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Privacy Policy
Even small combat robots can be dangerous! Learn proper construction and safety techniques before attempting to build and operate a combat robot. Do not operate combat robots without proper safeguards.
A Simple Indicator
Q: Hi, I want a power indicator for my combat bot, but I am not sure which one to use, can you suggest some good LEDs or strobe lights? Also while researching on protective cases for leds in order to not damage the LED during battles, I found polycarbonate cases for LEDs meet my needs but I am not sure where to get the stuff? Can you help me with this?
A: [Mark J.] The requirement for a power indicator is typically something similar to the SPARC ruleset section 8.6:
If you want a discrete power LED you do not need a protective case, just mount it out of the way.
You can certainly construct your own indicator light but the components (plug, cable, resistor, LED) are difficult to purchase in small quantities and some calculation is needed to select the correct resistor value. Itgresa.com offers Robot Power LEDs with a cable that can be plugged into an unused port on your receiver. Six colors, easy to mount, wide voltage range, cheap. Buy a couple and keep one as a spare.
An Italian Dinner
Q: Greetings! I hope you're doing well, I did a bit of searching and wasn't able to find anything so I figured I'd go ahead and ask, do you have any tips for creating wiring harnesses to not be spaghetti messes / hard to cram into bots? It's a habit I've had for years now that I finally want to take the time to address to work on overall build practice and cleanliness. Any advice is greatly appreciated!
A: [Mark J.] Thank you for your kind greeting. All is well for us here at the Run Amok homestead, and I hope the same for you.
Until recently my general advice on fighting spaghetti was to get your soldering skills up to where you weren't afraid to cut all those wires down to their shortest possible lengths. That helped clutter and also saved a surprising amount of weight.
But now you can take that up another level. Just 'Cuz Robotics produces a wide range of custom power distribution boards for small robots that range from simple connector organizers to full "motherboards" with BECs, power switches, power lights, servo support, and receiver integration. If you crave clean and neat you'll find all you need there.
Fishing for Bolt Heads
Q: Magnets: specifically, electromagnets
from what I know, there are no rules against using electromagnets as part of your weapon, IF it doesn't interfere with opponents' electronics. would it be possible to have a toggleble electromagnet on a lifter arm, and be able to have a more secure hold? and then turn off when over hazards. I know very little about magnets, and wondering if you had any advice.
Thanks!
A: [Mark J.] Let's get you a little magnet knowledge. Here's a 9 minute video that will give you a crash course in magnetism. Go ahead and watch it -- come right back.
Great! I just needed a few minutes to make a fresh pot of coffee. Where were we? Magnets? Right.
Magnets in combat robotics have a long history of being difficult to control well enough to get the expected and desired results. On problem is that magnetic attraction decreases quite rapidly with distance. A magnet that has 50 pounds of attractive force when directly in contact with a thick steel surface might have only 5% of that power from half an inch away. You can play around with this Magnet Pull Force Calculator to see this effect. The calculator is for permanent magnets, but electromagnets have the same properties.
For the electromagnet to be useful it needs to be VERY close (direct contact is best) to a magnetic surface.
Hero of the Revolution
Q: HHEEEEELLLLLPPPP!!!!!!! I signed up for Australian Robowars thinking it was a protest against Taco Bell... BUT IT WASN'T!! I’ve never seen a robot fight before! My friend told me to come here and ask what I should do?!?!?!?!?!?!- Mistro Deb Hamper
A: [Mark J.] Make yourself a nice cup of herbal tea and take a deep breath. I'll get you thru this.
Just because Robowars didn't think they were a protest doesn't mean they couldn't become one. Pop out and buy yourself an R/C trailer truck, paint "Taco Bell is Murder" on the side, and stuff it full of those little Taco Bell hot sauce packets. Go back to the robot fight and toss the truck into the arena. Some nasty spinner robot will vaporize the truck and coat the inside of the arena with bloody red hot sauce and burst plastic packets. Nobody there will ever go to Taco Bell again and you will be a hero of the revolution.
Q: Hey Mark, just wanted to let you know my video editor said she was having trouble relating to combat robots, so I sent her here. She has a history of blowing up in peoples faces (you should see the credits of the IceyBots pilot episode!) so I told her to keep it down a notch. She goes by "Mistro Deb Hamper", by the way. - sincerely, Iceywave
A: No problem, Icey. She totally took your advice and was entirely calm and collected by the time she got here. I think I solved her problem. Thanks for the referral.
You wouldn't happen to have an actual combat robot question, would you?
Q: In response to your question, yes I do!
