Questions and Answers about Combat Robotics from Team Run Amok.

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7525 Questions and Answers about Combat Robotics
from Team Run Amok

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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.

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☆ [West of San Antonio]

A: [Mark J.] Thanks, Icey! We can't let a few megabytes come between friends. Let's try this:

A Secret Portal Opens. A Large File Passes Thru. The Portal Fades Away.

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!
-sincerely, Iceywave

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:
  1. (more minor) The integration done on the Calculations tab assumes that gravity is a constant resisting force, when it's a varying force that resists by cos(angle) (peak at horizontal in a standard 180 degree swing), but by the impact at 180 degrees it's fully adding to the system energy. Not accounting for this throws off the spreadsheet's optimal gear ratio recommendation by 5-20% based on playing around with a fixed version.
  2. (more *impactful*) The total system energy is KE + Torque, not just KE (Since 1Nm = 1J). For spinning weapons, Torque can usually be ignored since it's minor, but since hammers without an energy storage system (flywheel/pneumatic spring) are so inefficient in terms of motor weight to impact energy, it's actually a massive factor. For example a 1Nm torque motor output at impact speed, 0.25m arm, 10:1 reduction has a motor energy of 1*10/0.25 ~= 40Nm of applied torque at point of impact = 40J in addition to the KE. I'm assuming most real systems will have a clutch or the impact would risk damaging the system too much, but the limited torque could be substituted post clutch quite easily.
The net result in the configurations I've been playing with is that the optimal setpoint for the gear reduction is typically a slightly higher reduction, and the actual impact energy is 2-2.5x what the existing spreadsheet suggests. This raises hammers from ~1/10th the impact energy of an equivalent weight allocation traditional spinning weapon, to maybe 1/4, which is still atrocious but closer to viable given the typically weaker top armor and lack of reliance on relative velocity that hammers can take advantage of.

Since this is a Q/A, any errors in my math/methodology? Cheers, Joseph Duchesne [Ontario, Canada]

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.

  1. Cosine correction exists: In the spreadsheet there is a hidden tab named "Data Table" which you may or may not have discovered. If you 'unhide' this tab you will find in cell M4 the following formula that corrects the gravitational force in the manner you suggested above: =Calculations!D10×9.8×COS(RADIANS(M3)) The cells beneath M4 adjust available motor torque based on this correction.
  2. N-m comes in two flavors: A newton-meter is used to describe both a unit of work (energy) and a measure of torque (force) -- but the two are not interchangeable:
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.

  • Up to the moment of impact all torque is being used to accelerate the hammer; and
  • Following impact the force of motor torque will be limited to the amount needed to lift the front of the hammerbot off the arena floor -- which has likely already been raised by impact rebound.
Q: With regard to the cosine correction: Yes, the correction is there for the starting condition, but it needs to be integrated across the whole hammer swing, since the newtons of downforce (adjusting the effective torque of the system) "swing" from resisting the hammer at 0 degrees, to not resisting the hammer at all (90 degrees) to aiding the hammer swing (180 degrees). The correction in the spreadsheet applies to the starting condition. ~Joseph D.

A: You're killing me, Joseph. Why would I have written that nice collumn 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...

Hammer Spreadsheet v2.5 First, I want to thank you again for the time and effort you have put into crawling my Hammer Spreadsheet with a critical eye.

I woke up this morning with a clear head, determined to sort out the evolution of my Hammer Spreadsheet.

  • Over my first cup of coffee I was able to trace the origin of the "starting condition only" gravity correction. Let's just say that it served the original purpose of the spreadsheet.
  • By the start of my second cup of coffee I had determined that your suggestion to integrate gravitational effects across the whole hammer swing had undeniable merit.
  • Half way thru my third cup of coffee I settled on implementing a varying time constant as the method by which I might implement your suggestion.
Some hours later, I am pleased to anounce the release of version 2.5 of the Hammer Spreadsheet. As your experiments predicted, full gravity correction reduces the calculated optimum gear reduction and models slightly improved energy and time-to-strike curves. Electric hammer weapons remain poor, but we now have a more accurate modeling of just how poor.

