Ask Aaron: questions and answers about combat robots

Questions and Answers about Combat Robotics from Team Run Amok.

7747 Questions and Answers about Combat Robotics
from Team Run Amok

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.

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.

Ask Aaron is a simple little question and answer page. People ask questions about combat robots and we do our best to answer them.
Recently I've received some messages where the bulk of the text is used to express views or opinions that would be better suited as social media posts. Although I found the topics of these messages personally interesting, I did not publish them and I will continue to reject submittals of this type. I won't have Ask Aaron turned into Reddit. Let's keep it to combat robot questions, please.

One... Two... Three...
Q: On a previous post (can't remember which one) you said flippers like 'Lucky' and 'Ziggy' wouldn’t be classified as three-bar lifters. Where’s the fourth bar?
- sincerely, Iceywave [West of San Antonio ✪]

A: Mark J. The gif you sent along with your question does not accurately depict the flipper mechanisms of 'Ziggy' (pictured below) and 'Lucky'. Both use true four-bar mechanisms with a short rear element. Bar mechanisms have no sliding elements. More about 4-bar mechanisms.

From a 2015 post in part two of the Robot Weapons archive:
The internet is full of references to '3-bar' mechanisms, but this is a misnomer. What they're calling a '3-bar' is actually a '4-bar' in which they fail to count the base as the 4th bar. A true 3-bar mechanism forms a triangle and has zero degrees of motion freedom - it won't move at all. Lifters use a 4-bar mechanism. Don't spread the incorrect 3-bar usage.

Q: Ohhhhh… that makes sense. I've corrected my flipper animation to be more accurate. Thanks!
- sincerely, Icewave

P.S. did anyone win this year’s 'Most Prolific Contributor Award'?
A: Repeating the 'Most Prolific Contributor' award would be poor game theory - it would be expected. For 2024 I gave a "Most Prolific Answerer Award" - it was delicious.

Conditional Bests and Worsts
Q: A question I'm sure you’re used to getting is: "What's the best combat robot ever?" The answer is either redacted, redacted, or some obscure beetleweight that won a single tournament, then retired before it could rack up any losses. But something I've been wondering is: What's the best combat robot to NOT win a championship? (Best win/loss ratio, or most fights won total)
Another question: What robot has the worst win/loss ratio, or most losses total?
- sincerely, Iceywave [West of San Antonio ✪]
A: Mark J. I do get a lot of "Who's Best" questions, but I direct them to Reddit where such questions belong and are frequently discussed. I'm pleased that you deflected to questions with more quantitative answers.
It is a great shame that BotRank.com crashed and burned. For many years they kept by far the best records of combat robot tournament results and analysis -- until event organizers decided that it was too much bother to send in their tournament results. In 2021 the BotRank data base corrupted and, without new data being submitted, it just wasn't worth the effort to repair. A great shame that reflects poorly on event organizers.
Fortunately, the Wayback Machine has a working mostly pre-corruption copy of BotRank from May of 2021 that is useful for historical questions such as you pose. A few highlights:

Heavyweight (220) with the most wins: "Sewer Snake" (81)
Heavyweight (220) with the most losses: "Sewer Snake" (34)
Heavyweight (220) with the best win percentage (no title and 10+ wins): "Voltronic" (70.6% - 12 wins 5 losses)
Heavyweight (220) with the lowest win percentage (10+ matches): "redacted" (20.0% - 3 wins 12 losses)
Any Weight Class: highest win percentage (25+ matches): antweight "Dark Pounder" (87.1% - 81 wins 12 losses)

I'll let you sift thru the archived BotRank for other 'bests' and 'worsts'.
Side Note - Although Combat Robot Hall of Fame member 'Rust in Peace' does not appear in the BotRank database, it has a verified record of 45 wins and 2 losses for a 95.7% win percentage. If you are willing to judge a robot by its performance at the time and place of its career, that puts it in contention for the most dominant combat robot of all time.

