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![Fifteen Years of Ask Aaron [Click Me]](pic2/Ten_2.gif)
Team Run Amok receives a lot of email about designing and building combat robots. In 2003 my son and team member Aaron Joerger (then 12 years old) asked for a question and answer page to document our responses.
We welcome combat robot questions. Check the Ask Aaron Archives first to see if your question has already been answered, then click the blue button.
Click to browse thousands of previously answered questions by category, or search for specific topics. Includes  
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.
Two Into One
Q: Can I splice the signal and ground wires of two ESC's (brushless in my case) and have them plug into the same channel in my receiver? I want to be able to drive them both simultaneously, but they don't need to be perfectly in sync with each other. [Parker, Colorado]
A: [Mark J.] It would help to know exactly what you're doing but in general, yes. You can drive two unsynched ESC/motors from a single receiver output port signal. Do not try to drive a single brushless motor with two ESCs. Very Different Properties
 Hey, I just realized the sheet of UHMW I thought I bought is actually a sheet of acetal copolymer. I’m not too familiar with plastic properties, and I’m looking to make saifu kit-style rounded wheelguards. Is acetal copolymer a bad choice for something like that? [Philadelphia, Pennsylvania]
A: [Mark J.] There are very good reasons why builders use UHMW-Polyethylene for those Saifu-style wheel guards: it's light, slick, bends easily, flexes to absorb a lot of energy, and stretches rather than breaks. Acetal Copolymer (POM-C) has very different material properties:
Spindizzy
Q: Are there any Heading Hold Gyros that you could recommend? I just read your page about them and they sound like the perfect thing for my bot, however I don't know what I should be looking for in a gyro when buying one. [Yuba City, California]
Particularly with lighter weight classes, a good weapon hit can send a 'bot spinning so violently that a 'heading hold' gyro can lose its directional lock and behave erratically. Many builders have switched to 'rate' gyros that do not try to keep a heading lock because they are less susceptible to this type of confusion. You lose some of the 'on rails' feel a heading hold gyro provides, but your 'bot won't go crazy if it takes a good hit.
What you're looking for is a single servo gyro with a remote gain control. These used to be fairly common, but with R/C aircraft moving toward integrated 'flight controllers' they are now hard to find.
What Goes In the Box?
Q: Do you have any sort of guidelines on how many spares you bring to tournaments of each part? Obviously it depends on the bot design and tournament format, but I have no baseline estimate for how much damage I'll expect to take on each part and what's most likely to break. I'm using a Viper wedge kit in a double elimination tournament, so I assume it's reasonable to have at least one spare of everything going into the arena, but what needs to be prioritized? At the moment I'm thinking extra spares of wheels and the front polycarb/metal wedge are a must, but are motors and ESCs likely to break? What about the receiver? [Philadelphia, Pennsylvania]
A: [Mark J.] Repair time can be a limiting factor at a tournament. Highest priority for spares are components that:
If I were going to BattleBots I'd have two complete spare robots ready to pull out of their crates and toss into the arena, plus enough parts to build one more 'cause that how TV works these days. Your spares list should probably fall in-between these two extremes.
 20 Years in Combat Robotics 
This year marks Team Run Amok's 20th anniversary in combat robotics. We dove straight into the deep end of the competition pool, starting our career with a win at the nationally televised 'Robotica' tournament. In the years that followed we won more competitions, travelled to compete in England twice, and finished in the top three at more than half the events we entered.
I have several things planned to observe our anniversary year. For a start I've restored a few of our first-year web pages that have suffered from obsolete formats and outdated code. Check the Team Run Amok webpage for a full list, and check back for updates! Not Gonna Update Them All
Q: Also, I noticed in your old Armor Guide you mention that 6061-T6 Aluminum and mild steel are both solid choices to hold up against spinners, but in your discussion with the "Xmas Viper Guy" you say that both these materials aren't worth our time. Have spinners just become too powerful for those materials in the time between those answers, or what's up? And if so, would it be worth putting out an updated Armor Guide so people don't make the mistake of using any other outdated materials from that guide?
Thanks for your time, man. [Philadelphia, Pennsylvania]
A: [Mark J.] Yes, spinners are MUCH more effective now than they were fifteen years ago when the armor guide was written, but I think you should re-read it. The guide states that mild steel and 6061-T6 aluminum are cheap and easy to obtain, but that other alloys are stronger. There's nothing about 'solid choices' or holding up to spinners. It also says that you should do your homework and:
If I go back to the start of Ask Aaron and update one old question every day it will take me nineteen years to get back to this question -- I'll never catch up! The archives all have date markers every year or so to help readers judge the age of the question they're reading, but I can see the merit in posting a specific warning notice in the armor guide. I've added a note.
Into the Briar Patch?
Q: Hey Mark, just stumbled across your "You be the Judge" page and found it super interesting. Have you considered making a similar one for the Battlebots ruleset? I imagine this type of thing would be a great teaching tool to link when people claim the judges are idiots, but I doubt using the old Robot Fighting League D/A ruleset would do a very good job of explaining the current TV rules for the uninitiated. [Philadelphia, Pennsylvania]
A: [Mark J.] I'm happy to hear that you enjoyed my judging guidelines quiz. The RFL guidelines attempted to be very specific but caused some unexpected outcomes if they were closely followed. The purpose of the quiz was to point out those odd decisions in hopes that the guidelines could be adjusted to eliminate nonsensical results.
