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Q: The spreadsheet absolutely does not like my mechanism. The rear bar rise isn't dropping to the value I gave, so the entire mechanism is skewed at a weird angle. So, I'll leave the measurements I got to you, and hopefully something will decide to work.
Known for sure, directly from the CAD model:
A: My apologies. I sent you off to talk the spreadsheet into giving a "perfect" model of a system that was too far outside 4-bar parameters it was made to handle. You don't need a perfect model -- you just want to know what happens when you try to lift a 2.04 Kg opponent out at the end of your slider and crank mechanism with a 60 kg servo on the crank. As the French philosopher Voltaire observed, The best is the enemy of the good.
Modeling your slider and crank as a conventional 4-bar where a short pivoting bar replaces the linear slider will underestimate the torque requirement near the center of the range of motion by a few percentage points, but that's more than good enough for our purpose. Here we go:
A: Mark J. Restricting your motor source to Amazon is a severe limitation. The only workable antweight drive motor options available at this time from 'The Everything Store' are the ubiquitous 'N20 gearmotors'. A good pair of N20's are a satisfactory and inexpensive choice to push around plastic ants in a club setting, but the N20 designation is a general design description for motors made by multiple manufacturers -- some good and some poor. I have sources for the good ones from actual robot suppliers, but the limited information supplied in an Amazon listing is inadequate to tell the good from the bad.
The Vex 29 ESCs are certainly adequate for N20 motors, but they do have some quirks. Here is a reprint of an Q&A from the Ask Aaron Radio and Electrical Archive that you may find useful:
What I'm trying to do is just to connect one motor and ESC to my receiver, and to run that one motor. I'm using a Vex Motor Controller 29, and I made the alterations to it like it says in Jameson Go's blog post. I'm running this to a Servocity 730rpm planetary gear motor. The battery is a 4s 850 mAh Turnigy LiPo. [Photo at right]
So what I have is the two wires coming off the ESC onto the motor, those are all good. Then on the other end of the ESC, I have the white signal wire and the a black ground wire going to my receiver, as well as an orange positive current wire and another black ground wire going to the battery, but when I plug them in, nothing happens.
Is there something I'm missing in the wiring system, or must it be an issue with my soldering or something else I've done? Any help much appreciated.
A: Mark J. You appear to have correctly modified the VEX 29 ESC for high voltage operation. You have also properly connected the ESC to the battery, motor, and receiver. Unfortunately you're missing a vital component.
A: Mark J. This is a 'first'. The question wasn't terrible. Perhaps the submitter thought the text was too personally revealing, or perhaps they didn't like my advice. Either way, the question has been expunged and we move on.
1. If I were to print the feet entirely from TPU, would they be prone to excessive lateral deflection and bending? Would this be solvable by using a different material for the compliant and non-compliant parts?
2. I couldn't really see in his article - is it safe to assume he's using bearings on the cam to feet connection, since the material choices are all quite high friction-wise? Would sleeve bushings work fine at this weight category?
Thank you! [Odense, Denmark]
I will give you the best answer that I can, but I will caution that I wrote that article as a summary of a little bit of experimentation that I did but I have never actually competed with a shuffler so far. I (mostly) built a 4.5lb shuffling ring spinner for my daughter using the exact compliant design from the article, and the shuffler system worked just fine, but it got abandoned for other reasons and I haven't come back around to another shuffler design again yet.
Thanks, Ryan Clingman
if there is a calculator or a way to know how much my motor can handle the load properly, please feel free to mention it if you dont have the time to help me with the specific down force [Amman, Jordan]
A: Mark J. I remember you writing in several months ago with questions about your spinner weapon. I'm pleased to hear that you are continuing to develop your robot!
The Ask Aaron version of the Team Tentacle Drivetrain Calculator will give performance and current consumption figures for a given robot drive system -- and will calculate the change in those figures for added magnetic downforce. You attached an image of your gearmotor spec sheet and I have converted those numbers into inputs for the drivetrain calculator:
The calculator shows that even without magnetic downforce the motors are flowing about 47 amps each under maximum pushing conditions. That is already placing the motors under dangerous heat stress, so I cannot advise placing additional load on these motors by adding ANY magnetic downforce. You can add downforce in the calculator and watch the impact on power consumption.
If your wheel size is significantly smaller than my assumed diameter it might be possible to add some small amount of magnetic traction assist, but do not over do it! An On-Line Magnetic Attraction Force Calculator from K&J Magnetics will give an estimate of downforce for a neodymium magnet of specific grade, size, and distance from a 'steel plate' floor. They also provide links to their inventory for magnets of the type entered into the calculator.
I watched the channel a lot when I was younger (2018 - 2020 specifically), and feeling nostalgic, I've been watching the new seventh season. It has invigorated me to rediscover why I loved this sport and Robot Arena 2 so much to begin with! Now, I'm sure we all remember my troubles with "Flamin' Yon". I still have him sitting in a box to this day. Well, I will be turning him into a new bot so I can finally enter my first competition!