The link to download the most current version of the Hammer Spreadsheet is always on the Ask Aaron Combat Robot Design Tools page -- but I'll save you a page jump:

Download Excel Hammer Spreadsheet v2.5

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☆ [West of San Antonio]

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:

  • The specified team was expelled from the specified event after the competition began.
  • There were multiple reasons for their removal, but my sources do not confirm the specified offense you mentioned.
I prefer to leave it at that.
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.

  • Temperature sensors are seldom found in robots below the heavyweight class. In heavyweights they may be used to identify design problems during testing, but during a match you can't back off just 'cause something overheats.
  • Given that the magnitude, angle, and location of impacts in combat are unpredictable, the data from impact sensors is effectively useless. When a part fails, replace it with a stronger part.
All of our robots include a non-structural piece of wood. If the wood bursts into flame we know that it's getting hot in there.
Crank Up the Noise!
Q: Hi Mark, it’s Iceywave here. I wanted to do something interesting this time around, so here’s the very first ever Ask Aaron audio question!

-see you April 1st, Iceywave☆ [West of San Antonio]

A: [Mark J.] For those who prefer to read:

Wow, our first audio question and our first 1.4 megabyte commercial for somebody's YouTube channel! It seems a shame to answer your early April Fool question in regular text, so I went with Morse code:

.. -. / - .... . / .--. .-. . -....- -... .-. ..- ... .... .-.. . ... ... / .-- . .- .--. --- -. / -- --- - --- .-. / -.. .- -.-- ... / .. - / .-- .- ... / ...- . .-. -.-- / -.-. --- -- -- --- -. / - --- / ..- ... . / -.. ..- -.-. - / - .- .--. . / .- -. -.. / -.-. .- .-. -.. -... --- .- .-. -.. / ..-. --- .-. / .- -. - .-- . .. --. .... - / .- .-. -- --- .-. .-.-.- / .. - / .-- .- ... / - .... . / ..- .... -- .-- / --- ..-. / - .... . / -.. .- -.-- .-.-.- / - . .- -- / .-. ..- -. / .- -- --- -.- / .-- .- ... / -. . ...- . .-. / .- / ..-. .- -. --..-- / .-- .... .. -.-. .... / .. ... / .-- .... -.-- / .. - / .-- .- ... / .. -. -.-. .-.. ..- -.. . -.. / .. -. / --- ..- .-. / .-- . .-.. .-.. -....- -.- -. --- .-- -. / .-.. .. ... - / --- ..-. / -.. --- -. .----. - ... ---... / -. --- / --. .-.. ..- . --..-- / -. --- / - .- .--. . --..-- / -. --- / --.. .. .--. / - .. . ... .-.-.-
For any non-telegraphers in the audience:
Gotta Be Tight
Q: Hello, I am building a 1lb undercutter bot based on Jameson Go's 'Silent Spring/DDT' build, but am not sure how to securely mount the weapon to the bottom. I am currently planning on using a pulley driven disc on a dead shaft, with bearings in a printed hub/pulley attached to the disc. Do you think a long nut/coupling hex rod in the chassis above the blade with a nylock nut on the end would support the weapon shaft? or what would be a more robust way to make sure the weapon shaft does not go anywhere? I don't want the blade to bend upwards and chop my weapon belt. Attached is a mock up of the basic structure. Thanks! [Redmond, Washington] A: [Mark J.] That's how 'Silent Spring' does it: a socket head shoulder bolt with a nylock nut (photos below). Note that you're going to torque this down, so you're going to need a substantial spacer block around the shoulder bolt between the two chassis plates to take the pressure.

I wouldn't trust a printed hub holding both bearings to take the loads this style of weapon will put on it. 'Silent Spring' has the top bearing in an aluminum pulley and the lower bearing in the weapon disk itself.

