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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: Mark J. The description of your robot is quite sparse. You say it is a grabber, but only mention two metal forks, a metal box, and an unspecified number of wheels. Is there a servo powered clamp? I'm imagining a design something like 'Jawbreaker' from 'Robotica' (pictured below).
Reply: Thank you for your feedback! Here is a sketch of my robot:
A: The render helps. Your design has very little weight on your drive wheels. When you add a good chunk of your opponent's weight onto the front forks you're going to have very little traction to push your opponent around and real difficulty in executing a turn. I would suggest smaller diameter wheels moved well forward so that an opponent clamped above them could add weight and improve traction. You might need to extend the forks upward to keep your trapped opponent away from the wheels if the new wheels extend too high. That should give you enough maneuvering control to set them right on the pit edge and drop them in.
I'd also add a rubber tip to the "grabber". Your motor is unlikely to have enough power to get that sharp point to dig in and hold.
Reply: According to SPARC, if the robots are stuck together when entering a pit they will be separated and taken back to the arena. If I am still clamping the robot on my dustpan will the count as us being stuck together?
A: There are two paragraphs in the SPARC Match Rules covering this situation. The first says whoever goes in first loses:
Should the motor be mounted on oval screw holes such that it can be slid back and forth to determine the perfect tension?
Timing belts have effectively zero 'stretch' and brushless outrunner motors are not designed for lateral loading on their cans. This combination leaves precious little distance between "too loose" and "can deformation destroys motor". Adding or subtracting a single tooth changes the circumference of an XL belt by 0.20", which is far too coarse an adjustment for a friction-only belt drive.
The preferred method of getting the tension right is to gather the weapon components (hub/motor/belt) and mock up the system on your workbench. Snug it up, measure the distance between hub center and motor shaft center, and transfer that distance to your weapon mount CAD.
Yes, do use elongated holes for motor mounting to get your final adjustment after testing. I add hot-glue to fill in the elongated holes once the screw positions are set to prevent unexpected tension failure if the screws loosen.
A: Mark J. For best traction you want as much weight on the drive wheels as possible, but leaving too little weight on the front of your 'bot will allow it lift up off the arena floor under acceleration and make it vulnerable to attack. Designing for 65% of the robot weight on the drive wheels gives good traction and leaves enough front weight in most cases.
Note 2 - Magnet downforce may be used to correct traction and lift problems in a steel-floored arena. Combined gravity and magnetic weight of 65% on the drive wheels will still be a good starting point.
A few general comments:
A: Mark J. I'm not a big fan of this approach to weapon belt drive.
A: Mark J. Builders who regularly use a 3D printer get that method stuck in their head.
- Abraham Maslow, Psychologist
3D printers have a large up-front cost in terms of both skills and expense. Once you have paid that price the printer becomes a quick and effective tool. But if you have not paid that price it is more effective to use techniques and skills with which you are comfortable. You can build a simple robot simply by gathering compatible components, bolting them down to a stiff baseplate, and adding protective structures and offensive capability as you see fit.
I'll also point out that there are combat robot kits -- with or without a chassis -- that allow you to quickly construct a functional combat robot you may later modify as you see fit.
Could you give me some tips on how to make it balance better? (Also the weapon bar itself is balanced.)
Cheers! [Eaton, England]
The spinner bars for 'Icewave', 'Moros', and 'Bloodsport' are all precisely horizontal -- the rotational axis of the weapon remains pointing straight up when the robot turns. You have elected to place "...a screw in the back to put the blade at an angle." That angle causes the direction the weapon axis points to change when the robot turns. Combined with the huge rotational inertia of your weapon this causes a strong gyroscopic reaction, which raises one side of the 'bot, which then causes additional changes in the weapon axis, which then... you get the idea. This is why you don't see angled horizontal spinners.
