motors for a 20 kilo robot. Even with six of them, you'll need small wheels (about 2.5" diameter) to generate maximum pushing power without stalling the motors, and the top speed will be only 2 MPH. Sitting duck! Consult our Optimum Gearing for Combat Robots guide for information on speed, torque, and gearing.
The ability of one robot to 'push' another robot depends on many factors. Interestingly, the torque and speed of the drive motors are NOT directly among those factors. Correctly geared, more powerful motors won't give you more direct pushing power, but you'd gain much greater speed and ramming ability.
I don't have the space or time to run thru the full course in kinetics principles, but here are the high points:
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A: Kind of a broad question. We've discussed the design of 4-bar mechanisms many times previously -- you can find those discussions in the archive. Search there for '4-bar'.
If you have specific questions on topics not previously covered, write back.
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A: A very ambitious project! Several comments:
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A: Great decision to start small and simple! Your Sabertooth motor controller is a good choice for a 30-pound wedge, but your other components aren't going to work:
Here's a low-budget suggestion: buy yourself a pair of Harbor Freight 900 RPM 18v Drills. They're usually on sale for about $20 each. The quality isn't great, but there have been countless low-budget robots powered by Harbor Freight gearmotors. A quick web search for "harbor freight drill hack robot" will get you plenty of info on using these motors in a combat robot. With 3" diameter wheels they will provide enough speed and power for a 30-pound wedge, and they are a good match to your Sabertooth 25 amp motor controller. For your money you'll get:
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Q: The makita 12 volt battery isnt really recycled. It almost new and can easy be recharged once again.
A: Why are you even considering that Makita 12 volt battery with unknown specifications when you're looking at 18 to 24 volt motors? Get rid of it.
What exactly is your plan to take the power from the motor and get it to the wheel? The motors you're considering don't have nearly enough torque to directly drive a wheel, so you'll need significant gear reduction. For $20 Harbor Freight sells you a motor/gearbox combination that just happens to have the right gear reduction for a 30 pound robot with a 3" wheel, and they throw in a free 18 volt NiCad battery. My recommendation is to buy and use two of them for your low-budget featherweight.
If you really want just an inexpensive motor, the HTI motor [no longer available] would be a reasonable choice. At 18 volts with a 20:1 gear reduction and 3" wheels, a pair of $8 HTI motors would provide good performance in a 30-pound wedge -- but how are you going to get that 20:1 gear reduction?
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A: If you find that knowledge somewhere, please tell me. DARPA would pay well for it.
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A: Mark J. here: the calculations involved in the operation of a Self Righting Mechanism (SRiMech) are far beyond what I can provide in a short answer here, and are beyond the capability of most robot builders. I believe that most SRiMechs are developed by trial and error -- with a little forethought on the principles of stability and center of gravity.
I can give you a start by directing you to a web discussion on stable positions and to an article on something called a Gömböc.
We developed the SRiMech on our own pneumatic flipper 'The Gap' entirely 'by eye' as the build went along. When complete, we tipped her over, hit the weapon switch, and she popped right back onto her wheels. If she hadn't, we would have examined the position obtained by inverted weapon activation and extended a bit of the flipper structure as needed to give a proper 'tip over'.
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P.S. -- Somebody really should tell us what 's going on in the Indian state of Maharashtra. Judging from the recent surge in questions from that area, it's become the robot combat capitol of the world.
Mark J. here: thanks to the Indian robot builders who wrote in to tell us about recent developments in their 'Robowars'. It seems that there are major rule changes underway that require their robots to become more similar to western combat robots. No wonder Indian robot builders have so many questions.
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The whole bot is a 6.5 by 11 with a titanium wedge on the front. The wedge leads up to a pair of spinning disks that are 3.5 inchs in diameter by 1/2 inch thick. The two teeth make the tip diamater 4 inchs. They are joined together with a smaller 1 inch by .375 center disk that functions as the weapon pulley. They run on a pair of needle roller bearings on a 1/2 inch steel shaft.
The motor I'm using is a 700 watt 2360kv inrunner (.02 ohms) at 4s. It's geared down about 2.2:1. The drive motors are 2 banebots 540's with 20:1 gearboxes driving 2-5/8 wheels. 0.125" titanium makes up the wedge and armor. I will run 3/16 uhmw as a wheel guard and ablative layer.
My questions are: is the armor "thick enough" to take the hits from other spinners? According to the Team Run Amok Spinner Spreadsheet, will the spinner hit 'hard enough'? I think the joules were 400+ at full spin (I don't have access to the spread sheet right now). Is there anything I may have missed? Thank you for your time and help.
A: It would be really handy to know the weight class of the robot. I'm guessing from the size and drivetrain choice that it's a hobbyweight but I could be off by a full weight class, plus or minus. Assuming I'm correct, a few notes:
Q: Disk spinner/wedge guy again. yeah it's for a 12. The disks are meant to function as a pair, kind of like how K2's disks work. The rotating mass is closer to 3 lbs I think, since each disk is a half inch. I made a mistake, each tooth is sticks .5 inchs out from the disk. I can machine the disk to give it a larger diameter while decreasing tooth size. The disks are held together by bolts that go through the disks and center hub/pulley, with the belt going in between them. I have a slower 610kv outrunner that I can use. The armor is 6-4 grade 5 Ti. what rpm should I shoot for to get good bite? what type of drive motor would you recommend instead of the RS540? should I increase the disk diameter? and make the teeth smaller? sorry if I wasn't clear before, I get rambley when I am excited. thanks for your help.
A: I understand the functioning of your weapon, but you haven't mentioned the disk material. I assumed they were aluminum, and that the weight of the teeth was negligable. Each half-inch thick, 3.5" diameter aluminum disk would weigh very close to 0.5 pound. If they're steel, the weight goes up close to 1.5 pounds each. Weight of the shaft an pulley do not add significantly to the rotational 'moment of inertia' since they are near the rotational axis. Your goal in designing the weapon mass placement is to maximize the weapon's 'moment of inertia' for the mass allowed for your weapon.
There are many posts in the archive about weapon 'bite' -- search there for 'bite' and read up on the topic. At 16,000 RPM you have a weapon tooth flicking past your oncomming opponent every 0.002 seconds. How big a chunk of your opponent do you think you can stuff into the weapon damage radius in that length of time?
Lightweight 'K2' spins its similar weapon at about 5000 RPM with good results. Their steel weapon disks are about 7" in diameter by about 1/2" thick, weigh a combined 11 pounds, and deliver close to 2500 Joules of energy. Scaled down, you're going to aim for 500 Joules at a similar RPM for good bite and impact. Play around with weapon diameter, mass placement near the outer edge, and disk thickness to reach that goal. Pick a weapon motor that can meet that RPM target with a reasonable belt drive reduction and maintain a good spin-up time.
As to the drive motors, see how much weight allowance you have left over once you get your weapon optimized. If you still have enough for the RS-540s, keep 'em. If not, pull out the
Tentacle Drivetrain Calculator and find the best solution for the weight you have.
How should we build the structure for a wedge? Since the wedge part is always outside the remaining robot(cantilever), how do you suggest to join the robot chassis and wedge so that it has good structural strength? The wedge we're planning is a ramp type wedge for a middleweight.
Also can you please suggest how other people have build the structure for the remaining robot (chassis)? [Czech Republic]
A: This is way too big a topic to deal with here! There are whole books on chassis design and weapon integration, and there are so many possible types of chassis that it isn't practical for me to even list them here.
Some suggestions:
A: This is probably something you don't want to 'bodge'. The shafts could be knurled to slightly increase the diameter, but if you want a precision press-fit it's best to get shafts the correct diameter.
I've done some research on gyroscopic forces to try and understand how I can better place and balance components inside my horizontal disk spinner antweight to counteract the "gyro pull" on start up and while driving, but I'm nowhere close to understanding this matter.
What I've got so far is this: I know my lipo is by far the heaviest part inside my chassis so I thought I'd place it on the opposite side of the "gyro pull" when I start up my titanium 130mm disk so it's weighted down, but would this be enough to counter act the "gyro pull" on start up and while driving?
Can you elaborate on this subject a bit or point me in the detection of where I can get more info on this matter?
A: Mark J. here: the torque reaction on weapon start-up is not technically a gyroscopic force -- it's a simple inertial response to the acceleration of the spinner mass. 'Last Rites' has a VERY heavy spinner bar with a high moment of inertia, and a VERY powerful weapon motor. When the spinner motor works to spin the bar up to speed, the inertial resistance of the bar acts to spin the rest of the robot in the opposite direction. Once the weapon is fully 'spun up' there is no further torque reaction, and a horizontal spinner can drive and turn without encountering any gyroscopic interference.
Increasing the moment of inertia of the robot chassis by shifting heavy components away from the weapon can slightly reduce - but not eliminate - the reaction. If you want to stop the torque reaction you need to apply a counter-force. A peizo gyro spliced in between your R/C receiver and your speed controller can detect the torque reaction and automatically command the drive motors to apply torque in the opposing direction and negate the 'pull'. Very handy for a horizontal spinner.
However, when looking at some other robot frames such as Biohazard and even all of the pre-assembled "battlekits," it appears that these arrangements have bearing mounted directly to the outer panels. Am I over-analyzing this? Am I making this more complicated than it should be? Thanks!
A: You aren't over-thinking it -- structure and armor are two different things. 'BioHazard' had beautiful titanium drop skirts to deflect impact away from he chain drive galleries running down each side, and the BattleKits are promoted as 'mobile platforms' upon which you can add components (like armor) to build a combat robot. Close tolerance drivetrains require protection to prevent disastrous 'tweeks'.
A: The Team Run Amok version of the
Team Tentacle Torque/Amp-Hour Calculator has a nice, friendly 'Help' button about half way down the right side of the window. I spent a fair amount of time editing that help file. It defines the terms used and offers tips in use of the app. Go read that, then if you have specific questions write back.
You can typically find the motor specifications the calculator asks for - like the torque constant (Kt) and voltage constant (Kv) - at the web site of the motor's manufacturer or distributor.
A: We have many posts on building your first combat robot. Start by reading the FAQ and browseing the Ask Aaron Archives to get some construction and design ideas.
A: Many team websites used to include detailed construction notes and photos, but it's hard to find a nicely detailed description like this anymore. I appreciate the effort Team Near Chaos made to put up this Instructable of their robot "Algos'.
I don't generally like to critique a robot built by a third party. However, since Near Chaos made a full set of drawings and a parts list, I will make a few comments for the sake of builders seeking to copy the design:
I am going to be mounting bearings on the ends of a shaft that includes a keyway for securing sprockets. I know that traditionally it is not wise to mount bearings over a keyway because it could force the inner ring out of round. Is this just overlooked in most cases, considering that the load on the bearings is relatively light in this kind of application? Otherwise, how would you go about creating a shaft that is round on both ends for the bearings with a keyway in the center for the sprockets? Even partially-keyed shafts are keyed from one end inwards. Thanks.
A: Mark J. here: to my experience, the relatively small area of the inner bearing race left unsupported by the void of the keyway can be quite safely overlooked.
A: Ask Aaron answers questions about combat robots. We offer no information about industrial robotics, like robot arms.
You wouldn't happen to be with the Nuclear Technology/Research Center in Esfahan, would you? How are those bombs coming?
Anyway, I'm selecting drive motors, and I know this is a little bit backwards.. But I've already got some Victor 883's laying around, so I'm trying to pick motors that will draw current under their 60A continuous rating. I'm on a budget which is why I'd rather use what I've got and fill in the gaps, even if it is a little counter-intuitive. I was planning on buying an ungeared motor and gearing it down myself (I have access to plenty of sprockets/bearings/roller chain). I've been looking at the Ampflow E30-150 and E30-400. I've done some hand calculations, and confirmed my numbers with the Tentacle Robotics online torque calculator.
I know that motors achieve a peak HP somewhere around 50% of stall torque. For that reason, even though the 400 is beefier, would the 150 suit me better in this case? At only 3.6 lb, it seems to be on the small side for a middleweight. Let me know if there is some glaring detail that should swing me one way or the other.. or if neither of these motors is a good option!
Thanks for your help and sorry for the long submission! Regards, Paul
A: It certainly isn't common to 'back into' a combat robot design based on existing speed controllers, but let's see what we can do.
First, you made an error the stall current of the E30-150. The old E-150 had a stall current of 63 amps, but the new E30-150 is a different motor. The torque constant (Kt) of the A30-150 is 5.70 oz-in/amp, and the stall torque is 710 oz-in. That makes the stall current: 710/5.70 = 125 amps. It would generate peak power of 1 HP at about 63 amps. I've just updated the Run Amok version of the
Tentacle Drivetrain Calculator to include the new 'E' and 'F' series AmpFlow motors. That should avoid future confusion.
A combat robot with a properly designed drivetrain should NEVER stall the drive motors under normal conditions. In general, correct gearing should assure that sufficient torque is available to break traction and 'spin' the wheels at around 50% of stall torque -- with allowances for special design considerations such as high-power rammers and very small or large arenas. It's not necessary to calculate stall conditions at double weight -- under what possible conditions would you need to be pushing at full throttle against an immovable object when your opponent is already on top of your robot? A little sensible driving goes a long way.
Since we're limited to the 60 amp continuous current rating of the Victor 883 ESC, the AmpFlow E30-150 motor looks like a reasonable choice. Two horsepower is entirely reasonable to move around a middleweight robot with an active weapon. Selecting drivetrain gearing that would spin the wheels at around 50 amps (all-wheel drive assumed) would give a reasonable top speed and fair acceleration. Switching to the E30-400 will give a similar top speed and pushing power, but acceleration will improve: in 8 feet the robot will accelerate to 10 MPH in 0.9 second, versus 8 MPH in 1.1 second with the E30-150s. Many middleweights have more power, but you aren't going to be able to squeeze much more thru your Victors.
There are other motors you might consider, but the AmpFlow motors have the advantage of relatively low RPM for their power output which makes drivetrain construction much simpler. However, they are heavy for their power output. The venerable DeWalt 18 volt drill motor could provide similar performance at less cost and much lower weight, but would require much greater gear reduction. Overall, I think that either of the AmpFlow motors you're considering are good choices.
A: You've got it backward -- if you want to gear up for more speed you need the larger (15 tooth) sprocket on the Powerdrive and the smaller (12 tooth) sprocket on the wheel shaft. That will give you a 0.8 to 1 gear ratio and a 25% speed increase to just under 10 MPH.
Consider using larger sprockets with a similar tooth ratio -- it will place less strain on the chain.
A: Realistically, no. I'm not sure I understand your design, but it's a poor idea to split your weapon weight allowance into multiple small weapons. Successful combat robots put all the available weight into a single durable large weapon.
Q: If that could not work, could i make the drums attached to the body so it is all on the body with a body hit but with a moren occasianal but weaker drum hit. It would look kind of like ziggy with a vertical bar in the middle to which the drums are attached.
A: Simple design coupled with getting all the 'little things' right is what wins matches -- particularly for first-time builders. You'll have more than enough on your plate trying to integrate battery selection, charging systems, electronic speed controllers, radio set up, channel mixing, exponential response, chassis construction, drive motors, gearboxes, armor materials, tire selection, driving practice, and between-match maintenance/repair. Adding on a horribly complex weapon system is a guaranteed fail.
A: You want to build a 30 pound version of 'Gyrobot' (video) for backyard fights?? The only real competitive advantage the design has comes from the 'non-wheeled' weight bonus it is allowed at some competitions. It's extremely slow, difficult to control, won't back up, and would require a large [and expensive] servo to change the tilt of the spinning weapon to 'wobble' forward in so large a version.
You can find the post about how 'Gyrobot' works by searching this archive for 'gyroscopic precession'. A link there points to a web article that explains the physics, but I'll warn you that the concept of torque-induced gyroscopic precession is difficult to wrap your head around. I had to buy a toy gyroscope and play around with it before I caught on to the principle.
I have to mention that a big spinner is a VERY nasty design to turn loose in a backyard -- stay safe!
A: It's a chassis with wheels and motors -- no electronics. There is some odd lifter weapon made from a converted screw jack, but I have no idea how it works. I don't recognize either the drive motors or the lifter motor. The chassis appears to be made from fairly thin mild steel.
I'd pass on this one. The workmanship is questionable, the weapon is indecipherable, there would be considerable expense to complete it (radio, speed controllers, batteries...), and I doubt that it would stand up to current competition conditions.
A: This is a BIG can of worms, but I'll stick to real-world answers and avoid as much theory as I can.
Think wedge or electric lifter, and take care to keep your opponent from lifting you.
A: Mark J. here: from decade-old memory, 'Ram Force' (aka 'Sir Force A Lot') had a single pair of 'Industrial' 2-horsepower motors mated to planetary gearboxes providing 4-wheel drive via chain and sprockets. The battery was a large hand-built NiCad pack. ESC was custom made. An electric rotating tiller weapon was added for Robot Wars -- I don't know what motor was used for the weapon.
My worrys are ground clearence and space. I was planning on using 2.5 inch colson wheels but I couldn't find any mounting hubs for them. Do you have any solution for that? Thank you so much for your help.
A: A short (6" long) box with two drive wheels centered is going to have traction problems. On acceleration the back edge of the box will push hard into the arena floor due to a torque reaction -- offsetting the motor torque applied to the wheels. The closer the back edge of the box is to the axle centerline, the greater the percentage of weight the torque reaction will take off the drive wheels. The robot will receive no support from the hinged wedge/pan extensions, and the rear edge of the chassis is only three inches behind the axle. Once an opponent's weight is on either the wedge or pan, their weight will offset the torque reaction and you'll be OK, but free acceleration will be squirrely.
The numbers for the drivetrain check out, although the battery capacity is about twice as great as the
Tentacle Torque/Amp-Hour Calculator says you'll need. You can save some weight/space with a smaller battery. Acceleration is very good (if you can get traction), and top speed seems adequate for a small arena. The .3125" thick wedges are probably overkill for a hobbyweight, but as a guess I'd say you're still pretty well underweight. The wedge hinges need to be VERY sturdy -- preferably full-width.
Colson wheels require custom hubs. A combat robot machine shop like Westar Bot Shop could make you a set of hubs to your own drawings, but it would be fairly expensive. Probably easier to use the BaneBots wheels and mount them inside the armor perimeter for protection.
Q: I changed the design that I came up with so that it uses .25" 7051 aluminum for the wedges, one on either side. When right side up the front functions as a wedge and the back a dustpan, and when flipped the back functions as the wedge and the front as a dustpan.
The top and bottom is still made out of 1/4 UHMW and the sides are now 3/4 inch uhmw with a .08 inch titanium armor plate on top.
I plan on using 4 banebots RS540 motors and 26:1 p60 gearboxes. A sabertooth 12x2 RC is my motor controller, I plan on getting a 2.4 ghz system and I am thinking of using a 1800 mah 4s lipoly battery instead 2250 mah to power it all.
I plan on using 4 2-7/8 by .8 banebots wheels with the hex hub mounts instead of just two.
The over all target dimensions are 8.5" long (on the outside, 7" interior) by 13.5" (12"interior) wide by 2" high with the wedges each being 4" long by 12" wide. What are your thoughts? my weight at the moment is 183 oz
A: I like the change from two to four motors and wheels -- it will greatly improve your traction and stability. In a very small arena (8 or 10 feet across) the 26:1 gearboxes are a good choice, but if you'll be in a larger (12 foot +) arena you should probably drop down to the 20:1 gearboxes: speed will increase, acceleration and pushing power will still be very good, and current at full push will still be OK for your 12x2 Sabertooth.
I still think it would be a good idea to put the wheels inside the UHMW for protection -- you haven't mentioned if you have them exposed or protected.
Your battery selection is fine, but you could drop the mAH capacity a little if you're short on weight or space. The Team Tentacle Torque/Amp-Hour Calculator says you'll use less than 900 mAH for a full 5-minute match. Some reserve is important, but you probably won't need double the anticipated capacity.
Q: The wheels are behind the UHMW wall. Sorry for forgetting to mention that. I'm up in Washington and the arena there I felt was kind of small since beetle weight robots look fairly large inside of it. I think the arena is 12x12 But I am not sure. I will definitely look in to getting those lower reduction gearboxes. Thank you so much. About 50% of what I learned about combat robots came from this site.
A: You're very welcome.
The last time I checked, the Western Allied Robotics (WAR) arena was 12' by 16' with a sunken pit in one corner. The 20:1 gearboxes would be a good choice for that arena.
A: US and UK combat conditions are very different:
The extreme acceleration and vertical thrust angle of a US-style single-pivot flipper may flip itself as well as the opponent, but that is part of the equation. Repeated actuation of the flipper generally gets the inverted flipper back up on its wheels -- after a few tries.
A: Gyrobot's vertical spinning blade and weapon motor assembly are mounted to the chassis via a strong but simple pivot that allows the weapon assembly to 'tilt' a bit to the left and right. A powerful servo controls the tilt.
A better question might be WHY the weapon was designed to tilt. You may notice that Gyrobot has no wheels, moving legs, or propulsion motors -- yet it still makes its way around the arena. That is what should make you curious.
Search this archive for a post that discusses Gyrobot's propulsion technique.
A: Dan Danknick's lightweight (60 pound) 'Archetype' had a huge (21 pound) Briggs & Stratton Etek motor spinning a simple bar weapon -- the first (and possibly only) use of the Etek in a lightweight robot. Tank-steer 4-wheel robots do have some trouble turning smoothly because the turning motion inefficiently drags the wheels sideways. Dan was concerned that the large torque reaction from the huge weapon motor might make the robot difficult to control, so he angled the wheels a bit to make the tank-steer turning motion more efficient.
The angled wheels do drag a little sideways when the robot moves in a straight line, wasting power and decreasing top speed. Dan figured that with a weapon this big he would gladly take improved maneuverability in trade for straight-line speed.
A: We really appreciate simple and effective design here at Team Run Amok. Team Toad's lightweight 'SnowFlake' was quite effective, considering that it had a 12 year-old driver! SnowFlake's design might benefit from a few small tweeks. Bringing the wheels in closer to the body and providing just a little protection for the front and rear edges of the wheels would keep them from being 'spinner bait'. I'd also be tempted to re-shape the front steel 'brick' into a little smoother scoop profile.
Thanks, New York
A: I don't get it, New York. You follow our advice, enter your first tournament with a REALLY simple robot, and you win that event - undefeated. Now you want to build a much more complex robot with an active weapon, and you're looking for ways to take proven designs and complicate them further.
If you lose a match it is NOT because your robot isn't complex enough. Success depends less on design than it does on craftsmanship and driving skill. Build it strong and keep it simple!
Q: Okay, what do you think the next best step would be for my second bot?
I was thinking of the other designs just for thinking's sake, and different designs that could beat drum robots, because as you said, there needs to be more variation in robots, and almost every robot is the similar drum bot. That is why I thought of the new drum design, and this under cutter, which I thought was not that complex since I thought Fiasco has the same design. It was just food for thought, and me trying to apply what I learned from the competition and running it by you. That's all.
A: Mark J. here: you have us confused with someone else. I pretty sure we've never said that there should be "more variation in robots", but we often say that there should be greater variety in combat robot events. We aren't pleased that combat has become all about destruction in a flat-bottomed plastic box. The similarity in events has resulted in a similarity in design because specific designs have proven effective in these events.
Ask Aaron exists to provide support to combat robot builders who want to win matches. Your best chance of doing that is to stick to simple proven designs and to work hard on getting the details right. That's the thought behind our team motto:
If you're trying to impress other builders with your imaginative design skills that's fine, but we aren't going to advise inexperienced builders to build robots that will fail to win matches. 'Fiasco' was built by a very experienced builder using advanced construction techniques. It's a beautiful robot but in spite of the builder's experience its record stands at 20 wins and 19 losses - a hair above 50% wins. Will you be happy with a robot that wins just half its matches?
Do not emulate a design because you think it looks cool or because you can imagine it doing well. Go with the numbers to find out what actually works and what you can sucessfully build.
Q: Oh... my bad for getting confused with what you said. Sorry!
On a different note, what do you think a good second robot would be, that would be more advanced, but not overly so, from 'Hangar 11'? Basically, what is one step up from the first time bot? I know that the first time bot is simple with a sturdy wedge and no active weapon. Of course, I know that you guys can't say exactly what I should do , that would be a design service, but just some thoughts. I think I would like to build a robot from scratch, without any prebuilt setups.
Thank you, and sorry for the poor q's, New York
A: Your's is an unusual case, New York -- you've won every match you're ever fought. I recommend that builders seeking inspiration look to see what successful builders are doing, but in this case you'd be copying yourself. From the video I've seen of the tournament you won I think there are a couple of lessons you could take from your win.
You say you see a lot of drum weapons, so if you want to build a new 'bot you might build something that can reliably defeat a drum. A sturdy spinner-killer scoop might be a good choice. Don't get so 'advanced' that you start losing!
Think of rattler 1 the drum bot, or even fluffy for a 15 lb robot. My idea is kinda simple. On the sides of the drum built into the frame of the bot (not actually the drum) are two linear servos with small wedges built into them. they can be moved in and out during the fight, so that they can be positioned infront of the drum completely, making a wedge, a wedge that would have a wedge that you would have to go up to be hit by the drum (think the Brain from USF RIG), or they can be moved all the way back so that the drum has nothing in front of it like Rattler 1. If I pin someone on the wall with the wedges out, I can then spin up my drum with them T-boned on the wall with the extended wedges, and then I could retract the wedges while driving forwards, allowing for a huge hit with the drum that is spinning already at a (close to) top speed.
This could also be useful if your drum stops working, since you then have an effective wedge. It is also useful since you can change the strategy of your bot in the middle of a fight, from a wedge, to a drum that you would need to go over a wedge prior to being struck by the drum, or an exposed drum.
I know you guys are against complexity, and I understand that. I think, however, that this is not too complex. What do you think about the design?
A: Mark J. here: I have a simple test to determine if a design is 'too complex'. Look for a competitive robot more complicated than your design. If you can find one then there is at least a chance that your design is not 'too complex'. Your design has a drum, plus a drum motor, plus a drum motor controller, plus two sliding wedges, plus two linear actuators, plus a sliding track mechanism to support and locate the two wedges, plus controllers for the wedge actuators. I don't know of any competitive 'bot that complicated, so your design fails my complexity test.
I don't see how the design offers 'a larger impact each time'. Your one scenario for a large impact occurs only when you are able to pin your opponent against a wall, which seems to be an unpredictable and irregular event. Perhaps it is your opponent who will pin you.
I think this is an example of the 'two weapon fallacy'. Quite a few robots have been built around the concept that 'two active weapons are better than one', but none of them have been successful. You only have a certain amount of weight to devote to your weapon, and if you split that weight between two systems you end up with two puny weapons that belong in a lower weight class. Better to put the full weight allowance into a single well designed and reliable weapon, IMO.