Jump forward a decade. The judging guidance for the BattleBots reboot is less specific and has corrected many of the problems I had with the RFL guidelines, but a number of controversial judging results have appeared each season. The guidelines are constantly updated in response to builder input, but there is still a lot of heated discussion on fan sites that official BattleBots explanations have done little to resolve.
I appreciate your suggestion, but I don't believe that throwing myself into that particular briar patch would help the situation. I'll pass.
Weakness Leaving Your Robot
Q: This question feels obvious enough that it must exist somewhere, but the keywords I was searching with turned up no results. What do you think the best at-home testing you can do for a finished robot is? Obviously there's no true replacement for competition, but is there anything you typically do to your bots to attempt to replicate mid-fight scenarios? Maybe things you use to simulate impacts from different directions and see how well your bot handles them? [Philadelphia, Pennsylvania]
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:
"Damage is weakness leaving your robot. If it breaks, make it stronger."
- Team Juggerbot
Robotica on Paper
Q: I've been watching the Robotica series on YouTube and some of the robots are wild. Were there any toys or models of the Robotica competitors?
[Sacramento, California]
A: [Mark J.] Yes, kinda...
"Cut and Fold" paper models of combat robots were a thing at the time. I know of three printable paper models from the Robotica series:
Era of COVID-19
Q: What kind of robot would be most effective/useful in this era of COVID-19? (Preferably in the form of a haiku)
[Pittsburgh, Pennsylvania]
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.
Best Unused Meme
Q: Im having trouble finding a name for my new beetleweight. I'd like to use a meme, but theyre all taken. What have I missed? A: [Mark J.] This name is perfect for a beetle and I haven't seen it used. All Messed Up
Q: I'm having trouble with my R/C mix on my beetle. I have an elevon mix, but when I pushed the stick forward it spun to the left. I tried to fix that, but now when I push the stick forward it spins to the right and when I push the stick right it backs up. How do I sort this out?
A: [Mark J.] I get a fair number of questions about fixing R/C mixes. In the past I referred such questions to a multi-step process to diagnose and correct the mix. It worked, but it took a while and the diagnosis sometimes had you changing things and then changing them back. Inefficient.
I recently finished an online javascript 'expert system' to handle this type of question. The Run Amok Mixer Fixer asks just three questions about your mix and then tells you exactly how to fix it -- no trail and error! Give it a try.
Hold it Together
Q: Sorry if this is kind of a dumb question but I wanted to build a larger robot (~12 lb) and all I want to do is build a box on wheels using 1/4" thick 6061 aluminum stock and plate. I can cut them to the right size but how to I actually join the pieces? I wanted to tap the plate but Im worried it's too thin. [Parker, Colorado]
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.
Rendered in Banjo-Kazooie?
Comment: Robotica Champion Run Amok... as rendered in Banjo-Kazooie: Nuts & Bolts.
For those unfamiliar with the game, "Banjo-Kazooie: Nuts & Bolts" was the progenitor to games like "Besiege" and "Robocraft". Released for the Xbox 360 in 2008 in celebration for 10 years of the release from the original Banjo-Kazooie game. The objective is to build various vehicles that solve puzzles and perform tasks in various environments. (Carry 'X' to 'Y', knock down this object, win this race, etc.)
I know Run Amok has four wheels, and this one technically does, but I intentionally put large wheels in the back and smaller ones up front so that the entire vehicle tilts forward and has near zero ground clearance. My biggest gripe with Nuts & Bolts is that nothing truly has a "wedge" unless you do something fancy with the wheels like this, so that was a trade off to have a wedge that literally scrapes the floor in the game. It was purpose-built to do a sumo challenge in the game against an AI opponent that doesn't know the HOT TIPS like I do.
Under the hood there's actually a row of three of those big wheels in a row, that's why there's wheel covers on the vehicle so you can't see the "creative liberties" I had to make under the hood. I filled in the sides of the robot too just for aesthetics because otherwise you'll see how it all works and in Nuts & Bolts that sometimes looks pretty ugly. Anyways I was building bots and I did this one and 'Bite Force' because they're two of my favorites that I was able to build.
The arrow should be just on top of the robot and not on the wedge, but since the robot isn't long enough to put the arrow on top the wedge is still a good secondary location. It is distinctly still "Run Amok".
You Took It All Away
Q: I am trying to use a Scorpion Mini ESC in conjunction with a servo powered lifter; both the drive & lifter are powered by a 2S battery. I snipped the BEC jumper because it limits power to the servo to 5v, which I don’t want. However, the ESC won’t talk to my HK-T6A RX now. The ESC blinks meaning it isn’t getting a signal, and the RX doesn’t light up. I have tried recalibrating the ESC, re-binding the RX, and replacing the RX, but nothing changes. The bot DOES work when I put in an un-snipped ESC, which narrows it down.