It's been a lloonngg time since I've read the official SPARC ruleset but, just to be safe, I want you to look over my design to see if it violates any rules. I call it the Distract-O-Net! What do you think? -sincerely, Iceywave : )
Change your door locks and call the authorities if you see Craigybot prowling around. Oh, and your design looks just fine -- assuming that the net launcher does not actually work.
Are there and good motors and gear box suggestions that can withstand the abuse of hitting other bots? My weapon design will be a vertical spinning blade. Ive been looking at the bane bots and REV robotics, but I'm not too sure what to look for. Any advice? [Social Media]
See the Ask Aaron Spinner Weapon FAQ for guidance on weapon motor selection.
Q: Some things that I discussed today with my team was if we should use a belt drive, or do a direct drive for the weapon. I'm using a SunnySky motor for my weapon. How does the impact effect the motor? Is it overall better to use pulleys and a belt to absorb some impact or should a direct drive be better?
A: Hobby aircraft brushless motors are designed to be light in weight and spin small mass propellers. Their internal structure and bearings will not survive the direct shock loadings of multi-pound spinner weapon blades. Isolating such motors from impact loading is essential in all but the very smallest combat weight classes.
A: Mark J. There is no particular static sensitivity to the commonly used combat robot electronics, including the Malenki Nano. Standard precautions (handle boards by the edges, avoid touching exposed pins and pads...) are entirely adequate. Most builders don't even bother with those.
The Malenki Nano manual adds these precautions for your own safety (really):
The next test will use in of those fancy worm gears that are curved. I'll also have to encase the worm gear and generally tighten up the tolerances. I also plan on shortening the arm. Is there a better way to have a crushing jaw? I had also considered some sort of screw mechanism which would mean I don't have to have a wheel.
A: Mark J. Very nice test rig! Before I open the plastic ant crusher can of worms I must give my important and entirely sound "first 'bot" advice:
I assume that the metal screw on the tip of your crusher is for evaluation of your test rig. You won't be allowed a metal crusher tip in the plastic class. Depending on what types of plastic your rules allow you might consider a soft grippy plastic tip to hold your opponent securely 'cause I don't think a sharp plastic tip is going to pierce.
A: Mark J. Now that you mention it, I haven't seen Rodger the Web Gerbil for at least six months. I just now went down to my workshop and found a note on his little desk saying he was "going walkabout" and that he should be back by Guy Fawkes Day. This explains why I had to fix the "Form-to-Email" problem runamok.tech had last month.
Rodger did get most of the work for the Team Run Amok homepage March, 2026 update done:
No worries. I believe my web skills run deep enough to find and change the two numbers that have ruined your day. Consider it done.
Q: And Mark, I've been thinking about something. If no Combat Robot Hall of Fame [CRHoF] honorable mentions get listed on 50% of the ballots during the voting period, what happens then? It would seem very anticlimactic to wait for two years only for no new robots to get inducted into the Hall. -sincerely, Iceywave
A: The rules for the Combat Robot Hall of Fame have no provision for such a contingency, but I'm not worried. On nine occasions the Baseball Writers' Association of America failed to elect a single new member to the National Baseball Hall of Fame. Both baseball and the hall survived.
I have faith in the ability of the robot combat community to be correct in electing - or not electing - new members to the CRHoF.
Secondly, most vertical spinners designs include "ears" at the two-o'clock position on the spinner (see Calvin Iba's Lynx for a very clear example). How do these contribute to making the bot capable of the rudimentary self-righting when inverted, and how best would I design for that use case? [Unknown Server]
A: Mark J. Aw shucks, t'aint nothin. Just paying back the help given to me.
The vert spinner 'ears' prop up the front of the robot chassis when the robot is inverted such that the spinner weapon has enough clearance to spin without dragging on the arena floor.
A: Mark J. Is that you Iceywave? My new form service is still a little glitchy and I can't resolve server locations at the moment.
Yes, take the left at 4th and Central. "I knew I should've made a left turn at Albuquerque" is a famous running catchphrase from classic Looney Tunes cartoons where Bugs Bunny realizes he took a wrong turn and ended up in a bizarre, unintended location.
Pop culture historians tie the joke to downtown Albuquerque, specifically at the intersection of 4th Street and Central Avenue. When Route 66 was rerouted in 1937, it shifted from a north-south alignment down 4th Street to a straight east-west path along Central Avenue. Missing the turn or taking the alternate path historically confused drivers navigating the Southwest crossroad.