Q: My idea is that you could keep the wedges extended as you pursue your opponent, and then you can push them to the wall and retract the wedges, allowing for the drum to deliver a huge blow. One of the things I noticed when I was at the USATL in Florida was that the robots would commonly end up on the wall ( one pushing the other) since the box is fairly small.
Your opponent is now on the wall being held by your wedges, your drum is at a high speed, and you then drive forward while retracting your weapons for a huge hit.
The way that I could save weight is that I can afford to have a drum mechanism that takes longer to spin up, which will save me weight. The drum has longer to spin up because of the wedges, and you can start the fight with the wedges extended. I could have weaker armor since the wedges would be strong and I would have to keep them facing at the opponent, but this could be a weakness in the bot. I could use UHMW for armor.
I think that this could bring something new to combat robotics, and since the two weapons work in harmony, unlike a 'normal' dual weapon robot, is in't to complex. That being said, what do you think about my solution to the weight problem and complexity?
A: I understand your attack strategy -- I just don't like it. Take a look at section 6.3.1 of the Riobotz Combat Tutorial. The rate of closure on your opponent is a key factor in calculating weapon 'bite', as is the rotational speed of the weapon. A very slow closure rate combined with a lighter weapon spinning faster to attain adequate energy storage combine to give a weapon with VERY poor bite. Lack of bite will turn your 'huge blow' into a chattering grind.
The two weapons 'working together' does not make the design any less complex. Your design has more components, more moving parts, and more things to go wrong than does a conventional weapon. I don't like complex weapon systems and I don't like 'situational' weapons that depend on circumstances that may or may not develop in a particular match.
A combat robot is a tool for defeating other robots. The best tools are simple, reliable, and easy to use.
Q: Would the bite of my weapon increase if I used a one tooth drum? Thanks a lot for the advice.
A: Fewer teeth on a spinning weapon equals more bite, but your bite parameters are so poor that your bite would only improve from 'practically none' to 'a tiny bit more than practically none'.
Note also that if your opponent is pinned against the arena wall, any impact you do get from a large drum weapon can't push your opponent away from you -- but it certainly can throw your 'bot away from them.
Q: Is there a modification to the wedge drum bot that you think would allow it to have more bight? When I was at the USATL fight, the ability to take an opponent to the wall and then hit them with a fully spun up drum appeared very useful. There are a lot of robots with drivers that, with 15lb bot, lack the ability to get away from a pin followed by a large hit. I hope I am not harping on this, but I am trying really hard to think of a solution to the complexity while retaining the purpose. Thank you very much for your advice.
A: Three things go into the bite equation:
Seriously -- give up on the slow-retracting wedge. It's a major handicap on the effectiveness of your weapon. Add a nice passive wedge and put the saved weight back into the drum weapon.
Q: Aaron, is there a lighter and faster alternative than linear actuators since I do not need any torque, and all I need as for the wedge to reach and hold a location, or is this just a lost cause? A really light hobby motor that can spin in two directions might be faster for an increase in bight, and I could still make it hold a position (I think).
Could this be more effective as a heavier bot, like a 30lb robot?
A: Not to pick on you, but this is EXACTLY how to get into trouble when designing a combat robot. You have an idea for a robot that will perform a specific action in a very specific situation. The true value of that action is unproven, but you are willing to add complexity and steal precious weight from other systems with proven value. When examination of the first design concept shows a terminal problem, you start looking at other design solutions that are potentially still more complex and less reliable. Down the slippery slope you go.
I think I've made my opinion of this design very clear. I consider it to be too complex, potentially unreliable, unuseable for the purpose you intend, and overall less effective than the more standard and proven drum/wedge designs in use in any weight class. If you believe in it, go ahead and build it -- but don't ask for my opinion again.
A: See #7. Read the rest of the FAQ while you're there.
Learning to design and build a combat robot requires much more than a web tutorial. A couple good and complete sources for how to actually build a combat robot:
A: I can't comment on worth. 'Nyx' would be an expensive sportsman feather to duplicate, and I don't recommend building a direct copy of any combat robot. 'Nyx' (2 wins, 2 losses) has already achieved modest success, but a copy is rarely as good as the original for a variety of reasons. Not everyone chooses to build robots the way Near Chaos Robotics does, but it's certainly useful to take a look at their design, material, and construction choices.
Thanks for writing in, and thanks for sharing the build on 'instructables'! Nyx is a beautiful machine, and now that the 'break in' bugs are fixed I think you'll have great success.
A: Mark J. here: I've grouped these questions together because they have similar answers.
Watch some combat videos and see how often the robots are more than a short distance away from each other. It's very rare that one robot has the opportunity to back up and make a screaming full-throttle charge across the whole arena to crash into their opponent. The effective rammer strategy is to maneuver quickly, collect up your opponent in the ramming scoop/wedge/spikes, and shove them HARD into a convenient wall. That requires acceleration, pushing power, and speed -- and those three things add up to a requirement for Massive Power Overkill!
The Tentacle Drivetrain Calculator has a sub-page accessed by clicking the 'Acceleration Calculator' button that shows the speed a robot can attain in an arena of given size. For a rammer, I'd suggest aiming for gearing that can attain top speed in about half the width of the arena. Remember, you'll be taking another robot along for the ride, which will slow your acceleration by at least half.
That Indonesian featherweight with two RS-550s has a power-to-weight ratio of more than 30 watts/pound -- plenty of power for most attack strategies, but pretty puny for an effective rammer. Results from the Acceleration Calculator, with gearing and wheel size selected for 10 MPH:
The Massachusetts builder should aim for a similar power-to-weight ratio and back into the calculation for speed based on arena size and acceleration. Since I don't even know what weight class the 'bot is competing in or any drivetrain details, I can't offer specific guidance. Aim for 60+ watts output power per pound, gear it so that it reaches top speed about halfway across the arena, and settle for whatever speed that works out to be.
Q: hi Aaron, it's the rammer/spinner killer guy again. After checking with the Tentacle Drivetrain Calculator, i've picked the 2 BB RS-775 chain driven to 4WD with
20:1 ratio and 3 inch wheels, the Tentacle Drivetrain Calculator said that the bot will move at 8.7 MPH, HOWEVER, it also said that the bot can reach top speed in 7.5 ft (with no overvolting). is this good?
A: How large is your arena? For a 15 foot arena that would be good.
Q: The arena is as big as the normal basketball arena.
A: Basketball court?!? Get yourself some speed! Crank the gear reduction down and/or the wheel diameter up to get the acceleration to top speed distance to around 25 feet. You'll still have P-L-E-N-T-Y of pushing power.
A: The best SRiMech is one integrated into a weapon system, like a lifter/flipper that can be modified a bit to provide self-righting. Our heavyweight lifter The Gap can self-right thanks to a small extension projecting above the lift actuator. A stand-alone SRiMech system uses up weight that could likely be better used in making your 'bot flip resistant or invertable. Take a look around -- there aren't many dedicated SRiMechs out there anymore.
A: Practical combat robot gear ratios depend on:
For most combat robot designs you aim to spin your wheels at about half the stall amperage for the motor.
A: A proper job of putting the curve in a metal plate scoop requires a specialized piece of equipment called a roll bender. A well-equipped metal fabrication shop will have one.
Q: Aaron, in the picture of Breaker Box, it looks like it has a 'paneled' front scoop, as in the scoop is made of multiple peaces. I gather it is not, but why does it look this way? If it was bent, and then the angle was continued, and then bent again in segments, wouldn't this take away from the durability of the scoop? [New York]
A: Titanium has unusual properties and can be a difficult material to work with. The scoop is smoother than it appears in the photo, but some areas bent a bit more sharply and gave it that segmented look. The durability of the scoop is not significantly compromised.
A: Rammers have to be QUICK -- acceleration like a bullet. If you can accelerate like that, you'll have the torque and traction you need to push as well.
A: People will argue, but from a practical standpoint - not really. 'New Cruelty' (8 wheels) and 'War Machine' (10 wheels) were both super-heavyweights that added on extra power by simply tacking on extra gearmotors and wheels. The solution was appealingly simple, but the extra wheels themselves did not provide any advantage.
Six-wheel drive with two motors and chain/belt drive to the wheels has proven very effective in combat. The center wheels are set just a bit lower to provide a pivot for turning, while the front and rear wheels provide stability and traction. More than six wheels creates maneuverability problems and is just showing off.
Q: I'm sorry, I was the wheel guy, how does eight or more wheels create control issues?
A: A skid-steer robot with more than two wheels has to drag tires sideways when it turns. The longer the robot is in comparison to its width, the more difficult it becomes to drag those tires sideways. With eight or more idependently powered wheels, the robot is going to be quite long and will have a lot of tires to drag sideways when turning. That takes a lot of power and results in sluggish turning motion.
As noted above, six-wheeled robots typically have the center set of wheels set just a pinch lower than the front and rear sets, which takes weight off the tires that must drag sideways and eases turning. You can't do that trick with independently powered wheels like 'New Cruelty' or you'll waste power spinning the lightly loaded wheels.
A: 'Ramming studs' aren't going to do any significant damage to your opponent, but they will give a spinner weapon some exposed edges so they can get a grip on YOU! If you really want studs, spikes, or other 'ramming accessories' make them removable so you can take them off to fight spinners. Keep exposed surfaces smooth - DON'T BE SPINNER BAIT.
A: Mark J. here: well, I'd rather you wear out my server using it online -- but OK:
A: The general rule is included in your next question...
Q: Does your rule of armor "make it as thick as you can and still [make] weight" apply to lexan or other plastics that need to bend?
A: Yep. Thin sections of Lexan have to bend a lot and thicker sections have to bend less. Just don't restrict the bending of plastic armor by your mounting method.
I would like to use a lifter as my weapon, preferably one that would function as a spinner killer (probably a scoop), one that would provide self righting, and one that is easy to build. I posted a while ago about the weapon design of Breaker box. I was thinking something like that? Also, I have no access to machine tools. I have a cordless drill, some hand tools, and a reciprocating saw but probably with a useless blade but if I need to I could find a proper blade. I also have a soldering Iron.
Is this possible? If it is, what specific parts would you use? If it isn't possible, what alternative design should I build? I will probably just order the parts you recommend.
The reason I thought a lifter would be good was since I thought it would be simple yet affective since it can function as self righting, and there is a pit in the competition which plays to the advantages of the viper kit. If you think there is something better, I would love to know what it is and how to build it.
Thank you so much, I am really exited for my first ever combat robot and my first ever combat robot competition! [New York]
A: My advice, as stated here MANY times, is that first-time robot builders should keep their robots as simple as possible. I advise against active weapon systems in a first robot for several reasons, not the least of which being that robots with passive weapons are more successful in combat than robots with active weapons.
You have a very few days to design a weapon, order parts, build a weapon, integrate the weapon into your existing robot chassis/electrical/radio systems, test the robot, repair any problems, and practice the operation of the robot under combat conditions. I wouldn't care to take on that challenge for an active weapon, and I cannot recommend that you do so either.
Build a sturdy wedge, affix it to your chassis with strong bracing, and spend the rest of your very limited time testing and practicing your driving technique.
A: No. UK rules have long required multibots to enter the arena as a 'connected' unit, but I don't recall any 'bots that could effectively function in that configuration with all elements contributing.
A: Increasing wheels size is equivalent to descreasing the gear reduction. So,
A: Mark J. here: I've seen this used for both propulsion and weaponry. This type of friction drive transfers power thru a very small contact area compared to a belt wrapped around a pulley, and a large amount of force may be needed between the elements of the friction drive to prevent excessive slippage. The ability to adjust and maintain that force is critical. It looks good on paper, but a friction drive is both inefficient and generally unreliable in practice.
A: Spring mounting works both ways -- it reduces impact on you from outside sources and it reduces your impact on others. If you're gonna be a rammer you need to be FAST and HARD. They don't make hammers out of Lexan and springs -- think steel.
A: It depends on who's ruleset you care to use and how you interpret those rules.
Team Misfit's antweight 'Gyrobot' (video) tilts its vertical spinning weapon blade side-to-side to 'wobble' forward via torque-induced gyroscopic precession. RFL member 'California Insect Bots' has allowed 'Gyrobot' to compete as a 2-pound 'non-wheeled' robot in their weight class, but 'non-wheeled' as defined by the RFL is not the same as 'true walker'.
The Northeast Robotics Club (NERC) ruleset says:
Given that 'Gyrobot' has only a single "limited-travel rotary actuator" which arguably does not "produce linear travel", I think it fails their test for 'true walker'.
The current BattleBots ruleset also excludes gyroscopic precession as a 'true walker' (StompBot) on several points. Most notably:
I'd say 'non-wheeled', yes -- 'true walker', no.
"Sand Flea is an 11-lb robot with one trick up its sleeve: Normally it drives like an RC car, but when it needs to it can jump 30 feet into the air. An onboard stabilization system keeps it oriented during flight to improve the view from the video uplink and to control landings. Current development of Sand Flea is funded by the The US Army's Rapid Equipping Force. For more information visit www.BostonDynamics.com."
Q: I saw the video on Sand Flea and do you know how he can jump so high?
A: 'Sand Flea' jumps via a rear-pointing "piston actuator" that fires after a lifting mechanism raises the front of the robot to the desired angle. Boston Dynamics isn't providing details on the piston actuator beyond 'variable power' and 'up to 25 actuations from the on-board fuel supply'.
Q: On the 'Sand Flea' video there is an edit at 0:17, do you know why? Or have any speculation? I think it may be so that we don't wait ten minutes watching it pump its air tanks.
A: There are 'cuts' all thru the promotional video. Have you ever counted the edits in a TV commercial? Speculation: the robot landed upside-down from the first jump and someone ran in to flip it over. I'm not certain that its lifting mechanism is invertible, although it should be.
I'm pretty sure 'Sand Flea' doesn't pump its air tanks. From the description it's not even clear that it uses compressed air to power the actuator.
A: I don't think its correct to say that there are 'many' current bar/skirt robots. A search thru the Builders Database shows few skirted designs in current competition, and the bar/skirt combination is vanishingly rare. A few spectacular videos of failed skirts may overstate the popularity of this design.
Note that properly designed skirts will not interfere with a bar spinner weapon. The skirts should have motion limiters to prevent them from raising into the weapon path.
A: Depends on the battery. A small and light LiPoly in an antweight might be adequately secured by an ample patch of Velcro, but the larger the battery is the greater the need for restraint. I've seen many batteries come loose under heavy impact and it's very often terminal. When in doubt, overdo the battery restraint.
A: I can't find any wheels at RobotLogic, but they do have a variety of mixers and other R/C interfaces. The wheels are available from other sources. A search of the Ask Aaron archives for 'Mecanum' will find multiple posts on omnidrive robots and supplies. Read the Wikipedia articles on Mecanum wheel and Omni wheel. Finally, a web search for 'holonomic robot' will find video of robots with Mecanum and omni wheels in action.
Both omniwheels and Mecanum wheels have rollers as the contact surface of the wheel. This arrangement allows the driven wheel to provide thrust in one axis and to slip without resistance perpendicular to that axis. The difference between the two designs is the orientation of the axis of the rollers to the axle: omniwheels have the roller axis prependicular to the axle, while Mecanum wheels have the roller axis set 45 degrees to the axle.
Omniwheels can typically be found in either 3 or 4 wheel configurations, while Mecanum wheels are most commonly found in 4 wheel designs. A motion diagram for a 4-wheel omnibot is shown above. Applying power to different wheels in different directions will cause the robot to move forward, backward, and rotate like a conventional tank-drive robot -- but it can also move diagonally or directly sideways without turning.
The RobotLogic page for each of the mixers has a link to the associated users guide which has detailed instructions on wiring as well as a wiring diagram.
A: How can this not qualify as a Robot Wars question? I'll make it brief: 'Milly-Ann Bug' fought in three Robot Wars competitions and never won a single one-on-one combat match. Scaling it down to insect size would yield equally awful results.
Q: I am the Milly Ann Bug guy, the reason I thought that it might not count as a Robot War's question was because I was interested in what you thought of the design, not it's records or battles.
A: That isn't an unreasonable thought. Unfortunately, we had to cut off all questions that referenced any Robot Wars event or competitor. See #37 for a brief summary of the reasons. I'm happy to talk about articulated robot design, just please don't mention a specific Robot Wars competitor.
The concept of an articulated combat robot has been put into practice elsewhere. Team Gray Matter built the articulated 'Hammerhead' to compete at the third Robotica tournament. The design has merit for a competition that features uneven terrain or other obstacles. In a standard, boring, flat-bottomed arena the design has no benefit.
A: We no longer answer questions about UK Robot Wars events or competitors, but we did describe the operation of Razer's winged SRiMech in an earlier post in this archive. Search for "pretty slick".
A: You can start by reading the .
A: Not every robot can be an original design. A unique design will get you more interest and respect than an obvious copy, but getting out there and kicking butt is the most important part. Most everyone's first 'bots are based on other designs -- originality comes with experience. Copy away.
A: If you're 12 years old and have no experience with mechanical construction projects, your first combat robot should be simple and inexpensive. Hack a toy, or strap a couple of cheap drill motors onto a chunk of plywood and bolt on a wedge. If you have success with it, build a larger and/or more complex robot based on what you learned from the first one. Becoming a robot builder is a process; you can't jump to the top level on your first try.
The usual planning process is to set a budget, then figure out what type of robot you can build for that budget. You've painstakingly (a lot of the pain has been mine) planned out a top-of-the-line hobbyweight spinner 'on spec' without checking in with your finance people (mom and dad) to see if there's any money. Sigh...
For the benefit of other builders: around $800 to $1000 is about right for a top flight hobbyweight. The parts list 'Battery Guy' put together has some extra items as well as some things left off:
Mark J. here: I agree with Aaron. If we had known that you were 12 years old we would have steered you away from a complex active-weapon robot that requires considerable mechanical skill and experience to successfully complete. We've often said that the success of a combat robot depends about 20% on the correct components and 80% on the design and construction skills of the builder. I've seen many 'Hazard' knock-offs that never came close to being winners; the secret to Hazard's success was not in the deceptivly simple design, but in the ability of builder Tony Buchignani to get all the 'little things' absolutely correct.
'Hazard' was not Tony's first robot -- his first was a simple wedge. He worked on 'Wedge of Doom' until it was a champion, then he moved on to more complex robots. Start simple. Build something suited to your mechanical skill level. Learn from your mistakes and improve your skills.
Thank you, New York
A: Mark J. here: we've talked about this before, New York. There's a saying, "it isn't the wand, it's the magician." In this case, it isn't the tool, it's the craftsman. If you want to learn the craft, look around for a community college or trade school that offers classes in metalworking and dive in -- but many a robot has been built with hand tools and a good imagination. Start building. Make mistakes. Get better.
A: Mark J. here: you aren't going to find a 'paint by numbers' tutorial to construct a generic combat robot weapon. Books like "Combat Robot Weapons" deal with design concepts and comparison of strengths and weaknesses -- not step-by-step construction. If you have experience in mechanical construction technique you don't need instruction on that level, and if you don't you aren't going to get that experience from a book. It's a process: dig in, get your hands dirty, learn from your mistakes, and improve your next effort. Don't expect your first robot to be a world-beater.
The approach recommended many times here at Ask Aaron is to browse build reports from successful teams to see how they construct their robots. You can start with Team Cosmos. See what construction techniques they use for designs similar to what you have in mind. Evaluate your skill level to decide if you can use those techniques. If not, modify your design concept and start again.
We recommend that your first robot NOT have an active weapon. Integrating battery selection, charging systems, electronic speed controllers, radio set up, channel mixing, exponential response, chassis construction, drive motors, gearboxes, armor materials, tire selection, driving practice, and between-match mainenence/repair is a big enough chunk for your first bite. Even if you do your homework and have friends (like us) steering you away from major mistakes, you're still going to get a lot of it wrong the first time.
A: One battery is all you need. Take a look at #19 for a wiring diagram.
I'm concerned about the Sabertooth 12 / RS-545 combination for your weapon. That combination will work well for the robot drivetrain that you've previously told me about, but if you bog down the RS-545 with the big horizontal bar you've previously described it may pull more amps than one channel of the Sabertooth 12 can handle. The Sabertooth has overcurrent protection, but if that kicks in your weapon spin-up time will suffer.
Q: So, because of that, what ESC would you recommend? i think i'll be using a Victor 884, but i have a question for you. how do you insert the booster cable that you MUST buy for the Victor to the Reciever?
A: I can't make an ESC recommendation without full specs on the weapon. If this is still the 50cm X 3cm X 1cm steel blade I ran calculations for previously, the RS-545 motor does not have enough power to spin it up in a reasonable length of time. The RS-550 has four times the output power of the RS-545 -- suggest you switch back to the RS-550. The Victor ESC will work well.
One end of the Victor booster cable plugs into the ESC, the other end plugs into the receiver. No trick to it.
The power cable branches shown in the circuit diagram are simply a convention used in drawing circuits for clarity. You do not need to place physical branches in your wiring; you can simply run separate wires from the connector to each ESC. Alternately, you can run power to one ESC and run jumper wires from there to the second ESC.
Q: No, the weapon will be 50cm X 5cm X 2cm now, and will be made either from spring steel or mild steel (which one is better?) By the way, after hearing lots of advices from you, here's my list of the stuff i'll buy for my robot:
A: Ummm... have you added up the weights of your components? Your new larger weapon blade weighs 8.6 pounds all by itself. I recall that this design is for an approximate hobbyweight, so I think you're overweight!
A heavier blade also requires new calculations for weapon motor reduction ratio. To get the same spin-up time as the original 2.6 pound blade you'd need a 14:1 reduction ratio -- very difficult to attain in a single-stage belt drive. I suggest you go back to the original blade size. If you do that, the list of components looks fine.
Several different steel alloys are commonly called 'spring steel'. They share a common property of being able to absorb punishment and 'spring' back to their original shape. Given a choice between generic mild and spring steels, I'd go with spring steel for a weapon blade -- but either should do for your weapon.
I'm reading Imahara's book [Kickin' Bot]... Its awesome! Thanks, New York
A: We don't claim current knowledge or expertise in shop tool selection. There are many forums that deal with this type of information; try asking for guidance from one of them.
A: What's wrong with side skirts?
You can make your robot as low as you like by choice of wheel diameter and selection of the mounting point for your gearmotors, but low can cause problems. Arena floors are rarely perfectly flat and they get more uneven as the tournament progresses. Too low and you get stuck on irregular sections of the floor. Skirts are great because they self-adjust and 'float' over irregular seams and gashes.
Thanks! New York.
By the way, does imahara's book tell me which tools are good for which weight cats?
A: Mark J. here: my recommendation is that you wait for your copy of Grant Imahara's book to arrive and give it a good read before you think any more about spending $2,000 to $4,000 on a 1200 pound machine tool. A good quality machined part requires both a good machine and an experienced machinist -- consider farming out your machining needs. A great many builders get along just fine with hand tools.
Q: Dear Aaron and Mark, what does farming out your machining mean?
A: 'Farm out' means to hire an external service provider to do the job for you. Someplace like Westar Bot Shop is accustomed to quick production of custom robot pieces made to your order. They are better equipped than a home workshop, have experienced machinists, and have materials on-hand ready to go. Draw up your plans, send them off, and get the part back in the mail.
Q: I bought two copies of "kickn' bot" [book by Grant Imahara], and I have one on my knee right now. I already had it when you asked but thats ok because I had not started reading it. He never specifies which tools are good for which weight classes. Also, he says that the miniature versions of the machine tools are great, but does not specify how mini or which ones. But dont get me wrong, the book really is excellent! It goes over everything, and the project is a great addition.
My question is this: For the purpose of a combat robot, which tools should I get if I do not want the job to take forever and have accuracy? I know that you can do curves with a jig saw, but which tools would be more beneficial than that?
What I mean is that I am trying to find a reasonable plan that falls in between using a hand saw and jig saw and purchasing a cnc mill. I don't really want to outsource. Do you have any recommendations for this? Basically, I am trying to find a reasonable medium so that the job does not take forever and the tools dont take too much space.
I hope I have explained this well, as I really love what you guys are doing and I dont want to waste your time. Also, I hope I am not being to demanding, as I hope the hamburger is not bad.
Finally, I might have missed something in the book, as I just gave the section a scan, and I also read all of the first chapter. If you think I have missed something vital, feel free to point it out!
Thank you very much, New York
A: I have a problem answering your question. If you wanted to listen to music, I couldn't recommend that you go out and buy a violin because I don't know if you can play a stringed instrument. Likewise, I can't recommend that you stock a workshop full of machine tools because machine work is a skill that does not come with the machine. If you have a good machine tool and a poor machinist all you get is ruined material and possible injury.
If you had training with machine tools you wouldn't be asking these types of tool selection questions. I think I would be doing you a disservice to give you a quick and easy answer, but I can't teach you correct machine technique either. The best I can offer is to encourage you to soak up as much information as you can from Grant's book and work on your construction skills.
Your hamburger is fine. Keep reading Grant's book.
Q: You are totally right, that question not that smart. However, I have read some of the first bit, and now I have specific questions. He seems to recommend using a jig saw a lot. My questions are these:
a) How good quality will this tool produce? Basically, which bots have had a jig saw used for them?
b) A drill press is the next level above cordless (unless you are using it in the pits). A band saw is the next level above a hand saw. A jig saw is to a what? For making curved cuts as well as straight, what tool is better and do you recommend this over a jig saw. I just don't know if a jig saw is really the tool that should be used here. Is a mill the next level? He only mentions mills once, and does not include them in his index. He says there are mini versions of the massive ones for hobbyists, but that is it. Where should one use one? Do you have a recommendation for the size of mill adequate for combat robot building?
Thanks so much, I hope I am not asking to many questions! Feel free to tell me if I am!!! -New York
A: I don't believe you're approaching this correctly.
B) There are not 'levels' of tools - although one tool may be more versatile, faster, or more precise at some specific task than another. If you're fabricating something, you first decide EXACTLY what needs to be done, then you select a tool suitable to the task. You do not stock a room full of tools that you do not know how to use and then decide what to do with them.
If you're comparing a jig saw to a mill it's obvious that you have no idea what a mill is or what it does. You don't need one.
Like I said earlier, I can't teach you how to be a metal fabricator.
Another thing about this set... i've got a question for you:
Because the Battlepack is 12 Volts, that means that i'll be mildly overvolting both the weapon ESC and motor. Is it okay?
A: Some problems:
Q: Dear Aaron, after reading your advices, i've revised my list to be this:
A: Better!
Q: So, should use the batteries from the drills(DeWalts) or should i use the LiPoly Battery?
A: Use the LiPoly. The DeWalts are more prone to damage and bursting into flame if abused -- and combat will abuse them. We have full specs for the Lipoly: it has very high charge and discharge rates, it's compact, it's newer technology, and it's safer.