How are you mounting the weapon motor? Your mock-up appears to have the spinning can pressed into the chassis plates and the motor base sticking out unsupported. Can I assume that's just a rendering error?

Q: On the topic of the latest post of a Silent Spring inspired bot, I can say that it can work out well even with a printed pulley since that is exactly what I did for my 1lb Shock! kits [GrabCad]. The big thing I did was adding a pair of concentric washers between the bearings to take the compressive loads and help axially retain the pulley and disk in place. [Newark, Delaware] A: [Mark J.] Thank you, Ryan. Your 'Shock!' weapon design is well thought out with the lower bearing in the weapon disk itself and the upper bearing in the printed pulley. In their question, Redmond spoke of a design with "bearings in a printed hub/pulley attached to the disc" which led to my comment that I wouldn't trust a printed hub holding both bearings. I think you might agree that placing both bearings in the printed pulley/hub would be risky.
Q: Hello, Redmond undercutter guy again. Good call on the bearing spacing, I will implement one into the disc and one into the pulley rather than both in the pulley. The weapon motor will be mounted similar to 'Silent spring', but I have not designed a housing for it yet. However, a few more questions about the shaft mounting:

1. Do you know how he mounts the shaft so securely to the frame? It looks like just a hole in the print with a nut on top, but wouldn't the print deform/break in big hits? Ive been looking around at various undercutter designs but can't seem to find exactly how they keep the shaft from moving or bending at all.

A: The mount is exactly as it appears. Take a look at the assembly instructions for the Shock! kit. Steps 9 and 10 cover weapon assembly. When assembled and torqued down the shoulder bolt turns into a structural element that locks the two chassis plates together. The Shock! chassis plates are cut from high-strength carbon fiber composite material.

'Silent Spring' has a thick, single-plate chassis printed from NylonG (early versions) or NinjaTek Cheetah TPU. Printed chassis plates do flex - it helps to absorb the energy of the hit - but they snap back into place (you hope). Design note: wider spaced chassis plates make a stronger base for an undercutter.

2. How thick of a bolt do you think is safe enough to assume won't break? Thanks!

A: The Shock! kit used this 1/4" shoulder bolt. Please note that a shoulder bolt (about $8) is hardened alloy steel and is MUCH STRONGER than a nasty hardware department bolt made to mount the horn on your bicycle handlebars. Do not go cheap on this critical part.

El Escarabajo Vibrante
Pregunta: ¡Hola!
Mi girador vertical de 3 libras tiembla violentamente cuando el arma gira. Ya leí "¡La hamburguesa es mala!", asì que aquì te dejo una foto para ilustrar mejor mi problema.
¡Àdios! [Al Oeste de San Antonio]

Respuesta: [Mark J.] He examinado cuidadosamente tu fotografìa y no veo nada malo. Quita las ruedas y la Liga Nacional de Robots Havoc te darà una bonificaciòn de peso.


Powerful Forces at Work
Q: Howdy Mark, Hopefully some quick questions that I hope you can help with due to your experience. [Warren, Ohio]

A: [Mark J.] In my experience, nothing takes longer to properly answer than a couple of "quick questions". I'll do my best to be concise.

  1. I've seen some people talk about battle hardening outrunner brushless ESCs (i.e. Robert Cowan's wonderful guide/video on the topic and others) and I was wondering how many teams/bots (not really looking for a discrete value just an approximate percent) you know of that can attribute the hardening to saved matches or motors? Our team is building a heavyweight, and we don't exactly have the resources to replace a set of smoked motors that overheat because of glue prior to competition. The current team thinking is to assume that the motors are protected enough by the frame and armor that we are more likely to burn them up electrically vs break them mechanically.

A: I can't give you a meaningful percentage, because...

No one knows when their effort at hardening saved a motor, they only know when it didn't.
I understand and share your concerns about heat retention from encasing stators in a thick layer of epoxy and glass 'microballoons' in the fashion demonstrated by Robert Cowan -- one of few areas in which we disagree. See this archived post for my approach to stator hardening, which maintains a large surface area and aids cooling via improved thermal conduction. A similar approach works well to secure rotor magnets. More epoxy ≠ better.