Maybe a School Project
Q: Working on making a small battle bot that will fit within a cubic foot. Could you recommend a power supply to use if we need to power 2 motors of 12V and 2 Amps. [Lima, Ohio]
A: Mark J. I don't know of any robot combat event that requires a competitor to fit in a "cubic foot", so can I assume this is a low-budget school project?
Matching a battery pack to a combat robot requires more information than you have provided. I can only give you a couple of general options:

The limited motor specs you provide would be common for a one-pound 'antweight' combat robot. A typical antwight robot with such motors might use a rechargeable 3S Lithium Polymer battery of about 300 mAh capacity. Lithium batteries are both light and compact but they require a specialized charger and must be charged and stored with care to prevent spontaneous fires. The cost of such a battery plus an inexpensive 3S charger could be around $40.
Some budget minded robot builders run their antweight robots on an 9-volt alkaline battery via an adapter cable. Your 12-volt motors will run a bit slower on 9-volts but will operate well enough. Alkaline batteries cannot be recharged, but a good quality 9 volt battery might power a simple antweight robot for over an hour before replacement.
I will mention that combat robot motors are often "over-volted" to provide greater power and speed. If you switched to 6-volt motors, they would provide improved performance over equivalent 12-volt motors when run on a 9-volt battery. Most small 6-volt gearmotors will survive quite well at 9-volts for the short periods combat robots are operated -- if the wheel size and drive train gear reduction are reasonable.

The Brushless Version
Q: Humorous Post Is there a specific transmitter you recommend to help control the ludicrous speed of brushless drive motors used in insect-class combat robots? [Brushless Hipster]
A: Mark J. You're in luck. Check out the 'Master Speed Control' on the new FlySky FS-i6 'Brushless Version':
Flashback: an archived post from 2016

Very Specific
Q: when did 2.4ghz radios become popular? [Havertown, Pennsylvania]
A: Mark J. February 3rd, 2008 at 10:24 AM pacific standard time.
Q: that's very specific.
A: That's when RoboGames decided that tracking transmitter frequency crystals was too much bother and mandated spread-spectrum radios for their combat events. The 2.4 gHz radios would have taken over eventually, but RoboGames pushed the issue.
About that same time RoboGames also decided that the single most popular large combat class - Hobbyweight robots - was too much bother and dropped it. Superheavys and Feathers followed. Power corrupts.

Robotica Video Library

Team Run Amok's friend in Erskine, Scotland has gathered together dozens of 'Robotica' videos from UK and US sources for the Robotica Episode Anthology Library on YouTube. Playlists include full episodes, commercials, and individual matches culled from a variety of sources. Save as a bookmark or subscribe for future updates.

Check the Charge
Q: I'm wiring up a beetleweight Peter Bar Kit with Rectified Robotics 35A bi-directional ESCs and Repeat Robotics Max Drive motors. On power up the drive ESC lights go blue, then quickly solid red. The drive works but the throttle is inconsistent. Sometimes there is limited power and sometimes the motors will run full speed. Any thoughts in what is causing the solid red light? [Redacted] A: Mark J. Have you checked the charge on your LiPo pack? A red LED on those reprogrammed READYTOSKY ESCs is a low voltage warning: maybe reading voltage too low for a 4S but too high for a 3S. Put a full charge on your battery and give it another try.
You might also want to clean up those solder connections and remove the stray solder on a couple of your power chips. It looks like your soldering iron has too little heat for this type of work. Some soldering paste and pre-tinning the wires would help a good bit, as would some practice on something less sensitive and expensive than an ESC.

Gram-for-Gram
Q: You often mention garolite as a suitable material for a combat robot. I replaced a damaged 6061 aluminum panel on my beetle with G10 garolite but had it fail under similar conditions. Isn't garolite supposed to be stronger than aluminum? Am I using the wrong type of garolite or is it just used if you need to save weight? [The Other Windy City]
A: Mark J. I'm gonna guess that you replaced the failed aluminum panel with a garolite panel of the same thickness. Except for density (aluminum weighs 50% more than an equal volume of garolite) the physical properties of G10 and 6061 are similar. The failure modes of a metal and a fiber composite differ but if an aluminum panel fails, a garolite panel of the same thickness will likely fail as well.
Gram-for-gram, garolite is stronger than aluminum. A garolite panel 50% thicker than the failed aluminum panel would weigh the same while offering greater strength. For improved strength think equal weight, not equal thickness.