Q: According to the list, what power switch would you recommend for it?
A: Check your ruleset to see if there are special requirements. You may be able to get away with just plugging/unplugging the battery. If not, I'd use a removable link -- search the archive for 'removable link' for a diagram.
Q: It's a dilemma. Because you said that i can only use 1 battery for simplicity sake, if i use the batteries from the DeWalt, i'll overvolt the brushless motor and ESC. If i use the LiPoly packs, i'll undervolt the DeWalt Motors. Which one is more safe?
A: No dilemma. The DeWalt isn't really 12 volts -- its Li-ion battery only produces 10.8 volts under load. DeWalt motors are commonly overvolted by as much as 33% in combat robots anyhow. Use the LiPoly.
P.S. -- it's generally 'safe' to undervolt a permanent magnet DC motor; it will just run a little slower.
A: See the Wikipedia entries for omni wheel and Mecanum wheel, plus multiple posts in this archive under 'omnibot'. Omni wheels are not good at high speeds and do not provide great traction. Their strength is entirely in the amazing maneuverability they can provide. Try a video search.
A: 'Spinner killer' scoops and wedges do present a problem for spinners. The usual attack technique is to avoid a direct front attack and veer a bit to one side to 'catch' the edge of the wedge. Spinners love to attack sharp edges on their opponent.
Q: Dear Aaron, if spinners love hard edges (which I am sure they do) why does Breaker Box, a very successful bot and and [maybe...] the best 'killer of spinners', have sharp 90 degree angles all around it?
A: Most robots have a lot of edges because it's much simpler to build a strong boxy robot than any other shape. Jim Smentowski does his best to keep the boxy body of 'Breaker Box' hidden behind the big, smoothly curved titanium scoop in combat. Combat robot design is always a compromise, and Jim has struck a good balance this this 'bot.
A: I don't know what aluminum alloy you'll be using, the details of your design, or the construction techniques you will employ. See #17. As a pure guess, the side panels seem thick for a hobbyweight and the top and bottom seem a thin -- particularly for a dustpan.
Q: 1 more thing, i'm new to the competition, so, i can't give you predictions about how the competitor's bot gonna look like. But all i know is that someone in my school robotic extracuriculum (i'm in it too, only i and that guy's gonna attend the combat robot category at my competition) is gonna look like Roadblock with a drum.
A: We've said before, a combat robot's success depends about 20% materials/components and 80% on design/construction/detail. What your opponent 'looks like' doesn't count for much.
A: Have a look at the build report for omni-hobbyweight 'Skittlebraü'. RobotLogic makes a radio mixer for a three-wheeled omnidrive that will simplify your radio set-up. They also make a Mecanum mixer for four-wheel omnibots.
Search this archive for 'omnibot' to find several posts and a diagram covering omniwheel setup.
A: Go take a look at a bicycle drive chain mechanism. Simple case: attach a small sprocket to the motor, and a larger sprocket to the wheel. A chain joins the two sprockets. Greater gear reduction requires a multi-stage chain drive -- see BattleKits for some example photos.
A: Methods for joining 'plates' very according to material thickness. Thick plates can be fastened directly together by drilling through one plate into the end of the other, end tapping, and securing with machine screws. Material too thin to end tap can be fastened by drilling into a full or partial frame of square rod or formed angle material. Examples of both techniques are shown in photos at right. Some teams prefer to weld the structure of their robots.
Lexan (polycarbonate) plastic has great resillience if allowed to flex, but will crack if used in an application with high localized stress. Success as an 'armor mount' would depend on the specific design. In general, there are better materials for mounts.
Q: The diagrams you've just showed me are used to connect side panels. how do you connect those side panels with the robot's lid/top panel?
A: The baseplate and top panel connect with the same techniques shown for the side panels.
A: The only combat robots with printed chassis I know of are in the 150 gram UK antweight class. The nylon material commonly used is fairly strong, so durability will depend the specific design. For heavier classes, more conventional methods of chassis construction make more sense. I wouldn't want to be the first builder to roll a printed plastic chassis into a US competition against a spinner.
A: I like all of the Team Plumb Crazy 'bots. They're designed well, they're built well, they're driven well, and they win. What's not to like?
In particular, the electric lifter design used in 'Pipe Wench' and 'Wipe Out' is clean and effective. The final stage of the lifter drive is high and somewhat exposed, but the high pivot gives great versatility to the weapon without requireing unrealistic torque.
Q: Is the design suitable for sumo robot? 3KG robot.
A: All you need for sumo is to lift enough to break traction. The high-lift design is overkill.
A: Mark J. here: we have referenced the Riobotz tutorial many times (search the archives for 'Riobotz'), but we have not written a formal review. Given that you can download copy at no cost direct from Riobotz, we think you can read thru it and form your own opinion.
I will tell you that the focus of the Riobotz work is on the classical engineering approach to materials and design. The tutorial is well worth a read and has much valuable information , although we do not agree with all of their recommendations. Much of their analysis is based on assumptions that work well if you're building an airplane, but which may not apply to the unpredictable destructive forces encountered in a combat robot.
The focus of Grant Imahara's book is on actual combat robot construction techniques. The book is unique in this focus and has our highest recommendation -- there is no substitute.
A: Possible, yes. Desireable, no.
Shufflers have no weight bonus under the current rules, so there is no reason to build one. The requirements for a true walker are very stringent, and the rules state that the extra weight cannot be used for excessively powerful weaponry -- so there is no reason to build a walker either, invertible or not.
i was making a concept on a bot that i will use on RSC (Robotic School Cup) 2012, and i was coming across a 4 wheeled bot with 2 fly wheels in the front and the back which will shape like BioHazard. but i was worried about the motors for the flywheels because i'm afraid that it would either be expensive, or will be too heavy (i'm going to compete in the heavyweight competiton). should i bolt the motors directly to the fly wheels, or should i use a speed reduction like the wheels? and what is the best but light flywheel design? i don't want my bot to smoke like Hypno-Disc.
A: Start by reading thru the MANY posts on spinner design in the archive and drivetrain motor selection in the archive. Most of your questions are answered there. A few comments:
A: I don't follow the BotsIQ 15 pound class and don't feel qualified to comment on specific BotsIQ competitors.
A: A good robot does everything well. 'Gilbert' is very quick and low enough to be difficult to hit, but its real strengths are a well-sorted radio set-up and excellent driving. Speed is not an asset if you can't make effective use of it.
A: The focus of combat robotics is very different in the UK versus the US. Arenas in the US run up close or flush to the enclosure walls and competition is based on destruction with lots of spinners. The UK arenas leave space between the arena and the enclosure walls that allow a robot to be ejected from the arena. Many (most?) UK matches are won by ejection rather than destruction, and flippers are more effective than spinners in this type of competition.
With spinners being less prevalent, a UK flipper can 'afford' to have a relatively thin full-body armor covering the flipper structure. A US flipper must concentrate thick armor in compact vulnerable areas, leaving the flipper structure exposed.
A: We don't believe twackbots are effective under the current judging criteria and we do not recommend them. We don't like to see people spend their time building ineffective designs.
A: I have no idea how much power your motors provide, but the speed is reasonable to power a ping-pong ball collector. They'll be slow, and I don't know either the amperage draw of your motors or the capacity of your 'electronic relays'. I'd strongly suggest building a prototype to make sure everything works.
A: The load on axle shafts will vary with the length of unsupported overhang and whether there is axle supported on one or both sides of the wheel. A 'general rule' can be misleading here. There's also the question of the shaft alloy and if it has been heat treated for added durability. My best advice is to find successful robots with designs similar to yours and see what they use. When in doubt, go bigger.
Note: you did not specify what weight class you're building. If following on, please mention the previous post in your question. See #10.
Q: I asked the question on shaft sizing. The robot is 30lbs. I will probably have heat treated steel shafts and the outer end of the shafts will be unsupported. I was thinking either 3/8 or 1/2 inch shafts. Would either of those be strong enough?
A: You still aren't telling me about the overhang length. Overhang is the distance from the outside edge of the tire to the outer edge of the axle support bearing. Double this distance and the stress on the axle doubles. Good design calls for making this distance as small as practically possible.
I can tell you that a typical featherweight might run 3/8" axle shafts, but I don't know enough about your design to make a specific recommendation -- see #17. I encourage you again to visit builder websites and compare their designs and materials to your plans before making a decision on axle size.
Q: Drive shaft question again. The overhang length is around 2.75 to 3 inches and it is a rambot. Wheels are 4.5 inches tall x 2.5 wide and driven by DeWalt Powerdives. I know it's hard to give a general answer about a robot you have little information about and I'll take your advice to look around to see what other builders are doing as well, but I value your experience and would like to hear your opinion.
A: OK, since the Team Delta splined drive shafts for the DeWalt Powerdrive are 1/2", why not use them? They're overkill in your design, but the weight penalty is small and you'll never have to worry about one failing.
As a note, those wide tires will not give you additional traction in the typical dirty, greasy, and dusty combat arena. They will make precision turning more difficult. A rambot that can't hit its target isn't much good.
A: See #21 for guidance on motor and ESC selection.
A quick check with the
Team Tentacle Torque Calculator shows that two DeWalt Powerdrives are WAY more than enough to power a featherweight rammer. Four would be MASSIVE overkill, a waste of money, and likely too squirrelly to drive. Use two and a chain drive.
If you did choose four 18v DeWalts at 24 volts with tire diameters useful for a 16 foot arena, the TTTC calculates that each motor would pull less than 6 amps to break traction and spin the wheel freely while using less than 4% of the torque available from the motor. That's a huge waste. You could use very small ESCs to handle that type of load since you'd never come close to stall loads on the motors. No more than two DeWalts, please.
A: Mark J. here: a set screw is typically used to secure a pulley/gear/hub to a round shaft against both rotation and axial movement. The small contact area between the small screw and the shaft provides poor security when more than modest torque loads are involved. Set screws fail at an unacceptable rate under the variable, reversing, high torque loading common in combat robots. Once the hub starts to loosen, complete failure follows rapidly. Thread locker and a flattened 'detent' on the shaft help only a little -- there is a lot of force concentrated on the tiny contact area of that very small screw.
Other methods of preventing rotation of a pulley/gear/hub on a shaft that rely on more than a small point of contact are greatly preferable: square shafts, keyed shafts, hardened pins, and splines are common examples. See Carlo Bertocchini's tips page for more info.
When working with very small shaft diameters, a set screw may be your only viable option. Use a liquid thread locker, grind a flat detent in the shaft, and check it for tightness before every fight.
A: A great many successful combat robots have been built with simple hand tools in small spaces. Stephen Felk built hall-of-fame heavyweight 'Voltronic' in the kitchen of his San Francisco apartment. It is entirely possible to design a 'bot that can be built with a hand drill, a hacksaw, a screwdriver, and an adjustable wrench -- but you'll probably want a few more tools than that.
The best money you can spend: buy a used copy of Grant Imahara's 'Kickin' Bot: An Illustrated Guide to Building Combat Robots'. The book covers tools, workspace, components, and design considerations to make the most from your limited shop environment. Buy this before you buy anything else, consider your own skills, then match up the type of 'bot you want to build with the tools you'll need to build it.
Q: Dear Aaron, thank you so much for the recommendation on the workshops!!! I am showing a bunch of my friends this site!
About the books, how do you think 'Building Bots: Designing and Building Warrior Robots' would do for this subject of Workshops? I already have this book but I am more than happy to get Grant's book. I just want to make sure I get the best info I can get on the workshops. And as an overall book, which do you recommend more?
A: We have reviews of both of these books (and others) on our robot combat book review page. I don't think much of 'Building Bots' for reasons mentioned in our review. Author William Gurstelle is not an experienced combat robot builder, and the book most certainly does not adequately cover tools, techniques, and practical building methods.
Grant's book comes with my highest recommendation. Have a 'Look Inside' at the table of contents and browse a few pages to see how much practical information this book covers. I believe it contains more useful combat robot building information than all the other books on the subject combined. Buy it, read it, and keep it on your workbench.
A: Mark J. here: knife edge coutersinking is really poor practice. Take a look at the Mechanic Support site (archived) for recommendations on avoiding countersink knife edge. They reference aeronautic fasteners with a 100 degree bevel that are designed for thin sheet fastening. These military spec MS24694 screws are available from on-line sources. Don't hesitate to use more, smaller screws as needed.
Alternately, I'd consider a redesign of the wedge mount to move the fasteners off the wedge face and switch to round head fasteners.
What would you say is a good value for top speed(in MPH) and acceleration (time to top speed in seconds) for a 15lb 4WD wedgebot? I've been using the Team Tentacle Torque Calculator, but I don't know what to do with its "Acceleration" Table values. How fast do most 'bots go?
The smallest cage we compete in is an 8ft by 8ft square, a medium sized one being a hexagon with 8ft to a side, and the largest a 16ft by 16ft square. When does a 'bot become too "zippy" and uncontrollable? (fishtailing, smashing into the walls of the arena, etc.) I was hoping you could help me hone in on the balance between control, speed, and effectiveness as a half-wedge, half ram-bot. Thanks in advance!
A: The acceleration window in the Team Tentacle Torque Calculator is there as a 'reality check' on the speed value given on the main page. The main window might say 10 MPH, but if the acceleration window says it will only reach 5 MPH in your small arena you'll need to work smaller tires and/or greater gear reduction into your design to improve acceleration and get the most from your motors.
As a VERY general rule, I look for gearing that will get the bot to maximum speed in about half the distance across the arena. The next time you watch a robot fight, make note of how often the combatants have more than that much room to make a run on each other. A great deal of the fight happens with the robots quite close, so responsiveness and control are most often more important than maximum speed.
How quick is too quick? That's a highly variable driver preference. I see many bots that are quicker than their driver's ability to control them, which makes for a lot of frantic and ineffective maneuvering. My best advice is to find a robot in your weight class with a known drivetrain and watch some video to see if it looks like it would be comfortable to drive. Be realistic about your driving skill. If it looks good, run its design thru the Tentacle Calculator and try to match the performance figures with your drivetrain.
Competing in arenas of different size does present design challenges. Remember that you're going to spend a lot of time in close quarters no matter how big the arena is. However, a really slow robot - particularly a ramming wedge - is not going to impress the judges. Speed/control/power is a major design conundrum with a lot of trade-offs. Best luck.
Mark J. here: a tip on different size arenas. Adjusting the mixing and exponential response settings on your transmitter can help tame a robot that feels 'too responsive' in a specific arena. Our Transmitter Programming Guide was written for a Futaba radio, but the explanations of adjustments are applicable to any computerized R/C system.
A: It looks like the 'web' did more harm than good. The soft aluminum angle used to support the web bent badly and looked far worse than any damage 'Enforcer' likely could have done to the polycarbonate top of 'Shish-Kabot' (that is polycarbonate, I hope). I think the web was a mistake.
Q: What do you think abput Shish-Kabot? (In General)
A: A practical sportsman design, well built and well driven.
A: Being taller than the jaw opening of the well-known 'Retired European Hydraulic Piercer Robot' would make it very difficult for the piercer to get a bite. 'Terrifying Overhead Axe Robot' did show up at an internationally televised event with extra-tall polycarbonate side armor to take advantage of this approach, but did not draw 'Retired European Hydraulic Piercer Robot' in the tournament. 'Retired European Hydraulic Piercer Robot' was surprisingly lucky(?) in avoiding competitors who had the best chance of beating it.
Thank you so much! -a frequent viewer and questioner:)
A: A robot combat arena is a hectic and chaotic environment where it's very easy to go into sensory overload. If your lifter gets flipped, you don't want to take time to stop and figure out which way you have to jiggle that control stick to get the robot oriented back the way you want it. The 360 degree rotation on 'Shazbot' allows Jim to just mash the lifter control and back off when things look about right. Stress relief!
A: Look at the left side of the screen at the top of the page. See that green square with the yellow gears? Click it. That will pop up the 'Team Tentacle Torque/Amp-Hour Calculator'. Learn to use it -- its a robot designer's beast friend.
Extracting the motor info from the specs on the page gives:
Try plugging in specifications for other gearmotors until you find something that is a better fit. The BaneBots 16:1 P60 gearbox with an RS-540 motor might be a good place to start.
Q: Following my query on the 30lbs 4AWD wedge battlebots. I've decided to switch to Banebots 26:1 gearbox + RS-540 motors with 4" banebots wheels. I've tried the Team Tentacle calculator and came up with the theoretical top speed of 7.86MPH (correct me if i'm wrong). Will this provide strong enough pushing power for my battlebot in a 11' battle arena? Apart from the theoretical top speed value, i didn't quite understand what the other values tell. If you don't mind, would you clarify:
A: Your calculation of top speed is correct. I really should write a guide for users of the calculator, but do note that there is a 'Help' button on the right side of the calculator about half-way down that offers brief definitions of the terms used. Here are some expanded definitions:
Q: Hi Aaron,still on the 4AWD bot but i've decided to add a 4" drum weapon. I plan to use the 5" banebots wheel on invertible body so that the drum weapon is smaller than the wheel in diameter & can be functional upside down. My questions are:
A: By the numbers:
Q: I didn't get the same calculated amps of 11amps per motor as you mentioned. I've used the Tentacle Amp calculator but only got a low value. Where should i actually look? Neither the amps per motor to spin wheels & total peak amps is below 2 amps. Please help to guide me on this.
A: You're looking in the right place, but I think you failed to enter the correct weight for your robot. More weight on the wheels requires more torque/amps to break traction and spin the wheels. Check your entry values against those in the picture.
Q: Hi Aaron. I start with a wedge design, switch to one with drum weapon & now i've decided that I want to build a battlebot with a wedge on one end and a drum weapon on the other. Can you recall any existing battlebot with this type of design?
This bot would be 4AWD with 3" Banebots wheels. Each wheel will be driven by Banebots P60 26:1 gearbox + RS540 motor. I've used the Team Tentacle calculator and come out with these readings:
On the weapon, a wedge will be formed at one end. I plan the wedge to be as low as possible but i'm not sure at what angle would it be most effective. Please advise me on this.
On the other end, i plan to add a drum weapon (because the competition i want to enter require at least an actuated weapon). Since i still want to stick with an invertible design, the drum weapon has to be smaller than 3" in order to be functional upside down. At this point i still don't know what type of motor to be used. How much RPM & torque would be adequate to drive a drum with these details: mild steel, 2.5" diameter, 10" length, 0.12" thickness.
Thanks in advance! I'm looking forward to your response.
A: Quite a few drum spinners have had a drop wedge on the other end, commonly for defense. 'El Diablo' comes to mind. Not a bad design if you have the weight to spare.
Your drivetrain selection is well suited to the small arena. My performance calculations are just a little different from yours:
There is quite a bit of discussion about wedge angle in this archive. Search for 'wedge angle'.
That's a really small diameter drum for a featherweight! Pound for pound, a large diameter drum stores much more energy than a small diameter drum at the same RPM. Spinning a small drum very fast to make up for the difference creates real problems. Fast drums have trouble getting enough of their impact tooth onto their opponent for good 'bite'; they tend to just 'skitter' along the surface without damage. Add to that your need for a very fast spin-up time, and you've got some serious weapon design problems. There is a lot of discussion on spinner design and speed in the archive -- start reading.
The Run Amok Spinner Excel Spreadsheet shows that a drum with your specs would need to spin at 13,000 RPM to have a barely respectable 1000 Joules of energy, and that's way, way, WAY too fast! Worse, you need a really quick spin-up time to get some power into the weapon before your opponent is on top of you in that really small arena. Even a powerful DeWalt 18 volt drill motor running at 24 volts and a 2:1 reduction will spin your drum up to only about 350 Joules at 4000 RPM in half a second on its way to 1000 Joules at 13,000 RPM. That half-second is about as much time as you've got. Consider a re-design.
One last note: an inverted drum spinner with the front edge of the drum spinning downward isn't effective. You'd just launch yourself upward when striking another 'bot. You could reverse the weapon direction with a reverseable ESC, but that takes time and it's one more thing to worry about in combat. The successful drumbots I can think of are non-invertable and run a large diameter drum.
A: The Team Tentacle Torque/Amp-Hour Calculator (see question above) can estimate battery requirements for a theoretical robot drivetrain, and the Team Run Amok Spinner Excel Spreadsheet (red square under the Tentacle calculator at top of page) can estimate weapon battery needs.
I would guess that 400 mAH is ballpark correct, but you should be using the calculator and spreadsheet to maximize performance of your drivetrain and weapon anyway. Plug in your numbers and get a real answer.
Thank you so much, Ask Aaron daily viewer.
A: I'd very much like to help, but Team Run Amok never has used CAD software to design our robots. We are not knowledgeable in this area. I think you'd be best advised to ask at the Robot Fighting League Forum.
A: I can't answer that in a few sentances! Take a look at How Robots Work at the Discovery 'HowStuffWorks' site. For information about combat robots, you can start by reading our .
Thank you and your father for all your helpful guidence and support! - Anthony
A: There are two things you need to get pushing power: torque and traction. A pair of RS-540 motors with a 130:1 gear reduction and reasonably sized wheels provides about a dozen times more torque than a 30-pound robot can use for pushing, so adding more motor power will not solve your problem directly. A gear reduction of about 25:1 with 4" wheels would still give more than twice the torque needed for pushing and would greatly improve speed.
Getting traction to make use of that torque is a more complex problem. All-wheel drive (like 'Mangi') is best, but a two-wheel drive can provide very good traction if components are arranged to put most of the robot's weight on the drive wheels.
Re-do your gearing to get better speed and move your weight around to get weight on the drive wheels. Motor power is not your problem.
My strategy is to shove the buy against the wall with the lifter scoop, and then the pincers would crush them from top to bottom once they come out of the vertical slit. This might be hard to visualize, I understand if you can't. Think of breaker box with a slit and vertical pincers come out when your opponent is one the scoop and pushed on the wall.
Do you have a solution or a 'known way' for the pincers? Also, how feasible do you find this to be? Lastly do you see any major design flaws that should be changed. I understand if the 'hamburger is bad.' No matter what, thank you so much for your valuable input!!!! Thanks
A: The reason 'pincers' worked for the Robot Wars 'house robots' is that they did not have to abide by the weight limits imposed on the competitors. Simple weapons win in combat robotics -- not retracting crusher claws. Feasibility: 2 out of 10.
In the history of fighting robots there has been exactly one successful crusher robot. It took the team several years to develop it into a champion competitor. There are multiple posts in the archive about crushing robots and the design problems they present. Unless you are a professional hydraulics engineer, I'd recommend that you design another weapon. Keep it simple.
Q: Dear Aaron, I am sorry to keep pushing, but do you know of any way to Incorporate a way to deal damage on a breaker box style robot? If you know of any way to damage and not be completely defensive that would be fantastic. Any Ideas? I know I have already asked to much for your time! Thank you so much, I recommend this website to my friends. No joke. Thanks!
A: Damage or spinner killer - pick one. Splitting your weight allowance with halfway measures will leave you inadequate in both areas.
A: We've written quite a bit about 'Last Rites' (29 wins, 19 losses) previously. It is brutal, and that's the way builder Ray Billings likes it. That brutality got it into the Combat Robot Hall of Fame. It breaks itself almost as often as it breaks its opponent, but if it's still running at the end of the match it has probably won. It is a tribute to Ray's building prowess that it EVER survives a match. Like it says in the Hall of Fame, "Brute Force has no better friend."
A: Chris published 'Combat Robots Complete' in 2002. It is 311 pages in length and does have chapters covering a 'complete' range of combat robot topics with many photos and drawings. The glossary is particularly complete and useful for new builders. The included CD has evaluation versions of design software packages, combat videos, and tables of material and component information.
The 'weapons' chapter in 'Combat Robots Complete' is a very brief (six page) overview of weapon types and design considerations. In 2003 Chris released 'Combat Robot Weapons' - 207 pages of design, analysis, and component discussion for eight classes of combat robot weapons. A CD is included here as well, with CAD models and material to support the information in the book.
Take a look at the Team Run Amok Book Review page. Follow the book title links there to Amazon.com and click on the picture of the book cover. You can then 'look inside' to see the full table of contents and read selected sections of the book.
Both of Chris' books are enjoyable reading and are recommended for a builder's library. However, if you're looking for a real 'shop manual' guide to robot building, my highest recommendation goes to Grant Imahara's 'Kickin' 'Bot' -- also featured on our book review page.
I figured that a lot of robots with spinning bars have wider set wheels, maybe to prevent them from turning on impact so much? I'm not really sure. But there is one wheel on the outside, and one on the inside. So, if the outside one gets damaged, it will still run because the wheels are on the inside, too. Plus, it gives that added width to the wheel. Please tell me what you think!
A: Mark J. here: I don't see benefit from your design.
A: I'm puzzled by the design of sportsman 'Shish-Kabot'. It isn't terribly effective, and it appears to violate the 'No Wedges' provision of the sportsman class rules. Granted, the lifter spike is very narrow -- but it can and does act as a 'wheel lifting' passive weapon. I think the event organizer is being very liberal in allowing this design to compete in the sportsman class. I wouldn't.
A: James Underwood's 'Defiant' was a pneumatic 4-bar lifter that won the lightweignt (50 pound) division at the 1997 US Robot Wars. 'Defiant' returned for the 1999 BattleBots event in Long Beach, finishing second in the Kilobot (lightweight) division.
Defiant's weapon was modeled after the 4-bar mechanism in BioHazard, replacing the electric actuators with pneumatics. There are some good photos of BioHazard's lifter mechanism at the BioHazard mechanical design page -- copy it just as James Underwood did. Note that a low profile design such as Defiant's does not yield the same efficiency as an upright design.
I don't know what motors 'Defiant' used, but robot drive technology has improved in the last 14 years. Why use outdated motors? The wheels appear to be small diameter Colsons.
A: Previously discussed. Search this archive for multiple posts on this topic.
A: Not a short-answer question. I suggest that you download the current RFL and FRA rulesets and watch some US and UK combat videos to get the broad answer to your question. Write back with more specific questions of you like.
Q: ok. I saw that the uk FRA didn't have any spinners with cutting devices. They seemed to have very powerfull flippers and a few ax bots and pushers. Almost everyone was a flipper. Is this because the arena side wall is so low?
In addition, the american combots did not have any of the euro style co2 crazy high powered flippers. Are there any other notable differances? Thanks a lot!
A: The European combat robot tradition grew out of the Robot Wars paradigm: low side bumpers and a good amount of space between the bumpers and the arena wall. Judging criteria are complex, and hurling your opponent over that low bumper makes for an easy win. From my limited experience, the euro-competitors also lack the violence obsession common to the typical American competitor - they would just as soon toss you over a wall as cut you in half. If they can do that from the center of the arena, so much the better.