Battle hardening is not done to protect motors them from direct mechanical damage in the way your frame and armor can. Many builders have difficulty wraping their heads around the magnitude of the acceleration forces encountered in robot combat. The forces generated in abruptly stopping a weapon motor spinning at thousands of RPM can run into hundreds of Gs, as can the forces exerted on the entire weapon or drive motor from the acceleration imposed by a spinner weapon hit to the chassis. That is what you harden against.

  1. Is there a good way to attach JST or JR/Futaba servo connections to receivers and ESCs without just covering the connection in hot glue? In the RC world, everyone just seems to just plug it in a go for it. I'm worried about serviceability, especially while testing. If I need to replace an ESC during a tournament, I realize I will be cutting out hotglued connectors because we are in a bad spot. However, while we are testing and tuning the robot or practicing our driving, I'm concerned about random disconnects.

A: Connectors in "the RC world' are not expected to continue operating after being exposed to the forces we encounter in combat robotics.

The connectors themselves are usually less an issue than the length of wire attached to them. A three-wire receiver cord that weighs a tenth of an ounce at rest can exert well more than a pound of force under the acceleration forces referenced above. Tie your wires off as close to the receiver as practical -- ideally to the receiver itself so they may move together as a unit. A slender zip-tie will suffice and is easy to cut and replace when needed.

Like epoxy, a little hot glue goes a long way. If the wires are correctly tied off you only need a dot of hot glue at the connector for insurance.

Comment: Also, as a team that decided on using VESCs like a fellow poster who asked about them the other day, I think they got their hypershock blog posts mixed up with the VESC manual about optoisolators.

Reply: That clears up some of the confusion. Thank you!

It's a Zen Thing
Q: If the first design you should build is a wedge, what's the second? [Saratoga Springs, Utah]

A: [Mark J.] When you have built and competed with your wedge you will better understand:

  1. The magnitude of the challenges presented by differing types of weapons; and
  2. How well your knowledge and skill level suit those challenges.
Your next step will be obvious.
Zen teaches that enlightenment is achieved through the profound realization that one is already an enlightened being.

Fairies, Ants, and Beetles
Q: Will you do my homework for me? [West of San Antonio]
If a=51, and b=rate divided by time, how many minutes would a Volkswagen traveling at 78 mph take to travel 37 miles if 24% of the distance traveled is up an incline of "o", if o=increase in property of (a + -0)?

A: [Mark J.] The last Volkswagen I owned was a 1964 Beetle that wouldn't do 78 MPH if you nailed the throttle pedal to the floor and pushed it off a cliff.

(っ◔◡◔)っ It Has No Bottom
Q: I do have an ACTUAL question today. How many bots have competed in both BattleBots and U.K. Robot Wars (just a different paint job and name isn’t enough to qualify as a different bot)?

Off the top of my head...

  1. Razer
  2. Killerhurtz
  3. Suicidal Tendencies
  4. Mortis
  5. Panic Attack
  6. Bigger Brother / Little Sister
  7. The Piecemaker / The Executioner
  8. Spitfire / Dantomkia
Am I missing any?
-sincerely, Iceywave☆ [West of San Antonio]

A: [Mark J.] You're asking me to go down a deep rabbit hole, Iceywave. The answers depend on what you think is the same robot, what qualifies as "competed", and what you consider to be "Robot Wars". I'll add eight to your list of eight, but I'm not going to attempt a complete list.