Raising the Roof
Q: How effective would adding spacers to shock mount the lexan top panel be to counter the new, devastating hammer saws like Strikepoint in the beetleweight class? (On a 4WD wedge) Although having the armor resting above the chassis would lead to a less than ideal outcome against horizontals that manage to rip into the gap, I figure that it would buy me a few hits against overhead disc spinners and saws by giving it some distance away from the electronics. [Behind a Cloudflare Curtain]
A: Mark J. Any specific guidance I might give would depend on design details you have not provided. Beetle, 4WD wedge, Lexan top panel -- are we talking about a BotKits D2? General comments:

Lexan (polycarbonate) gets much of its strength from its ability to flex and stretch. Think of it as stiffened transparent rubber.
Lexan cracks and fails when it is fastened in a way that concentrates the stress of flexing to a small area. I typically recommend oversized mounting holes with rubber grommet inserts to allow some 'give' around the fasteners.
Raising a top panel on small spacers removes the support of the chassis edges and increases stress around the fastening points. The added height also increases stress on the fastening screws. You haven't mentioned how much additional space you are considering.
Is damage from overhead weapons something your 'bot has actually experienced, or is this speculation on your part? If this is an actual problem I might suggest simply replacing the top panel with something that does not flex enough to endanger your internal components: carbon fiber, garolite, or perhaps thicker Lexan.

Antweights for Tots
Q: Recently, I remembered watching a lost (?) BattleBots related charity event. It was held (I think) in late 2018 and was live streamed on Twitch. It featured several builders from the show competing with antweight versions of their robots. The bots I remember seeing were:

Wrecks
Stinger
Yeti
Huge
Free Shipping
...and
Battle Royal with Cheese

I've tried searching for this event, but I can’t remember what it was called. Do you have any more info?
- sincerely, Iceywave [West of San Antonio ✪]
A: Mark J. Pretty obscure, Icey. That was the BotBash Toys For Tots Charity Tournament, circa 2019.
"The Bot Bash Charity Brawl invited many of Battlebots most renowned contestants to our shop to fight with MINIATURE BATTLEBOTS in a tournament format! Miniature versions of Skorpios, HUGE, Tantrum, Free Shipping and more were all featured in this all out micro-brawl."
Here's a link to a twenty match video playlist on YouTube.
Q: Thank you for the fight playlist!
One more thing. I’ve also recently remembered seeing a TV interview with Michael Mauldin around 3-6 years ago, where he talked about The Lazy Toad Robotic Club and Grille. I’m pretty sure it aired on my local PBS station, 'KLRN'. I know you live in Oregon, but I thought I might as well ask, since I can’t find it online.
- sincerely, Iceywave
A: I do have an informative lecture given by the venerable "Fuzzy" Mauldin from that period, but he does not mention the Robot Club and Grille and I'm fairly certain it never aired on any PBS station. I'm afraid it will have to do: Fuzzy's 2019 BattleBots Lecture.
Alexa... remind me to start charging for questions like this.

You Already Have Gearboxes
Q: I want to get my D2 beetle running again, but I want to use something stronger than the generic Botkits 22mm gear motors to stay competitive and I can't get the Botkits motors to last on 4S. The Just 'Cuz Dragon 22mm Dartbox Gearmotors look great, but the weird clamp drive motor mounting system the D2 uses won't work with a square Just 'Cuz gearbox.
Any alternate recs for good 22 mm brushed gearmotors? [Social Media]
A: Mark J. Let me save you some money. The motor bolt pattern on the BotKits 22mm gearbox is correct for 130-size Dartbox motors, so just remove the stock motors and bolt up any of the brushed Nerf/Dartbox motors you like. You may need to shorten the shaft just a bit and/or transfer the pinion gear from the old motor.
If you want to stick with the 4S lipo pack I'd suggest the Just 'Cuz Gecko replacement motors for the Dartbox Pro. They're dirt cheap, will run all day on 4S, and at 16 volts pull only 7 amps each at stall. The Dragon motors can pull two-and-a-half times that many amps at their 12 volt max, require extra heavy duty ESCs, and are complete overkill for a four-motor beetle.
Reply: Nice, thank you
Flashback: an archived post from 2021

