Questions and Answers about Combat Robotics from Team Run Amok.

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7620 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.

The Plans Kept Changing
Q: I have to ask, because this is really nagging me. Seeing on the R.W. Wiki that Robot Wars: Extreme Warriors was planned for a third season and be filmed during Extreme Series 2, would you guys enter with Run Away even though you were retiring it, or focus on The Gap with Max Chapin and enter it, or maybe build a new robot and enter that in the planned third season? And how do you think either robot would fair against Mr. Psycho and Growler if the third season went ahead and they were introduced to the American audience? [Not far from Oneida Lake, New York]

A: [Mark J.] The answer requires a little background. When Team Run Amok was invited back for RWEW-2, I sat down and drew up plans for 'The Gap' as our entry. I took the sketches and dimensions over to Max Chapin at 'Creative Steel' who had done the major metalwork on 'Run Amok' and her conversion into 'Run Away'. We had started pulling together components and materials when I got another call from Robot Wars saying that they were looking for a few more competitors. I said I'd call them back in 20 minutes. I looked over at 'Run Away', scratched my head, and called Max Chapin to see if he and his family would like a free trip to England to take over driving duties for the old girl. You know what his answer was.

As we got closer to crating up the 'bots to ship them off I became a little uneasy about turning Run Away over to new hands. 'The Gap' had come together well and was by far the easier of the two 'bots to drive. Given that I had plenty of experience operating 'Run Away' it made sense to give Team Creative Steel their better shot by running 'The Gap'.

For the proposed RWEW-3 tournament the plan was for Team Run Amok to reclaim 'The Gap' and for Team Creative Steel to put together a new 'bot of their own design. Thru the spring I worked on wringing more speed and power from The Gap's high-lifter weapon, which I was able to show-off at the DaVinci Days technology fair and the Oregon Clandestine Street Fight. Rumors kept flying about a third Extreme Warriors, but confirmation never came.

Creative Steel never settled on the design for their new 'bot so I can't speculate on its chances against the new house 'bots -- but I was very disappointed that 'The Gap' had a house bot straddling its lift platform at RWEW-2 and couldn't actuate the weapon due to an electrical issue. I would have loved a chance to put another house 'bot out there -- the bigger the better.

Keep Adding Wheels
Q: I already know that no one is going to hack the Battlebots prototype for GameCube however if Tazbot was in it which version would you say would be the very best? I would say for me the season 2.0 version that looks like the grip n' grappler which I have if you happened to be really interested that is [Erskine, Scotland ☆]

A: [Mark J.] I say you'd want the Destruct-A-Thon Tazbot in the video game 'cause snakes have no armpits.


A: You mean they do?

With a Belt Drive Reduction
Q: What is the outrunner motor that is used in the endbots vector kit? [Sacramento, California]

A: [Mark J.] The beetleweight Vector kit used a Sunny Sky X2212 980Kv outrunner to belt drive its horizontal bar spinner.

Q: What type of material is the weapon pulley and motor pulley for the endbots vector?

A: The weapon hub, motor hub, chassis back and sides were 3D printed carbon fiber filled nylon (Markforged Onyx).

Hot Off the Printer
Q: I've seen some very nice 3D printed robot replicas starting to appear on Thingiverse. Team Orby has put up a beautiful Warhead replica. I'd like to CAD a simpler combat robot replica just to work on my skills. Is there a robot model you'd like to see? [Baltimore, Maryland]

A: [Mark J.] For more than twenty years I've badly wanted a model of Robotica mascot "Shrapnel", like the one the young fan was carrying in the TV commercial where Shrapnel is signing autographs.

Note: I've recently added a playlist of five Robotica season 1 commercials to my YouTube channel.

Far Too Biased
Q: At the 3 seasons and 21 episodes of Robotica which episode do you think is your favourite episodes in almost the and which season is the best of the series? [Erskine, Scotland ☆]
= Episode List Redacted =
A: [Mark J.] Pop art icon and film director Andy Warhol was often asked, "What is your favorite movie?" Sometimes he would respond with the 1962 scifi film "Creation of the Humanoids", but depending on his mood of the moment he might claim any of a dozen other movies were his fave.

I also have moods, and I have an understandable bias in attempting to rank 'Robotica' episodes. I can say that the season two and three finals were laid out in a way that did not set well with me:

  • Reducing the field from six to four robots after 'The Gauntlet' was unfair to the 'bots who had 'The Maze' as their stronger event.
  • Promoting the losing Gauntlet 'bot with the highest score enabled some teams to "game" the system and select their opponent in 'The Maze' by holding back on their Gauntlet score.
The season one tournament structure was straight forward and had none of these problems, so it gets my nod for best of the series. Pick your own episode.