  • Multiple entries in "Robot Wars Extreme Warriors" had BattleBots alter-egos. A few examples:
    • Tricerabot / JuggerBot;
    • Propeller-Head / Agitator;
    • The Revolutionist / Phrizbee.
  • Team Storm's BattleBots entry 'Photon Storm' is a rebuilt 'Tiberius' from Robot Wars.
  • 'The Grim Reaper' fought in BattleBots Comedy Central season 5.0 and the Third and Seventh Robot Wars.
  • 'Basher' fought in the unaired Robot Wars Series 8 pilot episode and went on to fight as 'Beta' at BattleBots.
  • Robot Wars champion 'Apollo' fought in an un-aired qualifier bout for the 2015 BattleBots reboot as 'Chronic' and was accepted to fight in a nine-robot rumble that was cancelled due to time restraints.
  • Under the Combat Robot Hall of Fame eligibility rules, Robot Wars champion 'Carbide' could be considered to be the same robot as the 2016 BattleBots competitor 'Cobalt'. The 2019 onward version of 'Cobalt' is a converted 'Tungsten' from "This Is Fighting Robots" -- but that's a different crossover.

You're Just Messin' With Me
Q: 1mm titanium vs 5mm aluminum: which is better? I’m asking for my "Break-Your-Fist-on-my-Face™" configuration for Flamin'Yon. It's still a standard Viper wedge kit (so no bad hamburgers, I'm assuming?).

-sincerely, Iceywave☆ [West of San Antonio]

P.S. I... don't actually have anything else to say. It just feels so weird sending a post that isn't unnecessarily L L O O N N G G : )

A: [Mark J.] Come on, Iceywave. I know that you've read every word of all the Ask Aaron archives and sub-pages -- including FAQ #17 and the Bad Hambuger page. You expect me to believe that you can't recognize bad hamburger when you see it? You're just messin' with me:

  • To what use will you put the material? I'd guess 'wedge', but you aren't specifying.
  • There are MANY aluminum alloys that range in strength from '3003' found at your local Home Depot that folds up like cardboard to '7075-T6' that has 90% of the strength of 304 stainless steel at a third of the weight.
  • Titanium also comes in various grades. Grade 2 (pure) is no better for structural properties than a poor aluminum alloy, but Grade 5 (Ti-6Al-4V) is strong and super-tough.
Titanium alloys are only about 1.6 times as dense as the aluminum alloys, so the proper weight-for-weight comparison is 3mm titanium vs. 5mm aluminum. Titanium throws pretty sparks when hit while aluminum smears. The stock 3mm polycarbonate Viper wedge weighs 27 grams:
  • If you want the better performance for a given weight of wedge: 3mm Grade 5 titanium (100 grams).
  • If your choice is between 1mm titanium and 5mm aluminum: 5mm '7075-T6' or '2024-T3' aluminum (100 grams). What's the difference?
  • If it was my choice: 2mm AR400 steel (116 grams) for its toughness and hard surface -- but you didn't ask for another option.

Introduction to Vector Analysis
Q: It is my understanding that wedges "counter" horizontal spinners, by deflecting them with relative ease. I was wondering if having an angle on the blade would solve this issue. For example, if there was a 'bot with a 45 degree wedge, could I make my impactor angled to match their angle to "counteract" the deflection? [I-95, West of Boston]

A: [Mark J.] Nice try, but no. The angled wedge is effective in deflecting the blade because the wedge sits at a shallow angle to the horizontal blade's motion vector, which is parallel to the arena surface. Matching the angle of the wedge with an angle on the blade edge would only make the blade slide up the wedge more smoothly.

Changing the blade's vector by angling the axis of the spinning blade downward to match the angle of the wedge would negate much of the wedge's deflection ability, but the downward impact vector would induce a strong upward 'kickback' to toss your 'bot skyward. Wedges are awesome.

Speaking of Vectors...
Q: For my horizontal spinner, the motor I want to use is too tall for the robot with the pulley attached as well. There aren't any shorter motors available that can handle the current I need to run, and making the chassis taller would be a waste of weight and harm the rest of the design. I've heard that some robots put the pulley directly on the outside of the brushless outrunner. How would I go about attaching this to, say, a BadAss 2305? [I-95, West of Boston]

A: [Mark J.] The "belt-around-weapon-motor" technique generally uses a custom 3D-printed pulley that presses tightly onto the weapon motor can. The pictured can-pulley for a timing belt was used for the horizontal weapon on the EndBots Vector beetleweight kit (discontinued) that used a Sunny Sky X2212 weapon motor. You can see the pulley being installed on the motor in the Vector assembly video.