Q7000: Ready for Anything
Q: When I went to Norwalk Havoc (as a spectator) I noticed a sawbot called 'Whittle by Whittle'. I happened to notice that this robot - as well as 'SawBlaze' on the rare occasion they use the saw - use a certain type of circular serration saw blade that differs from the common very-serrated design. The blade seems to be much flatter and stable, however it also seems to not be able to cut as quickly. Are there any reasons why different bots use these different saw design?
As always, Go Run Amok! [Worcester, Massachusetts]
A: Mark J. If you know specifically what type of material you'll be cutting with a circular saw you can match the saw blade design to that material and get an optimum cutting rate. The selected saw blade might have twenty teeth or a hundred and fifty teeth, and those teeth might be steel, carbide, or something more exotic. For some materials you might choose a blade made entirely from an abrasive ceramic.
If your're planning to attach a saw blade to a combat robot you're going to face some unusual challenges:

A wide list of very different materials you may need to cut into;
Poor control of the 'feed rate' of the material into the saw; and
Unpredictable and potentially damaging impacts to the saw blade itself.
The single best overall blade for this environment is a general purpose 'diamond saw blade' that consists of industrial diamond particles embedded in a carbide ceramic base that is then brazed onto a segmented-edge steel disk. It isn't the best blade for cutting rapidly into soft materials, but give it enough power and it won't 'jam' while carving thru any material all the way up to hardened steel. These are the cutting blades used by 'SawBlaze' and 'Whittle by Whittle'.

Heat Kills Motors
Q: Are there any brushless outrunner motors in the 2822 size class that can handle 14.8 volts? (can't find any online) If not, what will happen if I try to spin one only rated for 11.1 volts with a 4S? I'm doing an antweight based on the Fingertech mini beater bar, and I want to use a 4S for more drive and weapon speed, but although the page for the beater bar electronics bundle claims that it can handle 14.8 volts, the page for the motor itself (2822 1100 kv) says it can only accommodate a 2S-3S lipo. [Close to D.C.]
A: Mark J. The maximum voltage a motor can handle depends in part on how much load is placed on it. Too much load will 'bog down' the motor during spinup, causing it to draw extra current over an extended period of time. Extra current means more heat, and heat kills motors.
The FingerTech antweight beater bar kit has a relatively small weapon spun via a 1.7:1 reduction timing pulley set. This reduction reduces the torque load on the motor, shortens spin-up time, and prevents overheating on a 4S battery. If the same motor was used with a 1:1 direct drive it would not be prudent to run it at 4S.
If you want more weapon speed I would suggest sticking with a 3S battery and selecting a higher Kv 2822 weapon motor. Greater drive motor speed can make a 'bot difficult to control and is rarely usable in an insect-size arena. See the post Traction and Reflex Limited in the archives.
Q: 1lb beater bot guy here. I found out that Fingertech sells 2600 kv 2822 motors, which should do nicely for increasing the weapon speed. However, the page for the motor says that the motor draws 24A, and "over double the power output [of the 1100 kv motor] requires a larger ESC." The 40A ESC is a full 6 grams heavier than the 20A ESC, which I also may or may not have already ordered, so I decided to seek a second opinion.
Palm Beach Bots appears to be reselling this motor with the claim that it is compatible with the 20A ESC, so I'm at an impasse here. Should I bite the bullet and grab the 40A, especially considering that I'm still planning to use the 14.8V battery which would probably draw more current on spinup? (since more weapon speed on a vert = good, and I drove a D2 kitbot at 4S for a couple years, so I'm reasonably confident that I can handle whatever speed two Silver Sparks can output) Or will the max current being above the ESC's rating be irrelevant since the motor will stop drawing a lot of current after spinup?
A: You're operating under a number of bad assumptions. Where to start...