There is no fix other than tilting the spinner axis back upright and making sure it stays like that. 'Bloodsport' and 'Icewave' are four-wheeled chassis to help keep their blades 'flat' while 'Moros' is two-wheeled but has the center of mass well back toward the trailing rear skid for stability.
Yes, setting your bar fully horizontal raises the weapon up too high to be terribly useful. Call it a rookie mistake. Do not be tempted to 'droop' the impactor end of the bar -- that causes a different type of instability.
A: Mark J. Our insects all fought before video was easy. The only footage runs in my head, and you don't want to go in there.
Q: 'Ramfire 100' won [the heavyweight class at the] 1994 US Robot Wars, then fell off Earth as far as I know. Do you know if ANYTHING else happened to it? [Lehi, Utah]
A: Mark J. Michael Sorenson's 'Ramfire 100' fought two matches at the 1994 US Robot Wars and won them both to become the heavyweight champion. Depressed that there were no more opponents to defeat, 'Ramfire 100' made its way to the center of the Golden Gate Bridge and leapt off - only to land on the deck of a freighter bound for Finland. After hitching a ride into Helsinki, 'Ramfire 100' worked as a forklift in a paper mill for several years and saved every penny until it had enough money to open a small cigar shop. It married a lovely girl named Helmi and had four children: a girl, two boys, and a fax machine. The family is doing well.
See also: Aaron's Madlibs.
Q: What about 'Chrome Fly'?
A: Oh, that's completely different! Embarrassed to learn that its direct-drive spinner weapons (that work pretty well in 1-pound robots) instantly self-destruct in the 250-pound class, 'Chrome Fly' heads home from the 2016 BattleBots tournament but makes a left turn off I-15 at Provo and drives west until its hat floats. It sank into the deepest part of the Great Salt Lake, which isn't all that deep. The end.
- sincerely, Iceywave
A: Mark J. I'm quite proud of 'Rat Amok' -- she is a one-of-a-kind antweight that won her first tournament and was later victorious at the "King of Robotica" match between myself and season two champion Mike Konshak with a clean OOTA ejection. Her one-shot weapon struck fear into her opponents, and the suspense of "when will it fire?" added much to the drama of her matches.
A 'snail cam' mechanism is quite bulky due to the large spiral cam. It would be difficult to translate the linear motion of the cam follower into a 180 degree rat trap reset. I suspect this is why no one has attempted a snail cam version of 'Rat Amok' -- but your question got me thinking...
I just now took Rat Amok off the shelf and measured the torque required for a reset against the torsion springs. A full 180 degree reset requires an initial torque at the axle of 12 kg-cm that rises to 29 kg-cm at the end. That is well within the capacity of high-torque R/C servos that weigh about 2 ounces and have up to 270 degrees of motion.
Rather than a snail cam, I believe that the 'Servo Latch' (fourth of four designs on our Spring Flipper Designs page) would be more easily modified to reset the trap, latch it, and trigger the release. Might be fun!
A: Mark J. I'll guess that 'the math' referred to here is the the Square-Cube Law which points out that directly upscaling an optimized design requires disproportionally greater mass to be allotted to structural components, which leaves less mass available for things like weapons. But I think the poster has it backwards -- smaller robots require less proportional mass for structure which leaves more mass available for weaponry.
The chart below is from our Spinner Weapon FAQ. It shows typical spinner weapon motor weight as a percentage of robot weight for 1-pound thru 220-pound robots. A typical 60-pound lightweight weapon motor weighs about 30% greater per pound of robot than does a typical heavyweight weapon motor.
There are good reasons multi-bots aren't generally effective, but a reduction in the total available weapon power of a multibot swarm compared to a single heavier robot is not one of them.
However: If you're going to toss four 60-pound robots into an arena with a 250-pound robot, you'd best build those lightweights with thicker armor than they would need when facing robots of their own weight. I figure the added armor mass will just about negate the weapon weight bonus from the square-cube law.