I have seen robots that simply wrap a timing belt directly around the can without a pulley of any type on the motor. This 'pulleyless' design requires precise alignment, accurate belt tensioning, and a fair amount of 'fiddling'. I'll note that the narrow flat space on the BadAss 2305 can makes it a questionable candidate for a pulleyless design -- you might consider using a round belt with its easier to design pulleys.

The large diameter of the motor can means that you will not be able to get much speed reduction between the motor and the weapon pulley.

Testing, Testing, 1 - 2 - 3
Q: I already have experience building simple wedge and lifter bots and am looking into building my first spinner. This bot would be a 1 pound antweight. How would I go about building a safe and functional test box where I can practice and test my bot? [Camarillo, California]

A: [Mark J.] You've made a good decision to build a test box for your antweight spinner. You may want to consider building a test box capable of handling slightly larger 'bots to be ready for your next steps. I know of several guides on the construction of insect-class test boxes:

  • FingerTech Robotics has put together a very nice set of step-by-step plans for an inexpensive antweight test box, including a parts list you can fill from your local home center.
  • Absolute Chaos Robotics has an outline of the construction of their new beetleweight test box that includes a bill of materials. The photo they include of their earlier antweight test box made from a steamer trunk may give you some ideas as well.
  • Just 'Cuz Robotics offers a 12 minute 'How to Build a Test Box' video about their sliding-top beetleweight test box. Includes a bill of materials in the comments section.

It's Absolute Chaos
Q: Ryan Clingman from Absolute Chaos Robotics here,

I thought that I would just submit a minor correction to Peter's rating of beetle motor options (out of self interest) since part of the information seemed out of date or inaccurate.

Peter erroneously lumped the motors from my site (Absolute Chaos Robotics) in with generic Chinese gear motors in quality, but this is far from the case.

  • First, the motors in my shop (and the Jolt! kits) provide more torque than either the Servo City or BotKits motors.
  • Second, my gearboxes have a double gear train that while not as durable as an all metal planetary gearbox is far more durable than a general spur gearbox (and plenty durable for combat robots).
  • And third, while the BotKits motors originally featured hardened S7 tool steel shafts like Peter mentioned, they quietly dropped them years ago for an unspecified "hardened steel" that was presumably cheaper to manufacture.
So the motors I offer on my site have more powerful motors and approach the gearbox durability of the BotKits motors while being about half the price, so I feel that there is justification to put them on the same performance tier as the BotKits motors rather than the bottom of the pile with the no-name Chinese options. [Newark, Delaware]

A: [Mark J.] I appreciate the corrections, Ryan. I'm certain that these were honest errors. I've edited Peter's commentary to reflect the information you've provided.

Guest Commentary - Beetle Motors
[Mark J.] Peter Garnache of Repeat Robotics recently gave comments on the current beetleweight drive motor solutions in answer to a question in the Facebook Combat Robotics group. Peter was kind enough to allow me to repost his comments here as a guest commentary. Thanks, Peter!

Q: What's a good motor & gearbox for beetleweight robots?

A: [Peter Garnache] My recommendations for drive motors from my 6 years of building 3lbers are as follows:   Prices rounded - February 2024