Publicité Ennuyeuse
Q: Ask Aaron semble être loin derrière son jour de foin d'il y a plus de dix ans, et cela n'a aucun sens ! Ce site Web m'a servi, ainsi qu'à d'innombrables autres. Alors, comment se fait-il qu’il soit en retard par rapport à TikTok et Facebook ? Eh bien... après une longue introspection, je suis arrivé à la conclusion. Ce site manque tout simplement de « PIZZAZZ »! Voici mon guide pour savoir comment l’améliorer.
  1. Embauchez des personnes pour répondre à des questions qui ont des personnalités radicalement différentes. Lorsque les gens posent des questions, ils peuvent obtenir une réponse de colère, une réponse déprimée, une réponse libre d'esprit ou une réponse réellement utile.
  2. Offrez aux lecteurs un prix gratuit chaque samedi. Cela peut être quelque chose d'utile ou quelque chose de peu pratique et bon marché.
  3. Inondez la barre latérale de photos de chats en surpoids. (Personne ne se soucie des équipements.) Vous pouvez commencer par « Monsieur Mitaines ».
  4. Organiser le vote pour le CRHoF tous les deux jours au lieu de tous les deux ans. Cela pourrait résoudre nos deux problèmes.
  5. Mettez « ICEYWAVE EST IMPRESSIONNANT » en néon brillant quelque part sur la page d'accueil. Une publicité ennuyeuse reste de la publicité!
Ces changements devraient aider cet endroit à se remettre sur pied. :)

- Cordialement, Iceywave

A: [Mark J.] Your suggestions did not impress me in English, but something in their rhythm suggested that they might read better if I translated them into French. I was mistaken.

I assume that you are baseing your assesment of Ask Aaron's vitality on my previously posted chart showing the number of questions answered on Ask Aaron over time -- but "questions answered" is not the measure of website success.

Below is a chart showing the relative number of unique visits to Ask Aaron per calendar year for the last nineteen years (I consider the absolute numbers proprietary). As you can see, 2023 was the top year for visits in the history of the website. No doubt people flocked here to read your posts.

With Friends Like This...
Q: Humorous Post I have another question about my fairyweight drum spinner. I was thinking of reusing the LiPo from a Hexbug SawBlaze. It runs for about 10 minutes with all four motors running (and takes roughly one hour to charge, and given that I would have roughly 20 minutes between matches, it should be fully charged before every match) so I thought it could power a robot with two N10 motors and one weapon motor. What do you think?

A: [Mark J.] Awesome.

Q: Speaking of the weapon motor, I found this one at Hobby Lobby and wondered if it would work for different fairyweight design (like a horizontal spinner). It weighs 30 grams, which is a bit overkill for a 150g bot, but I was still wanting to know your opinion.
-sincerely,Iceywave [9031 Miles West of Mumbai ✪]

A: Go for it. Use five of them.

My Frustrations
Q: Power consumption [Tamil Nadu, India]

30 seconds later...

Q: How to calculate average power consumption [Tamil Nadu, India]

A: [Mark J.] I no longer answer questions from builders competing in India due to serious safety concerns for builders and spectators at many robot combat events in the region.

I am also frustrated by my interactions with Indian builders. Here is a 2021 post from the Ask Aaron Archives that both answers the current question and illustrates my frustrations:

Really Bad Hamburger
Q: Sir my motor amp is 520 a how much mah battery is required for 4 minutes in robowar arena sir please answer my question [India, via a proxy in New Jersey]

A: [Mark J.] You have not provided enough information to calculate the requested answer. The hamburger is bad. See: Example Drivetrain Analysis using the Tentacle Torque Calculator for the information and process required to define motor loading and calculate the battery requirement.

A few hours later...

Q: Sir I want to select a battery for Robowar in I am using 2 propdrive 50-60 motor each on 200amp on 22.2v for weapon and 2 R997 motor on 60amp each on 22.2v for drive motor for 66 lbs category and total total time should be active is 6 minutes please answer my question sir [India, via a proxy in Oregon]

A: You didn't bother to read the link I provided, did you? A quick summary: current drawn by electric motors is proportional to the loading placed on them. You have information about your motors, but you need to know the wheel size, drive gear reduction, and physical details about your weapon in order to estimate motor loading.

Ask Aaron is not a free engineering service. We provide tools and information needed to solve your robot design and construction calculations, but we won't do your homework for you. Since you aren't willing to use the tools or instructions provided by Ask Aaron, you might learn something by watching Robert Cowan go thru his process of estimating battery capacity requirements for a robot with a large spinner weapon: Robert Cowan Video: Battery Capacity Calculations

The Axle Does Not Spin
Q: Some shell spinners (Ziggo, Mega/Gigabyte) have a pole on top that doesn't spin with the shell. How are those attached? I'd expect the shell to spin on an axle that would have to be mounted exactly where the pole is mounted instead. [Beavercreek, Ohio]

A: [Mark J.] The top pole is an extension of the non-spinning weapon axle. The images below show 'Megabyte' with and without the weapon shell mounted.

  • The weapon axle is a large diameter non-spinning "dead shaft" attached to the chassis base and supported where it passes thru the top of the chassis.
  • In the 'naked' photo you can see the tall weapon hub with integeral bearings riding on the dead shaft.
  • The hub includes a pully that is spun by the weapon motor via twin V-belts.
  • After the shell is bolted to the hub, the top pole is clamped onto the axle stub that extends above the weapon hub.

Because They Worked
Q: Hi Mark! First time caller, long time listener; love the site and thanks for all the help you've given the robot combat community over the years.

I don't have a question, more a curiousity; I'm interested to learn how the typical electronics circuit (or wiring layout? Not sure the correct term) of heavyweight robots has changed over time, and why older ways of doing things made sense at the time. (I'm still trying to get my head around why early bots used servos and microswitches instead of speed controllers, for example...)

Do you fancy indulging me with a brief history? - TJ [South East UK]

A: [Mark J.] Thank you for your kind appreciation. To paraphrase Blaise Pascal: I would like to have written a brief history on this topic, but I only had time to write something a bit too long.

