Questions and Answers about Combat Robotics from Team Run Amok.

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7642 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.

It Started As A Joke
Q: Is it true that the National Havoc Robot League is going to have their tournaments broadcast on ESPN? When do they start and what night will they be on? [Social Media]

A: [Mark J.] Rumors started flying when the June 2024 NHRL Teams Tournament webcast shut down after the qualifying rounds. NHRL was being cagey about why this happened and when the video of the finals would be available. In mid-July the NHRL announced that ESPN2 will air a 24 minute NHRL video on August 1st at 11pm Eastern as part of their 2024 "Ocho" programming:

NHRL Teams: Robot Fighting Championship: Sixteen elite teams featuring the world’s most dangerous and exciting robots clash in a high-stakes tournament, to fight for a share of $50,000 prize money and a prestigious Golden Dumpster.
The problem is that ESPN's The Ocho is literally a joke that started as a fictional TV channel that broadcast obscure "not quite sports" competitions in the 2004 movie "Dodgeball: A True Underdog Story". Starting in 2017 ESPN embraced that joke by putting together an irregularly scheduled program block of wacky, obscure, and geeky pseudo-sports. Here are some of the other featured segments in the 2024 Ocho line-up:
  • Waiter Waitress Competition
  • Uncut Beard and Mustache Competition
  • Speed Jigsaw Puzzling
  • Rubiks Cube Speed Competition
  • Jump Rope Tournament
  • Freestyle Trampoline
  • Speed Chess Championship
  • Battle of the Buoy 2 (stay afloat in New York City)
  • National Beach Tennis Invitational
  • Carjitsu Championship (Jiu-Jitsu inside a car)
  • Ultimate Tire Wrestling
  • Roofball World Championships
  • Adult Big Wheel Races
There is no weekly NHRL show. There is only a 24 minute "laugh at the geeks" video that will likely run multiple times in August.

Puttin' On a Gear
Q: How would I go about attaching a printed gear to the output of a servo? Right now I can only think of gluing the gear to a servo horn but I presume there's a better way. [South of Sacramento]

A: [Mark J.] For components that will disable a critical system if they fail, the general rule is No Glue - No Tape - No Zip Ties -- but there are exceptions. It would greatly help to know how large your gear is and what you will drive with it.

  • It is possible to print an internal spline to match your servo output shaft -- but it takes a higher-resoultion printer than you likely have. 3D printing RC servo splines.
  • If your gear is large enough, you may attach it to the top of a servo horn with small screws. This is not ideal for highly stressed components.
  • You can purchase pre-made gears with splines that will directly attach to servo splined shafts from sources like goBILDA and Servo City.
  • You can file/cut away the splined servo output into a square output shaft and print a gear to match. You will lose the fine position adjustment of the splines, but your transmitter may be able to adjust well enough for your application.
I forgot one: Print the gear with a 'press fit' onto the servo shaft. You can then drill an axial hole along the junction of the shaft and hub and drive in a self-tapping screw to locate the hub and lock rotation. This is known as a 'Dutch Key'. Machinists consider this sloppy work but it can be useful.
Somebody's Gonna Lose a Trailer
Q: Hey there!

I am currently trying to make plans for an upcoming competition, in which I am driving an undercutter beetle.

While thinking about strategies for opponents, I am wondering: What happens when two horizontal blades hit each other? What changes if both blades are spinning the same direction vs. different directions? Is there a rationale for gaining the upper hand in those situations (eg. higher tip speed, spinning the same way, attack speed, etc)?

Thanks for your time! [Milwaukee, Wisconsin]

A: [Mark J.] Vertical spinners are easy. Nice and predictable. Going weapon-to-weapon the higher tip speed wins. End of story.

Horizontals are a mess. Utterly chaotic. Going weapon-to-weapon usually goes to the weapon with greater energy storage -- except when it doesn't.

  • If you're confident that you have the stronger weapon, set your rotation Same Direction (clockwise vs. clockwise or counterclock vs. counterclock) and press for a weapon-to-weapon showdown.
  • If you fear your weapon is lacking, set your rotation Different Direction (clockwise vs. counterclock) to "mesh" your weapon with theirs. Keep weapon speed up and aim for non-weapon targets.
  • Attack speed and 'bite' are wildcards in this situation. If a fast charge isn't working, slow it down -- but keep your weapon speed up.
  • Your undercutter weapon belt may be vulnerable to attack by a mid-cutter. Keep that in mind when choosing a defensive stance.
For the benefit of other builders, the time to think about the attributes your robot will need when matched against specific opponents is during the design phase. Once the 'bot is built, your range of adaptive options is limited.
Twist My Arm Off
Q: I have a cordless impact driver that claims to have over 800 foot-pounds of torque. How does it generate that much torque? Why doesn't it twist my arm off? Could I use it to drive an effective crushing weapon? [Not Far from Here]

A: [Mark J.] An impact driver produces pulses of high "instantaneous" torque that each last only a few thousandths of a second. In between these pulses there is only a small "holding torque" while the mechanism stores up energy for another torque pulse. It's a very clever mechanism: slow motion video of impact aparatus.