Off-The-Shelf Gearmotors

  • below $10 25GA-370 1000 RPM Spur Gearmotor - Super cheap but not very powerful or durable. Various flavors available from eBay or Amazon.
  • $15 Absolute Chaos Double Spur Gearmotor - An inexpensive option with good power and torque. While not as durable as an all metal planetary gearbox, they are a big improvement over the generic spur gearmotors. Added by Mark J.
  • $26 Repeat Compact Brushed - Super light (45 gram) 22mm dual bearing gearmotor with billet 4mm hardened steel shaft. Added by Mark J.
  • $30 Servocity Gearmotor - Tried and true, used on plenty of bots. Kinda expensive tho.
  • $32 Botkits Gearmotor - Planetary 22mm gearmotor built for combat. Hardened steel output shafts and reasonable amounts of power.
  • $36 to $49 Just 'Cuz Dartbox - Super high power brushed planetary with low weight. ESCs are expensive and large to be able to handle the power of the motors. 6mm shaft upgrade is very helpful for direct drive applications.
  • $45 Rectified Brushless - Very light but the 4mm output shaft is suboptimal for direct drive applications. Also available as a $25 Brushed Drive.
  • $51 Fingertech Mega Spark Brushless - Plenty of power with the durability of a 24mm planetary. Great option for any drive system.
  • $55 Repeat Drive Max Brushless - Highest power beetle brushless commercial off-the-shelf option. Super chonky 24mm planetary gearbox is unlikely to break in combat. Hardened 4130 steel 6mm output shafts. 6S ready out of the box. $35 Same gearbox with a 3S brushed motor.
Assemble-It-Yourself Gearmotors Direct Spur Gear Drive
  • Custom Just 'Cuz Single Stage Brushless CAD - Requires more engineering work to make happen but with a 1000kv motor and single stage gear reduction it can be the most compact and lightest drive option. It's a 1000 Kv drone motor with an R/C car pinion gear driving a spur gear on the wheel.

Seventy-Five Hundred
Q: With my next question, AskAaron will have made it to 3/4 of ten thousand questions! So I guess the 7500th question is, how does knowing the above information make you feel? [West of San Antonio ☆]

A: [Mark J.] It makes me wonder what else I might have done with all the time I've spent answering combat robot questions.

Q: Also, I seriously don't know when I’ll start my YouTube channel. Things have gotten really backed up on my video production pipeline, so that late-January channel creation date I mentioned a while back will definitely not happen.

Before I go, there’s one more thing that's been on my mind. What is the most successful multibot ever made (by 'most successful' I mean the greatest win/loss ratio)? -sincerely, Iceywave

A: Assuming that you're interested in traditional multi-bots and not a lopsided heavyweight/minibot combinations, UK clusterbots appear to have had the most overall success. Win/loss records for UK robots are complicated by their appearances in events other than two-bot battles, but I believe the title for "Most Successful" goes to the Robot Wars flipper twins 'Gemini'. Their 4 win, 5 loss record includes victories in the Series 4 Pinball Warrior Tournament and a three-bot quailifying fight. 'Gemini' also won Series 4 awards for Best Design and Most Original Entry.

 Annoying marquee BattleAnts logo 

Q: Sorry for the late post, but do you have any information on the Season 5.0 BattleAnts event? I’m very surprised no one has asked you yet, since you’re pretty much the most reliable source for early 2000s robotics.

A: Whaddya mean pretty much?

The April 2012 issue of SERVO magazine has a very nice article on the origins of the antweight class that includes coverage of the BattleAnts demonstration event at BattleBots 5.0. The article has photos of the sixteen competitors at the invitation-only event. The full tournament tree has been lost, but I have it on good authority that Derek Young's shufflebot Hoser'd defeated Team Sinister's tracked plowbot Oishi in the finals for the tournament victory. The event was held well away from the audience and was not televised.

Q: Also, I once heard a rumor (an actual one this time) that a BattleBots sanctioned event held in 2011 had a DVD release. I don’t remember where I heard this from, but is there any truth to it?
-sincerely, Iceywave ☆

A: That would be the 2011 BattleBots IQ event in Miami. A film crew was present at the event to shoot a documentary that followed three high shool teams. The resulting film is called Bots High. This is probably the rumored DVD -- but it is not a video of the tournament itself: 'Bots High' on YouTube

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.

Two photos of Aaron Joerger 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   
Killer Robot drawing by Garrett Shikuma

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.

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