In the 1990's the entire combat robot community consisted of a few dozen slightly loony tinkerers. There were no electronic components made for combat robots, and the explosive development of electric hobby airplanes and drones from which robot builders might 'borrow' components was still years away. You could not jump onto the internet to pick and choose from a wide array of R/C interfaced switches and motor controllers to suit your design needs as you can today.

You could pop down to your local hobby shop and buy (at some considerable cost) a hobby aircraft twin-stick 72 MHz R/C transmitter/receiver set with servos and a small NiCad battery pack. You would then send off the set to a service that would (for further cost) convert it to the 75 MHz 'surface radio' frequency to make it legal for use with your robot. In the UK I believe you could simply purchase a 50 MHz system that was acceptable for robot use. Plus one for the UK.

Once you had the R/C gear, the next challenge was interfacing controllers to the radio output. The only electronic motor controllers capable of speed and directional control of DC electric motors that were powerful enough to push around large combat robots came from sources like golf carts, miniature ride-on trains, camera dollies, and industrial applications. Few of these controllers would accept the output from a hobby remote control receiver as an input, and designing an interface was beyond the capability of most robot builders.

In the US you could purchase motor controllers with R/C interfaces from Vantec, a company that had ties to special effects builders in the movie industry, but they were expensive. A two-channel reversible motor controller rated 60 amps continuous per channel was $500 -- more than $1000 inflation adjusted to 2024. These had no over-current protection and when abused (as often happens in robot combat) they would fail abruptly and without warning. The 4QD motor controllers from the UK were much more sophisticated, but it took some time before R/C interfaces for them became available.

Simple on/off control of motors, actuators, and pneumatic valves was also a problem. R/C interfaced electric switches/relays were uncommon, often unreliable, and (wait for it...) expensive. You may recall I mentioned above that R/C transmitter/receiver sets of the day came with R/C servos. If you bought a 6-channel set you got six servos. It did not take long for some unknown and desperate robot builder to look at that stack of servos and decide to use one to mechanically trigger a pair of microswitches. See also: Solenoid Control of Combat Robots

Why did these strange and primitive ways of doing things make sense at the time? They made sense because they worked and we had no affordable alternative solutions. Builders today have it easy.

Interesting related article: A History of R/C Technology.

[Mark J.] Friend of Ask Aaron "Iceywave" sent me a very excited message. After a long search, Icey found the archived post from 2016 that inspired him to launch his infamous Iceywave Troll. I thought I might re-print this seminal post in hopes that it might inspire others. I'm pleased to see that my positive evaluations of Designs #1 and #6 were proved correct when they were implemented in BattleBots competitors 'Tantrum' and 'Malice'.
Q: Greetings:
I was wondering how effective the following weapons would be on a robot. Note that I've ordered these roughly from "least likely to work" to "most likely to work", and am only seriously considering building the last three.
  1. A vertical spinning weapon on a pneumatic piston
  2. A horizontal spinning weapon on a pneumatic piston
  3. A drill/'Niterider'-style weapon on a pneumatic piston
  4. A pneumatic piston on a horizontal spinning weapon
  5. A lifter that deposits the opponent onto a spinning weapon on top of the robot (if you need a better description I can link you to a picture.
  6. A horizontal spinning drum weapon
  7. A "face spinner" (think 'Invertibrat' from Season 4)
  8. A front-hinge flipper a la 'Firestorm' or 'Cassius', except the lifting arm is replaced by a blade to potentially damage the opponent (obviously this would have to be a high-powered pneumatic flipper)
And yes, I know your "efficient, simple, easy to use" mantra, I just wanted your opinion on this. [Portland State University]

A: [Mark J.] I don't consider any of the weapons to be practical, so let's talk about the designs purely from a conceptual standpoint.

  1. A spinner weapon gets much better 'bite' if the closing speed on the opponent is greater. In close quarters, having the ability to quickly thrust the spinner forward is conceptually valuable.
    Conceptual score: A
  2. Same benefit as #1, but horizontal spinners throw both the attacker and target in opposite directions. Less desirable.
    Conceptual score: B
  3. 'Niterider' had a 'disemboweler' spike intended to penetrate another robot then twirl some stiff wires around to chop up internals. Would work really well if combat robots were armored with cardboard and filled with eggs. Adding pneumatics won't help.
    Conceptual score: F
  4. Whaaatttt?? How does that accomplish anything except sudden imbalance?
    Conceptual score: F
  5. I really hate dual-weapons. Decide whether you want to flip 'em or shread 'em, then put all your weight allowance into a single effective weapon.
    Conceptual score: D
  6. OK, maybe this one is practical. The drum stores more energy than a bar or disk, so it has some promise. Keep the drum fairly short and with a large diameter and you might have something.
    Too practical for a conceptual score
  7. 'Invertabrat' was an unsuccessful 'flipper' robot that violated the 'two-weapon rule' and added an ineffectual milling head to the back of the robot. Spinning at full speed the milling head might possibly leave a nasty scratch on aluminum or plastic. Enlarged, one edge goes up (good) and the other edge goes down (bad). Hit with the wrong edge and YOU fly upward.
    Conceptual score: F
  8. Blades can't cut modern robot armor, and a sharp edge makes it easy for your opponent to slip off to one side or the other. If you wanna flip 'em, flip 'em. If you want a pneumatic pickaxe, build that. Points for visual appeal.
    Conceptual score: C

I Have Pages for That
Q: I should really stop saying "I'm not going to be back until (insert date here)" because that’s the signal for my brain to start thinking of some crazy combat robot ideas : /

Anyway, I’m going to attempt my first ever bot with an active weapon! It's a 150g drum spinner, and I've gotten most of the design figured out. The only part I need your help with is the weapon.