There is no reaction kickback from the torque pulse back thru the driver handle. As shown in the video, the hammer is released as a free-spinning mass before it strikes the 'anvil'. Any hammer rebound is absorbed by the energy storage spring. See how clever?

Effectiveness as a crushing weapon is doubtfull. The mechanism itself is heavy and the actual output power is no greater than a good drill gear motor.

Keep Yourself Safe Out There
Q: Long time viewer to this website because I love how detailed it is. I have a couple of questions.

First you said that you don't think that Robogames is safe enough to the contestants to warrant recapping anymore so my question is what 10 commandments would you give to Robogames or any Robotic Combat event to make it safe enough to work?

My second question, my apologies if this has been asked before but will you ever get around to adding like Roaming Robots or the British equivalent of Robogames and the Olympian and the other like independent Robotic Combat events? Or is it because that there's no right information to send?

Thank you for reading this, I hope you have a great day, I love the

Best regards

Tim Sillery. [Birmingham, England]

A: [Mark J.] Glad to hear you are enjoying Ask Aaron, Tim. Thanks for writing in.

Question One Presenting Robogames results alongside those from other major events has become degrading to the properly run events. "BattleBots Update" has an article entitled Everything I Know About Arena Safety I Learned From Robogames that well covers the continuing problems with Robogames.

I don't need ten commandments to keep robot combat events safe. I can do it with three:

  1. Consult with other event organizers to learn and implement the "best practices" for robot combat safety in the weight classes you will host.
  2. If you experience a safety issue at your event:
    • Shut the event down;
    • Fix the problem;
    • Be transparent about the problem and its solution; and
    • Make sure the same problem does not happen again.

    You may then restart the event.
  3. Do not allow an egotistical maniac to run your event.

Question Two I would be very pleased to present the results of major UK events, but I simply cannot reliably find full tournament results for them. There has been no European entity that compiles full tournament results, and the individual event organizations are lax in this matter. It is becoming increasingly difficult to find full results for US events as well. If competitors do not insist that full results are compiled and published they simply are not considered important to the event organizers.

There's More To It
Q: I need to know what type of motor I need for my heavyweight sumo robot. I need high torque and a rotation speed of about 80 to 120 RPM. It would be 4 wheel drive, can you help please? [Sunderland, England]

A: [Mark J.] You haven't told me enough about your robot or your competition for me to recommend drive motors. The Hamburger is Bad. I'll be happy to help, but I need more information.

  • "Heavyweight" means different things at different sumo competitions. How much will your robot actually weigh?
  • Pushing power is limited by traction. Once the wheels meet their traction limit additional torque does not increase pushing power. To calculate the traction limit I need to know: the robot weight, the wheel diameter, and the type of arena surface (wood, steel, formica...).
  • With 80 to 120 RPM the robot will be VERY slow. Just how slow depends on wheel diameter. How large is the sumo ring?
  • Are there limits on battery voltage?
  • How much are you willing to spend on your motors?
Take a look at a sample analysis of a robot drivetrain to see how this all comes together. If it doesn't make sense to you, send me the information and I'll see what I can come up with.
BattleBots 25th Anniversary
Q: July marks the 25th anniversary of BattleBots, so I put together a game to commemorate the occasion. No prizes. It’s just for fun!

I've built 24 models of BattleBot competitors young and old in Robot Arena 2. Your job is to guess what bots they're supposed to be. I'm eager to see if anyone can get all of them!

I'll post the answers on July 2nd @ 2:00 p.m. central time. Any submissions that come after that won’t count.
-sincerely, Iceywave [West of San Antonio ✪]

A: [Mark J.] I made a new page for your BattleBots 25th Anniversary Celebration Contest to keep it from getting lost. I'll collect entries and score the results for you.

The contest is over and we have a winner! Iceywave's BattleBots' 25th Anniversary Contest.
My encoded entry list appears below. If you're interested, copy the coded text block into the "decode" window at the Vigenere Cypher Encoder/Decoder and enter UNIQUE as the key.
gnucixbq qumiwgwh amanjoni xrijbviy tlfexgpu cqjntulw iawvqlsn kxckcaak wgmriiir njwxudue lnrbrkfn rbmhvibm hrtefpco wjjvyfak lixewfqe lzisbmhr zxcriqwk vpynouhx nuzuybrk fnrbgroq nihgwbig ewimamhf cbiraomq wljumhyv inltixze mdtcnvur yvqbtvyp ypbhcgln gnrbrkfn
I scored 29 points -- which was not enough to win. Go take a look at the contest and see if you can do better.