The American combat robot tradition came from the BattleBots paradigm: a sealed box with side bumpers right up against the arena all. No escape - two 'bots enter, one 'bot leaves. Judging criteria are simple: you get points for continuously moving toward your opponent and for damage you inflict upon them - period. The simple way to win a match is to immobilize [demolish] your opponent. Gratuitous violence is considered to be a bonus, and is much appreciated by the audience.
These differences have led to different types of robots and styles of fighting. You've correctly identified the major differences in robot types. There is also a tradition in the UK of taking pride in how little money you spent on your robot -- winning with a scrapyard find gains popularity points. In the US, a good sector of the builder population likes nothing better than to show off their polished, waterjet-cut, CNC milled, exotic alloy endowed, CAD designed wonderbots.
There are other more subtle differences as well, but I think this covers enough for now.
A: Mark J. here: well, to be honest it wasn't much of a fight. Two robots with ineffective weapons having trouble maneuvering well enough to even run into each other. No damage and very little aggression. That's a little harsh, but it's an honest opinion. Where is this leading?
Q: Hi Mark. Follow up on the video that i share (the local competition in Malaysia). The battle is a straightforward 3 minutes match between 2 battlebots with a weight limit of 15kg (including radio/controller) in a 3.6m x 3.6m square gamefield. To win, you have to immobilize your opponent or getting more points (points given for attacks/hit).
Which type of battlebots (drivetrain? weapon?) do you think is suited to this kind of battle? If you were to enter the competititon, how your robot design would be?
A: I don't know the specifics of your rule set (there has to me more than you've mentioned), the details of your arena (hazards, internal rails, space to 'flip out"), the preferences of your judges and their specific scoring criteria, or the types of opponents you are likely to face. I would study these factors for days before I could start to design a robot. You should too.
If I had to build a 'bot with the very little information I do have on your tournament, I'd be tempted to build a high-power 4-wheel drive wedge/rammer. Hit 'em 'til they break!
Q: I'm looking at one of your bots, 'The Gap', and wonder if i could use similar design for a 15kg flipper. Will that be more effective compared to the high-profile wedge-flipper? The opponent can also be trapped against the low-profile platform, so the lifter have 2 effective functions.
My questions about The Gap:
A: 'The Gap' is not technically a flipper, but a lifter. The mass of the lifting platform is too great to be an effective flipper, but the extended reach and low angle of the lifter arm makes it a very effective lifter. I don't know how your judges would respond to a lifter 'bot, but the design should translate to the sublight weight classes.
Q: Hi Mark, if i were to scale down the Gap to fight in a 15kg weight class, what do you think would be the right choice for the drive motors n wheels? The maximum size of the robot must be under 0.8m x 0.8m x 1m height. I have few motor selection in my mind...
FYI, the battle arena is 4m x 4m square with floor layered with zinc plates. The match is 3 minutes, 1 vs 1, and the winner is determined either by knockout or by hit/aggresive scores. Please let me know if you need further details. I could also email you the competition rules n regulation if necessary.
A: There really has to be more to the rules than you're telling me, and more to the scoring preferences of the judges. We are pleased to help builders with general advice, and we have provided design assistance tools in the Ask Aaron Archives. We don't, however, have time to analyze the details of an unfamiliar robot combat environment and design your robot for you. I can give you some general advice about lifters.
Lifter/flipper robots are not about drivetrain power. It's better to save weight on the drivetrain and use it to improve the weapon power and durability. Both of your potential motor selections are overkill for a 15 kg flipper. Go smaller. Something like the PD27M gearmotor [no longer available] would be entirely adequate. The
Team Tentacle Torque & Amp-Hour Calculator is of great use in selecting suitable motor/gearing/wheel diameter combinations, and there are many posts about correct use of the calculator in the archives.
Lifter/flipper robots are also not about traction and pushing power. Look at what wheels your competitors are using. Select something of suitable size and durability and you'll be fine. A set of Banebots wheels and hubs would likely be suitable.
Also did you expect last rights to lose, it looked so much more powerful!
Thanks! Great site! Also thanks for recommending the show it was epic!
A: There was a much greater diversity of weapon types back in the BattleBots era. Over the last decade it has become clearer as to what weapon designs worked best and the less efficient weapon types have died out. That's natural selection and evolution in action. Similar refinement happens in all forms of mechanical sport.
'Last Rites' and 'Sewer Snake' have fought each other many times, going back to 2005. Sewer Snake's win at RoboGames gives Matt and Wendy a six-win, three-loss record against Last Rites, so I am not surprised by the result. We've said it before, Ray Billings is a wild man who believes in simply building a huge weapon and pointing it toward his opponents. Sometimes brute force works, sometimes it doesn't. Either way, Ray has a good time.
Also, it seemed that the combots robots had extremely powerful driving mechanisms and pushing power however there was not a huge amount of variety. There were however outliers like last rights however,
A: 'Sewer Snake' has an electric lifter wedge with interchangeable attachments that is designed for a completely different attack strategy than a high-pressure pneumatic flipper. Which is 'better' depends on the arena structure and the judging criteria. You also cannot evaluate the weapon separate from the rest of the robot -- everything has to work together to make a great robot, and 'Sewer Snake' it the perfect example of all robot systems working in harmony.
See the question above for an explanation of the reduced variety.
A: Mark J. here: linear motors are not generally used in robot combat. They are very good at precision movement of heavy loads, but not at the violent thrust and hold requirements associated with robot weapons. I am not familiar enough with commercial linear motors to suggest a replacement for your application, but maintaining that level of force at a greater speed will require a more powerful (heavier, larger, more expensive) motor.
Pneumatic systems are widely used for lifter weapons for very good reasons. You might want to re-think your 'electric' approach.
Q: Thanks for your reply Mark. For the linear motor replacement, i've think about using a pneumatic system as the actuator but i'm afraid that the total added weight of using the pneumatic system will cause the robot to exceed it's weight limit. My battlebot is in a 15kg category. Do you know any robot in this weight class that use an effective pneumatic powered flipper?
A: There are several. The Finnish 12 kg robot 'Purse' is an effective example (video). Nyt kuluva robotti potkaista aasi! It can certainly be done.
Q: Hi Mark, thanks for your reference link to the Finnish robot. Few questions popped in my mind:
A: By the numbers...
Is there a way to build your robot on a computer and then see if it works, and then put it together. This would mean that you know your design will probably work. Thanks for your great site!
A: Well, you can design your robot with a CAD program that will make sure everything fits where it's supposed to go, but this will tell you nothing about the performance of the robot.
The PC game 'Robot Arena 2' features a virtual robot workshop that allows you to design and build a virtual robot that you can then test and enter in virtual tournaments. However, the components available do not reflect real-world robot parts, and it is possible to build a virtual robot that simply would not work in reality.
No short cuts -- you have to build your robot and try it out.
Q: Hello Aaron, I saw you mentioned Robot Arena 2 in that other post (not mine). What robot video game is the best in terms of realism for making a robot? If there is none, what comes the closest? thank you!
A: I mentioned 'Robot Arena 2' for good reason. It has by far the most realistic combat and the finest design and construction capability available in a video game. No contest. You can even download a virtual 'Run Amok' for the game.
A: See the thwackbot article at T.i. Combat Robotics (archived).
Q: Hey Aaron,why would someone choose a thwack bot to build over a full body spinner? I see no advantage to the Thwack bot. They all seem mediocre. Thanks a lot!
A: Spoken like someone who has never built a robot. The main advantage is simplicity in construction -- a FBS is a complex robot, and not at all easy to get right. Most FBS are more dangerous to themselves than their opponents. A thwack can also use ALL of its mass to store kinetic energy when spinning, which gives it a theoretical advantage over a shell spinner.
Thwacks, however, are not currently in favor due to the 'damage/aggression' scoring system in place at most tournaments. It is difficult to be aggressive with a robot that cannot attack and move at the same time. There are several builders who continue to develop the 'meltybrain' or 'cyclone' electronics that can modulate the propulsion motors and get some motion control with a thwack. Results are... mixed.
A: Mark J. here: 'Panzer' and the BattleKits have 'lots of small chains' because their drive systems provide both multi-stage gear reduction and power distribution to the wheels -- something that cannot be done with a single chain. They also have separate chain systems going to each wheel so that no single chain failure will incapacitate the robot. Redundancy is good practice!
Team Hunt's 'Hunter' runs a single-stage gear reduction chain to the back wheel, and a long chain from the back wheel to the front. It is difficult (impossible?) to get adequate reduction in a single-stage chain drive, and if that single chain from the motor to the rear wheel fails they're toast. No redundancy - poor practice.
Of course, you can avoid chains entirely by driving each wheel with a dedicated gearmotor, or reduce chain usage with a gearbox to achieve your torque multiplicaion before transmitting the power to the wheels.
A: You're probably thinking of BattleBots middleweight 'El Diablo' (pictured) or its heavyweight stablemate 'El Diablo Grande'. 'El Diablo' (6 wins, 3 losses) was a very popular competitor; one of the R/C BattleBot toys was modeled after it.
Q: Ahh yes, I can't believe I forgot about El diablo! fail on my part. I should say have there been any since his time.
A: None come to mind, but BotRank.com currently lists 4,222 combat robots that have competed in North and South American events, and many more have fought in Europe, Asia, and Australia. I don't claim to know the design details of all of the world's robots.
I will point out that while drum weapons are common, treads are not -- for good reason. Tank treads add weight, complexity, inefficiency, vulnerability, and expense to a robot and return little or no benefit in the typical flat and smooth combat arena. They do, however, look really cool.
Q: What was your favorite bot with treads?
A: I've always been partial to 'Ronin'. Must be the flags.
A: Multiple motors per wheel has certainly been done: Team Minus Zero used eight Jensen motors for their four-wheeled Robotica entry 'Wendingo' (pictured), and Banebots offers gearbox adapters that mount two motors to power a single shaft.
Multiple motors per wheel generally isn't done because it's mechanically simpler to use one motor for the purpose. If you need more power, use a more powerful motor. Keep it simple.
I personally think that they should be counted as walkers. Nobody builds either true walkers or shufflebots, but I think giving the latter the same weight bonus would help.
Sure, it may just be a cam powered system, but it isn't another [deleted] wheeled robot.
A: Mark J. here: the current requirements for a 'non-wheeled' combat robot are so stringent that nobody even tries to meet them, so the class effectively does not exist. 'Mechadon' would have qualified, but I think that it and sister 'Snake' were the only examples of combat robots that would qualify under the current RFL rules, which read:
A: Not that I recall, and there are very good reasons not to build one -- like enormous drivetrain inefficiency, no reverse, and a complete lack of pushing power. I suppose you could put one under a Full Body Spinner if you just wanted to be strange, but I think your opponent would 'sweep' the arena with you.
A: I've seen this done, but it has several disadvantages. It has less pushing power than 4-wheel drive and dragging the unpowered wheels sideways in turns causes poorer turning than if they were powered. If traction is broken on one end of such a 'bot you lose differential steering capability and your forward/reverse is impaired. Control under hard acceleration is also an issue.
If you're short on motor space you can belt-drive the other wheel on the same side for true 4-wheel traction and handling from two motors.
A: A proper safety cage is not a simple or inexpensive project. Plexiglass (acrylic) is many times less impact resistant than Lexan (polycarbonate). Do not consider using acrylic for a robot enclosure - it shatters! See Frequently Asked Questions #38 for some arena building resources.
Rather than build a test enclosure for the robot, a safety shield for the driver and observers would be much simpler to construct. Stay safe!
A: Yes - quite a few invertible Full Body Spinners (FBS) have been built. A spinning 'ring' is suspended around the perimiter on one huge diameter bearing or several smaller bearings. The most successful was probably heavyweight 'Ringmaster' (video), who won four matches at BattleBots 5.0.
Was my design overkill? Should I even bother with getting spare armor plates?
A: It's difficult to judge armor from a text discription because something critical may go unmentioned. A picture would help, but it sure sounds like you have a serious 'brick'.
Armor overkill depends on how insane your opponent's weapon is, but I don't think you'll need any replacement panels to get thru a tournament. Pack a hammer in case you need to bang something back square and you should be fine.
A: I don't think a thwack is good by itself, and adding a twack to a wedge just makes a bad wedge. A wedge requires pushing torque and stability, while a thwack needs speed and is inherently unstable. Pick one - I'd pick the wedge.
A: Creative thinking is a wonderful thing. You have correctly identified a problem with the maneuverability of four-wheel robots and stability of two-wheel robots and have come up with your own solution. I'm not too keen on the retractable wheel part - let me tell you about a similar solution used by other builders.
Six-wheel robots usually have their center set of wheels set a fraction of an inch lower than the other wheels. If the weight distribution of the robot is correct, almost all of the weight rests on those center wheels. That allows the front and rear wheels to slide easily when turning and gives these robots great maneuverability. Under acceleration (in either direction), weight transfers to the rearmost wheel set and provides additional traction and stability. There is no need for any retracting or skids, and the robot's full weight is always supported by driven wheels. We use this system on our beetleweight 'Zpatula' with good results.
A: Mark J. here: I'm not a fan of thwackbots, particularly for 'large multi robot battles'. A thwack needs clear space and time to spin up - both of which are difficult to find in a crowded arena. A thwack also needs opponents dumb enough to attack while you sit in one spot and spin.
Some clarification on things you mentioned:
For your thwack that means very powerful, correctly geared drive motors. Something like a pair of DeWalt 18 volt drill motors with the gearboxes locked in 'high' driving 5" wheels is ballpark correct. Keep your center of gravity close to the axle centerline by placing all of the available mass (batteries, electronics, etc.) well behind the axles to help offset the hammer mass. You may need some additional 'ballast' behind the axles.
Your hammer head should be hard, dense, and blunt. A sharp weapon has a much higher chance of getting stuck than a blunt impact head. The last thing you want in a multi-bot battle is to get your weapon stuck in another robot - you'd be a sitting duck.
A: We often advise builders to model their designs on those that have achieved success for other builders. Off hand, I can't think of an angled spinner like 'Malvolio' that has achieved much success.
If a design hasn't worked for other builders, you'd better have a very good reason to believe that it will work for you before you build it.
A: The two robots you mention were very different. 'Dark Star' was constructed from completely inadequate materials - the design concept wasn't bad at all. 'Malvolio' was well built using correct materials - the design seemed reasonable on the drawing board but proved unworkable in practice. A combat robot is no better than its weakest element.
A: The generic two-wheel wedge is as simple as a combat robot gets. I can't start to count how many examples of this design have been built. The fact that some have been successful while many have not shows how important the 'little details' are in robot design and construction. Simple takes work.
A: Don't get annoyed, just take a look at the photos and text descriptions of the design at the Team Cool Robots website. The wedge is attached to the rest of the robot by large diameter bearings coaxial with the propulsion driveshafts. The 'reaction hammer' portion of the robot can flip forward and back without moving the wedge.
The wedge could be attached by bearings directly on the driveshafts, but a driveshaft isn't a good place to stress with additional impact loads.
A: Mark J. here: brief current surges are unlikely to damage your battery, but prolonged amperage draw above the capacity of the LiPo battery will create damaging heat. A properly selected speed controller with current limiting will protect itself, the motors, and the battery from excess current. Some speed controllers, like the RageBridge have adjustable peak current limiting, but most have a fixed threshold. The drawback is that amperage is equivalent to torque - limit one and you limit the other.
The prefered approach is to match the capacity of the battery to the predicted peak amperage draw of the drive train so that you don't have to worry about cooking the battery. The
Team Tentacle Torque & Amp-Hour Calculator
can calculate the predicted peak amperage for you. Selecting a drive train with gearing that will not allow the motors to stall is probably the best current limiting you can get.
Q: I've recently bought the RS-550 Banebots Motors with a 26:1 gearbox. I'm using LiPoly batteries, and so I need to make sure that my motors don't draw over the rated current of the battery. However, I have gone to three different sites and received three immensely different stall current values: 35A, 85A, and 148 A. I really don't know what to believe anymore. Is my solution just to not stall the motors at all costs?
A: There are many different 'flavors' of the 550 motor with very different specifications. If these are the original motors as supplied by BaneBots then believe the figures BaneBots supplies: 85 amp stall current @ 12 volts. You can verify this with a fairly simple test -- search for "D-cell" in the archive for details.
A properly designed combat robot drivetrain will not allow the motors to stall under combat conditions. Your gearing should be selected to 'break traction' with the drive wheels at not much more than half the stall amperage -- that is the max horsepower output point for permanent magnet direct current (PMDC) motors. If your batteries can handle the break-away amperage, you're good. Run your design thru the
Team Tentacle Torque & Amp-Hour Calculator to see what amperage you actually need to cover.
Q: I noticed that the LiPoly batteries from the brand "ThunderPower" have a "burst" rating that is about 2x the continuous amperage. Do other LiPoly batteries (such as PowerEdge) have this burst capability as well, even though they do not advertise it as such? Would a 66amp continuous PowerEdge battery also be able to have a comparable "burst" to a 66amp continuous Thunder Power battery? They are the same voltage.
A: As noted above, LiPoly batteries can take brief bursts of amperage draw above their current rating. How high this burst can be depends on the internal structure of the battery, the details of the battery chemistry, and the length of the power burst. I think it's very brave/foolish of Thunderpower to try to quantify this number.
You may be worrying too much about babying your battery. Your first fight will likely be against a mega-spinner that will vaporize your robot -- battery and all. Live dangerously! Go down smoking and spewing flames .
A: I don't remember any that had more than Team Delta's 'War Machine'. Each of the superheavyweight's ten wheels was powered by its own 18 volt DeWalt drill motor.
A: Many robots have carried video cameras into combat to get 'first person' video footage. I hope you're not thinking of trying to operate the robot by viewing a live video feed -- your perspective from the sidelines is much better!
A: I don't know of any combat robots that use an 'internal stabilizing flywheel'. Weight is too precious to expend on such a device. The stability provided by such a device would come from the gyroscopic effect exerted by the flywheel. Combat robots with large spinner weapons are very familliar with the effect.
In addition in first case some say that the co-efficient of friction used should be co-efficient of rolling friction rather than co-efficient of static friction, as wheels have rolling motion. The co-efficient of rolling friction is much less(of the order of 0.001) compared to static friction(0.1 - 0.8). So, the torque calculated also varies.
A: Mark J. here: there's a lot of confusion on this topic. The problem seems to come from the phrase 'required torque' - required to do what?
Q: With regards to method #2 how can we include MOI of rest of the robot mass? Thanks Again.
A: Since we're dealing with linear acceleration, the MOI of the rest of the robot is equal to its mass. To calculate acceleration use the mass of the entire robot and the available force: acceleration = force ÷ mass. Generally, the effect of the rotational mass of the wheels is so small that it is not considered. Note that the torque available from a PMDC motor decreases linearly with with increasing motor RPM, so acceleration falls off with increasing speed.
Aaron here: if you're not following this discussion, don't worry much about it. The
Team Tentacle Torque & Amp-Hour Calculator handles these calculations for you. Let the physicists and engineers quibble over the details while you go get your hands dirty and build your robot.
A: Two things you should forget exist when building a combat robot: twist ties and duct tape. I'm not keen on plastic zip ties for anything that weighs more than about an ounce, either. A pair of metal hose clamps can make a simple and secure mount for a small air tank.
Cut two slots in your chassis plate the width of your hose clamp and about an inch apart. Open up the clamp, thread the free end down thru one slot and up thru the other. Wrap it around your tank and snug it down. Repeat at the other end of your tank. There are ways to improve on this simple design, but I'll leave that to you.
A: Very low clearance may cause unexpected problems. Consider the possibility of debris in the arena. Consider that the arena joints may not be level or even. I can't generalize on how low is 'too low', but I have seen many low clearance 'bots lose matches because of problems caused by their lack of clearance.
A: Mark J. here: how much material and from where it can be removed depends on the forces expected to be applied to the part in question. The problem is that the location, direction, and magnitude of force that will be applied to a combat robot chassis is very difficult to predict. Take a look at section 2.4.5 of the RioBotz Combat Tutorial for some guidance.
A: I've seen this type of non-symetric drive configuration used before. It can make design sense if your gearmotors are long and width is limited. However, the design comes with some serious drawbacks if you don't use a belt or chain to power the remaining wheels.
Under hard acceleration you'll get 'weight transfer' to the rear axle, resulting in reduced traction at the front and less potential thrust on one side of the robot than the other. This may cause difficulty keeping the 'bot accelerating in a straight line: a serious problem for a rammer! Another issue: if one end of the robot is lifted clear of the arena floor while pushing, the 'bot will lose all the power from the motor at that end and the remaining motor - driving a single wheel - will exert a turning force.
As you suspect, you will also get better pushing power by going to 4-wheel drive. The maximum amount of 'push' available to a robot is a product of the weight that is supported by driven wheels. Any weight supported by non-driven wheels will reduce the robot's potential to translate power into force.
Recommenation: run a chain or belt to the undriven wheels.
Mark J. here: note that the
Team Tentacle Torque & Amp-Hour Calculator assumes that all weight is supported by driven wheels. If your design has significant weight on non-driven wheels or skids, click the 'Help' button in the calculator and read the section under 'Tire Coefficient of Friction' for a correction factor.
A: We have a great deal of information in this archive and the and archives about the drivetrains, motors, and wheels used by hobby combat robots. We have no specific information on commercial or military unmanned vehicles, but I suspect they do not typically use belt drives.
A: A 'scoop' is a simple concave-curved wedge that diverts objects upward. A 'plough' is one or more angled scoops that divert objects both upward and off to one or both sides. House robot 'Shunt' had a plough on one end and a scoop on the other.
A: I don't think I understand the question. There were examples of robots from the same team that resembled each other but that compete in different weight classes - like vertical spinners 'Nightmare' (heavyweight) and 'Backlash' (lightweight) from Team Nightmare. There were also examples of various weight robots from different teams that had strong similarities - like pretty much all of the 'tuna can' spinners. I don't know why you'd want five pairings of such robots.
Q: how would they be able to down size and make a robot that is the same as the same one in a bigger weight class if you know what I mean. [N.I.Person]
A: No, I still don't understand your question. I do know of a couple of robots that fought as superheavyweights and could then remove some equipment (redundant drive motors, extra batteries, a couple of armor panels) to fight as heavyweights. Is that what you mean?
Thanks & have a good day! Looking forward to your feedback...:D
A: OK, by the numbers;
A simple and effective wheel solution would be the BaneBots 3-7/8" wheels. They are available in three different traction compounds and are inexpensive enough to allow you to buy a set of both soft and hard compounds to match traction to the arena conditions. The BaneBots T81 hub will mate these wheels to the P-60 gearbox shaft.
Q: Hi Aaron.. Regarding your reply to my previous questions:
A: More numbers:
Q: If i decide to build an invertible full-power ramming bot/thwack bot with sharp steel blade around the perimeters as passive weapon, which motor would you suggest instead of the RS550. Bot's dimension is around 50cm (length) x 50 cm (width) x 10 cm (height) with 4 directly driven 5 inch wheels.
Thanks!
A: It isn't easy to fit a 'perfect' motor into a design that's already fixed. Ideally the motor choice should be part of the design process with the other components to allow a 'best compromise' selection of the whole design.
Like I said, I think you should become familiar with the Tentacle Torque Calculator as a design aid. You have details of your design and expectations of performance that are difficult to fully pass on to me. That said, a good starting point for your selection might be replacement of the RS-550 motors with RS-540s. You'll save almost 10 ounces of weight, have a controllable amount of torque, and retain plenty of ramming speed and acceleration. If possible, a wheel size closer to 4" would give better ramming performance in a 3.6 meter arena. Ramming isn't really compatible with thwacking, and a four-wheel thwackbot is a poor concept.
A: I don't think that's really the question you want to ask. It takes almost no torque to move a robot across a flat arena -- but you'll accelerate very slowly! More torque equals better acceleration, but gearing for torque reduces your top speed.
Combat robots are typically geared to give them enough torque to break traction and spin their wheels when pushing hard in order to avoid a motor-killing stall. So the real question is: "How do I calculate the torque needed to spin my wheels when pushing to avoid motor destroying stall?"
The
Team Tentacle Torque & Amp-Hour Calculator can help you balance the requirements for speed and torque for robots of any weight based on the motors used, the tire diameter, the gear reduction used, and the size of the arena. There are LOTS of examples of selecting the correct motor and gearing in the archive. See also #21.
Q: I get it, but what seems to bother me is how to get a rough idea of torque needed for the motors. Then after this as you said we can balance the speed and torque requirements. Thanks again
A: You're welcome. Aim to spin your wheels at less than 60% of the motor's stall torque and you'll be fine. If that gearing doesn't give you enough speed, pick a more powerful motor.
A: I don't know about 'robotic engineers', but see #7 for ways that combat robot builders do it. The Ask Aaron archives have tools and formulas to assist in drivetrain and weapon design. See the and archives.
A: Entering 'clampbot' in Google seems to work pretty well...
I was wondering if you thought that using a small number of large screws or a large number of small screws would be better? And also, what else should I consider when mounting a wedge?
A: In general it's better to spread the loading with a lot of small screws rather than a few large ones.
Remember that your wedge is going to take the full brunt of your opponent's fury. Splurge here on both material quality and weight allowance. Provide as much support as you possibly can.
Q: Should 1/4 thick 2024 aluminum bolted in shear with a crapload of brackets and 4/40 machine screws be strong enough to withstand a standard hobbyweight spinner? In simpler terms, would that armor setup be okay for the 12 pound weight class?
A: See #17. There are too many things I don't know about your design and craftsmanship to allow me to pass judgment on the theoretical strength of your wedge. 'Crapload' isn't a variable in any standard engineering formula.
I can say that 1/4" 2024 aluminum alloy is an entirely acceptable material for a hobbyweight wedge and - if properly angled and supported - would well withstand a 'standard' spinner. Countersink those screws!
A: Some general design guides:
Consider a peizo gyro to improve turning response and control under all conditions. Omni wheels on the rear of the robot can provide great turning precision when paired with a gyro, but will cost some traction.
A: We believe that combat robot audiences like variety; that the most excitement is generated by something unique. A single flamethower 'showoff bot' can create a lot of interest, but if there are suddenly a lot of flamethowers they become much less interesting.
Our 'Robot Wars' robots were each designed to be unique. 'Run Away' is a side-wheel spinner, a weapon design not seen before or since. 'The Gap' is armed with a huge one-of-a-kind lifting platform with unheard of extension height. If you want to give the audience a show, look around the events you plan to attend and see what's missing.
I will point out that we don't recommend active weaponry for your first robot. A fancy weapon won't have much of a chance to entertain if it fails to get thru the first tournament round. Learn your basics, then get fancy if you like.