What’s the best motor to use for the spinner? I tried searching the archives for "fairyweight weapon motor" but couldn’t find any recommendations. [West of San Antonio ✪]

A: [Mark J.] Inputs of "150 gram robot" and "drum spinner" do not give me enough information to supply a "best" output. Weapon motors should ideally be matched to the Moment of Inertia of the specific weapon which varies with the mass, shape, and specific dimensions of the weapon.

  • Your drum might be very large for a fairyweight and have a large MoI;
  • Your drum might be very small for a fairyweight and have a small MoI;
  • You may be spinning the weapon with a belt drive with some amount of speed reduction from the pulleys;
  • You may be driving the weapon directly.
I can provide two bits of general guidance:
  1. The weapon motor size formula in the Ask Aaron Brushless Motor Selection Guide pumps out a motor weight of about 12 grams for a fairyweight spinner. That is a VERY GENERAL number to make sure you're in the right ballpark.
  2. 'BE 1806 2300Kv' outrunners (18 grams) are popular weapon motors in both kit and scratch-built 150 gram spinners. They are a little 'overkill' but should be adequate for a direct-drive drum about which I have no other information.
Q: I was also gonna make it a single-toothed spinner. Is there a method to calculate the center of gravity of an asymmetrical spinner? If needed, I can send a picture of the weapon. -sincerely,Iceywave

A: A good CAD program will give you the CG for an object like an asymMetrical disk or a single-toothed drum. It isn't something reasonably done by hand calculation.

I'll mention that single-toothed drums are a pain to machine and balance. A common and very effective substitute is a symmetrical drum or beater bar with offset teeth: two teeth set outboard on one side, and two teeth (or one wide tooth) centered inboard on the other side (see images below). For insect-class robots the 'teeth' are often large screws inserted into threaded holes for ease of replacement. Several beater bar kits are made this way.

P.S. very random question, but I counted 120 bots on my ICONIC Combat Robot Hall of Fame Ballot but the results say I had 117. Which three didn’t count?

A: Nope. I'm not gonna go dig thru last year's Combat Robot Hall of Fame voting to find your ballot and re-score it. As I recall it took me some considerable effort to do that the first time. There WILL be a maximum ballot size next year.

From memory I believe you cast separate votes for a few robots from the same team in different weight classes that would be considered a single robot for purposes of The Hall, like featherweight 'Huge' and heavyweight 'HUGE!'. Those votes would have been combined as a vote for a single robot in the tally. See CRHoF Eligibility for clarification.

Q: FACE PALM - I never considered making the drum with offset teeth! That idea is much better than what I was thinking. Thanks!

The spinner will be belt driven, so there’s much less strain on the motor that way. I take your building advice seriously. :  )

Lastly, are there any kits for fairyweight spinners? Robot Combat Wiki doesn’t list any. If there are, then I could use all the electronics and make a custom chassis for it.

A: Glad to hear you've been paying attention about direct-drive spinner motor strain -- but you'll find that almost all 150 gram class spinners are direct drive. The Square-Cube Law tells us that you can get away with higher stress loadings on small structures (like a 150 gram robot) than you can on larger structures (like a heavyweight robot). The smaller the robot, the less sense the added complexity of weapon belts and pulleys makes. For a fairyweight drum supported at both ends, direct-drive is worth considering.

I know of no full kits for fairy spinners -- but Bristol Bot Builders offers component kits for this weight class:

You may not want to order your parts from the UK, but you can certainly use the kits as a parts list and grab components from US sources. I would likely build around a Malenki Nano integrated receiver/ESC.
What About the Blue Wire?
Q: so hi i just recently got into this amazing hobby and I am making an antweight for the first time. I want to have tank drive so i can move two motors sepretley so I bout an esc made to control 2 motors. There is a small issue though i cant find anywhere how to control the two motors with one esc separately so i can turn. I can do this because there's only one output wires so i can either have all motors on one channel or another.

For reference I'm using the flip sky dual drive bidirectional esc (brushed) with two brushed motors hooked up to the basic fly sky i6x receiver controller by the fly sky i6x please ask questions if you need more details to help. [Dillsburg, Pennsylvania]

A: [Mark J.] One of the problems with buying an inexpensive product for your combat robot is the lack of an understandable user manual. The instructions available on the FlipSky product website are a poorly translated jumble of incomplete and contradictory information, and their wiring diagram is entirely wrong. Before purchasing a component for your robot I recommend that you download the manual to see if it makes sense to you. If it does not, find another product. Let's see if I can sort this out for you. In your problem description you refer to "only one output" wire:

  • I'm guessing that you're talking about the 3-wire (white/red/black) cable that plugs into the CH2 port on your FS-iA6 receiver.
  • There is also a single blue wire with a small connector. That wire plugs into the top pin of the CH1 port on your FS-iA6 receiver
I've made a sketch of an 'end view' of your receiver showing the receiver ports. I've color-coded the pins that the two receiver cables plug into: There is a tiny three-position switch near the blue wire attachment to the circuit board. This switch is used to select one of three ESC modes. One of these three modes will give you single-stick "mixed" control of the two motors on CH1 and CH2, but the FlipSky instructions for the switch make no sense:
This ESC has three modes, choose it before before power on (toggle switch):
  1. Mixed control (differential speed) control mode by toggling switch inward
  2. Two-way synchronous control mode (switch inward)
  3. Two independent control modes (switch extension)
From your description you have the ESC in synchronous control mode -- both motors controlled by a single R/C channel. Move the toggle to another position and see what control result that gives you. If that isn't right just power down, move the switch to the third position, and power back on.