A: [Mark J.] Cuting the BEC jumper on your Scorpion ESC does not allow full battery voltage to flow to the receiver -- it removes ALL power output from the ESC via the three-wire receiver cables. Your receiver is no longer getting any power at all.
You have two options to supply full battery voltage to the servo:
Needs More Arrows
Q: The RioBotz Combat Robot Tutorial has a diagram that shows advantage/disavantage for a given robot design versus other designs. Is it really that simple? [Tempe, Arizona]
Mouse-over or 'tap' the image to see if my version makes more sense to you...
Somebody Else's Problem
Q: I understand how gyroscopic forces affect vertical spinner designs, but I feel like I am seeing some kind of related type of gyro effect with my undercutter design as well.
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 'Somebody 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).
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. Easy Tank Steering
Q: I bought a FlySky FS-i6 to use with a BotKits D2 beetle for my son. He’s 5 and I figure "tank style" steering with the forward and reverse from the left stick powering the left wheels and the right stick controlling the right wheels will be the quickest and easiest way to learn. Looking through the guide I don’t see this option available in your FlySky Combat Guide. Can you tell me how to set this up? This is all a bit new to me and I’m not familiar with some of the terminology, but we are learning and wish to get it going soon.
A: [Mark J.] Dual-stick tank steering is not a popular option, but it is easy to set up the radio for this style of control.
If you are using the BotKits-recommended 'Scorpion Mini' dual motor controller or another dual motor controller with "on-board mixing" you will first need to turn that off. For the Scorpion controller this is done by removing the "MIX" jumper on the circuit board. Two jumpers are located next to the calibration button: LIPO and MIX. Remove the MIX jumper by pulling it upward away from the board. Consult the user manual for other dual motor controllers.
Confusing Terminology
Q: For those of us still learning the ways of radio control, what would be the purpose of "mixing" and "inverting"?
A: [Mark J.] The terminology can be confusing, but the purposes are easy to understand:
What Can I Expect?
Q: Hi Mark!, as you probably would have guessed, I a pretty new builder having built one UK antweight and currently working on a second. I haven't yet been to an event. What can I expect from the event? What is the community like? What robots should I bring? What spare parts and tools should I bring? How long do events last?Thanks!
A: [Mark J.] The only UK events I've participated in were heavyweight tournaments at Robot Wars -- I don't think my experiences there would translate to a local UK antweight event.
I'm going to refer you to the Fighting Robots Association Forum. The builders there can provide you with relevant answers to your questions. In general I recommend attending an event as a spectator prior to signing up as a competitor.
A Bad Smog Day
Q: I'm newer to building Bots. I finished my first antweight and I'm working at a beetleweight. I researched how to properly store the Lipos, so I keep them at proper storage charge in a ventilated heavy steel box. I have a pretty large house and I have the batteries in the all-concrete basement. I don't really know how much toxic smoke they would output of they "went off". Is it enough to go through my home ventilation system and kill everybody or what?
A: [Mark J.] You probably have a dozen lithium ion batteries in your home: laptops, tablets, phones, drills, and 'bots. They all have the same base chemistry. You hear about lithium ion batteries in polymer cases (LiPos) blowing up because they suffer from much greater abuse in hobby service. Promptly dispose of any damaged, swollen, or 'puffy' LiPos.
Spontaneous ignition of properly stored LiPos is quite rare. The smoke from a LiPo fire is toxic and should be avoided, but the quantity produced by a couple insect-sized batteries 'going off' in your home is much more "bad smog day in SoCal" than "kill your family in their sleep".
See also: Lithium Polymer Battery FAQ
Many : A Few : A Pair
Q: How many batteries for a heavyweight combat robot?
A: [Mark J.] There isn't a simple answer to that question that would not be misleading. A typical heavyweight combat robot will wire together - in a series-parallel assembly - multiple packs made up of dozens of individual 3.7 volt lithium cells in order to provide the voltage and current capacity needed for the specific drive in use. A separate assembly may be required to operate a weapon motor at a higher voltage than the drive system. So:
They Don't Get It
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]
A: [Mark J.] My robots don't care. My robots don't spread, suffer from, or die from Covid-19 -- but you can. Don't be selfish. Follow the science. Stay safe.
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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A: [Mark J.] It's been a few years since I wrote the 
Reply: [Mark J.] Yes, it is distinctly 'Run Amok'! Thank you for remembering the old girl. I will assume she won the sumo challenge -- she's good at that.
Any idea how I can make a BEC-disabled Scorpion work? [Social Media]
A: [Mark J.] They left out a few arrows.
Centrifugal forces in a turning 'bot cause the mass-centers ahead of and behind the center of rotation to seek a common plane of rotation parallel to the rotational plane of the robot. In your 'bot this effect applies an upward force on the weapon-end in an attempt to achieve that common rotation plane. If this force exceeds the weight on the weapon skid, the weapon will pivot upward a bit and the weapon axis will deflect rearward. Gyro forces may then lift one side of the bot and aerial gymnastics commence.
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.
Thank you for the help. [Direct Email]