I’ve heard from various sources that in sometime in 1998 (during the severe dry spell of American combat robotics) an obscure event was held under a bridge(?) that included the likes of S.L.A.M., Ginsu, and a few others. Do you have any additional information on this?
A: Someone as interested in the early days of combat robotics as you are really should own a copy of "Gearheads: The Turbulent Rise of Robotic Sports" by Brad Stone. You can buy a nice used copy for less than $8 shipped.
In Gearheads, Newsweek technology correspondent Brad Stone examines the history of robotic sports, from their cultish early years at universities and sci-fi conventions to today's televised extravaganzas -- and the turmoil that threatened the whole enterprise almost from the beginning.
By turns a lively historical narrative, a legal thriller, and an exploration of a cultural and technological phenomenon, Gearheads is a funny and fascinating look at the sport of the future today.
Three Designs and a Bowknot
Q: I was wondering if any of these designs were viable for a combat robot. A: [Mark J.] Wow! Click Here for a full analysis of your designs. Q: Will you also give me step by step instructions on how to bind my model airplane to its transmitter? Thank You!
A: Sure.
Tossing the Caber
Q: I am designing an antweight (1lb) brushless lifter that I would like to be able to throw opponents (not into the ceiling or anything). I am planning to use a Flash Hobby 1204 2500Kv motor, connected to an 135:1 planetary gearbox. The lifting arm is 6.22in long, and the robot will be powered by an 11.4V LiHV battery. At 211.11 rpm, do you think that this would be too fast? Would it provide enough torque to not be too slow under load? (The manufacturer does not give stall torque.) Also, I know that brushless motor torque depends on the ESC, so I am planning to use AM32. Would you say that this is necessary? Thanks!
A: [Mark J.] The unsensored brushless motors and ESCs we use to build small robots are borrowed from the model aircraft hobby industry. They are designed to spin-up lightweight propellers to about 80% of their free RPM and run at that speed for several minutes. That task is far different from being bogged down against a heavy load right at zero RPM and being asked to develop enough torque to accelerate that load upward against gravity fast enough to toss it into the air. It's like asking a chicken to toss the caber -- they aren't made for it.
Add to this handicap your choice of a brushless motor that weighs 6 grams 0.21 ounce and puts out about 50 peak watts of power maybe 10 watts at low RPM on a 4S lipo and you're running 3S. A typical antweight brushless spinner weapon motor that has a couple seconds to come up to speed against its load weighs perhaps 30 grams and pumps out more than 200 watts of power (see Brushless Motor Selection). With that tiny motor you're not going to be tossing opponents into the air, and the strain of moderately quick lifts may drive the motor into thermal failure.
As noted in FAQ #17 Ask Aaron is not a free engineering service - I'm not going to model the performance of your weapon for you. However, we do supply design tools like the Team Run Amok Electric Hammer Spreadsheet that can be used to model flipper designs. A lifter/flipper is effectively an overhead hammer with a very heavy hammer head (your opponent's 'bot) that traverses a small arc.
I brought up the Electric Hammer Spreadsheet and plugged in the numbers for your flipper. Rather than make guesses about the torque curve of that tiny brushless motor I put in the specs for a brushed RF-370 motor that has comparable output wattage. The brushed motor has low-speed torque better suited to lifter duty than the brushless motor, so calculated performance will be a 'best case' model. I ran multiple simulations to determine the optimum gear reduction for the RF-370 motor:
Walking Distance
Q: Will you be attending any competitions in the next few months? (Of interest specifically to me is Robogames.) And if you've been to Robogames in the past whether you have any recommendations of places to check out while in San Jose. [Ohio-ish]
A: [Mark J.] There are no events on our calendar, but Team Run Amok has spent some time in San Jose.
Mathematically...
Q: mathematically (not realistically, I do not want to know if it is realistic or not, just want to know your take) what is the best combat robot design for a combat robot, with a combat robot being 1, 100, or 250 lbs, and best is the greatest advantage of the following:
A: [Mark J.] Mathematically:
The Center Isn't Off
Q: I am trying to make a combat robot for the first time, and with the right joystick in the center resting position it reads as half power and turns the motor on. I have looked across the internet on how to make the resting position read as off and if I go down the motor reverses and forward it goes forward. I’m using the fs-i6s transmitter and a TOYTENSI 20A esc. [Social Media]
A: [Mark J.] Your radio is not the problem - the problem is your ESC.
All the TOYTENSI ESCs I can find are for model airplanes. An airplane ESC is uni-directional with the zero-throttle stick position all the way down. Some aircraft ESCs can be switched to forward/reverse response with center off, but the functions available on the TOYTENSI programming card do not include this option. You need a different ESC.