Scrambled SPARC
Q: Not sure if you (or anyone) was aware, but the SPARC combat robot forum got removed some time ago. (Along with a complete revamp of the entire website.) I noticed the link was still there on FAQ #6, but it leads to a "404 Page Not Found". Just wanted to let everyone know. -sincerely, Iceywave :) [West of San Antonio ✪]

A: [Mark J.] Thank you, Icey. I spent the last hour finding and correcting half a dozen effected links in the Ask Aaron FAQ. Updating the links in the archive took a bit longer but are now complete.

The Webmaster's Code

A proper webmaster leaves a trail of breadcrumbs and redirects when they 'revamp' a website such that visitors following an old link will be treated better than being dumped into a generic '404 Page' or an unexpected menu system. Anything less is sloppy - just saying.

May or May Not
Q: What shaft to use for a beetleweight robot? [Indianapolis, Indiana]

A: [Mark J.] 'Ask Aaron' is not a free engineering service. Even if we were, no competent engineer would spec material or thickness before knowing a great deal more about the design than you have told us. The Hamburger is Bad.

If you're asking about a weapon shaft I can tell you that the Repeat Robotics Peter Bar Beetleweight Weapon Kit uses a 5/16-18×5" Grade 8 bolt, well supported on both ends. Something similar may or may not be suitable for your unspecified design.

They Are Cheap, But...
Q: I'm making my first fairyweight. I'm about to add a weapon but need a brushless ESC. I'm wondering what the main difference is be between a Chinese one and purpose built one. I can get one from Ali Express for a few dollars, which I imagine would suit my beginner needs, local hobby stores have drone ones for 4-5 times the cost at cheapest.

Second question would be, what amp rating do I need? I can see 5, 10, 12, 20, 30A options. Battery is a 300mah, 2S Lipo, weapon motor is a BE1806 2700kv. [The Antipodes]

A: [Mark J.] Aside from price, the main differences are:

  1. Quality Control - If you buy from Ali Express there is a fair chance that you'll get a bad ESC 'cause quality testing appears to be non-existent. I recommend ordering two or three to improve your chances of getting at least one that's usable.
  2. Documentation - The ESCs from your local shop may have instructions that make sense -- check this before buying. Instructions from China-direct sources are gibberish (see achived post below). As this is your first exposure to brushless ESCs you may want to spend a few more bucks to avoid frustration in getting them to work.
A standard 1806 outrunner on 2S spinning a reasonably sized weapon will be fine with a 10 amp ESC.
Flashback: an archived post from 2020
Q: I've got a FS2A mini receiver from Banggood bound to my FS-i6X transmitter. The transmitter failsafes are all turned on but the receiver just ignores them. The failsafe setting instructions on the Banggood site don't make sense to me:
Failsafe settings:
The receiver can normally receive the transmitter signal, push the rocker to the the failsafe set, long press the receiver bind button, the blue light flashes quickly several times and then always bright, failsafe settings is successful.
I know that other builders use this receiver. What am I doing wrong? [Punta Gorda, Florida]

A: [Mark J.] The Banggood FS2A receiver doesn't communicate with the transmitter in the same way a real FlySky receiver does, so setting the failsafes has a different process. I can't read Chinese, but I've become pretty good at translating Banggood English to Actual English:

  • "The receiver can normally receive the transmitter signal"

    "Turn on the transmitter and receiver."

  • "Push the rocker to the the failsafe set"

    "Move the transmitter sticks and switches to the desired failsafe positions and hold them there for the next step."

  • "Long press the receiver bind button, the blue light flashes quickly several times and then always bright"

    "Hold down the receiver bind button 'til the LED flashes, then stays steady."

  • "Failsafe settings is successful"

    "You're done."

That's what the instructions are trying to tell you. Next time buy a receiver with instructions that you understand.

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.

Max worked his metal magic and turned my dimensions and angles into the beautiful curved tube structure of the pneumatic lifter platform. 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.

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.

One Day Later

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).

A Couple Days Later

Q: What size is the timing belt for the weapon on endbots vector?

A: The weapon timing belt is a 90 Tooth x 0.25" XL.

Let me save us both some time and tell you where I'm getting the answers to your Endbots Vector questions. I'm using the Internet Archive Wayback Machine to access the old and the pages from 2020. Now you can too.

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.

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.

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.

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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