Which type of combat robot do you think will have a bigger chance to succeed in this kind of game? I already have a Sabertooth Dual Motor Driver 25Amp, and Sabertooth Single Motor Driver 25Amp. Does this type of motor driver suitable to be used to control Ampflow E-150? Does the 25Amp current capacity enough to control the Ampflow motor?
I'm thinking that the robot should have these features:
If i want to use BaneBot RS550 12v as a drive motor & mount it straight to 5" wheel with a supporting hub, which gearbox is the most suitable to give the perfect balance of speed & power? Or do you have other suitable motor to suggest?
A: Mark J here: if this isn't a class assignment then why am I abruptly getting multiple design assistance requests for a competition I've never heard of from people who write like engineering students? Send me a link to the website for this competition -- I'll need to review the full rules and event details before I can give any reasonable advice.
I'm just a bit concerned about audience/crew safety. The arena fence is 'metal' and 'acrylic' of unspecified thickness, there is no arena roof, and spinners are allowed. "Would you like a side of shrapnel with your apam balik?" Let's hope Malaysian spinners aren't as powerful as their American counterparts.
Several observations:
A: You can run a simple drivetrain simulation with your choice of weight, motors, gearing, and wheel diameter with the
Team Tentacle Torque & Amp-Hour Calculator. Use the 'BaneBots 42mm 16:1 RS-550' motors as a proxy for the PDX16* and set 'Motors per side:' to '3'.
The trials I ran for a featherweight in a 24" arena show a pair of DeWalt 18 volt drill motors with transmissions on 'high' [with 5" wheels] outperforming the three pairs of PDX16 motors [with 6" wheels] in both speed and acceleration. Wheel sizes were optimized for the respective motors by finding the quickest 'side-to-side' arena acceleration time.
Maximum wheel diameter for a motor is dependent on gear reduction, robot weight, number of motors, and desired performance. A single pair of the DeWalt 18 volt drill motors can be used with wheels larger than 12" in a featherweight without stalling the motors, but acceleration would be poor. Play with tire size and gear reduction in the Tentacle calculator until you get the best acceleration and speed for your arena size.
A: See #21 - read the whole FAQ while you're there. The archive will provide help on selection of radio equipment, and lifter design help is in the archive and in a recent question further down this page. Start reading.
Q: What servo would you recommend for an antweight lifter like Shazbot?
A: There is plenty of discussion on servos for antweight lifters in the archive.
A: It may be acceptable to lead with a caster if the special rules are in play that make his jacks autonomous on his loss, but you may pay for it when it comes to the terminus.
Q: By "lead with the caster" I meant "position the caster(s) further forward than any of the powered wheels on my robot." Sorry if that wasn't clear before. Same question: is that something you should never do?
A: Sorry, I thought you were a Warmachine player. It's generally a poor strategy in that game to lead play with a Warcaster - 'caster' for short.
Back to robots! There have been many successful robots with front caster wheels, so I don't think you can say 'never'. There are disadvantages - primarily the relative ease with which the nose of the robot can be pushed aside. Benefits may include maneuverability, enhanced weapon exposure, and weight reduction. Some weapon designs and attack strategies benefit greatly from front casters or skids. Our own 'The Gap' requires a small front roller for support while fully exposing the lifter platform.
I'm going to say that you need to weigh the merits and disadvantages of front casters in the overall design of your robot - just like any design element. It's definitely not a 'never'.
A: Previously discussed. Short answer: nuts, bolts, machine screws, and careful design. Find a copy of Grant Imahara's book Kicking 'Bot for very complete instructions.
A: No weight class 'needs' a tubular frame. There are multiple options for chassis style in every weight class. Box style monocoque chassis are popular for hobbyweights.
A: Air hockey - it's only fun if you aren't the puck.
A: Yes - I've seen a couple of different designs that use a spinning weapon as a source of motive power. Gene Burbeck has a refinement over your idea that allows for variable speed in forward, reverse, and turning (your design won't back up). Search this archive for 'wackerdrive'.
Comment: Thanks for that link to Gene Burbeck's design. I had more elaborate ideas for getting controlled motion from the spinner weapon, but I appreciate the elegance of his implementation.
A: All combat robots require a 'sturdy' chassis, but you don't need a welder or a shop full of specialty machine tools to build one. Although such tools can make the process quicker and less labor intensive, you can do wonders with common hand tools. I strongly suggest that you find a copy of Grant Imahara's book "Kickin' Bot: an Illustrated Guide to Building Combat Robots". It has five hundred pages worth of shop technique, design tips, material selection pointers, and electrical advice. It will show you how to get the most out of the tools you have.
One of the biggest problems with traditional thwackbots is that no robot is going to approach it while it is spinning in place. The two solutions are either to create a melty brain or to somehow make the thwack spin up fast enough in a single rotation to do damage. As both are difficult tasks, most people don't build thwacks.
However, I thought of a relatively simple way to get the thwack to spin up MUCH faster. The key would be tot place a flywheel inside the robot. When the robot is on, this is constantly spinning at a high. Normally, a gyro would nullify the gyroscopic effects, but when the driver wants to attack, he would turn off the gyro and spin in the direction of the flywheel. In theory, the inertia should allow the thwack to spin up very quickly. Hopefully, it would be fast enough to get damaging speed in a single turn.
Was this clear?
A: Mark J here: yes, quite clear. Several observations:
Q: Thanks. It is still an idea I hope to tinker with. In my opinion, being unique is more important than being simple or effective.
A: People build combat robots for a variety of reasons. Build what you enjoy building. Best luck.
My question is: Do you think it would be a better idea to screw the titanium straight into the aluminum or add small rubber grommets so it's shock mounted?
A: If you're going to wrap the .025" titanium as wheel guards the way 'One Fierce Lawn Boy' is set up the titanium is going to have plenty of flex to it. I don't think you'll gain much by shock mounting in that application. Save shock mounts for stiff panels.
A: The answer is 'power'. The lightweight 'Dr. Inferno Jr.' had as much power as most heavyweight competitors. Jason Bardis packed four overvolted 18 volt DeWalt drill motors into a robust chassis and had the skills to make use of that power. I once saw him drive two antweights at the same time - in competition! The rest of the robot was just window dressing to make it 'cute'.
A: No, you couldn't. No event organizer would allow it because what you describe is classed as a felony in 46 states plus the District of Columbia and a misdemeanor in the other four.
Q: Did even thinking of that idea make me a sick person? I often like to speculate about hypothetical concepts, and the immorality of this idea had been bothering me for a while.
A: Hey, we aren't the thought police -- you're free to think about whatever you like as long as you exercise proper discretion in your actions. I just didn't think the details were appropriate for the audience here at Ask Aaron. No problem.
A: A sucessful combat robot will not rely on just great power, or just fine engineering, or just correct weapon selection, or any single factor. A successful combat robot has all of the above going for it plus a lot of modification based on combat experience and an experienced driver.
As to the heavyweight drum weapon -- I've said this many times but people simply don't want to believe me:
Nightmare was perhaps the most extreme counterexample of your statement. The robot itself was designed around the weapon, and if that weapon was disabled, Nightmare was screwed. However, that disk was what made Nightmare so feared. He couldn't really push, he couldn't really ram. All he could do was kill.
Nightmare may be an extreme example, but many others also go against your statement. Many spinners such as tombstone are just the same way, as well as a few flippers.
A: Mark J here: you've missed the point. A weapon can certainly be made the main focus of a robot's design, but that simply places too much emphasis on a system that contributes less toward winning matches than other robot atributes. Drivetrain, radio set-up, general construction practice, and weapon/chassis balance are all much more important than the type of weapon you choose. There are plenty of examples of winning robots with ineffective weapons, and there are many more examples of losing robots with awesome weaponry. If you get the basics right you're going to have an above average robot no matter what weapon it carries.
'Nightmare' is a good example in support of our claim: overall record 8 wins and 7 losses - barely a winning record in spite of the massive weapon, fine engineering, top quality materials, and an experienced builder. Why? Because too much emphasis was placed on the weapon system at the expense of more important considerations. Nightmare was able to win a fair number of matches only because of the expertise of its builder.
Many beginning builders believe that the secret to winning is all in the weapon. The point we make is that concentrating on the weapon above other considerations is an error. If you have a poor robot, slapping a high-power weapon on it is not going to improve its success rate. Winning robots get the basics right and achieve balance in their design.
Not convinced? See: What Weapons Win.
Q: Having looked at your response and "what robots win," I think I see your point, but I still think your claim is too harshly worded for its own good. After all, the weapon is still an important part of the robot, and saying otherwise would go against everything new builders have seen during their time as audience members, making it hard for them to accept. Starting a full blown argument isn't much use, but I do want to say that in my opinion, a better way to word it, which will also make it easier for new builders to swallow, would be:
A: Our statement is harsh. We started out with more diplomatic and gentle advice about the need for balance in combat robot design. After many years of answering questions and watching new (and some not-so-new) builders make the same mistake time and time again, we decided the message wasn't getting thru. One proven way to get someone to stop and think is by creating minor outrage.
Your wording for the same concept is certainly correct, but I don't think it will get builders to question their mistaken belief that their robot has to have a mega weapon or it won't win. A major goal of 'Ask Aaron' is to keep new builders from becoming frustrated and abandoning the sport, and if it takes a virtual slap across the face to do that -- we're game.
A: With so many possible designs I can't be specific on an assembly order. In general, and making many assumptions:
A: You can get good straight holes with a drill guide if you take your time. Clamp down the material, mark your hole locations with a center punch, and use sharp bits of an appropriate type.
The sure way to get aligned holes is to fix the pieces you're joining in place and drill the holes thru both pieces at once. Where that isn't possible, a drilling template can be made from scrap material and carefully positioned to pinpoint the hole locations for multiple pieces. Grant Imahara's book Kicking 'Bot has a whole chapter on drilling and tapping holes.
My best advice is to design a robot that you can build with the tools and skills you have available. We don't have a drill press, lathe, or mill - but we've done pretty well.
A: 'Swerve drive' is a generic term for an omnidirectional drive system where all the wheels can turn to point in any direction for enhanced maneuverability. 'Crab drive' is a specific type of swerve drive where the turning mechanism for all the wheels is linked so that all the wheels turn but always point in the same direction. The two terms are sometimes incorrectly used interchangeably.
Swerve drive is fairly common in FIRST robotics competitions, and swerve drive kits are available for the Vex robotics system. Brian Nave entered the swerve drive 'Mechanicidal Maniac' in the second season of Robotica. Videos of swerve and crab drives in action are available on You Tube.
A: I can't recommend an actuator (electric? pneumatic? hydraulic?) without very specific weapon design details. Likewise, SRiMech design depends on the layout of the rest of the robot and is rarely 'simple'. See #4.
A: A table wouldn't be of much use. There are differences in traction provided by different arena surfaces, plus combat arena floors tend to be covered with variable amounts if dust and grit. A 'sticky' tire may actually give less traction than a hard rubber tire in a dirty arena. The default value for coefficient of friction in the calculator is about as good an estimate as you're going to get unless you take measurements under your specific conditions.
A: You should be surprised -- and angry. Online Metals has both the equipment to do the job correctly and a quality obligation to their customers. Delivering off-square corners and wavy edges is just sloppy. They have a guarantee on dimensions for the custom cuts you ordered, so call them on it!
Q: When I said "not perfect," I meant it quite literally. The angle issues I am talking about are matters of a few degrees. (i.e. 87 vs 90) Or millimeter sized imperfections on the sides. Is that enough of an error to contact them?
A: Online Metals guarantees custom cut dimensions to +.125" -0". If the pieces are inside those tolerances then getting them closer to perfect is up to you.
You haven't told me the type of material, the thickness, or the size of the pieces you're working with so my suggestions will have to be pretty general. A stationary belt sander is the preferred tool for cleaning up angles and edges on metal pieces, but if you had access to one you probably wouldn't be asking your question. Your best option may be to scribe a reference line, mount the piece in a vise, and get busy with that hand file. Take a break every few hours or your hand will cramp up
A: Machine screws are not self-tapping! You cannot just drill a hole and force-thread the screw in if you want anything close to maximum strength.
You first need to drill a hole of specific diameter. For a 4-40 thread a #43 drill bit is called for, but a 3/32" bit is very close to the same diameter and will do in a pinch. Next you must 'tap' the hole to cut threads for the screw using a 'hand tap'. You can buy a T-handle tap wrench and individual taps at your local hardware store.
There's plenty of advice and help on thread tapping on the 'net but the best guide I've seen is in Grant Imahara's book Kicking 'Bot, which should be in every combat robot builder's library.
A: It is difficult and possibly dangerously misleading to talk 'in general' about combat robots. There is so much variability in design and construction technique that any advice I might give without knowing very specific elements of the robot design could lead you very far astray.
I'm not certain what you're trying to mount onto what. Are we taking about a flat baseplate onto which you want to mount vertical sidewalls? What materials are you using?
Q: My plan is a .1 inch 6061 aluminum baseplate. Depending on your answer, it will either have .25 2024 aluminum side armor screwed directly to it (I found a way to make the weight work) something thinner if you suggest brackets, or perhaps something in between that uses both.
A: Good practice calls for the material thickness being end tapped to be no less than twice the diameter of the machine screw going into it -- so you could use .125" diameter (4-40) machine screws to end tap into the .25" side panels thru the bottom plate. However, it's also good practice to not use machine screws where they are placed in shear loading (across their diameter) which is exactly the situation you have. Unfortunately, any simple bracket design would also be under shear loading. I think I'd go ahead and end tap directly into the side panels. Use plenty of screws!
A: Mark J here: the RioBotz robots have achieved good success in competition, so they must have a pretty good grasp of what they're doing. Their analytical approach to robot design has merit but can be difficult to digest for non-engineers. I'd say they are on the right track about 80% of the time, with the other 20% missing some critical point. That's engineers for you The trick is in figuring out which parts to believe and which to ignore. Take it with a grain of salt.
I also read that the wedge should be as smooth as possible, which makes sense -- but I was wondering about how to attach my wedge. I originally though about bolting it straight into my triangular aluminum mounts with the heads counter sunk into the wedge surface. Thinking about this... that provides catch points for many spinners, so I should probably steer clear of that?
Should I build tabs on the back to bolt it on with? Also, I have a nice sheet of .05 titanium 6al-4v which obviously is not enough for a wedge on it's own, but would making the surface of the wedge out of 6061 aluminum and then topping it off with the .05 titanium be a good idea? (in order to provide a harder surface) I don't have the money to buy thicker titanium or I would do that.
Also I've been wondering how in the world to push a spinner around in the first place. Every collision I see ends with both 'bots further apart, I've only seen low drive power FBS's getting pushed around, slow and steady. Is it even possible? (while their weapon is working)
A: I don't like the 'wedge design' part of the RioBotz Combat Tutorial. The section is filled with equations and diagrams, but when they get down to making recommendations the equations are abandoned and it turns into opinion with questionable assumptions - IMHO. Combat robot design is full of compromises.
The first priority in mounting your wedge is making sure it stays put. A few neatly countersunk hex socket screws aren't going to give a spinner any bite and provide a simple, direct, and strong approach. Don't get fancy.
I'm not a fan of layering different materials for a wedge or armor. If you're not very careful it's easy to end up with the worst properties of both materials instead of the best. Have your 6160 wedge heat treated to a T6 temper to harden it up and you'll do well.
I'd re-think trying to push an active, spinning 'spinner'. Spinners come in such a range of heights and styles that it isn't practical to have one wedge design that could be effective against them all. You'll see some teams with interchangeable wedges/scoops/bricks to adapt to different opponents -- one design just isn't going to get it done for all spinner types. Best general wedge design? I like a shallow scoop like Breaker Box.
Q: You mentioned heating my 6061 wedge to a T6 temper... Would this provide enough strength? I plan on all my 6061 being T6 temper, but I figured this would be too soft to effectively use as armor still, especially for a wedge. Are there any examples of 6061 being used for a wedge?
A: First, don't confuse 'hardness' with 'strength' or 'toughness'. Armor and wedge material needs high toughness to be able to absorb abuse and surface hardness to resist scars and gouges. You haven't told me how thick your wedge is, so I can't discuss its 'strength'.
My comment about T6 temper meant to indicate that I'd rather have just the 6061-T6 than the same with the titanium overlay. That thin a titanium layer could be subject to 'tearing' which the judges would score heavilly for your opponent. It could also cause a lot of 'sparking' on impact, which again sometimes sways judges. The 6061-T6 aluminum may gouge because it has a softer surface than steel or titanium, but it won't spark or tear.
Lots of robots have used 6061 for both armor and wedges. I believe superheavyweight 'Shovelhead' is an example.
A: There have been hundreds of combat robots built with hand tools. A drill, hacksaw, file, screwdriver, wrench, and a wire stripper/crimper will do quite well if that's all you have. Keep your design realistic and bolt everything together - no welding or fancy machining needed.
For those unable to participate by building robots, contact an event organizer and volunteer tor help at the next event. There is an incredible amount of work that needs to be done to put on a robot combat tournament and all help is appreciated.
Currently my featherweight is going to have 3/8" 6061 side armor (vertical) but I haven't worked out what to do for armor yet. I was playing around with some ideas of decreasing the side walls and then adding a second pair that was shock mounted to the inner pair, also thinking about shock mounting my front wedge since it will take most of the impacts.
I guess what I'm asking is would just simple rubber shock mounts like these work well for this? I know these are what 'Mitch' used (until ripped apart) but I talked to Ray and he said if he rebuilt 'Mitch' it would be with a massive hinge instead. Is it a common practice to shock mount a wedge? I don't see any drawbacks except less structural strength and even that can be worked around with a good design.
And also a question about shock mounting motors, how? Would small rubber dampers be used on the mounting holes for these as well? Why not put them everywhere! hehe
Thanks again
A: Mark J. here: double-sided foam tape is commonly used to mount electronics in sub-light robots. It will work, but it isn't bulletproof. Don't forget to tie down your wires as well: high g-loading can cause a floppy wire to pull itself loose. That's very embarassing.
I'm not wild about the 'dual layer' armor you're thinking about. The way matches are scored really calls for a thick single layer to avoid even the appearance of damage. Shock mount the whole thing if you like.
Shock mounts made from rubber grommets and large washers are lighter, more compact, and more adaptable to specific design applications in robots than are 'off the shelf' industrial components. Check the previous post in this archive for a diagram -- search for 'rubber-mount'. Shock mounting of armor or major components is not common practice in combat robots, but you can certainly experiment with shock mounts in one or two locations. If you like the results, expand.
A: I don't know when the three-wheeled omniwheel drivetrain started being called 'kiwi drive' -- I'm used to it being called omni-drive. The patent for the omniwheel dates back to 1919 by an american inventor named J. Grabowiecki, but I can't find a record of its first use in the holonomic omni-drive. In the 1970's, swedish inventor Bengt Ilon refined the omni wheel concept and developed what would become known as the mecanum wheel with angled rollers and built a functional four-wheeled holonomic forklift using them.
There are several posts about omniwheels and their use in this archive.
A: Sure -- the hacked BattleBots custom series toy has good mounting surfaces for your wedge and a brace. There is enough clearance to simply bring the brace straight back and mount it to the bottom of the chassis.
Since I don't know the width, length, height, thickness, or angle of the wedge you plan to build I can't give you a good estimate the weight of either the wedge or the brace -- can I? See #4.
Q: Well the thickness depends on the weight of the brace, because I dont have the titanium yet. It will need to be 3" x 4.5". The angle of the wedge will be 35 degrees.
A: So, you don't know how much your wedge weighs but you want me to tell you how much the brace will weigh? If the wedge is too thin it will need a thicker brace, and if the wedge is thick enough it won't need a brace at all. Welcome to combat robotics! Estimate the weight of the brace at 30% of the weight of the wedge and go for it. If you're overweight, start drilling lightening holes -- if it crumples like tin foil, build a thicker wedge and save weight somewhere else.
Q: Okay thanks. One more question. If I had spikes on the side and spun the whole thing, would that be considered a FBS? I think it would be more like a horizontal thwackbot because the outside doesn't spin independently from the chassis. Thanks for all the help!
A: You're welcome. You're right, your design would be a thwackbot.
Q: I know I said one more question...but how thick would be thick enough to not have a brace?
A: See #17. That small brace adds a great deal of strength and rigidity to the wedge assembly. A wedge thick enough to survive on its own would weigh substantially more than an equally strong braced wedge. Build the brace!
A: First, these types of stats are not commonly featured on team websites. You may find battery info, but that will vary with the type of motors used and not likely apply in an 'average' sense. You can quickly estimate the battery requirement for your robot with the
Team Tentacle Torque & Amp-Hour Calculator.
Second, armor and chassis material thickness information will do you very little good without considering the design of the elements involved. Relatively thin material can we used to good effect if mounted well, angled properly to deflect impact, and supported by chassis components. Likewise, thick armor can be entirely ineffective if critical design factors are ignored. Also in the mix are the metal alloy used (there are LOTS of different aluminums, titaniums, and steels) plus any specific heat treatments used to harden or toughen the material. Plenty of variables on non-metal armor as well. This all applies in spades to chassis material thickness.
With the above said, my best tip for links to team websites for current competitors in specific weight classes is to start at BotRank.com, pull up the ranking list for the class, click on the score for a competitor, then click the 'Search for this bot at the BuildersDB.com' link and click on the photo of the robot. If the team has a website it should be listed there.
Q: And back about the armor question. I realize that the armor depends on multiple factors, and I've read you say this in multiple questions -- however I'm only looking for an estimate.
Let's consider my front wedge. I'm going to have 1/8" - 1/4" aluminum triangles with the armor placed on top. I recently ran into some cheap .05 titanium 6Al-4V and was wondering if this would make decent armor.
I plan to put 1/8" thick 6061 aluminum plate and then top that off with the .05" titanium and I just curious if this was average, above average or below average. Thanks!
A: Mark J here: I realize that I'm starting (continuing) to sound like a 'Dick' about this, but we really can't answer your question in a way that will be of any use to you. If you walk thru the pits at a large event, you'll quickly learn that there is no such thing as an 'average' combat robot. So many differences in design and construction render the utility of determining the 'middle range' to be futile. That's why we resist any specific recommendations on material thickness.
Since you're pressing me for an answer I'll give you one and guarantee that it's worth every penny you paid for it: your suggested armor is below 'average' for the featherweight class.
Q: You are saying that the armor depends on the design, etc, however I've given you what I plan to do for my front wedge.
Can you think of any specific armor types and thicknesses for 30lb wedges? I know you gave me the "yes it is too little" because that is the safest answer to give, but I was fairly confident in my design...
I figured 1/4" triangle aluminum supports (spaced every 3") supporting a 1/8" sheet of 6061 aluminum topped off with .05" titanium would be overkill (along with the rest of my robot!). I'm looking at the wedge making a 30 degree angle with the floor. If not, can you think of anywhere where this front wedge could improve?
A: I was quite careful to not say that your armor was 'too little'. You asked if your proposed armor was "average, above average or below average" for the featherweight class. I gave you an accurate and verifiable answer based on the information that you provided and I am offended that you now accuse me of blowing you off with a 'safe' response.
Your wedge design is appropriate for a structure which will be subjected to a well distributed and predictable loading, such as an aircraft wing. Combat robot wedges and armor are exposed to localized high loadings which will cause such a structure to fail. I advise that you examine designs used in successful robots and use a variation of those proven principles.
If you neither trust nor value my answers (and it is quite apparent that you do not) you should seek advice from another source. Either way, I believe I have said enough on your questions.
A: It depends on the specific application, but in general mechanical fasteners like machine screws and nuts are likely your best bet. There are adhesives, but selection and application can be both very tricky and unreliable.
A: All great questions! Unfortunately, we aren't qualified to answer welding questions. We design, we don't weld. For our large robots we take our sketches to our metal fabricator, Max. We talk about the specific design and performance factors that have to be met and we discuss materials. He smiles and goes off to fabricate. We trust his judgement, and his technique is top notch.
We generally design for bolts or other mechanical fasteners anywhere we anticipate replacement of a panel or component at a tournament. If we get seriously damaged, all bets are off and we just turn Max loose. We got 'Run Away' stuck on top of another robot in a 3-way match at Robot Wars. It left the arena in several baskets. Max was there in charge of 'The Gap' -- he grabbed the baskets and ran off into the welding booth. 40 minutes later he came back out with a functional robot, but pretty much everything was held together with welds. When we got back to our home shop it took us a long time to grind away the welds and put the 'bot back into its original configuration, but if you're in a big hurry a good welder can put things right for you.
What we do know about welding we learned from reading the knowledge articles at Lincoln Electric. They have a comprehensive article there on prevention and control of weld distortion as well as a wide selection of tips and FAQs. Sorry we can't be of more help.
Q: The welding guy again. Thanks for those comprehensive links.
A: You're welcome!
A: We don't follow FIRST Robotics Competitions or competitors. The FRC events are cool, but they don't meet our definition of 'combat robotics'. Suggest you contact the Simbotics team directly with questions.
A: Mark J. here: the structural design of our robots is done on a 'that looks about right' method based on many years of building things, watching them fail, and rebuilding them until we got it right. In the words of Team JuggerBot, "Damage is weakness leaving the robot. If something fails, make it stronger." We also belive in examining the designs of successful combat robots and learning from them.
Finite element analysis has its uses. You can't afford a 'see what breaks and fix it' approach if lives are at stake, as in automotive or aircraft design -- but you need to know the loads under which each design component will be placed. In a combat robot the loads are often wildly unpredictable and the effort required to build an 'optimum' design is generally not well rewarded.
We do recommend the use of software to calculate drivetrain performance [
Team Tentacle Torque & Amp-Hour Calculator
] and spinning weapon parameters [Team Run Amok Spinner Excel spreadsheet] to assure that those systems have sufficient performance. We do the performance calculations for other weapon types on 'paper'.
A: A little grease won't hurt, but I can't tell you if it will keep you from getting stuck. The more gradual the taper and the smaller the diameter, the greater the chance that the spike will get stuck deep enough into the wood to hold. Sounds like a poor weapon design for that arena. Think about blunting the spikes, or try ramming the bot into a similar wooden barrier to see what happens.
A: The original question (farther down in this archive) asked about getting the lowest and most effective wedge. I listed a number of considerations and options on wedge design.
I mentioned scaleability as a reference to the 'square-cube law', which applies to a wide range of design considerations that change with increasing or decreasing size, not just wedges. Examples:
A: Have you looked down at the two quetsions immediately below? We are NOT going to do the coursework for every robotics student in Delhi! We only did Amith's calculations to show the proper use of the tools and steps needed. The tools are there, so go do your work.
A: Another 'urgent' robotics homework assignment from India. Sometimes I think the whole subcontinent's robotics program would collapse without our input.