If you need help setting up your FS-i6 transmitter, I have written a Combat Robot Guide for the FS-i6 Transmitter that might be useful to you.

If I did not correctly understand your problem, please write back with more information -- and next time spend an extra couple dollars to buy an ESC with readable instructions. It will save us both a lot of time and trouble.

If It Can Be Seen
Q: Can I use the receiver of my flysky i6xs led for my safety led in the us [Dillsburg, Pennsylvania]

A: [Mark J.] I answered this question from another builder a few weeks ago. From the archives:

The requirement for a power indicator is typically something similar to the SPARC ruleset section 8.6:
8.6. All Robots must have a light easily visible from the outside of the robot that shows its main power is activated.
In small robots this requirement is often met by an existing small LED on an ESC or receiver positioned such that it may be seen thru a transparent top panel. The light does not need to be visible from all angles...
If your receiver LED cannot be seen well enough to satisfy the event organizer, offers Robot Power LEDs with a cable that can be plugged into an unused port on your receiver. Six colors, easy to mount, wide voltage range, cheap. Buy a couple and keep one as a spare.
About Like Your Kitchen
Q: I wasn't going to ask this initially because I didn't want to be 'That Guy', but how loud (in decibels, preferably) are average insect weight fights? I ask because I don't usually see people wearing hearing protection during beetle/antweight events, but is that because their hearing is already bad? In Texas the arenas for insect weights have floors made of plywood and walls made of lexan at least 1/4 of an inch thick. I don't know how much that would increase/decrease the noise, but I thought it would be important info.

-sincerely,Iceywave [West of San Antonio ✪]

A: [Mark J.] The noise level at an insect-class fight is about the same as the noise level in your kitchen when you're making spaghetti. Maybe less. You likely won't need hearing protection at a Texas beetle fight.

Q: Thank you for assuring me about the noise level. Unless I have an unexpected emergency with 'Exa' this will probably be my last post before I finish my extremely belated April Fool's Day surprise (which I guess should now be called May-pril Fool's).

-sincerely,Iceywave :) [West of San Antonio ✪]

One last question, why did you change the look of the star beside my name?

A: The old star [☆] was fine, but I thought the new star [✪] looked a little more 'Texas Lone Star' for someone 'West of San Antonio'.

I Don't Usually Explain
Q: what rules would be needed to define a cardboard weightclass that would take up 5 pages?

-BackyardBots [Rocky Mount, Virginia]

A: [Mark J.] You're referencing theUnlimited Breadstickspost farther down this page, in which friend of Ask Aaron 'Iceywave' humorously proposes five changes to the National Havoc Robot League rules. The fifth proposed rule change is:

Fifth - Make a separate weight class for bots with cardboard armor. This will encourage more versatility in the designs.

Bad idea. NHRL would add five more pages to their ruleset to define exactly what qualifies as 'cardboard'.

My response to Iceywave's proposed rule change is a joke. I usually refuse to explain my jokes because explanation removes all of the joy, but I will make an exception this time because the NHRL probably does not get the joke either:
The NHRL ruleset is known for being lengthy and overly complete. Example: sub-section "2.1 Expectations and Standards of Conduct" has an introductory paragraph followed by fourteen bullet-pointed examples of "Prohibited Conduct" and a concluding paragraph describing the physical area in which these behaviors are prohibited.
Given this tendency by the NHRL toward over-definition, my joke hinges on an exaggeration of the additional length that would be added to define exactly what qualifies as 'cardboard'. You may now laugh.
Hey BackyardBots! Sorry about any confusion I caused. I have a l-l-o-o-n-n-g-g history of posting very satirical "questions" that are inspired by others who should've just asked The Cheerleader. Just go to the Team Run Amok and Friends archive and scroll down to see what I mean!

P.S. I really like your plastic antweight design. If I'm ever on the east coast I'll make sure to bring 'Exa' (the name of my plastic thwackbot, which you can also read about here).
- sincerely, Iceywave : )

Party Like It's 1994
Q: 2024 marks the 30th anniversary of the first major combat robotics tournament in history, and I did something BIG to celebrate! I made all the 1994 U.S. Robot Wars competitors in Robot Arena 2!

We've got...

Lightweights: 'Andy Roid', 'Julie-bot', 'Pain Mower', 'Saturu Special 1', 'Slo-Mo', CRHoF honorable mention 'Spiny Norman', 'TMZ', and 'Zomo'.

Middleweights: 'South Bay Mauler' and 'X1'.

Heavyweights: 'Doolittle', 'Ramfire', 'The Beetle', 'The Master' (both weapon choices!), 'Tiny Tim', 'TMZ', and the reserve 'Bloodletter'!

For once I can't take all the credit for a build. The saw version of 'The Master' was first created by user 'ProPlazRA2' on I made some slight alterations to the internals to make it perform better, and used the same chassis for the 'thwackbot' version.