I don't know where you got: more weapon speed on a vert = good. More speed equals more stored energy, but more speed also equals less 'bite' -- and bite wins matches. I suggest you read the Ask Aaron Spinning Weapon FAQ with particular attention to the 'Rotational Speed' section. Running a 2600 Kv motor with the FingerTech antweight beater at 4S will have the two-impactor weapon spinning at a theoretical 22,600 RPM. The weapon will have almost no 'bite' and - unless you get very lucky - will just skitter across the surface of your opponent.
The 2600 Kv 2822 motor Palm Beach Bots sells is "Viper compatible" but the specs and measurements do not match the motor sold by FingerTech. It is similar, but not the same.
When a specification sheet for a brushless motor gives a "Max Current" it is NOT the greatest current the motor can draw; it is the most current it can continuously draw without failing from thermal overload. A typical 2600 Kv 2822 outrunner might have an internal resistance of less than 0.05 ohm and can draw more than 120 amps if bogged down into its mid-RPM range. This is why it is important to load the motor lightly and let it pass thru the lower RPM range quickly.
Likewise, a "20 amp" hobby ESC can provide 20 amps of current for some (usually unspecified) period of time, and will provide much more for short periods.
Yes, increasing voltage does result in a proportional increase in current draw, both during spinup and perhaps disproportionately at max weapon RPM with a weapon that has a lot of aerodynamic drag.
Beater bar weapons have notoriously high aerodynamic drag. Attempting to spin one at well over 20,000 RPM will bog down your weapon motor enough to draw well more than 25 continuous amps of current and it will melt -- unless of course the brushless ESC fails first.
Driving a weaponless four-wheel-drive beetle on 4S is a whole lot different from driving a two-wheel-drive ant on 4S with a very fast vert weapon adding very large gyro forces into the mix. You'll spend a lot of time sideways on one wheel -- see Designing Around the Gyroscopic Effect.

I gave my best advice in answering your first set of questions. I have now given the background on that advice. More is not necessarily better, and more may bring disasterous consequences. Proceed as you please.

Less Cogging
Q: Is there a reason to choose a lower Kv motor for a given weapon versus a higher one if the higher one is capable of a higher speed/torque? I understand the argument of choosing a lower Kv to get better bite, but couldn't the same be accomplished by limiting the throttle from the radio? [Probably Sacramento]
A: Mark J. Yes, there is good reason to consider a lower Kv version of a given motor for an unsensored direct-drive spinner weapon. Even though a high Kv motor produces greater PEAK torque and power, a comparable low Kv motor has a smoother start-up with less "cogging" and better low-speed torque. A low Kv motor has a higher number of wire coils in the stator which provides better position feedback to the ESC, allowing the delivery of greater current at low speeds to boost initial spin response.
Limiting throttle to the weapon motor will reduce top speed, but it also reduces the current supplied to the motor which reduces both torque and power. If you can run a belt drive reduction to the weapon to take the torque load off the high Kv motor and let it spin up into its power band it can be a better choice, but for a direct drive weapon pick a Kv that keeps speed in the usable range for the weapon.

Stator Size Matters
Q: Do you know if the Sunnysky 2212 is roughly comparable in power output to a Repeat 2822? They both physically look to be the same size, but I cannot find any power information or a datasheet for the Repeat Motor. [Probably Sacramento]
A: Mark J. The two motors are difficult to compare because their motor designations refer to differing measurements.

The '2212' designation for the SunnySky motor refers to the stator dimensions: 22mm diameter and 12mm thick;
The '2822' designation for the Repeat Robotics motor refers to the external dimensions of the motor can: 28mm diameter and 22mm overall length.

A 2205 Stator
The can diameter of the two motors is the same but the overall length of the SunnySky at 30mm is quite a bit greater than the Repeat Robotics motor at 22mm, and it weighs a fair bit more as well. This represents a considerably thicker stator. For brushless motors with similar voltage constants (K_v) a larger stator generally means more power, so the 1250 K_v version of the SunnySky should be a good bit more powerful than the 1100 K_v version of the Repeat Robotics motor. This also holds for the higher K_v versions of the two motors.
I will point out that the Repeat Robotics weapon motors are quite popular, and they are marketed as being designed for durability in direct-drive applications. Motor selection is not all about power.
I emailed Peter Garnache at Repeat Robotics to ask about performance specs for his direct-drive 2822 weapon motors -- like their internal resistance or continuous output power. He was kind enough to respond quickly:
Mark,
I don’t have either of those numbers on hand. I find that the current draw of the motors varies heavily on the weapon system that they’re spinning and the speed they spin at. In general the higher KV motors will pull more current. I'd choose a kv to get your tip speed between 150-250mph, and then do some testing with a power meter to figure out what your actual current draw is.
Thanks,
Peter Garnache.