A: Mark J. here: OK, engineering student from Delhi, here is your first lesson in combat vehicle design:
You've given me the weight, but nothing else. What type of speed is required? How many wheels will the robot have? How many motors? How large will the wheels be? Will the vehicle be operating on irregular terrain? Will it need to climb hills - and at how steep an incline? Starting with motors and building a vehicle around them is a very poor design stategy. The motors are perhaps the last component to be selected -- well after the other systems have been established.
Once you have defined performance and environment, the
Team Tentacle Torque & Amp-Hour Calculator
will allow you to evaluate the performance of a very wide range of motors to see what best matches the requirements you have established.
About brushless motors: hobby brushless motors are derived from model aircraft designs that were built for low weight and high power while operating at high RPM. Attempting to use them for robot drivetrains exposes them to performance requirements very different from what they were designed to do; they will almost certainly fail under these conditions. It is also very difficult to find brushless speed controllers that offer a reverse direction. Do not consider hobby brushless motors for your drivetrain application.
Q: Thank you for replying.
I am Amith, and we plan to design a ground vehicle like the Chaos High Mobility Robot with four autonomous arms carrying treads, each with its own motor. We have done mechanical sketches of chassis and wheels and have listed some terrain challenges to be covered by our machine:
A: Several motors come to mind that would meet your requirements, but most would require construction or adaptation of a gearbox capable of around 50:1 reduction. The simple and proven power solution would be one of the DeWalt power drill motor/gearbox combinations. Four of the DeWalt 14.4 volt drillmotors mated to the DeWalt 3-speed gearboxes set to 'low' coupled to a wheel/tread drive diameter of 6" will give you the required speed and more than enough torque to climb any gradient your treads can grip.
Each motor/gearbox combination weighs just over 29 ounces. At 18 volts the motors each develop approximately 1.2 horsepower (0.75 horsepower @ 14.4 volts). Battery selection will depend on your required run time and the average percentage of peak power used - neither of which I can guess about.
That will power your treads. If you plan on 'walking' the treads like the Chaos HMR does, you'll need additional high-torque gearmotors to power the walking action. I hope this is helpful.
Q: Thanks a lot! You have made us half job done. We are pre-final year engineering students group (MECH, computers, electronics) doing all the paper work required to build that prototype.
We are considering powering the autonomous control using image processing and lesser technology as we saw in the DARPA autonomous race. Our next step is to decide on microprocessor, motherboard and interfaces with sensors and cameras... a BIG question. We are searching internet, but totally getting mixed up! Can you help us out?
Thanks in advance.
A: Sorry, but I don't think we can be of any help with this part of your project. You've moved way outside our area of competency -- we don't work with autonomous control systems of this power and complexity.
A: For a start, it would be nice to know what weight class we're talking about: heavyweight 'BioHazard' was about 12 cm tall, so you could be building pretty much any weight class. What are these design constraints? What about the rest of your robot -- all elements of a robot must work together to be successful, and any comment I might make about one element might be completely inappropriate if I don't know anything about the rest of your design. Write back and give me enough information that I have some chance at giving you a reasonable answer to your question.
A: Four and six wheel drive designs have different strengths and weaknesses. Four wheel drive robots are powerful pushers and very stable in a straignt line, but may have difficulty in precision turning. Six wheel drive robots usually have the center pair of wheels set downward just a bit, giving them greater turning agility (if the center of gravity is close to the center wheels). Six wheel drive robots usually have all wheels on one side chain or gear driven from a single motor as as least one of the wheels will have little weight and traction at any given time -- a dedicated motor for that wheel could not lay down much power. Four wheel drive robots have the option of a motor at each wheel for power redundancy.
Which design is more effective? I'd guess that six wheel drive robots have a higher win percentage than four wheel drive overall.
A: Oh no, I'm sorry. The correct answer was "We don't do your homework for you." Thanks for playing our game. Be sure to pick up your consolation prize on the way out.
A: No. Unlike internal combustion engines which generate little torque at low RPM, permanent magnet direct current (PMDC) electric motors generate their maximum torque at stall and have a linear declining torque curve. There is very little to gain from a Continuously Variable Transmission (CVT) or torque converter for the range of speed encountered in a small arena..
A: Previously answered - with photos. Search the archive for 'Sewer Snake'. You can find photos of their AmpFlow motor/gearbox/multi-chain 6-wheel drivetrain at the Team Plumb Crazy website.
A: For the benefit of others who may be confused, 'Alcoholic Stepfather' used mecanum wheels, not omniwheels. Mecanum wheels are designed with angled rollers that allow the wheels to be positioned in conventional co-linear pairs and still provide omnidirectional movement.
A: Mark J. here: I also often say, 'we are not an engineering service'. We are pleased to provide short answers to specific inquiries of general interest, but an 'evaluate and improve my design' request is outside the scope of what we can provide on this website.
When you do send in questions about your design, please remember that we have only the details you give us. Any assumptions we might make could lead to disaster, so we may choose to withhold an answer rather than risk leading you astray.
A: Welding is like playing a musical instrument; some people are good at it and some are not. Some people pick up the skill quickly and others simply don't. If you're trying to teach yourself it will certainly take longer than if you have a good instructor. We farm out our welding and major metal fabrication to a professional shop.
I will point out that a great many very competitive robots have been built without a single weld on them anywhere -- welding skill is optional.
A: There are as many Self Righting Mechanism (SRiMech) designs as there are types of robots that use them. I don't have time or space to go thru the designs in detail here but in general there are a few general categories:
Which type to use depends on the details of your robot design. I suggest that you browse internet videos to see various SRiMech designs in action and tailor what you see to the robot design you have in mind.
A: Design, materials, workmanship, and preparation -- the same as every other builder of reliable robots.
A: Mark J. here: builder Ray Billings is a wild man. He stresses the components of his robots to the maximum and simply does not 'back off' or 'ease up a little'. I don't think he knows how! If you're fighting Ray you can be sure that he's driving wide open full-throttle and will stay that way to the end of the match. He smokes a few motors, but that's because of the way Ray is wired - not how his robots are put together
A: If it made a big difference you'd see more robots with a lot of 'negative camber' to the wheels -- but there are some minor advantages:
A: Mark J. here: whatever money you can afford and then some, all of your spare time plus any extra time you can steal, several personal relationships, and a chunk of your sanity.
I think this sums it up pretty well. Since 1996:
Oh yeah, nearly my sanity (not such a great loss, not a sound mind anyway, see above).
- Ray Scully, Team Wetware
Thanks, Ray. I left out the blood, personal injuries, and humiliation to keep from driving new recruits away -- but fair is fair, they should be warned.
A: And yet wedges win a higher percentage of their matches than do spinners. Several things to consider:
Q: Okay, So the two lowest/most effective wedge types that I have perceived have been dragging wedges that simply sit on the ground (Original Sin is a fine example of this) and the other type being spring loaded wedges that are held down as opposed to just resting on the arena floor ( Biohazard and Wedge of Doom are examples of this type). Is one type inherently lower/ more effective than the other? (this assuming that all other variables between the two wedges are the same)
A: This is not a short answer question! Briefly:
A: As soon as somebody figures out how to make a successful full body flipper, I'll be happy to tell you how they did it.
A: Seriously, read thru your question before you send it to see if it makes any sense at all.
A: Any standard SRiMech will do nicely -- just make sure you don't activate it when the blade is spinning! Type and placement will depend on the design details of your robot.
Technically, if your robot is 'invertible' it wouldn't need a SRiMech; it means that the robot will operate when inverted.
A: My question is: 'effective for what purpose?' High-angle wedges can be used as part of a 'rambot' strategy, low-angle wedges can be used defensively, a curved 'scoop' design is common for nullifying the attack of a spinner. The wedge angle is only one piece of the weapon design, and the weapon must be integrated into the design for the rest of the robot.
If you're interested in an analysis of wedge design, have a look at the wedge section of the RioBotz Combat Tutorial. I don't think they have it quite right, but it's a good start.
A: Well, if a mommy robot and a daddy robot love each other very much...
A: I don't have nearly enough information to tell you if your design is 'sturdy'. We have a variety of information and design tools that could be of use to you, but we are not an engineering service. Of particular interest to you would be our Team Run Amok Spinner Spreadsheet which allows energy and spinup analysis of proposed spinner weapon designs.
A: Read down thru the end of that post in this archive and you'll find that the answer has already been given. It has nothing to do with that hole - which isn't square.
A: Mark J. here: I'm not a huge fan of the RioBotz Combat Tutorial. It was written by an engineering professor at a Brazilian university, so it is not surprising that it is written like an engineering text. Engineers have their own style, and most of the formulas are there just to demonstrate that the authors have thought thru their claims and recommendations. The good news is that you don't need to use or even follow their formulas to make use of their design ideas, although wading thru the 367 pages to dig those ideas out isn't easy
Team Run Amok continues to recommend the K.I.S.S. principle. Watch what successful teams are doing. Adapt proven principles to your own design. Keep the construction and maintenance uncomplicated. If something isn't working, change it.
A: 'Verbal Abuse' used the time-honored technique of attacking a spinner before it has a chance to spin-up to full speed. If you can stay on top of a heavy spinner and keep depleting its energy, it won't be able to do a lot of damage to you when it hits. 'Corporal Punishment' (AKA 'Polly Prissy Pants') tried a different tactic and paid the price.
Q: And why Corporal Punishment could absorbs Shrederator's hit well (In Robot Assult 2003)?
A: 'Corporal Punishment' has an I-beam sitting across the front of the robot as a 'bumper'. That's ideal for dealing with a flat-sided 'tuna can' spinner like 'Shrederator', but well less than ideal for an angled spinner like 'Megabyte'.
Q: It looks like Verbal Abuse's lifting plate is pretty hard to control and it always lets its opponents slips off - what caused that happen? Beacuse of that very fast servo motor?
A: I would guess that 'Verbal Abuse' had a poor radio set-up on their weapon channel -- too much emphasis on speed and too little on control. As to slipping off - it is just a flat metal plate. Nothing there to get a grip with.
Q: So... Could I say that Karcas 2 used the same strategy as Verbal Abuse when they were facing to Megabyte?
A: Yes, keep hitting the big spinner to keep it from gaining full speed. The specially designed anti-spinner plow is a big help as well.
A: 'Beta' had a shorter chassis than 'The Judge' and much more power. There comes a point when reaction forces are so great that you have to have some method to keep the robot form simply flipping over when the overhead axe is fired -- which 'Beta' would do without the magnets.
A: Mark J. here: I sympathize with your situation. The guidance from modeling and material properties will help you avoid a number of design mistakes, but there comes a point where the guideance runs out and you just have to build the weapon and try it. I can pass on advice from Team JuggerBot: "Damage is weakness leaving the robot." Make everything strong -- if it breaks, make it stronger.
For what it's worth, your drum design sounds plenty strong to me.
A: There's a saying: "It isn't the wand, it's the magician." In this case: it isn't the wedge, it's the very experienced builder -- not all wedges are created equal.
A: 'Totally Manipulative' (AKA 'Anorexia') was designed to be the thinnest featherweight in existence. The flat top of the robot is less than 2" off the arena floor. Add a very long (~14"), very low angle hinged wedge and you have a target so difficult to engage that many weapons will never even touch it.
The low profile does come with disadvantages. Lacking much offensive 'bite', it becomes nearly as difficult to damage an opponent as it is for an opponent to damage you. 'Totally Manipulative's record of 10 wins and 17 losses reflects this problem.
Q: Is it possible to create a robot with the lowest ground clearence?
A: Well, by definition some robot has the lowest ground clearance. It is entirely possible to make a hyper-low clearance robot, but it would probably create more trouble than benefit. See my comments on 'lowest wedge' in this archive.
A: Internal Combution Engine at Wikipedia.
A: There is a lot to consider when designing a self-righting a robot: possible inverted rest positions, center of gravity, maximum width, mass, chassis geometry, etc. A successful self-righting mechanism must be designed around these factors. Designing a robot with a hammer weapon that also works as a reliable self-righting mechanism is not 'easy'.
A: There have been a great many teams that wished their inverted robots had a Self Righting Mechanism (SRiMech). An invertable robot doesn't need a SRiMech, but an inverted robot that's off its wheels isn't going anywhere without some method of setting itself back upright.
Q: How does a schrmich like Razer's wings work?
A: We have previously described the operation of the 'Razer' SRiMech - search this archive.
A: Beveling the bottom will give greater ability to get under drop skirts and other wedges, provide greater strength, and offer better ability to glide over floor seams. Invertable wedge? Bevel both top and bottom.
A: The 'rolling sphere' robot design is just a small conventional robot placed inside a large ball. The robot drives inside the ball and the ball rolls along in the same direction.
I don't understand the self-righting question -- a rolling sphere doesn't need to self-right.
Q: The destruct-a-bubble wasn't a ball, like the others. It was just shaped like a ball, and had a wheel base, and a retracting spear for weapons. I don't think the ball shape self-righted it, but wasnn't it meant to be a schrimech?
Q: How do the rollbars used on Mega Morg, Spikasaurus, and Major Tom (series 6 version) work? These bars self righted these robots when they were flipped.
A: Both the ball-shape and rollbar designs are intended to be 'passive' righting aids. If you have a hoop, cylinder, or sphere with a 'heavy point', gravity will cause it to roll to put the heavy point on the bottom. If that heavy point happens to be the part of the hoop with your robot's wheels and the diameter of the hoop is large enough to provide sufficient rolling momentum, your inverted robot will roll straight back onto the wheels - with a little luck.
A: Not a SRiMech - see our Beginners guide to combat robot gyros.
One Fierce Low Ryda had a 15 inch titanium blade which tilted slightly to move the robot. The weapon powered the whole robot, as the gyroscopic forces moved the robot. The antweight Gyrobot is new and only fought in the 2009 Halloween Robot Terror so far. It also uses a servo to tilt its blade so it can wobble toward the opponent (video).
Which one do you think is more inventive? Better?
A: Aha! I remember a discussion about precessional propulsion as used on 'Gyrobot' on the RFL forum from a few years back. I didn't know that anyone had built an actual robot. Using precessional forces to 'wobble' toward your opponent has some disadvantages, as the video shows. It's painfully slow and can't back up - those are two very big problems.
Gene Burbeck's 'wackerdrive' as used on 'One Fierce Low Ryda' is different. It uses a domed wheel mounted flat on the end of the weapon live-axle rubbing against the floor to provide thrust -- not gyroscopic forces. The speed and direction are controlled by independently raising and lowering each of the two rear wheels with servos to tilt the axle relative to the floor. Very clever, plenty fast, and moves in any direction. Drawback - the very small drive contact with the arena floor makes it very difficult to control! The same concept was used by an ICE powered heavyweight robot with the descriptive name 'Tip Top' which fought at Robot Wars (fifth series).
Both designs are wildly inventive -- real 'out of the box' thinking. If I had to build a 'bot with one of the drives, I'd pick the 'wackerdrive' and spend a lot of time tweaking the controls.
A: Dominator's shape lets it sit at an angle when inverted. The kick against the arena floor generated when the axe fires will shove it back upright -- with a little luck.
A: You are mistaken - both Panzer Mk. 2 and Panzer Mk. 4 had a pneumatically positionable front wedge/lifter.
Q: And do you think a bigger claw can make Kassinator more competitive?
A: I won't second-guess the builders of lightweight 'Kassinator'. The combined clamp/flipper is an interesting design that will no doubt need some fine tuning.
A: The middleweight 'Zion' was successful - 9 wins/3 losses at BattleBots - but it's design was much more an economy version of 'BioHazard' than 'Complete Control'. The single-pivot pneumatic lifter could get lucky and trap an opponent against its own armor, but it lacked the ability to then raise the opponent off the arena floor. 'Zion' lost to 'Complete Control' at BattleBots 4.0.
A: Have you thought this thru? You can turn any motor into a vibrator by clamping an imbalanced flywheel to the output shaft, but a traditional vibrating shuffler is slow, weak, and uni-directional.
A: There's plenty of room in the pro-series chassis -- that's a weak excuse to have me go take a photo. Still, the Zpatula webpage could use a detailed interior shot. I've added one at the bottom.
A: Mark J. here: the challenges of building an invertible full-body spinner should be obvious. Try laying out a design for one and see for yourself.
In truth, most FBS robots are not successful -- only a very few memorable ones were. I'd say that the small number of invertible FBS robots were no better or worse than the average for the type.
An active SRriMech is generally not required for a FBS, and I know of none that have one. It's nearly impossible to invert a spinning FBS due to the gyroscopic forces generated by the body. An improperly designed FBS may flip itself due to the 'Tippy Top' phenomenon, but this can be corrected thru testing. As a precaution, a passive central pole (as used by 'Megabyte' and 'Ziggo') is all that might be needed.
A: More info needed: Dual ended or hinged wedge? Two wheels or four?
Q: A hinged wedge with 2 wheels.
A: For a 2-wheel wedge you want about 70% of the robot's weight on the drive wheels. Move your batteries and wheel location around to get close to that figure.
A: First, find what weight classes are supported at events you plan on entering. There's no point in building a featherweight (for example) if your local events don't fight featherweights.
Second, check your budget. Combat robots are expensive, and the heavier the robot the more expensive it gets. The heavier weight classes are also filled with very experienced teams who will be more than happy to rip a newbie into small pieces and scatter those pieces around an arena. Make sure you can afford that.
It's much less expensive to make rookie mistakes in lighter weight classes than up in the heavy leagues. Start in the lightest event-supported weight class that will hold your interest.
A: Only two:
A: The robot competitions that take place at Dragon Con are run under the Robot Battles ruleset. These rules do allow for robots operated thru control cables as well as thru radio control, but you are not allowed to pull on the cable! Rule 1b says:
If you're pulling on the cable you become a power source. Doing so opens you up to the consequences of Rule 0b - the Frankenstein Rule (I'm not making this up):
And you would deserve it, Sparkey.
A: We have discussed the problem with thwackbots many times previously. Current combat robot judging criteria score on only two factors: damage and aggression. A thwackbot design cannot effectively show aggression as it must spin in place. From the guidelines:
This is too big a scoring deficit to overcome. Thwackbots are 'dead'.
A: Mark J. here: We aren't an engineering service and we don't give out specific recommendations on 'how thick' beyond the comments in our armor guide. Medium alloy steel and grade 5 titanium are very different materials. Team Plumb Crazy is fond of steel for their wedges, but I don't know the thickness, alloy, or treatment they use. I'd suggest asking Wendy and Matt at Team Plumb Crazy.
A: Mark J. here: 'Maximus'? Good heavens, no! I have photos of robots with hinged wedges dating back at least as far as the 1996 Robot Wars event. That's five years before 'Maximus' fought.
A: Yes. 'Melty Brain' refers to any system that controls directional motion (translation) on a thwackbot by rapidly changing motor power as the robot spins. Team Velocity's 'Death by Translation' uses Rich Olson's custom electronics to measure rotational speed with an accelerometer and pass that information on to a micro controller to do the power changes.
The physics of spinning with a single tangential wheel are difficult to describe. It's a bit like a spinning cowboy lariat - it's only supported on one side, but spinning forces keep it relatively stable. The single-wheel configuration does cause some problems; directional control is not good at higher speeds. It's an interesting experiment, but it has achieved no combat success to date.
A: I don't think you actually need an email at your school to download. Very few sub-college students will have one. Go to the Autodesk Education Community website, register with your regular email address, and see what happens.
A: We were hit by 'Shunt' in 2002 and we weren't impressed by the power of the weapon. It bounced off a rather thin steel top piece and barely made a mark. By contrast, the overhead spike on 'Slam Job' went cleanly thru that same piece of steel in a parking lot match about a year later.
Shunt's axe had a compact 4-bar mechanism powered by a low pressure (about 150 PSI) CO2 cylinder with a 250 mm stroke. You can see a few seconds worth of video explaining the weapon linkage here: House Robot test video.
Shunt had the drive wheels close to the center of the robot to place most of its weight upon them. It also weighed a good deal more than the competitor robots; the official weight was 105 kilos, but I suspect it was about 50% greater than that. More weight on the wheels means more pushing power - simple physics.
A: You're reading section 2.2 of the RFL ruleset which lays out the special rules for the 30-lb Sportsman Class. From the ruleset:
A: It's pretty slick. Razer entered the Third Wars with a new set of 'wings' sprouting from the sides of the crushing arm. An inner extension arm on each wing is connected to the body of the robot by a cable running inside the crusher. When the crusher is raised to its highest position, the cable pulls on the wing extension arm and the wings move out to the sides to tip the robot back upright. It's a little slow, but simple and effective.
A: Not very often. See the discussion on 'lowest wedge' a few questions down this page.
A: What exactly do you think that huge 50 pound 3/8" thick titanium scoop with massive 1" thick solid titanium support arms is for?!? 'Breaker Box' was built specifically as a spinner killer and is perhaps most effective spinner killer ever to compete. I suggest you visit the Breaker Box website for details.
Q: Yeah, I checked Breaker's Box's site again and I'm sure it's pretty awesome, but does that mean Jim will give up the idea of Vertical Spining blades?! I really don't expect that happen!
A: Neither do I.
Q: And, do you think Behemoth's big lifting scoop could be a good weapon when up against spinners,too?
A: I don't recall offhand what Behemoth's scoop was made from or what kind of support it had, but the shape was close to correct.
A: Team Death By Monkeys is a 'local' NorthWest combat team and they are friends of Team Run Amok. If I say 'clever' you'll think I'm playing favorites. If I say 'not' I'll insult my friends. I think I'll just say that their logo is awesome.
A: Mark J. here: 'The Great Pumpkin' was a novelty 'bot that fought in one tournament. It had a four-foot diameter fan-inflated pumpkin attached to it's top. It was a joke - move on.
A: Mark J. here: we like simple. Pneumatic flippers are simple, powerful, and can be made from off-the-shelf components. The 'Flip-o-matic' device that Dale Heatherington built is ingenious and beatifully made, but requires a good machinist and extensive design skill. Dale has been very successful with his robots and is well utilizing his considerable talents, but I'm not going to recommend that other builders adapt his methods.
Q: What do you think of Amdroid-A? It doesn't seem very competitive to me by todays standards with spinners and everything. But the control system is pretty cool.
A: Another of Dale's robots - see my comments above. I've seen many homebrew radio systems. Dale's is probably the best, with extensive overload protection and a clever 'boost' function. However, my preference is to allow the robot operator the option of overstressing the electronic components as needed to win a match. I'd hate to be in a pinch and have extra power available but 'locked out' by my own software!
Team Run Amok's motto: "Complex design is easy - simple takes work."
A: Playing the 'lowest wedge' game isn't all that much fun. Many arenas have irregular floors, some with gaps or raised edges that can play havoc with a low wedge. We won a match at the RFL nationals when our opponent's very low wedge penetrated the space between two floor panels and got hopelessly stuck. You have to know a specific arena very well before you can decide how low to go.
Which dragging wedge wins? The sharpest. The front edge of the wedge must be knife-edge sharp and contoured with the leading edge right on the floor. At events with very smooth arena floors you'll see wedge teams honeing the leading edge with files and sandpaper between matches and examining the way the edge sits on the floor very carefully. A material that will hold a good edge is critical here. Like I said, this is not much fun as the sharpest wedge will also be more prone to surface irregularity issues.
With a 4-wheel bot the usual method for a dragging wedge is to mount the wedge on a hinge that allows it to drop by it's own weight to rest on the floor. See the question about the wedge on 'Original Sin' in the archive.
Q: Is there anyone talked about 'SABotage' before? I think it's a simple but pretty effective machine, and is it the only famous bot from Indiana.
Q: Do you know anything about 'Verbal Abuse' from Team Killerbotics?
Q: [Chinese Forum] What do you think of 'Verbal Abuse'? I know it did pretty well in NPC Charity event but there are very few information about it.
A: I'm not going to let this turn into a 'Fanboy' site. I don't have much interest in providing opinions on obscure robots, rehashing matches that had no particular impact on the sport, or discussing the merits of every robot that ever competed. Very briefly:
A: The main problem with a dustpan design is the current judging emphasis on damage. They are great at controlling an opponent, but control no longer counts in scoring. The small 'saw on an arm' used by S.O.B / T.D.D. can't do enough damage to really be a threat.
A well-built dustpan can be very tough and resistant to attacks by most weapon designs (they are sitting ducks for an overhead spike) but the lack of a damaging attack is a major drawback.
Q: [Chinese Forum] So, if there's enough space and weight allowance a "Dustpan" with a crusher could make some good damaging effects - am I right?
A: A vertical crusher needs a very solid base or 'anvil' to press against. The floor of a dustpan would be deformed by the force. I guess you could run a horizontal crusher, but then you wouldn't really need the dustpan to contain your opponent.
My first question is How do I measure the belts and pullys to make them fit together for weapons and drive systems? This is the important question I will need this a lot in the future.
A: There is a belt-length calculator on the FingerTech Timing Belts & Pulleys page. You can play around with pully diameters and center distances and it will tell you how long the belt needs to be.
Q: My second question is what does 25:1 geared mean? How would I determine what ratio it is?
A: A 25:1 gear ratio means that for every 25 revolutions the motor makes the output shaft makes one revolution. You can determine a gear ratio by seeing how many revolutions the input has to make to turn the output once, or you can count the teeth on each gear reduction stage:
For multiple stage gear reductions you can gount the gear teeth in each stage and multiply the ratios together:
Ratios of planetary gears are a little more difficult, but you can find general information on gear train types and gear ratios at science.howstuffworks.com.
Q: The Banebots P60 series do not have the torque listed for the gearbox. Is there any formula to determine the torque using the motor data and the gearbox ratio?
A: Sure:
Gearbox output torque = Motor torque × gear ratio
So, a motor with 10 inch-ounces of stall torque and a top speed of 15,000 RPM mated to a 15:1 gearbox will produce at the output shaft 150 inch-ounces of stall torque and a top speed of 1000 RPM.
A: Mark J. here: we answer combat robot questions and don't generally consult on class projects. One quick thought: a hinged top cover that flips forward to double the top surface of the vehicle. Thirty millimeters square? That's about the size of my watch!
A: Stephen Felk devoted a great deal of thought to the design and structure, and he did a very fine job of construction - particulary given the limited resources available in his 'workshop'. We have great admiration for builders who do so well with modest budgets.
A: 'Dantomkia' had some unusual features - like the adjustable castor height - but I wouldn't call it 'unique'. It was effective, winning 'Heat C' in both the Sixth and Seventh wars, but it went no further. Several other flippers did equally as well, and some did better.
Q: What make 'New Cruelty' a successful robot? He is neither very fast nor very agile, but it seems it's always well-controlled. Is that a cause? [Chinese Forum]
A: I suspect that eight sticky wheels, a ton of power, and a talented and experienced driver contributed to the success. Dick Stuplich from Team Killerbotics knows how to take advantage of an opponent's weaknesses and he knows how to minimize his own robots shortcomings. Most importantly, he knows how to build a robot that matches his driving style.