Thanks for keeping this site running. Here's to the next 30 years!
-sincerely, Iceywave [West of San Antonio ✪]

A: [Mark J] YOU CAN NOT BE SERIOUS! Did you actually do this? All sixteen competitors - plus a second weapon option and an alternate - from the inaugural 1994 US Robot Wars event rendered as fully operational and playable Robot Arena 2 'bots?? I can now entirely re-enact the first recognized combat robot event on the planet???

Pause while head spins...

I am flabbergasted. I'm deep into another project at the moment so it will take a day or two for me to to properly add the images and file links to the Robot Arena: Design and Destroy - Downloadable Models page.

Update: All done! The link above will take you straight to the Robot Wars 1994 section of the RA2 Models Page.

Short Post Titles
Q: I have a few questions about Ask Aaron...

1. What's the most questions you've received in a day? What's the longest you've gone without receiving any?

A: [Mark J] I don't track day-by-day question numbers. The closest I come is the graph posted down at the bottom of the Ask Aaron Anniversary page that I last updated this month. You can see on the graph that in 2010 Ask Aaron averaged nearly three questions per day:

2. It's been over five years since 'Clickbait Month'. Ever consider doing it again?

A: I never received any feedback on Clickbait Month. Nobody said they liked it, nobody said they hated it, and nobody linked to it. The concept slowly changed into theShort Post TitlesI put above each question.

3. Do you ever wonder what became of that bar spinner guy from Texas?

A: No, but I'll tell you what I do wonder about. When I warned "Texas" about having a very poor chance of being selected for BattleBots with an "it's been done" bar spinner design, his reply was:

As I see it with battlebots, you either have to have serious chops on the combat robot circuit (which I don't have in my wildest dreams) or a hook that appeals to the TV producers. I think I have the hook, time will tell.
I still wonder what his 'hook' was.
4. ...and do you still own 'John Jacob Jinglehiemer Schmit'?

A: I've never owned JJJS; I have a long-term lease thru 2028 with an option to renew.

P.S. If I "hypothetically" continue the RA2 models, what pixel dimensions would work best for their profile pictures?
-sincerely,Iceywave [West of San Antonio ✪]

A: I resampled your earlier model pics to 200 by 150 pixels for the Robot Arena: Design and Destroy - Downloadable Models page.

Unlimited Breadsticks
Q: Caution: Humorous Post I think NHRL's rules are too confusing (don't we all?) so I decided to fix them.
First - Only give weight bonuses to bots that are sponsored by 'Olive Garden', since everyone knows that you gain lots of weight when you're there.

[Mark J.] Can I just name my robot 'Unlimited Breadsticks'?

Second - Limit the amount of bots on one multibot team to only prime numbers. This change will appease math nerds like myself.

Change it from primes to the Fibonacci Sequence and I'm in.

Third - Allow water jets to be used as weapons. If your bot can't handle liquids then you need to up your game.

Let's just flood the arena with an inch of water. It would make the "ground game" much more interesting.

Fourth - Ban the color red from being painted on all robots. It's a hazard for near-sighted hummingbirds.

I don't like painted bots to start with. The paint shows damage.

Fifth - Make a separate weight class for bots with cardboard armor. This will encourage more versatility in the designs.

Bad idea. NHRL would add five more pages to their ruleset to define exactly what qualifies as 'cardboard'.

I think if all events adopted my rule set the world would be a much better place. Thank you for all the help with my thwackbot!
-sincerely,Iceywave [West of San Antonio ☆]
Q: what rules would be needed to define a cardboard weightclass that would take up 5 pages? -BackyardBots [Rocky Mount, Virginia]

A: [Mark J.] You're referencing Iceywave's fifth suggestion above, where I reply:

NHRL would add five more pages to their ruleset to define exactly what qualifies as 'cardboard'.
The National Havoc Robot League rulebook is known for being lengthy and overly complete. Example: sub-section "2.1 Expectations and Standards of Conduct" has an introductory paragraph followed by fourteen bullet-pointed examples of "Prohibited Conduct" and a concluding paragraph defining the physical area in which these behaviors are prohibited.

My reply is a joke based on satirical exaggeration of the length that would be added by the NHRL to define exactly what qualifies as 'cardboard'. I'm only willing to explain this because I think that the NHRL may not get the joke either. You may now laugh.

A Novelty Entertainer
Q: It's me, Iceywave. Here to ask an actual question about building a robot! 😲

I'm planning on making an antweight torque-reaction thwackbot - and before you ask, NO, I don't plan on winning any tournaments with it. It's a "novelty bot" intended for entertainment purposes and I was wondering about which 'SilverSpark Motors' to use for the drive.

Its design will be similar to the 2020 version of 'Axe Backwards' and (if my calculations are right) I should have around 6 to 4 ounces left to dedicate to the weapon, which will be sticking out about 3.5 inches from the circumference of the wheels. So, should I use high torque/low speed or low torque/high speed 'SilverSparks' for the bot? Even though it's a "novelty entry" I still want it to get in some good shots during a fight.

I hope I gave enough information. If I haven't, just let me know and I'll try to provide more details.
- sincerely, Iceywave [West of San Antonio ☆]

A: [Mark J.] So, Iceywave wants to build an overhead reaction thwackbot that Iceywave knows can be no better than a novelty -- but Iceywave wants it to "get in some good shots". The first answer I wrote violated General Order #26. I've shortened it a great deal.

'Axe Backwards' drew power from its full-body vert spinner to add power to its axes, but a true torque reaction thwack get its weapon power from the Newtonian reaction of a drivetrain attempting to accelerate/decelerate the mass of the robot chassis.