Invert Makes it Worse
Q: I just finished my invertible antweight horizontal spinner. My transmitter can't do an invert correction mix, so I added a tinyMixer module to do both the single-stick mix and the invert trick. When running upright everything is fine, but when upside-down I flip the invert swich and neither the throttle or steering are right. This is worse then no invert switch. Is there something wrong with my mixer? [Hidden in an iCloud]
A: Mark J. Your mixer is fine. It turns out that there are two different mixer module set-ups that give correct response to transmitter input when the robot is right side up, but one of them does not respond correctly when the throttle channel is reversed to compensate for inverted operation.
Here is an excerpt from the help file for the Team Run Amok Combat Robot Mixer Fixer that describes the solution to your problem.
Invert Switch - Some DESCs and mixing modules have an 'Invert' function that uses a switched transmitter channel to reverse throttle response for inverted driving. If you have correct throttle and steering response but your 'Invert' switch just messes up your steering, this two-step fix should get it working:

Swap the positions of the two mixer or ESC plugs on your receiver -- unplug them and plug them back into each other's ports; then...
Physically reverse the polarity of the power leads from the ESC to the right-side motor.

Telemetry Complication
Q: Hi, Mark. In the Radio and Electrical archive you mention the binding relationship between transmitters and receivers:
"A receiver can only be bound to one transmitter at a time, but you can have any number of receivers simultaneously bound to the same transmitter."
Does this same relationship apply to "telemetry" receivers that send a radio signal back to the transmitter? Thanks. [Sacramento, California]
A: Mark J. Telemetry receivers like the FlySky FS-iA6B make things a little complicated.

A telemetry receiver binds to the transmitter in the same way a non-telemetry receiver does: it stores a code supplied by the binding transmitter and checks commands it receives against that code to make sure the command is valid.
The complication arises because a telemetry receiver must store its own code on the transmitter so that its telemetry transmission is recognized as a valid source. The transmitter has only a limited amount of memory for this purpose.

The actual number of telemetry receivers a transmitter can be bound with varies with the transmitter protocol and with the specific multi-protocol adapter, if one is in use. Transmitters with which I am familiar have capacities that range from a dozen to sixty-four telemetry receivers at a time. Consult your transmitter documentation to find the applicable number.

Traction and Reflex Limited
Q: Hello,
If I want to make a competitive plastic ant with oversize drive motors, would you recommend brushed or brushless? Palm Beach Bots recently added a couple of brushed and brushless beetle drive options that both seem light enough to put in an ant, as well as the new dual brushless drive esc that was just released. This robot would most likely be a 4wd vert or 2wd drum with a hub motor powered weapon.
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.
Pushing power is limited by traction. Once the wheels meet their traction limit additional drivetrain torque does not increase pushing power. The maximum pushing force a robot can generate is dependent on the weight bearing down on the driven wheels and the traction of the tire/arena pairing:
Maximum pushing force = Weight Supported by the Drive Wheels × Coefficient of Friction
An oversized drivetrain will "break traction" and spin the drive wheels at a small fraction of its power, but will not by itself generate additional pushing force from the tires. If you are fighting in a steel-floored arena and event rules allow it you may use chassis magnets to increase the apparent weight on the drive wheels and make use of increased motor power -- but there are significant problems with magnetic downforce, as described by multiple posts in the Ask Aaron Archives.
Greater Speed - See Tentacle Drivetrain Calculator.
There is only so much speed that can us effectively used in an insect-class arena. Like pushing force, acceleration force is also traction limited -- excess torque will break the tires free and hamper directional control of the robot. Even small ant brushless drive motors like the 24 gram Repeat Mini Mk3 deliver more speed and power than most drivers can use. Oversized drive motors will simply increase your frequency of running into the arena walls.
To answer your questions:

For the reasons above, I do not consider oversized beetle drive motors in a plastic ant to be practical.
Unless you have significant experience driving insect-class 'bots and reflexes like an over-caffeinated cat, I would recommend a nice pair of Repeat Drive Brushed Mk2 drive motors.

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:

A speed increase of 5% from 5.96 MPH to 6.25 MPH.
An elapsed time decrease of 14% from 1.08 sec to 0.95 sec.
Do you think that's worth the effort? Even if the additional power did not adversely affect robot control, I would say not.