A: Mark J. The BTS7960 motor drivers are inexpensive and claim a continuous bi-directional output of 43 amps at up to 27 volts. They are a little bulky, but appealing for controlling brushed motors in intermediate weight combat robots.
The problem is that the BTS7960 is designed to be controlled by an Arduino microcontroller board rather than directly by R/C receiver output. There are seperate input pins for forward and reverse motor rotation, and each pin expects a full 0-100% duty cycle PWM signal. The FS-i6 just can't manage that and still provide single-stick control -- but I know a trick.
It just happens that the circuit board in an analog servo takes standard receiver output and splits it into the two PWM signals the BTS7960 is looking for. You'll need a couple old servos and a 5 volt power source:
Below is my circuit diagram with an inset showing the details of the input pin wiring.
An explanation of why this trick works gets technical. If you want the details write back -- if not just be glad it works.
Twelve Hours Later...
Great news!!! I've just got drafted to a team in Wisconsin! They don't have bench warmers so I won't be needing that radiator anymore.
- sorry not sorry, CRAIGYBOT [Not Wisconsin]
A: Mark J. Our most popular pages vary a bit over time, but in a typical month these are the top five runamok.tech combat robot pages:
On any given day one of the fan-oriented pages like The Historic Tournament Trees or The Combat Robot Hall of Fame may get a mention on social media and rocket briefly to the top of the list, but the technical pages are reliably found at the top.
My local competition recently added a multibot bonus mirroring the one found in NHRL, and I plan on competing with a control bot. Assuming competently designed, built and driven 'Bots on both sides, I can't think of a way to deal with them whether or not they are themselves control bots or have some sort of weapon.
A: Mark J. I had no idea that there were combat robot events in your country. I found photos from the April event that showed a nice arena, good attendance, and some interesting competitors. Congratulations.
It kinda bites to be a control 'bot under the current rulesets. Not all design challenges have solutions:
A: Mark J. I like the sound of this!
I'll assume we're talking about thin sheets of PLA to be cut/folded/assembled. While this could certainly work I'm personally very fond of cardboard as a construction material.
You might get a few ideas from this video: Build a Cereal Box Combat Robot!
A: Mark J. I reviewed the fight between 'Atomic Bomb' and 'Princess of Wales' (Clash Bots Videos Playlist) to take a look at the flipper cord you mention.
For some reason I suddenly want a bucket of KFC.
The simplest pneumatic flipper systems apply force to extend the ram cylinder, but must rely on gravity to return the flipper to its retracted position. It is common practice with such systems to add an elastic bungee cord to retract the flipper should the robot be in an awkward position where gravity will not suffice.
The cord does not strengthen the flipping action - it actually creates a relatively small force counter to the primary motion. The benefit is that the bungee may be able to reset the flipper to allow self-righting where the 'bot might otherwise be stuck.
Q: My design for an antweight full body spinner is very tight on space. I don't have room for regular gearmotors, even the little N10 size, and I can't find any right angle gearboxes small enough and fast enough to work.
Are there any alternative drive methods that might work in such a small space? [Social Media]
A: Mark J. I dug thru the Ask Aaron Archives and found a post from 2016 that described a couple unconventional combat robot drivetrains that require no gears, pulleys, or sprockets:
Tiny wheels If direct-drive for a normal sized wheel isn't practical, how about a really tiny wheel? Mount a very small wheel to the motor shaft and mount the motor at an angle to put the wheel in contact with the floor. Unconventional, but a successful antweight full-body spinner used this method as a space and weight-saving measure. The 'wheels' could be something as simple as a small plumbing washer, a short length of small diameter rubber tubing, or even a few layers of electrical tape wound around the shaft. They won't last long, but they're easy to replace.
A: Mark J.
You didn't hear quite right. It wasn't BattleBots, but a combat robots show on The Science Channel did piece together a fake tournament by cherry-picking fights from an actual tournament.