To directly answer your motor question:

The greater the torque that is applied toward robot acceleration, the greater the counter-torque that is applied to flip the chassis/weapon over in the other direction. This might lead you to believe that the better gear motor for the purpose would be the one with the greater torque, but torque is traction limited. This means that as soon as the drive train generates enough torque to break traction and spin the drive wheels no additional counter-torque is available to power your weapon strike.
Pull up the Tentacle Drivetrain Calculator and enter the specs for your motors and chassis. You will likely find that you will not require a low-speed Silver Spark to get enough torque to max-out the thwack performance -- particularly if your traction is reduced by having a big lump of mass out on the end of a weapon arm that leaves only 10 or 12 ounces of weight on the drive wheels.

Ideally your design should have large enough wheels to allow some counter-balancing mass to be placed behind the axle. This makes it possible to have a heavy weapon tip and still generate enough reaction force to achieve good weapon acceleration.

Q: So... I'm just realizing that I've somehow dug myself into a real life 'Boy Who Cried Wolf' situation. The question I asked today really wasn't a troll question, but I think I can provide more clarity on it.

I was wanting to know what 'Silver Spark' motors would work best for my design. I figured high speed would cause the bot to-while providing a much quicker attack—thrust backward, meaning that it wouldn't hit the opponent unless the opposing bot was moving towards it. Or worst case scenario, the motors wouldn't have enough torque to turn it over, rendering it useless. I was wondering what your thoughts are.

A: I didn't take your question as a troll, Icey. I think the unpublished 'long version' of my original answer covered this topic better than did the published 'short version'. Let me expand on my answer a bit.

Once you have enough torque to break traction and spin the wheels, adding additional torque will not accelerate the robot faster and it will not improve the reaction hammer action.
I wrote my original response before I had your design sketch. It looks like the wheels are about five inches in diameter. For purposes of your weapon actuation that means you've got about 3/4ths of a revolution to make things happen before you're out of range -- half a revolution for the weapon and a quarter of a revolution of the wheel.

Let's run some numbers thru the Tentacle Drivetrain Calculator, shrink the arena size to 0.8 foot, and compare the acceleration of a couple of the Silver Spark gear ratios thru that short distance:

  • The 50:1 Silver Sparks at 7.4 volts in an ant with 5" wheels have a top speed of 4.22 MPH and will spin from a dead stop thru 3/4ths of a revolution in 0.41 second.
  • The 100:1 Silver Sparks at 7.4 volts in an ant with 5" wheels have a top speed of 2.11 MPH and will spin from a dead stop thru 3/4ths of a revolution in 0.38 second.

Torque has been limited by traction such that acceleration and weapon actuation for the two motors is essentially identical. I'd pick the 50:1 for their greater speed. Note that attacks made by decelerating as you approach your opponent are also traction limited, but breaking from a higher top speed may impart greater energy into your weapon.

If your weapon won't 'turn over' because it's too heavy you'll need to swap some weight from the weapon tip to out behind the axle to partially counter-balance the mass -- or maybe boost voltage to a 3S battery. A lot of reaction hammer design is trial and error.

Reply: Thanks for all the very helpful info! You just managed to clear up so much confusion that I couldn't figure out on my own.
-sincerely, Iceywave

Q: I'm back with another question about my thwackbot, which has now been moved to the 'Plastic Antweight' class. Not sure if you can consider that a premonition [sic] or a demotion?

Anyway, the wheels are going to be 5 inches in diameter. Only problem? FingerTech doesn't make wheels that size. I was going to print them out using PLA (the same plastic that the chassis is made of) and wrap electrical tape around them to improve traction. Would you happen to know a better way to make custom wheels?
- sincerely, Iceywave [West of San Antonio ☆]

A: [Mark J.] You are not the first builder to include a component in your design only to discover that said component does not exist. However, having a 3-D printer on your workbench does not automatically make it the best option to solve your problem -- see: The Law of the Instrument.

There are multiple interpretations of "better way". Do you want something simpler? More durable? Providing greater traction? More impressive in appearance? Casting polyurethane tires on custom hubs is popular with builders looking for impressive appearance with optimal traction, but it is certainly not simple. Since your thwackbot is "for entertainment purposes" I think something a little wacky might be appropriate.

In the very early antweight days the popular drive motors were R/C servos hacked for continuous rotation. The rotation was slow, so large diameter wheels were needed to get reasonable speed. It was common to use plastic lids from peanut butter jars with a rubber band stretched around the circumference for wheels - electrical tape does not provide great traction. How about an update of that wheel style?

  • The screw-on lids for large jars of assorted snack items sold at Costco (and elsewhere) are 4.5" in diameter, made of polypropylene, and weigh 20 grams each.
  • Drill a bunch of holes around the rim and insert rubber grommets for traction. The grommet thickness will take the diameter out close to 5 inches.
  • Bolt a 3mm hub like the FingerTech Sumo Hub to the center of the lid and you've got a unique, entertaining, and functional thwackbot wheel.
If you want something off-the-shelf, they do make 5" diameter foam wheels for R/C airplanes. Bodge a hub and maybe coat them with latex.

Q: One more question. I'm currently designing the 3D files for the chassis but I ran into some problems with how I'll attach the top and bottom panels together. I was thinking of using 6-32 'Flat Head' screws (length doesn't really matter) and directly screwing them into place, but I don't know if that will work without the strips inside the holes. If it doesn't, the other option would be a nut-strip, but I don't know how I would attach it to the inside of the chassis.