An Appreciated Tribute
October is a somber time here at Team Run Amok. For several years after Aaron's passing I would shut down all of runamok.tech for part of the month. This year my spirits have been lifted by a tribute to Aaron posted on Facebook by "Robot Enthusiast and All-Around Man of Supreme Awesome" Alex Valentine. Here is an excerpt:
Day 15 of Bot-tober 24 is dedicated to the late, great Aaron Joerger. He's the lawnmower, you're the grass... straight from Robotica, it's Run Amok! As has become something I like to do as part of my drawing events, I've dedicated the midpoint of this year's run to another late, great roboteer. After Rex Garrod (2020) and Grant Imahara (2021), Day 15 of Bot-tober 2024 is dedicated to Aaron Joerger, and features his most iconic bot. Large, in charge, and through all comers he'll barge, it's the first-ever "Robotica" Champion and undisputed King of the Assault Course... RUN AMOK!

The invention of father-and-son duo Mark and Aaron Joerger, Run Amok was the very definition of "simple, yet awesome". Built around the chassis of a 1972 Murray ride-on lawnmower and powered by two 24-volt motors geared down for great acceleration and torque, it uses a specially-designed short wheelbase - with car steering and unpowered front wheels using chunky pneumatic tyres - to make use of its driver's background in asphalt remote-controlled car racing, and enable it to turn quickly in tight spaces.
The version of the robot shown here lacks active weapons, but can equip a steep chequer-plate wedge up front to get underneath and shove opponents around - note the "eye holes" cut into them; those are to stop the front wheels from catching on the wedge as they turn! - or remove it to raise the ground clearance up front to easily cross obstacles without getting high-centred, and bash its way through obstacles and enemies. Add that to a welded steel chassis and a 1.9cm thick plywood lid, and you had a machine that - while it certainly wasn't the fanciest - was as rugged and dependable as they come!
Run Amok's finest moment was definitely in "Robotica" Season 1, where its mix of toughness, driving skill and sheer ability to adapt to anything in its way earned it the Championship, taking out both Juggerbot (who would eventually become the first Rosie the Riveter) and Ram Force in the last battle. It also made frequent appearances on both "Robot Wars: Extreme Warriors" and "Nickelodeon Robot Wars", where it fought under the name of Run Away; receiving new active weaponry in the form of two vertical spinning bars, also receiving a new hazard-stripe paintjob (hence the choice of background). There, it finished Runner-Up in the Season 1 Tag Team event alongside General Chompsalot (from Day 4) and made Round 2 of the Season 2 U.S. Championship, as well as making its last appearance in the "Nickelodeon Robot Wars" International Tag Team alongside Zanzara.
While it ultimately had to retire due to irreparable damage to its gearboxes in the aforementioned bout, Run Away was restored after into its original Run Amok form, and made lots of appearances in events such as the "DaVinci Days" in Oregon, often alongside its sister bot, The Gap. The Joergers also became well-known for hosting the "Ask Aaron" Q&A blog and the "Combat Robot Hall of Fame" on their website, endearing them to a whole new generation of fans!
With its relatively simple box-wedge design, Run Amok was a nice change of pace from the complex death machines that I've been drawing for you all so far. The chequer-plate wedge was pretty fun to work out properly, and I'm overall very happy with the look; and hopefully, bot-fans, you'll agree. This one's for you, Aaron!
Here's a link to the full post on Facebook. Thanks, Alex.

Can You Trust the Gerbil?
Q: Hello, I am wondering what thickness of TPU I should use for my beetleweight minibot? I started off with quarter inch, but it turned out to be to heavy. What should I do? [South of Hartford, Connecticut]
A: Mark J. See Frequently Asked Questions #17.

Pssst! Down here... It's me, Rodger the Web Gerbil.
Mark is kinda touchy about questions that don't provide the silly little details that might give him a chance to come up with a quantified answer. This time though, I think he missed something. I have access to all of his notes and the exotic software that he doesn't share with the robot community, and I found this equation filed under "If All Else Fails":
cos² (x) + sin² (x) × (e^ix + e^-ix )² / 4 + sin² (x) × (e^2ix + e^-2ix ) / 4 + e^2ln(sin(x)) + 1/2 = What Should I Do?
Plugging your values into the equation I get: "Make it thinner 'cause making it thicker won't make it lighter."

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.

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
- Mark Joerger

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:
That's obviously
A question from your homework.
Do your own research.

Aaron's Greatest Hits! More of Aaron's Poems Aaron at Nickelodeon Robot Wars Aaron's Minecraft High Dive Video Aaron's World of Warcraft Player Guide

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