Here is what Aaron wrote about it at the time:
The tournament tree shown repeatedly during the "Killer Robots" show was a fabrication that stitched together matches from the preliminary round, the losers bracket, and the main bracket of the double-elimination tournament to make up a fictional tournament that greatly distorted the actual event. Why did they lie to the audience?
As a competitor in the 2011 robogames, I understood why they would choose to portray the matches as single elimination. The producers explained to us that they thought the double elimination system was too hard to explain to the public. I agree: it was hard enough for us competitors to figure out who we would be fighting next. I see why you are frustrated, but sometimes profit and popularity are more important than accuracy.
A: Mark J. here: I sympathize with the desire to avoid the complexity of presenting a double-elimination tournament, but I don't believe that putting profit or popularity in front of truth is an acceptable option.
Watch the Full 'Killer Robots: Robogames 2011' video.
Compare the Killer Robots and the Robogames Tournament Trees.
The producers of 'Killer Robots' went out of their way to mislead the viewers. Examples from their fictional tournament tree:
Q: The 'Sports Should Be Credible' post reminds me of something. There was a rumor that the 'USA vs the World' special from BattleBots 2018 was rigged. The rumor originated from The Robot Combat Iceberg Version 3 [on Reddit, 2021]. One commenter [u/murdock129] claimed that the Kraken vs Red Devil fight was just an exhibition match completely unrelated to the event. They also said that there were unaired fights [that together] would've changed the result to 3-4 in favor of 'The World'. They didn’t leave any links backing up their claims, so I was wondering if you had more info.
- sincerely, Iceywave
A: The comment at the end of my exchange with the RoboGames competitor where I say, "BattleBots never re-arranged a sequence of fights to deliberately distort the audience perception of the tournament" was true at the time I wrote it in 2011. The original Comedy Central version of Battlebots was an actual open-to-anyone combat robot tournament with hundreds of robots in multiple weight classes. That has changed.
See my archived editorial post: BattleBots is Not a Televised Sports Tournament.
'Ask Aaron' has a long history of receiving requests for very specific recommendations on materials or components that provide far too little information for us to give a useful answer. We needed a name for this type of question and a way to explain our problem in answering. In 2010 we published a webpage titled "The Hamburger is Bad" that uses a fictional exchange of questions and answers about whether a 1/4 pound hamburger is good to depict the problem. The meme caught on in the combat robot community.
So, "The Hamburger is Bad" is not so much a rule as a shorthand request to provide adequate information when asking a question.
A: Mark J. You came to the right place.
- sincerely, Iceywave
This one was on me -- the link is now correct.
Mark J. Rodger the Web Gerbil's new contract gives him the entire month of May off. Rodger used to negotiate his own contract, but this year a hard-nosed red tree squirrel claiming to be his agent showed up. The squirrel turned out to be a skilled negotiator. In addition to a full month off I had to throw in two pounds of pecans, a gym membership, and bottled water for his water bottle.
Q: Build: Repeat Robotics 16mm Brushed Planetary Motors MK2 and a Scorpion Nano 2.1 brushed ESC. When starting moving one motor stops. After a restart, the motor works again. I've switched out the Scorpion Nano, the motor, and the fully charged 3S battery. The issue remains.
Looking for some problem solving tips. [Social Media]
A: Mark J. OK -- it isn't the motor, it isn't the ESC, and it isn't the battery. Tell me about your radio system.
Comment: Ooo, good call. I'll switch to another Rx and Tx.
A: Mark J. I've never actually tried, but it shouldn't be very hard. You can only go where the rails go, so just give it a little throttle and toot the whistle once in a while.
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]
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Remembering Aaron Joerger, 1991 - 2013
The 'Ask Aaron' project was important to Aaron, and I continue the site in his memory.
Thank you for the many kind messages of sympathy and support that have found their way to me.
Aaron's obituary
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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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That's obviously A question from your homework. Do your own research. |
how to design and build a battlebot
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