Iceywave wrote back to confirm that the above post was from one of his alter-egos. He also wanted to discuss the 'Iceywave Era™' at Ask Aaron and update me on his current status. I consider his full post to be personal correspondence, but I will mention here that I have full editorial control over Ask Aaron and if I did not appreciate his posts I would not have published them. I think the last few sentences of his update are appropriate to reprint here:
"Life has been going well since I've been away. I'm no longer in to combat robotics, but I still check back on this website from time to time. I've also played Robot Arena 2 a few times during the past month, but haven’t found it to be nearly as fun as a couple of years ago. I may pop in every few months to lighten the mood of this site with my silly posts, but the Iceywave of old isn't long gone. He's more-so changed, and I’m happy with that! Now that that’s settled, I'll be heading to a non-4DX theater to see a certain roadrunner and coyote... - sincerely Iceywave : )>"
A: Mark J. Not all that many. The Ask Aaron archive has a complete list of our combat robots. Although they were few, Team Run Amok robots finished "on the podium" at more than half the tournaments in which we participated -- an accomplishment very few teams can match.
A: Mark J. I've never actually tried, but it shouldn't be very hard. You can only go where the rails go, so just give it a little throttle and toot the whistle once in a while.
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
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:
Q: I created a custom lifter mechanism for my beetleweight based off of a slider and crank. In this case, the slider moves passively along a channel in the top plate, with a servo-powered crank in the front and the lifter tongue extending from the crosshead. I did this since I could easily plug in the angles and lengths I wanted, and to do something unique (ignoring that Jeff Vasquez did something similar with Deb Bot back in 2001). However, I don't know how to calculate the torque requirements and am just assuming the 60kg servo I chose has enough power. Is there a general formula I can use or a way I can modify the 4-bar spreadsheet? [Fullerton, California]
A: Mark J. I'm happy to see the shout-out to Jeff Vasques. It tells me you've done your homework.
We're pushing the 4-Bar Spreadsheet a fair bit beyond its tested design limits. Your "Rear Bar Base Raise: Up" input will be a fairly large negative number, and both the "Frame (A)" and "Crank (B)" bars don't actuially exist -- but torque numbers should still be valid. If it blows up: write back in, give me your set of measurements, and I'll whisper to the spreadsheet for you.
Kinda iffy - I was going under the assumption that the point where A and B meet is directly below where D and C meet. The problem is either here or I've hit the limit of the spreadsheet:
A second problem is that the N20 comes in a wide range of gear reductions giving differing output speeds, and in 6-volt, and 12-volt versions.
Q: Hey, sorry in advance if any of this is super naive, but I'm in the process of building my first beetleweight, and I'm all but a beginner with electronics. I'm just messing around with it tonight, trying to make sure I understand something, but I can't seem to get it to work.
Your test circuit needs a 6V nominal (3.5-7.4V) power source to directly power the Element-6 receiver. This could be a stand-alone BEC connected between your battery and receiver, a small battery pack, or even another ESC that has its own BEC.
A: Mark J. I could offer speculative answers to your questions, but the best source is the author of the article: Team Absolute Chaos's Ryan Clingman. I forwarded your questions to Ryan and he was very quick to reply.
Let me know if there are any more questions!
A: Mark J. Icey! Thank goodness you wrote in. Just a few days ago your "friend" Craigybot wrote in with a long and rambling tirade about how he couldn't get in to see some movie about a long war. I think he's off his meds, but worse he's been prowling around your workshop. He attached a sketch for a robot that was VERY similar to the sketch you provided, but it was clearly not within the rules; it featured an electrical discharge weapon and the bucket-o-chicken was the forbidden "extra crispy" style (see section 27.4.2 of the SPARC rules).
A: Mark J. Do not run a gearbox to your weapon! The shock loading from weapon impacts in the 15 pound weightclass is far too great for small gearboxes to survive. A belt drive that can provide some slippage at high loads (round belt or timing belt with one smooth pulley) and is the standard method to get speed reduction and torque increase for spinner weapons.
There are Three Common Designs for insect-class crushers:
Design Notes
Check with the event organizer to see how they feel about using metal weapon drive gears. Metal gears are always allowed in plastic ant drive trains and may be allowed for your weapon drive. Running a metal worm and worm wheel segment would make your crusher drive more efficient and way more reliable.
Q: Hey, Rodger! On the Team Run Amok homepage it still says "March 4th, 2025 marks the 24th anniversary of Team Run Amok's victory at Robotica." You're supposed to change it every March. It's been 6 months!
He updated the Team Run Amok "World Domination" icon to reflect the 25-year span of our team.
Q: Firstly, just wanted to say thank you for hosting this site. It's an incredible resource for combat robotics (and robotics in general), and I cannot express how much modern bot builders owe to you.
The ears are angled a bit toward the rear of the robot so that they will be positioned directly under the spinner axle when the 'bot is inverted (see diagram). The exact angle depends on the diameter of the spinner and the distance to the rear drive axle.
Team Run Amok has retired from competition, but we do consult with several active teams. When we were building we had a number of design and fabrication people outside our family core who worked with us on our large robots. Several of them could be considered as part of our team. Our insect class robots were all built in my workshop with design input from Aaron, while my wife Alissa served as our tour manager and psycologist on trips to competitions both domestic and abroad.
Remembering Aaron Joerger, 1991 - 2013
That's obviously
A question from your homework.
Do your own research.
Copyright 2009, 2026 by Mark Joerger
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