A: It all depends on the arena.
A: There is a 'secret': Beginners Guide to Gyros.
A: Both of these robots from Team Coolrobots were 'reaction hammer' designs (see discussion in the archive) that are simple, but which do not deliver much weapon power. 'Overkill' was probably more successful than it should have been based on it's combat capability. Judges really liked the huge shiny blade. It was simply more visually impressive than the simple pick on 'Toe Crusher'
A: Sometimes the 'only thing you can afford' ends up costing you way too much.
Q: How about this Buehler gearmotor [dead link deleted]? Its faster than the other one.
A: Better - at least the motor and gearbox fit together. It's specs appear to be kinda similar to the ML-30 motor [discontinued], but you're still a long way from 'good'. The quality of the gearbox is unknown, the shaft is an unusual diameter, the motor is used, and 200 RPM is only going to give you 1.78 MPH with the 3" diameter Colson wheels. That's not even walking speed.
There are good reasons why popular gearmotors are popular: they work. If you go for an unknown and untested motor you're probably going to find out rather quickly why nobody else uses it.
You want affordable gearmotors for a beetle? Try the BaneBots MS250-20-180 [no longer available]. At 4.8 volts with 3" wheels they will push a beetle close to 6 MPH in an 8 foot arena with pushing power to spare. They are the same price as your 'surplus' gearmotors, will operate from a pair of 5-amp insect speed controllers, require only a small NiMH battery pack, and are simple to mount in your chassis.
The BaneBots 2 7/8" wheels and their 4mm hubs would be a good match for these gearmotors.
A: There's a reason that it didn't sell: Team Whyachi builds quality robots, but 'Y-Pout' was an experimental design that just didn't work. See a discussion of Y-Pout elsewhere in this archive.
If you're looking for a 'pit pass' just to go to the next BattleBots and hang out, Y-pout should get you in the door. I'm assuming that it comes without radio gear, support equipment, and spares -- be prepared to spend some money on those items. I'd rather build a 'bot than buy one.
Mark J. here: I'm not certain that 'Y-Pout' even qualifies for competition under the current BattleBots rules. Section 9.1.2b requires an active weapon which operates 'separately from the Mobility System'. I'd get an opinion from the BattleBots technical crew before committing to purchase.
I also wouldn't count too heavily on the November BattleBots happening. Just a hunch.
A: Nice group of guys. At Robot Wars Extreme Warriors 2 they walked thru the pit area and handed out autographed posters of 'Razer' to every U.S. team. I was off someplace and didn't get to talk with them, but I still have the poster hanging in my room.
Razer itself completely rocks! It has one very clever feature (plainly visible in many photos) that significantly adds to the success in deploying the piercing weapon, yet which I've never heard anyone mention. It is an unusual use of an uncommon combat robot component. Bonus points to anyone who can identify the component and how Team Razer makes use of it.
Q: Just a guess, are the barbed teeth Razer's distinctive feature????
A: No, the jagged teeth on Razer's weapon don't help with deploying the weapon.
Q: Is the component on Razer the wings? Team Razer used them to self-right.
A: No - the powered wings were unusual, but SRiMechs were very common at Robot Wars.
The uncommon components in question replaced very common components on Razer about the time of the Third Wars. Razer used two, and they were powered. All the other robots I've seen that had powered ones used three or four. 'Killer B' had two, but they were unpowered and mounted sideways at the other end of the robot! What are they?
Q: Is the component on Razer the omniwheels?
A: Yes! A pair of omniwheels replaced the conventional wheels at the rear of Razer. Conventional wheels remain in place at the front. It is most unusual to have two powered omniwheels in parallel at one end of a robot. Now - tell me why Team Razor did this.
Q: Team Razer did this so they could maneuver around the opponent's weapon and attack them?
A: A pair of parallel-mounted omniwheels does not give powered side-slip control (omnidirectional motion). You'd need Mecanum wheels to do that, and four of them. There is a discussion of omniwheel use in this archive -- search for 'omnidirectional'.
So, if the omniwheels on the rear of Razer don't give it controlled side-slip motion, what specific advantage do they provide for a four-wheel skid-steered robot? Hint: Team Razor installed a peizo gyro at the same time as the omniwheels.
Q: Did Razer use the omniwheels so it could spin its weapon around quickly to face its openents?
A: You're on the right track; I'll give it to you. I wondered if anyone had noticed the unusual application of omniwheels at the rear of Razor and had figured out what advantage they gave.
A conventional 'tank steer' four-wheel robot has to skid tires sideways in order to turn because all of the wheels are pointing straight ahead. This takes a fair amount of power and can result in difficult and unpredictable steering results. Omniwheels have no resistance to sideways motion because their tread surface is composed of rollers. The rear omniwheels don't have to 'chatter' in a turn -- they just passively sideslip which makes the robot as maneuverable as a two-wheeled robot but with the stability and pushing power of a four-wheel robot. Very slick!
Team Razer added a peizo gyro to keep the rear end from slipping more than needed and 'spinning out' in a turn. Added advantage to the design: if you try to push Razer from the side, the rear wheels slide around effortlessly and the robot pivots around the grabbing front wheels to put you right in the mouth of the weapon.
A: Robot Arena is a pretty fair physics simulation, but even small differences between the simulation and the 'real world' can allow unworkable design elements to appear successful. If you're fighting in the real world, look to proven designs from real robot combat for your inspiration.
A: I don't predict fantasy matches, and I don't evaluate fantasy robots. I will say that the weapon appears to store very little kinetic energy and applies it to the opponent only under specific circumstances. I'd build something else.
A: Mark J. here: we selectively use rubber or spring mounts only for special cases. Armor that is inherently springy (UHMW polyethylene, polycarbonate, titanium) does not benefit much from shock mounting, although we often do use rubber grommets when mounting polycarbonate to relieve stress at the mounting points. We believe the best candidates for shock mounting are stiff plates of relatively small size: battery covers, rear panels, wheel covers.
Panels that are shock mounted do not fully contribute to the structural rigidity and strength of the chassis. Shock mounting should be used only in designs that do not rely on integrated stressed armor panels for strength.
We did have the front wedge on 'Run Amok' spring mounted at Robotica and Robot Wars Extreme Warriors 1, but it was more trouble than it was worth. We reverted to solid mounting for RWEW2.
A: All at the back?? The benefit from 4-wheel drive comes in getting all the robot's weight on powered wheels. If the drive wheels aren't carrying all the weight, you aren't going to gain much benefit. If you're thinking of using more wheels to get it to track better in a straight line, a gyro is a very worthwhile alternative.
A: Mark J. here: sorry, I've never done any aluminum brazing. I cannot comment except to say that I don't know of anyone using the technique in combat robot construction -- there may be a reason.
A: Two-wheeled robots tend to be difficult to keep on a straight path, but a small weight offset isn't going to be noticeable.
A: That's a great idea... if the robots you plan to fight are armed with guns.
How about tests that more realistically model the type of abuse your robot will actually face? Your whole robot has to put up with serious punishment, not just the armor. Drive it into a wall at top speed - forward and backward. Pick it up and drop it a few times onto a hard surface from about four feet. Kick it across the room. Drop a bowling ball on it. Hit it with a hammer. If something breaks, make it stronger.
A: Mark J. here: heavyweight 'Y-Pout' and middleweight 'Why Not' were experiments by Team Whyachi in a mechanical solution to the problem of obtaining controlled movement in a rotating 'thwackbot' spinner. Several mad scientist combat robot teams have worked on electronic solutions to this 'translational drifting' problem, calling the result 'Melty Brain' or 'Tornado Drive' propulsion. There is a good explanation at the SpamButcher website.
The Team Whyachi solution has a small conventional robot in the center of the whirling larger robot that steers the three main propulsion wheels via cam actuated rods based on the position of the small 'NavBot' relative to the larger spinning mass. Two article reprints from "Real Robots" magazine attempt to explain this with photos and diagrams: Y-Pout and NavBot.
Y-Pout's record: zero wins, two losses. Why Not's record: one win, two losses.
A: You pay your money and you take your chances. The 28mm BaneBots gearbox is strong, but not bulletproof. I've seen them used in beetles without wheel protection or extra shaft support, but I'd be very worried about a good spinner opponent. The 6mm shaft isn't the problem, it's the gearbox itself that fails. Mount the wheel as close as you can to the face of the gearbox to reduce overhung load. Sandwiching the gearbox between two stiff chassis plates and securing it via all eight top and bottom mounting holes will help. The BaneBots wheels have some flex to them and might transmit less shock to the gearbox, but then I'd worry about wheel failure.
Beefier gearmotor? The BaneBots 36mm gearbox attached to the same RS-385 motor is 3.9 ounces heavier, has a 10mm shaft, and larger mounting screws. I'd stick with the 28mm geaboxes and use that extra 7.8 ounces to add some wheel protection.
A: First, there is more to pushing power than motor power. Once a motor supplies enough power to start spinning the wheels, any additional power is simply lost and no additional 'push' is achieved. Good pushing robots have all their weight supported on powered wheels and have appropriate tires for the arena surface.
Second, the BaneBots 'P60' is a gearbox that will accept several different motors; it is not a complete gearmotor. Your best motor option to fit the P60 gearbox is probably the RS-550.
For best overall pushing performance, a gear ratio and wheel diameter combination should be chosen to break traction and spin the wheels at about half the stall amperage of the motor. For a 30 pound robot with a pair of RS-550 motors at 12 volts and 4 inch diameter wheels, a 16:1 gear ratio is close to optimal. You can check motor performance with different gear ratios and wheel diameters with the
Team Tentacle Torque & Amp-Hour Calculator
.
A: Mark J. here: good practice for an end tap calls for the material thickness to be no less than twice the major diameter of the machine screw. An 8-32 screw has a diameter of .164" which calls for a minimum material thickness of .328. I don't know what your application is so I can't even guess at how much further you could shave that.
A: I can't recall any real jumping robots, but there was a net-dropping flying robot at the 1995 Robot Wars: J.D. Streett's 'S.P.S. #2'.
The current 'RFL Standard Extensible Rule Set' allows for 'jumping and hopping' as a means of controlled mobility. Also allowed are rolling, shuffling, and air-cushon hovering. Sustained flight is not currently allowed, although the event organizer has the final call on both jumping and flying.
A: Curt Meyers' superheavyweight 'Jaws of Death' first fought at BattleBots 3.0 in 2001. Its most recent appearance was at RoboGames 2008. There have been a number of design revisions over the years, but it has always had big hydraulic pincers. The hydraulic system is powered by an internal combustion engine. I cannot find specific details on the hydraulic system, but 15 tons of force from the hydraulic cylinder is entirely possible. Force at the pincer tips would be much less.
The robot has been modestly effective. Overall record for 'Jaws of Death' is 5 wins, 8 losses.
A: I suspect that their initial designs were both based on the more general theme of a bulldozer, but 'Behemoth' did evolve over time to more closely resemble the house robot. When 'Behemoth' first appeared at the Second Wars its only weapon was the bulldozer-like lifting blade. By the Fifth Wars it had added an overhead axe positioned to work with the lifting blade, just like 'Shunt'.
A: Mark J. here: most likely not. When you change the scale on a design the mass changes faster than the individual length/width/height dimensions and you change the need for strength in structural components. If you made an ant the size of an elephant it's skinny little legs would collapse under the weight. Conversely, an ant-sized elephant would have much thicker and heavier legs than it would need.
A: Yes, although the rules in force at the time did not refer to 'walking'. The 1997 Robot Wars rules allowed 'Legged' heavyweight robots to weigh up to 300 pounds, and the BattleBots 2.0 rules allowed the redesigned and beefed-up 'Snake' to compete as a 'Non-Wheeled' superheavyweight at a weight up to 488 pounds.
'Snake' would still qualify for a 100% 'non-wheeled' weight bonus under the current RFL ruleset, as it's motion is not dependent on rolling or cam operated mechanisms. Seems you don't need legs to walk.
A: BioHazard had no side shirts in it's debut appearance at Robot Wars 1996. The drop skirts appeared the next year. With 'BioHazard' on it's back, the hinged side skirts lay down flat against the ground. When it tries to roll upright, a skirt will fold up against the chassis and form a 'stop' that makes the rolling action too difficult to complete.
A: It takes nothing away from the classic combat robots to say that they are not a match for robots that have the advantage of seven additional years of design evolution. It's the same at the highest level of any sport: you don't race a seven year-old car, you don't play with a seven year-old racket, and you don't run in seven year-old shoes. Technology changes and you either update or become obsolete.
A: Building a hobbyweight ot featherweight robot is a lot like building a beetleweight -- just bigger.
A: Why do people write to a combat robot site with mousetrap car questions?
Most mousetrap cars are designed for distance, not speed. The best distance moustrap cars creep forward very slowly -- speed is inefficient. For distance you want large, skinny wheels like CDs or even old LP records.
If you're building for speed you have other considerations. If it's a drag race style event for lowest time over a fixed distance you'll want the entire energy of the moustrap to expend itself in about the first 3/4ths of the course and then coast the rest of the way. Size the wheels accordingly. The tires will need enough traction to avoid power-wasting wheelspin, so some type of rubber tire may be needed. Experiment!
You can find more help for mousetrap cars of all types over at the Doc Fizzix website.
Love the site. [BDsquint- FOBOT]
A: Mark J. here: thanks for the love, BD.
We both understand that the integrity of an arena depends on more than the thickness of the Lexan. The type of framing and fastening is critical in determining how much abuse an arena can put up with. That said, a well-constructed arena with 1/4" Lexan walls should keep you well ahead of beetleweight spinners for some time to come.
I can't give you a specific number of Joules beyond which I'd start to worry, but it's unlikely that your containment will fail abruptly and catastrophically. Lexan will deform and absorb a really enormous impact. You'll notice severe marring and obvious damage to the polycarbonate well before there is danger of a breach. As long as your framing keeps the edges of the Lexan from parting, you'll have plenty of warning when spinners get close to dangerous energy levels.
Many arenas have a 'bumper strip' of material set in just a bit from the polycarbonate walls about spinner-high. This dissipates a good amount of the energy from a spinning weapon before it can reach the outer wall. Good idea!
Update: sorry, you can scrap that question. I looked back through the archive and after reading some other answers in which you said "Make it as thick as you can and still make weight", I'm just going to do that. Thanks.
A: Mark J. here: thanks for checking the archive. The 'make it as thick as you can' rule is generally a good model to follow. I don't think that .0625 aluminum would be thick enough. Fiasco uses .375" 7075 aluminum. For a beetle you won't need to go that thick. The application of some very sketchy engineering formulas leads me to believe that a high-strength aluminum alloy at least 0.125" would be in the right ballpark. Thicker would be better if you have the weight to spare.
A: The A28-400 Magmotors are only 3" in diameter, and the rest of the drive train is built to be no taller than the motors -- small wheels, compact chain drive, tiny sprockets. The 4-bar lifter weapon folds down flat to nest inside it's own forward control arms. The linear actuators that power the lifter are very compact. No magic involved, just first rate design.
Every section of the Team BioHazard website is required reading for anyone building a combat robot. Motor tips, parts selection, electronics, and materials are all well and concisely covered.
Get reading!
A: Generally, yes.
A: First, check to find out what weight classes are supported at your local events and how many competitors are in each class. The events page at The Builders Database can give you this information. You don't want to build for a weight class that has no competitors!
Next, consider your budget. It's better to build a light robot with good components that can be re-used on future projects than stretching for a heavier 'bot made out of pieces that you'll want to upgrade for your next robot. Buying good components will save you money in the long run.
A: You can go buy a 1" hole saw, but for a small job like this I'd score the outline of the hole onto the aluminum and then drill a series of small holes just inside of the scored line and use a small file to break thru from one hole to the next. A curved file can then smooth out the hole to the scored line.
A: Mark J. here: a few thoughts:
A: All common questions that we have previously answered in detail. Click those green buttons near the top of the page to access the archives and get reading, pilgrim. Start with the .
Some short answers to get you started:
A: I don't wander thru the pits with a caliper in my hand measuring armor, but as a guess: 'Shovelhead'.
A: The rear chassis uprights on 'Ice Cube 3' are bolted in place rather than welded. They can be removed along with the rear armor to make it easy to change the motors and gearboxes. Sometimes it is worthwhile to sacrifice a little strength to make between-match repairs go more smoothly.
A: You'll need a gearbox! A gearbox reduces the speed of the motor and increases the torque. Without a gearbox, the motor would not have enough torque to give the robot any pushing power at all, it would use way too much amperage, and it would melt very quickly from the stress.
The heavier your robot is and the larger the wheels are, the more gear reduction your motors will need. The
Team Tentacle Torque & Amp-Hour Calculator
shows that a pair of the 'Small Johnson' motors in a 12 pound robot with 3" wheels would do well with a gear reduction somewhere around 12:1.
A: Mark J. here: I've seen many beautifully crafted, titanium armored, mega-powered combat robots that could not fight their way out of a paper bag. Why not? Because getting the basic design principles correct is way more important than all the exotic materials and CNC machining in the world.
Team Tiki got the basics very right with 'The Brown Note'. The robot was low, powerful, and very controllable. The steel wedge was so nasty to start with that it didn't really show any additional damage. Once 'K2's nasty spinner got hold of the plywood 'The Brown Note' was just so many splinters, but the lesson to be remembered is that you must spend the time and energy to design your robot around the functions it must perform well to be successful before you get to the less important aspects.
You may wish to examine the career of heavyweight 'Evelyn, a Modified Dog' from Team K.I.S.S. for additional support of this theory. As the builder of another plywood covered combat robot once said, "Complex design is easy -- simple takes work."
A: We've answered questions just like this before, so dig thru the archives, starting with the . Building a robot to 'just move around' is very different than building one for competition -- meeting the competition rules takes planning and added expense, so decide before you start to build. Read thru the archives, see our recommendations on books, and dig in!
A: There are advantages to both designs, but I'm a believer in the chains and sprockets approach.
A: Mark J. here: If you want similar performance to 'Vladiator' you'll need a similar power to weight ratio. Vladiator is a 340 pound superheavyweight powered by twin Etek motors producing a combined 30 horsepower: 340 ÷ 30 = 11.33 pounds per horsepower. To get that same power ratio in a 120 pound middleweight you'd need: 120 ÷ 11.33 = 10.6 horsepower.
The NPC-02446 motor that comes with the 'build your own gearbox' kit puts out about 0.75 horsepower. You'd need 14 of them to get close to the power you're looking for!
Three horsepower from four of the NPC motors will give more than adequate performance in a middleweight -- the
Team Tentacle Torque & Amp-Hour Calculator
shows a top speed across a 36 foot arena of 14 MPH in 2.7 seconds. You just aren't going to get the rubber-burning-mad-gerbil-in-a-popcorn-popper action that the high-end powerbots can display.
A: Sounds very good -- might even be overkill. Armor material and thickness choice depends on the design of your robot, how the armor is supported, and the combat tactics you plan to use. You're in the right ballpark.
A: I'm sure your design concept is very clear to you, but I'm going to need more information before I can make recommendations on motors. For a start:
Q: I'm thinking of making it a middleweight, and the weapon will be a pneumatic arm similar to that of the Judge's, and it will have a vertical spinner attachment, or else it can be swapped out for a flipper or a hammer. It will be mounted on a small housing that is held by and arm that will rotate it around the robot's body. Since the weapon will take up a a lot of weight, along with the armor the drive doesn't need to be fast or have a lot of pushing power. Also since the weapon will have some big stresses, what do you recommend for the arm, and the arm that moves the weapon around the body. Thank You.
A: A couple of suggestions:
A: Seems unlikely. Once flipped over it would be pretty stable resting on the rotor -- the 'bot body would just spin freely. You'd need a fairly complicated SRiMech to put it back upright. However, gyroscopic forces make a 'bot with a big spinning rotor difficult to flip over in the first place.
A: Mark J. here: clever thinking, but weight and mass are different properties. Mass is a measure of an object's resistance to change in velocity, while weight is a measure of force exerted on an object by gravity. The formula for kinetic energy is:
Magnetic downforce only increases the apparent weight of a robot, not the mass. The kinetic energy of your example robot can only be increased by increasing its velocity.
A: My best advice about tracks on combat robots is "don't do it". Tracks are way more trouble than they are worth on a smooth surface.
Most tracked 'bots are about 'square': the tracks are nearly the same length as the width of the robot. It helps maneuverability to have a tread support sprocket near the center of the track that is just a little lower than the front and rear support sprockets -- similar to the layout for a six-wheeled robot. Avoid the pain and go with wheels.
A: Set screws suck. They come loose at absolutely the worst times. You can bolt thru the pulley and use the radial prop mount holes on the motor case, or drill all the way thru the pulley hub and the motor shaft and drive in a small hardened pin.
If you have to use setscrews, file a deep flat spot on the motor shaft, use Loctite, and check it for tightness before every match.
Q: To attach a pulley to my Axi, could I just screw down the prop adapter around it really tight, and not use any set screws?
A: I don't have an Axi 5330 here to look at, but isn't the prop adapter held on with set screws? Set screws are not a good method of securing a mechanical linkage to a shaft. What is adequate for a propeller spinning in air is not adequate for a pulley that will encounter much greater forces.
You want a mounting method that relies on something other than friction to prevent rotation of the pulley and which will not fail if a threaded connection loosens a bit -- and a threaded connection being directly stressed will loosen!
A: A wide wheel track results in a stable and easily controlled 'bot with a slow spin rate when turning. This is desireable in ramming 'bots that must be carefully positioned for an attack.
A 'bot with a narrow track is more difficult to control in turns and has a higher spin rate. The higher spin rate is desireable in thwackbots that rely on a high spin rate for offense.
A: Since when are moustrap cars combat robots?
Larger wheels have lower rolling resistance than smaller wheels. They also make it easier to obtain a high ratio between the action of the trap spring and forward movement without efficiency-robbing gears. A really good mousetrap car will creep forward very, very slowly -- speed is not efficient!
I've seen mousetrap cars use old LP record albums (search your local thrift shop) as wheels. They work great!
A: Mark J. here: Beats me. Chassis strength depends on design, triangulation of members, gusseting, armor type, method of armor attachment, size, and construction technique as well as the amount and type of material used. Without knowing a whole lot more about your design and building skill level, I can't begin to answer your question.
A: No limit in the rules, but the larger the 'bot the thinner the armor has to be to make weight. Most builders keep them compact.
Q: How heavy is a typical featherweight?
A: The typical 'bot in any weight class is very close to the weight limit. The RFL featherweight limit (North America) is 30 pounds. UK featherweights have a 12 kilogram limit.
Q: What is the size of a normal featherweight?
A: A typical featherweight might be 16" square and about 4" high. There is a lot of variation and there are no size limits -- as long as it can fit into the arena.
Q: How light can a featherweight be?
A: There is no minimum weight specified in the RFL rules, but if you're at or under 12 pounds you qualify as a hobbyweight. Lighter 'bots are at a disadvantage in combat.
If you're serious about building a combat robot, you really must make the effort to attend a combat tournament and see a real competition. You'll get answers to questions that you didn't even know you should be asking!
Q: Can a DeWalt14.4v old style drill motor be good to power a wheel for a featherweight?
A: A pair of DeWalt 14.4 volt motors/gearboxes would be a good choice for a featherweight. With 3 inch wheels and the gearbox locked in 'high', the 'bot would have a theoretical top speed of 12 MPH at 18 volts. The motors could spin the wheels while drawing only 22 amps. All very good!
You can 'test drive' a selection of motor/gearing/wheel/weight combinations at the
Team Tentacle Torque & Amp-Hour Calculator.
A: Mark J. here: I have no idea what you're talking about. Perhaps if you explained your question in detail and included links I could help.
A: According to the archived Stinger website, their top speed is only 9 mph -- not at all fast for Robot Wars. Power came from twin Bosch GBA 24 volt motors -- about 1.25 horsepower each. The motors were geared for acceleration and pushing power. I think it's their quickness you remember, not their speed.
A: Mark J. here: torque isn't the issue -- total power is the issue. Clamping force and speed will depend on the geometry of the clamp as much as the torque of the actuator. You usually aim for a minimum three times as much clamping force as the weightclass you compete in, so about 200 pounds of force at the clamping point for a lightweight.
A: If the arena you compete in has a smooth enough floor for drag wedges to be sucessful, you can probably get away with a hinge on your wedge that will allow it to drag as well. Put a limit on how far the wedge hinge can move -- you don't want it to fold back under the 'bot, or flip upward.
A: Read down about seven questions for information on 'hubs'. Attaching a wheel directly to a motor is a very poor idea -- without gear reduction, performance will be awful.
A: Different arenas have different problems with floor seams. Even the same arena can have tight seams one time and problems the next because of minor changes in how and where it gets assembled.
I can't recommend a robot design that depends on the skill of the arena assembly crew. I also don't like the idea of a wedge that can fold back under pressure and lift the front of the 'bot up off the arena floor.
A: Possible, yes. Good, no. An overhead thwackbot like Toe-Crusher needs to have the mass of the robot nearly balanced on the drive axle in order for the acceleration/deceleration torque of the drive to be able to throw the weapon 'over the top'. The overhang behind the drive axle has to be able to clear the ground as the 'bot swings over for weapon impact. With six-inch wheels, you would have less than three inches of rear overhang -- that's probably not enough to pack batteries and other heavy components to counterbalance an effective weapon hanging off the other end.
Q: What's the best way to distribute weight in a thwackbot?
A: As mentioned above, an overhead (torque reaction) thwacker needs weight positioned out behind the drive axle to help balance the weight of the weapon out on the end of the boom. Place your batteries, electronics, motors, everything you have space for out in back of the axle centerline. I'd aim for about 85% of the total robot weight to be on the drive wheels with the remaining 15% resting on the weapon. If you get too much weight on the weapon it will become difficult to swing the weapon over for impact. If you have too much weight on the drive axle the weapon impact force will be reduced. Some 'trial and error' tuning will be needed.
The approximate weight distribution applies to traditional non-overhead thwackers as well, but you'll have more space behind the axle for weapon weight offset.
A: Mark J. here: I don't know what your chassis design looks like, but I'd drill and tap multiple mounting holes across the top and bottom of each the two aluminum plates and both thru the top and bottom plates of the robot chassis. The plates will need cutouts for the wheels. Additionally, I would use the existing mounting holes on the plates to bolt thru chassis tubes or into bracing blocks or bulkheads perpendicular to the plates. You do not want the plates to distort in relation to each other or the gears will die!
A: Ramiro Mallari built 'Punjar' from exercise treadmill parts. The very wide wheels are converted treadmill rollers. Perhaps he believed that super-wide tires would give super traction?