Did I say premonition? I meant promotion! Anyways, I love that idea for the wheels. : )

A: For un-threaded holes in firm plastic you'll want to use self tapping screws rather than "machine screws" made to thread into pre-tapped threads or nuts. Drill the hole in the piece the screw will bite into just a little smaller than the major diameter of the screw. A 6-32 self tapping screw typically requires a 0.012 diameter hole (#31 drill bit) and makes its own threads as it is driven in place.

There are special "thread forming" screws for low-density plastics like UHMW, but a generic self tapper will be fine for PLA.

Resistance is Not Futile
Q: I've built robots with printed hubs and O-ring tires that worked pretty well, but the O-rings that were mounted on the hubs cracked and deteriorated in a few weeks. The O-rings still in the bag were fine.

I've also used small rubber bands to tension my forks. I again found that the mounted bands became brittle and snapped while the bands remaining in the bag were still good.

The O-rings were from eBay and the bands were from a local discount store. Can I get better longevity with rings and bands from another source? Do I need a different type of rubber? [Social Media]

A: [Mark J.] Exposure to atmospheric ozone is the downfall of many types of rubber. Inexpensive O-rings made from Nitrile and 'Buna-N' rubber degrade quickly when exposed to air, and natural latex rubber bands have a similar problem.

It's easy to find both O-rings and rubber bands made of synthetic EPDM (ethylene propylene diene monomer) rubber that strongly resists degradation from ozone, sunlight, and common cleaning chemicals. Just keep them away from petroleum oils.

More info: Ozone Resistance of Rubber O-rings.

Shrink It and Watch It Move
Q: This isn't an 'Ask', more so an 'Answer'. I've seen a few people come here to ask about building shufflebots, so I decided to make a GIF showing how they work. I used Opentoonz, a free animation software. I hope you like it!
- sincerely, an intermediate animator : ) [West of San Antonio ☆]

A: [Mark J.] Prescient of you, Icey. I was just about to post the question below when your shufflebot animation arrived. If you're going to continue working with gif animation you'll want to know about Using this site I was able to edit your animation (remove excess frames, increase use of transparency, crop, shrink, change the frame rate, and gif optimize) to reduce its size from 105K down to 18K. You can also add text and rotate the gif. Very handy.

A good shufflebot build log.

Reply: Thank you for the recommendation. And could you add the website link for Opentoonz? Here it is: You need to keep the "/e/" on the end of the link, otherwise it will come up in Japanese.

A Well Disguised Triangle
Q: Hey there! I am a relatively new combat robotics builder that has just recently completed my first beetleweight robot named 'Faraday'. It's my own take and attempt at the design concept of "Monkfish", a very successful beetle which features a horizontal undercutter along with a shuffler drive mechanism.

I've worked on this robot for nearly 2 months now prototyping and testing the shuffler drive to work well. One of the main things I'd love to work more on is the shufflers, and specifically trying to improve the linear drive speed. While it's not slow, it's nowhere near the top speed of many other robots (including some other shuffler robots). Most of the dimensions currently present are either just assumed to be reasonable values or found through some testing.

I've done my best to work on figuring out the mechanics and math behind the cam system, including trying to find resources online, but it's been frustrating since there appears to be very little available for what I'm attempting to optimize here (lateral speed of the foot, primarily), since the slotted single cam mechanism appears to be used for very different applications in industry. Searching through the Ask Aaron archives yields extremely little regarding shuffler information so I thought I might as well ask if you had any sort of knowledge to start more work off of. I am currently using Repeat Compacts for the drive running at 4S, but I may look towards better motors in the future.

Thanks for your help. Your site has assisted me an extraordinary amount over the past couple of months while I am learning more about combat robotics.

Ryan D. [Terre Haute, Indiana]

A: [Mark J.] I've spent more than a bit of time contemplating the mysteries of the shuffledrive and I've found that optimization is simpler once you realize that a shuffle mechanism is simply a well disguised lumpy wheel. A classic three-plate shuffler propels the 'bot as would a triangular wheel with a 'radius' equal to your cam offset:
  • At slow rotational speed, a triangular wheel lifts its load by 1/2 the radius and allows it to drop back down three times per revolution. That wastes a lot of energy.
  • As speed increases the wheel load does not have time to fully drop back down onto the 'flat' of the triangle and the wheel loses contact with the floor for part of each rotation.
  • As speed continues to increase, the time of wheel contact further decreases. You cannot add to the forward speed of the 'bot with a wheel that is not in contact with the floor, so the benefit of a faster wheel rotation limits itself.
The greater the number of plates, the rounder the "disguised wheel" becomes: four plates equals a square wheel, six plates equals a hexagonal wheel, and so on. The rounder the 'wheel' the greater the amount of time it will spend in contact with the floor, and greater contact time equals greater opportunity to propel the 'bot. A shuffledrive with an infinite number of plates would perfectly emulate a round wheel.

'Faraday' appears to be a near-perfect copy of Monkfish and their 'pinned slot' shuffle variant which decreases the wasteful 'lift' phase of the cycle and extends the lateral motion, but other builders have further improved on this design. Take a look at at the article Experimentation in Shufflers by Absolute Chaos Robotics for an up-to-date review of shuffle design evolution. This short video of Jamison Go explaining a few points on the Silent X shuffledrive may give you some ideas.

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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