To keep things simple search for an ESC that specifies 'bidirectional' or 'forward/reverse', like the Repeat Robotics Brushless Drive ESC. ESCs that say 'thrust reversing' are different and will not give you the stick response you're seeking.
Just Point the Front Wheels
Q: With car-steering being obsolete in combat robotics for the past two decades, would you say there are any advantages to using it (as opposed to tank steering) in modern times?
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.
Anywhere But There
Q: I am part of a team that is brand new to combat robotics. We just completed and tested our very first robot and are ready to fight in our first tournament. Got any tips on how to find the right competition for our skill level? Thanks.
A: [Mark J.] The typical order of events to get into combat robotics is:
The IP address attached to your question submittal has ties to servers in Maryland, California, Florida, New Jersey, and maybe other states -- so I can't provide regional advice on beginner friendly events. You aren't likely to find more than a couple of events within reasonable traveling distance, so your list of options will not be long. There are two websites that list upcoming events in North America:
Plastic Traction
Q: dont know if you have any experience in the plastic ant category, but two things
first, what would be the best infill for high-impact hits with PLA plus secondly, what would be your thoughts on our current design, and issues that you can spot (yes I know it needs a top-plate, and there are no screws) Ive had problems in the past with traction, so that's mainly what I'm looking for. [Close to Raleigh, NC]
A: [Mark J.] It's a very pretty design, isn't it.
First question: I claim no specific knowledge in 3D printing PLA, but I do know that more infill equals more strength. How much strength you need depends on your design and expected impact forces. There are two groups on Facebook that might provide more useful responses:
Take a look at successful two-wheeled insect spinnerbots. They have the motors as far forward in the chassis as reasonably possible, with battery and electronics hanging out behind to shift the 'bot center of gravity closer to the wheels. Unfortunately, unless you switch to much larger wheels you don't have room for much rear overhang. This is a serious flaw.
The rule-of thumb for two-wheel 'bots is to put ~65% of the robot weight on the wheels. More than that may let the 'bot raise the nose off the floor under acceleration -- see Section 2.2.7 of the RioBotz Combot Tutorial. Given the wheel placement on your design I'm guessing that less than 50% of the weight is on the wheels, which will give both poor traction and poor turning response. No amount of latex or silicon rubber coating on the tires is gonna help.
Q: this was our earlier design, and it had the most abysmal center of gravity possible, which was over the forks, we are currently using 2.25 inch wheels, what do you thing would be the best size option?
A: You're not trying to tell me that the little circle marker on the current design render is the calculated center of gravity, are you? I'm entirely not buying that. Nope. No way.
From a practical standpoint, I'm really not sure your design is salvageable. That very large and heavy spinner hangs so far out in front that it's going to take a lot of mass out behind the wheels to make the drive work:
As I said at the start, it's a pretty design -- I just don't think it's practical.
Q: for the forks, would having what basically is a plastic popsicle stick going perpendicular to the forks help us with that issue [of being stuck on its side]?
A: I'm sure you have an image in your mind as to where that stick would be placed and how long it might be, but my psychic abilities are quite limited these days.
Hitting a Wedgeless Brick
Q: My team just competed at NHRL over the weekend and we have a question about the results of our hits. In the attached clip we hit 'Beast' twice with the big beater bar on 'ARES' only to spin them backwards. What’s the most probable reason for ARES recoiling backwards instead of launching Beast? Could this be a result of rake angle (0 degrees), too much bite, or something else? [Cambridge, Massachusetts]
A: [Mark J.] It is my considered opinion that this is a clear case of something else. Here's the full 3-second clip: ARES and Beast at NHRL.
Both of the hits in the clip have your beater bar impacting hard vertical surfaces on the front corners of the wedgeless brick Beast. Nothing to grab, and no downward impact vector to press down onto your opponent as a multiplier for the poor steel-on-steel coefficient of friction. The hits are just gonna slide up the steel wall and tap the brick and ARES apart.
Things that would help:
Worth the Trouble?
Q: I was desoldering a FingerTech Silver Spark and the little metal tab that I solder to the wire to broke off. I tried adding some solder to the remaining visible metal but its not sticking well. Is there anything I can do to save it or is the motor just screwed?
A: [Mark J.] The photo shows what the inside of the Silver Spark motor 'endbell' looks like. The nylon that the metal tab disappears into goes down a fair distance and becomes the support for a motor brush. If you're REALLY determined to save the motor, you can carve away some of the nylon to reveal more of the brass tab, then use a good quality soldering flux (I use Rubyfluid Soldering Paste) to tin the exposed brass. It will then be easy to attach the power wire.