Punjar had a long and successful career. Active from 1996 to 2001, Punjar racked up a 14 win / 8 loss record. That places Punjar 24th in the all-time heavyweight rankings -- 10th among those with 20 or more fights.
A: Not even close. Here's what the 2007 RFL rules say:
Pressure Drop's walking mechanism (archived) is cam actuated via a linkage from a continuous rotary source -- no weight bonus for that.
A: Go look around the Mechanical and Drive Components page at Robot Marketplace. While you're there, browse the rest of the site as well -- it will answer a lot of basic questions.
A: A wood baseplate! You don't see much of that anymore -- but I like it. A good quality plywood ('marine grade' is best) is really quite strong for its weight. Don't use woodscrews to fasten down your components; drill thru the baseplate and use a nut/washer/bolt to securely anchor everything.
There are a lot of choices for the rest of the chassis. Square steel tube can be cut with a hacksaw, drilled, and bolted together. Use nylock nuts or a liquid threadlocker to keep everything from vibrating loose. You'll want to gusset all the joints for strength. Armor can then be fastened directly to the square tube chassis.
I'd strongly recommend getting a copy of Grant Imahara's book, Kickin' Bot. It covers everything you could possibly need to know about chassis building, as well as every other aspect of combat robotics. It will save many times it's cost in time, materials, and performance.
A: It's usually a 'trial and error' process. Design and build your 4-bar lifter for its primary function as an effective weapon. Once the robot is working you can try extensions to the height and width of the top lifter arm until you hit a combination that will tip your inverted 'bot back onto it's wheels -- like the top 'claw' on the 'Pack Raptors' (pictured). Designs with greater lift will require smaller extensions.
General robot design can affect the ability to self-right as well. The original (1996) version of Biohazard was able to reliably self-right, but lost that ability when defensive side-skirts were added. A narrow or short 'bot is easier to self-right than a wide, long 'bot.
A: Robot Sumo! Great stuff. I'm guessing that this will be remote control sumo. Check the previous sumo tips in the Ask Aaron archives. A few specific suggestions:
A: We don't use Computer Aided Design software for our robots so I can't make a recommendation, but if you type 'free CAD' into Google, you'll find links to a ton of them.
A: Your problem isn't the weight of your armor, it's how the weight of your 'bot is distributed. I'm guessing that this is a two-wheel drive robot and that your drive wheels are too far away from the center of mass to get good traction. You need to either redistribute the heavy components of your 'bot to put more weight on the drive wheels, or move the drive wheels closer to the center of mass.
Q: That's a good answer, but I didn't tell you enough about my 'bot. I made it cheap -- it's a remote controlled car (worth £10 or $20) and the armor is what once looked like a dustpan but with a cover. It's covered in decorative foil and stickers. Is there anything I can do to improve the turning on the car?
A: I like your use of available parts! You've built a 'bot and you're out there having fun.
Your front tires are probably soft plastic and may not have enough grip to turn the 'bot. Their grip can be greatly improved by coating them with a thin layer of silicone rubber sealant, available at a hardware or auto supply store. Use the 'pure silicone', not 'siliconized' caulking or another type of sealant. Any color will do. Clean the tires with alcohol or another solvent and let dry completely before applying the silicone to get the best bond. The sealant is pretty thick and sticky to apply, but it doesn't need to be perfect. Let the silicone cure for a full day and give it a try.
Another possibility is that the weight on the front wheels is too great for the small steering servo to overcome. You can't replace it -- your radio isn't compatible with hobby-grade servos. If that's the problem, you're back to shifting weight toward the rear drive wheels to lighten the load on the front wheels. Best luck!
Q: I'm writing back to thank you for your help. The robot's steering has greatly improved and I owe all my thanks to you.
A: Glad I could help!
A: Rounding the edge armor of your 'bot could help resist hits from vertical spinners, but angled armor has to face all sorts of weapon attacks. Sharply sloped armor can be effective against many weapon types: vertical and horizontal spinners, bricks, and rammers. If you add drop skirts you have good protection against wedges, lifters, and flippers too. Rounding the armor as you suggest could retain some additional protection from vertical spinners when inverted, but would leave you very vulnerable to wedges and lifters. Are there really so many vertical spinners fighting at your local tournaments that you have to design specifically against them? Also consider how often you will get inverted if you have effective drop skirts.
If you are really worried about inverted protection, the best solution could be a V-profile plus a hinged drop skirt. The armor profile remains the same when inverted and you maintain protection from lifters and wedges. See the diagram.
A: The motors must be securely fastened to the chassis by mechanical means:
I don't know which 'Beetle Gearmotor' you're using, but they likely have some mounting holes that could be put to good use with some simple angled metal brackets. A pair of automotive steel hose clamps fastened around each motor and thru the chassis can be used in a pinch. Machined aluminum or UHMW polyethylene clamp mounts surrounding each motor and gearbox would be better. Look around the 'net and see how other builders do it.
A: The Robot Marketplace antweight battery packs are compact, light, and well made -- but they have only a 370 mAh capacity. Fine for an antweight, not nearly enough for a hobbyweight powered by RS-540s.
Pay attention to the 'estimated battery capacity required' that the
Team Tentacle Torque & Amp-Hour Calculator
provides. A hobbyweight powered by RS-540s plus a weapon motor is gonna want more than 1000 mAh.
A: See previous post on battery capacity.
A: I think you're asking about drop-skirts. They are armor panels hinged along the top edge that drop down at an angle and slide along the arena floor. Small 'bots can use strong tape to make the hinge, but larger 'bots need full-length mechanical hinges.
A: You rubber-mount armor by running the mounting bolts thru a large rubber grommet in the chassis. Be sure to use a 'fender washer' on the back side of the grommet, and self-locking nuts. Don't tighten the mounting nuts down very tight -- leave room for the rubber to flex and absorb impact. Rubber mounting is particularly useful for polycarbonate armor, which tends to crack at high-stress mounting points.
A: Mark J. here: A speed controller is one of the last components to consider when building a 'bot -- not the first. Your speed controller specs will be determined by the amperage requirements of the drivetrain. The process goes like this:
A: Robot sumo competitions have highly variable rules, and careful study of the rules is needed to figure out what designs will work well. Are you entering the autonomous or R/C category? What weight/size class? What material is the arena surface made of? Do the rules allow magnet traction aids? Do the rules allow vacuum traction aids? Are there rules about how 'sharp' the edge of your wedge can be? Are 'sticky' tires allowed, or do tires have to pass the 'paper drop' test?
Write back with details about your competition, and tell me more about your motors. In the mean time, try to find a copy of Robot Sumo: The Official Guide by Pete Miles in your local library.
Q: I am entering a R/C category. The maximum weight is 2.5 kg and the robot must fit within a 50cm X 50cm box with no height restriction. The arena floor is made of vinyl. The rules do not specify anything about traction aids (nor do I know what they are). There are no rules about how sharp the wedge can be. And, tires may not leave residue on the playing field. Thanks!
A: It's details that win R/C sumo competitions. A wedge is a winner only if it's better than your opponent's wedge. You need to make sure that it sets perfectly level all the way across it's width and that the leading edge is sharp and flush with the arena surface. Read thru those rules again -- there's usually some restriction on dangerous sharp edges. If not, make it razor sharp, but fit a cover to it between matches for safety. Side and rear drop-skirts are uncommon in sumo competitions and may be more trouble than they are worth.
Tires are another critical detail area. Super-tacky reusable lint rollers are very effective as sumo tires, and they leave no residue. See Dave Chu's Sumo Project for an example of their use. Clean and dry them before each match. Other tire compounds (polyurethane, silicone rubber) are useable if you're not willing to custom make your hubs and tires. See Pete Miles' book referenced above for details.
Traction aids are devices that make the apparent weight of the 'bot greater in order to get more traction. If the arena has a steel base, magnets can be used to pull the 'bot toward the surface with great force. A magnet-bot can climb right up the vertical face of a steel cabinet and even run upside-down on a metal ceiling! A similar effect can be achieved on non-magnetic surfaces with a vacuum fan system and sliding surface seals.
I'd suggest sticking with a conventional design for your first build. Finish it early enough to get plenty of driving practice. Keep things simple and sweat the details.
A: Mark J. here: Is that total stall torque from all motors at the axles, or stall torque available per driven wheel? I also need to know the wheel radius, the number of driven wheels, and the weight on the drive wheels to run the calculations.
'Punjar' was a scoop-fronted rambot with a lot of speed and pushing power. To duplicate that performance, you'll want to design for thrust available at each driven wheel to be about two times the weight normally on that wheel. Much more than that just smokes the tires and wastes weight (and money) on heavy drivetrains and batteries.
I'll guess that 788 inch-pounds is the total torque available per drive wheel for a two-wheel drive 'bot. Assuming a 3" wheel radius, that gives you (788/3) = 263 pounds of thrust and no more than 50 pounds of weight on the wheel. If my assumptions right, that's more than five times the weight in thrust -- way overkill. If that 788 in-pounds is the total of all your drive axles, you're pretty close to right.
A: It's simple to build a 'bot with a high spin rate, but it's very difficult to get it to spin and stop just where you want it. Your skill as a driver will be the determining factor. You also have to plan for unexpected situations where you aren't free to maneuver. Most builders armor-up all the way around.
A: Spinner killers are all about the scoop. For a great example, take a look at Jim Smentowski's middleweight actuated-scoop spinner killer Breaker Box. The scoop must start out at a very shallow angle - nearly horizontal - and curve up to around 60 degrees. Length and height are about equal, with a gentle and uniform curve. Jim's using 3/8" titanium for the scoop, with very heavy support arms. His scoop makes up almost half the weight of the 'bot! The simplest way to figure the surface area of a curved surface is to make a thin cardboard mock-up, then flatten it out and measure.
Another question about my spinner killer: do you think I should go with .25" S7 tool steel or 3/8" titanium 6Al-4V? I thought titanium would be better, but S7 tool steel is what impact teeth are made of, so it should be able to stop the spinners I guess. The tool steel would weigh about 3 pounds more for the size of my scoop, but would cost much, much less. What do you think?
A: Mark J. here: S7 tool steel is both hard and unyielding, which makes it perfect for transmitting energy from a rotary weapon to the target via small teeth. To resist the impact of spinning weapons you're looking for a material that can spread the force by deforming and then snapping back into position -- a property known as 'toughness'.
Although tough for a tool steel, S7 alloy is more brittle than titanium and in large sheet form may crack on heavy impact. You run the risk of a big weapon hit shattering the large plate like glass! If you want to use steel, consider a tough spring steel that can flex on impact, like EN47. Remember that you'll have to heat treat either metal after the scoop is assembled to obtain optimum performance, and this will add to your costs.
6Al-4V titanium is extremely tough and resilient. It will take enormous impact and come back for more. It's perfect for absorbing spinner attacks. It is expensive, but the experienced builders that use it wouldn't be spending their money if it weren't worth it.
A: Mark J. here: the conventional way to build a combat robot is to decide what the robot should do to give you a tactical advantage and then draw up a design for a robot that will do what you need. You've drawn up a design and now want to figure out what it will be able to do. I smell a train wreck.
A: I'm glad you're giving this project some thought. I have respect for builders that are willing to try something different. I did some research and found a lightweight 3-wheeled omnibot with a spinning undercutter blade weapon called Y-chromosome (archived) that fought at Battle Beach and BotBash. You might want to talk to the builders at Team Radicus.
Here are a few more things to consider:
A: The only active team I can think of is Zwolfpack Engineering. Their lightweight "1st Abe Lincoln on the Moon" has a successful implementation of Melty Brain. Note that the system got its name because thinking hard about how to get it to work causes such mental overload that it may actually melt your brain. Zwolfpack has obviously suffered significant cerebral damage as evidenced by the names they choose for their `bots.
The Zwolfpack website (www.zwolfpack.net) is not terribly helpful, and I don't have other contact info for them. You might try asking around at the RFL forum. My advice is to stay away from Melty Brain.
A: Search the Ask Aaron archives for 'hobbyweight', Peter. You'll find more than a dozen posts about motors, weaponry, radios, and battery capacity.
A: That depends on what you call a 'walker'. Shufflebots can be very fast -- Dave Hall's 'Drillzilla' claimed a top speed in excess of 30 MPH, but shufflebots are no longer considered to be 'true walkers' in the rules. In the British TV series 'Technogames' the walking sprint race winner 'Scuttle' covered the 25 meter course in just over 7 seconds, about a 7 MPH average speed. Scuttle doesn't qualify as a walker under the current rules either.
Building a true walking robot is very challenging. You might get some tips from looking at designs in Servo magazine.
A: I don't know of anyone currently building true walkers for combat. I'd suggest getting a copy of Servo magazine and looking thru the ads for walker kits. The makers of these kits may be able to supply parts and design ideas for your combat walker.
A: Instead of wheels, shufflebots have two or more long 'feet' on each side of the 'bot that are operated by crankshafts. Each 'foot' is lifted and set down again as the crankshaft turns to move it a little forward or back. The motion is bouncy and makes maneuvering tricky. Shufflebots once got a weight bonus as 'walkers', but a few years ago they changed the rules and shufflebots now don't get that extra weight.
A shufflebot requires a complex drivetrain and custom made parts to make a slower and less maneuverable 'bot than you'd have if you used wheels. Don't bother!
Note: Dear Aaron, the 2006 draft of RFL rules offer a weight bonus to non-wheeled robots including shufflers. [Ted J.]
Not true, Ted. Section 2 of the 'RFL 2006 rules' says, "There is no weight bonus for shufflers or other forms of locomotion which are predicated on rolling." Shufflebots are dead.
A: Mark J. here: I could use a little more info on what you're building! The selection of a proper bearing or bushing depends on how long the support needs to last, how precise the alignment needs to be, the type and magnitude of the force that will be applied, the speed of operation, and the depth of your wallet.
Since you're powering this mystery device with a servo, I'm guessing that the force and speed are both pretty low. Since it's in a combat robot, I'll assume it doesn't need to last forever and that extremely precise alignment is not an issue.
You can likely get away with just drilling an appropriately sized hole in a block of strong, slick plastic -- like UHMW polyethylene, polycarbonate, or nylon. If you need to absorb high shock loading, you might want to go with a bronze 'oilite' bushing. Oilite bushings are cheap, durable, and widely available in a variety of sizes.
A: Sounds like somebody wants me to do their homework for them.
An automobile gets better gas mileage when it travels slower, right? That's because friction and drag increase quickly with greater speed. It's much more efficient to move along at a slow and steady pace than to sprint forward and coast to a stop. A well designed mousetrap car can travel dozens of yards if it keeps speed under control.
Hard, large diameter wheels reduce rolling resistance, and when combined with a low gear ratio will reduce the torque available to accelerate the car and will keep speed down. A typical mousetrap car has one end of a thread wrapped around the drive axle, with the other end pulled by an extension bar from the mousetrap. The number of turns the rear axle makes while the mousetrap unwinds is the equivalent of a 'gear ratio'. A longer extension bar on the trap lowers the effective gear ratio.
Your goal is to keep the car just barely moving along for the entire time the trap unwinds. Tinker with the length of your trap bar extension to get a steady forward crawl -- lengthen it if you're going too fast, and shorten it if the car stalls.
Hey, this question isn't even about combat robots! Why am I answering it?
A: See the Wikipedia differential article.
A: Mark J. here: some machine shops just don't accept small one-off custom jobs, but a clear explanation of what you want and a friendly smile will improve your chances. Machine shop time isn't cheap -- do as much prep work as you can and listen to their questions and suggestions. Let them know that you appreciate their taking time to work with you.
A: Mark J. here: There are a variety of large-hole making devices that will fit in standard-size drill chucks. Here are some options:
A: You make something better by standing on the shoulders of giants.
A: Mark J. here: simple answer first: most hobbyweights I see are built around a hypothetical top speed of around 12 to 15 miles per hour. Hypothetical top speed is calculated by the formula:
Example: a 6000 RPM motor with a 6:1 gear reduction and a 12" circumference tire gives:
More complete answer: the hypothetical speed has little relation to the speed that your 'bot will actually attain in the arena. You also need to consider the acceleration of your 'bot within the allowable space. Two 'bots can have identical hypothetical top speeds, but the 'bot with the more powerful motor will accelerate much more quickly and will be much 'faster' in the arena.
Also think about the type of robot you're designing. A clampbot or flipper may not need the same speed and acceleration as a rammer or wedge.
For help with motor, gearing, tire, and battery selection, check the
Team Tentacle Torque & Amp-Hour Calculator. Be sure to investigate the 'Acceleration" button.
A: Mark J. here: in designing a combat robot, you have to think about how all the components of the machine will work together. A chassis design that would work well for one design could be a disaster in another design. Since I know nothing about your design, I can't comment on your frame.
You have a number of choices for a heavyweight 'bot. You can use welded tubular steel, bolted steel angle, interlocking aluminum flat panels, a stiffened composite pan, or bonded polycarbonate. You can integrate the armor into the chassis as a stressed component, or have a separate armor shell. Be sure to consider your skill level and experience in working with the materials involved, as well as your budget.
A: Mark J. here: That's over two pounds worth of motors in a six pound 'bot! How do you plan to use that much power in a small arena? By the time you add in batteries (lots of 'em for those motors), gearboxes, wheels, and a chassis you're not gonna have much weight left over for armor or a weapon. Keep your design elements in balance - go with smaller motors.
A: Mark J. here: Taps are available in diameters up to 4 inches, but they are expensive. You may also consider thread milling for large diameter holes. Unless you're going to be doing a lot of large diameter tapping, give the job to a machine shop.
A: Mark J. here: pocketing removes material from low-stress areas of a panel or component by milling away some of the thickness while leaving a border of thicker material. If properly done this results in reduced weight while retaining the majority of the strength of the original panel. The location and depth of pocketing requires extensive stress analysis of the component.
The exterior panels of combat robots don't really have any 'low-stress' areas. They can be exposed large forces from any angle and at any point. I do not recommend pocketing external 'bot panels -- although it looks really cool.
A: Building a successful combat robot requires experience in mechanical design, construction techniques, material properties, and control systems. See #2 for info on where to get help in these areas.
Robot builders use a variety of methods to design their robots. Some use computer aided design tools, some build detailed cardboard models, and some just design as they build. We like to sketch out the overall design, make a complete parts list - with prices and weights, and jump right in to the build. Our sketches wouldn't be much use to anyone else building a combat robot, and copying someone's exact design isn't as rewarding as designing your own 'bot, anyhow.
Keep your first 'bot simple and make sure the mechanical basics are well covered.
A: Combat robots don't have axle hooks. See web articles on mousetrap cars.
A: Technical question - Mark J. here: that depends on how many and what type of motors you use, the gearing, tire diameter, and driving style as well as the weapon motor type, how much you use it, and how heavy the spinning mass is.
Look at 'bots that have a similar set-up to the one you plan and use their experience to help you decide on a battery pack. You can also get some help from the
Team Tentacle Torque & Amp-Hour Calculator
which provides an estimate of required battery capacity based on motors and various design factors.
A: Hi, Nick! Since you're asking about windshield wiper motors, I'm guessing you're thinking about a hobbyweight or featherweight class robot? We built a hobbyweight with windshield wiper motors almost five years ago. Even though we were running the 12 volt motors at 24 volts, the gear reduction was so large that they were really slow! They were also very heavy for the power they provided. I'd stay away from them.
Keep your first 'bot simple. Wedges win more matches than 'bots with active weapons, so get some experience before you start showing off with fancy weapons. Cordless drill motors are fast, powerful, simple to mount, and pretty cheap. Fasten them down to a simple flat panel base, armor up, and bolt on a sturdy wedge. Spend some money to buy good speed controllers -- that's the one place you shouldn't scrimp. Search the archive for some other tips and book references. Best luck!
A: Try: www.shender4.com/thread_chart.htm for pilot and clearance hole sizes.
Once you have the hole, the tool used to put threads on the inside is called a 'tap'. The tool for putting threads on the outside of a rod is called a 'die'. You can purchase an inexpensive Tap and Die set, or you can purchase individual taps and dies at your local tool store. A brief guide to tapping holes with hand tools can be found here.
A: Mark J. here: Countersinking forms an angled cut-away around a hole for a flat-top fastener that leaves the fastener top flush with the surface to provide a smooth surface.
Counter boring forms a flat-bottomed recess around a hole to provide fastener clearance and/or offer a flat surface for the fastener on a curved, sloped, or irregular surface.
A: If you don't want to buy hubs, then spend the money for a mask so nobody will know who that guy was that had his wheels fall off. Read my post about hubs in the Ants, Beetles, and Fairies section.
A: Mark J. here: There are three broad categories of screws: wood, self-tapping, and machine. A 4-40 screw is a machine screw that is should be threaded into a pre-tapped hole. Drill a pilot hole with a #43 drill bit at low speed, then use a 4-40 tap to create the threads. Alternately, you may use self-tapping screws with Lexan. They will also require pilot holes, but will not require pre-tapping the threads. Cramming a machine screw into an unthreaded hole is a weak bodge - don't do it.
A: Mark J. here: Motor mount design depends on powertrain layout. If a large motor is being held in critical alignment for an open gear or chain reduction, it must be held very precisely with no wobble or the gear/chain system may fail. Such designs should secure both ends of the motor. Mounts for small motors with attached gearboxes (gearmotors) that do not rely on the mount for alignment of the gear reduction may allow or even encourage a little shock-absorbing 'give' in the mounting design and material.
A popular design for insect-class robots with small gearmotors is the wide circular clamp: a machined hole on a block of aluminum or plastic (UHMW polyethylene or Lexan) with a gap along one side that can be closed down with screws/bolts to clamp the gearmotor in place. The wider the clamp, the more secure the mounting. Remember, 'bots with exposed wheels put more strain on the mount.
I've also seen low-budget mounts made from wood blocks and steel automotive hose clamps that were surprisingly functional. You don't need a full machine shop to build a workable 'bot.
Mark J. here: They aren't thwackbots -- triangular 'bots with an omni wheel at each apex are called 'omnibots'. Yes, they can rotate, but the really cool thing is that by differentially powering the three wheels, they have the ability to move in any direction without turning -- that's called 'holonomic motion'. There's a cool video of a four-wheel holonomic omnibot (same principle as a 3-wheel version): holonomic at www.charmedlabs.com. An R/C omnibot requires a computerized transmitter with programmable mixing to properly do it's tricks.
Autonomous omnibots can be programmed to move (slowly) while spinning (slowly): Frisbee at www.charmedlabs.com, but doing it at variable high spin rates and variable directions under radio control is a REAL challenge. It's called 'Melty Brain', 'Tornado Drive' or 'Cyclone Drive' and many builders have spent years trying to get it to work. It requires on-board processors, motion sensors, sophisticated programming, and it still doesn't work reliably. Don't even try to cram all that into an antweight!
You need a 'hub' to connect a thin weapon to a small diameter shaft -- a precision machined connector that will hold the weapon in correct alignment and provide sufficient depth to allow a stable and snug fit onto the motor shaft. This hub will be the most highly stressed part of your weapon system, so don't try to bodge this.
Note that it's generally not a good idea to connect a weapon directly to a small motor. It is difficult to attach a hub securely enough to a small shaft to be able to transmit large weapon loads. Search the Ask Aaron archive for tips on belt drives that can give better weapon performance. Hubs and belt drives smaller than 3mm bore are hard to find.
A: Thanks!
Omnibots are way cool to watch! The can move forward and back and turn like a regular 'bot, but they can also move sideways without turning and even rotate while moving in a straight line! Check out the videos of the flame throwing superheavyweight omnibot Alcoholic Stepfather.
Omnibots may have three or four wheels. Each wheel needs it's own speed controller and dedicated radio channel. Check the earlier post on omnibots for more videos, and search the web for 'mecanum'. I think you'll pick up the idea after you see a few examples.
You actually have two challenges in running an omnibot: building the drivetrain, and programming the R/C transmitter to make the 'bot controllable. You'll need a computerized R/C system with multiple user programmable mixes or some double-fancy helicopter swashplate settings. If you get the 'bot built and need help with the programming, write back and we'll put our heads together!
Q: Could I make an omni-bot in the 'Robot Arena' simulation game?
A: Hmmm... There aren't any omniwheels or mecanum wheels available in the Robot Arena parts box, and the control options don't offer channel mixing for proper omnibot control. If you did manage to cobble one together, it would be a poor representation of the real thing.
A: Small 'bots usually have a skid of slick plastic -- like polyethylene. Bigger 'bots may have a ball caster or an omni wheel. Our heavyweight 'bot 'The Gap' has a wide roller machined out of Teflon in the front so it can slide sideways and roll forward.
A: Tech question, Mark J. here: the smaller timing belts (MXL series) are rated up to 20,000 RPM, and can transmit as much as 400 watts of power. They're much more effective at power transmission than other belt types. For a full engineering summary of timing belt selection and performance, see: Roymech Timing Belts.
A: Tech question, Mark J. here: The wider the belt, the more power it can transmit. Wider belts also stay in place a little better.
A: There are plenty of websites that give detailed information on autonomous sumo 'bots -- try
Dave's Sumo Robot Project Page for a start.
A: A tank-steer 'bot steers the same way no matter how many wheels it has: all the drive wheels on one side of the 'bot turn at a different speed and/or direction than the wheels on the other side. Robots with four or more wheels drag their wheels sideways a bit as they turn. That takes a little more power, but it works just fine.
A: If tracks were a real advantage, lots of winning robots would use them. They don't! I'd go with wheels.
Wheel/tire selection depends on many design factors with which the wheels will have to fit. If your wheels will be exposed to attack, use a solid or foam-filled tire that can't go flat.
For general use, I like the Colson wheels. They have been used on combat robots for many years. They're pretty light, durable, have good traction on arena floors, and are inexpensive to replace when damaged. Team Delta sells Colson wheels in different sizes and will even make wheel hubs to fit your drive shaft.
A: Thanks! How long it takes to build a robot depends on how complicated the design is and how much experience you have working with the tools and materials you need. Getting some friends who have skills you don't have will help a lot! I've seen experienced teams build a heavyweight 'bot in a week, but our larger 'bots take us about two months to put together. That includes time to design, get parts, build, and test.
A: Thanks, Coleman! Before you start building a 'bot there are a few things to take care of. First, read the rules for the competition you plan to enter very carefully. You don't want to build your 'bot only to find out you aren't legal for the competition! Next, take time to find as many websites from competitors who have been to competitions like the one you want to enter. Read everything they have to say. Finally, draw up a design that you can actually build. The coolest design won't do you any good if you don't have the skills (or money) to build it.
The words 'best' and 'cheap' don't go together in robot building -- especially with speed controllers. You don't want cheap parts that will put you out of the competition if they fail. See what other builders that have been successful use in their 'bots. It won't be cheap speed controllers! For reliable parts, try Team Delta (www.teamdelta.com), and the marketplace at www.robotcombat.com.
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