If your soldering skills are not good, I'd suggest buying a new Silver Spark and saving the gearbox as a spare.
Fifty-Six Megabytes
Q: I had a video planned to celebrate Run Amok's championship anniversary, but it said "only 8 megabytes may be sent at a time". The video file is 56 megabytes, and I can’t decrease the file size to the desired amount without a severe decrease in quality that I’m not willing to sacrifice. Hopefully I can post it to YouTube sometime.
Happy Anniversary! -sincerely, Iceywave ☆ A: [Mark J.] Thanks, Icey! We can't let a few megabytes come between friends. Let's try this: There, that wasn't so hard. Let's see what we've got here... Whoa, thanks, Icey! I've embedded your video recreation of the Robotica 'Fight to the Finish' below, and tossed a copy onto my YouTube channel.
Reply: I'm happy to hear you enjoyed my video! Turns out the file I sent was actually 59 megabytes. The original recording was 56 mbs, but I had to put it through some editing software to add fade in/fade out on the video. The models of Juggerbot and Ram Force were built by myself, in case you were wondering. I also have a big surprise coming April 1st, so be prepared! Bang Bang Bang Thud - Again
Q: Hi there, I've been playing around with the hammer calculator v2.2 spreadsheet and believe I've found two errors in the methodology that throw off the results by a very large amount:
Since this is a Q/A, any errors in my math/methodology? Cheers, Joseph Duchesne
A: [Mark J.] I appreciate your effort to "keep me honest" by digging through the code in my Hammer Spreadsheet, Joseph. Few people make that effort.
Given that I authored the spreadsheet eight years ago, my working memory of the calculation details is not terribly good. I would appreciate corrections to my comments below should your recent review prove them to be in error.
Flavor #1: Multiply the weight of of an object in newtons by the height the object is lifted to get the unit of work: a newton‑meter (N‑m). In this context 1 N‑m is a measure of energy equal to 1 joule.
Flavor #2: When measuring torque, a force of 1 newton applied at a radial distance of 1 meter equals a newton-meter (N‑m). In this context a N‑m is a measure of force rather than energy. Equating this flavor of N‑m to joules is fallacious.
We could resolve any confusion on this issue by building a miniature "Test Your Strength" carnival machine for a robot hammer weapon to strike. The height reached by the known weight could be quickly translated into a measured value for the hammer energy. I'm betting on my calculations.
Now please pardon me, I must take my medication and lay down for a bit. Q: Thanks for pointing me in the right direction with regard to torque vs. energy. I got tripped up since most times when the units check out, the physics does too. The missing part was that the actual unit of torque is best described as Joules/radian, but since radians are unitless, this misleadingly appears to just be Joules. A: It's a trap. Using the same units for two different measures will cause reasonable minds to make the same assumption you made. The usage really should be clarified and/or replaced. Q: Intuitively, I still feel like there would be a slightly harder hit if the motor torque is applied beyond impact, vs. becoming disconnected the instant before impact, but this is likely a very small fraction of the additional system energy I had been hoping for.
A: Yes, small.
A: You're killing me, Joseph. Why would I have written that nice column of equations and then failed to spread them across the full swing? Now I have to dig thru the code of an eight-year-old spreadsheet to look for the place where I dropped that thread...
I now recall the full reason I had front-loaded the gravitational correction in the model. From a standstill, a hammer with a 180 degree swing may spend half of the total strike time pulling up thru the first 45 degrees of arc where the retardation by gravity is greatest. The last 45 degrees where gravity is assisting the swing flashes by in about 15% of the swing time.
I've withdrawn beta version 2.5 of the spreadsheet. Version 2.2 does slightly understate the theoretical performance of an electric hammer, but it is closer to real-world values than is the flawed version 2.5.
Unspecified
Q: I know what I said about not being back until April, but I just remembered something. I heard a rumor that a specified team was asked to leave a specified event because they committed a specified offense. Is that true?
-sincerely, Iceywave☆
A: [Mark J.] I have removed the names of the team, event, and offense from your question. If I can neither confirm or quash a rumor of this nature from personal knowledge I don't care to spread it. Here is what I can tell you, based on reliable sources:
Just Keep Fighting
Q: Hi, when building battle bots which temperature sensors/ impact sensors do you recommend using? [Parts Unknown]
A: [Mark J.] It is the nature of combat robotics to push components well beyond their design limits.
Q: how can robots help us deal better with hurricanes and why? [Ontario, California] A: [Aaron] Few people in Nebraska are threatened by hurricanes, so send a swarm of killer robots into low Atlantic and gulf coastal areas to drive the puny human inhabitants toward Nebraska. Problem solved. Robot haiku:
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