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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.
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 : ) 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 Ezgif.com. 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 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. 
'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. Over But Not Back
Q: Hi, Its ghost with backyard bots again.
it's been fully printed out, and in testing, I give it the throttle and..... it flips over
I reverse, trying to flip over again, and it doesn't. why is this the case?
A: [Mark J.] I'm having a hard time imagining that your fully assembled 'bot with that heavy direct-drive weapon hanging out in front is flipping over at all. Perhaps the center of gravity is so high that it is causing trouble.
I have previously directed you to Section 2.2.7 of the RioBotz Combot Tutorial for their formula to optimize weight distribution for best traction for a two-wheeled 'bot while keeping the nose down. That should apply in either direction. Some thoughts:
Reply: Thanks for the advice! Turns out it's the screwheads, they are just long enough to keep us from flipping back over. Our competition is this weekend, but after that I'll definitely try some of those suggestions! Unfortunately, magnets are a no-go with the non-metallic floor arenas that are popular here. Quirky FlySky
Q: Thank you for your FlySky FS-i6 transmitter tutorial.
I have followed the steps for dual motor robot control on my FS-i6X transmitter and it mostly seems to work as it should. My biggest issue is that I must go through the set up every time I turn on the transmitter. This is very annoying as I have quite a few adjustments to make it to get the custom settings I want. Then as soon as I cycle the TX off and back on, the settings are wiped out and I must do them all over again. A possibly related oddity, when I follow the "Quick and Dirty Set-up" directions I have nothing on receiver ports 1 and 2. I must instead plug my motor controller into ports 3 and 4. Any idea why the settings are not being saved or why the output signals are going to ports 3 and 4? Any help is greatly appreciated. [Direct Email]
A: [Mark J.] The FlySky FS-i6 has a remarkable range of features for such an inexpensive transmitter, but quality control may suffer a bit at their very low price point. Sometimes you get a bad one, and I believe you have a bad transmitter.
I see an occasional mention of an FS-i6 transmitter that will fail to save settings in the way you report. Here is a video from someone looking for a solution to that problem. However, having an Elevon mix appearing on receiver ports 3-4 rather than 1-2 is both new and very strange.
This behavior is not normal. I would return the radio to the seller for replacement. If it is not practical to return the radio there are a couple of actions worth trying:
Assisting the Elderly
Q: Here's a PNG version of the SVG file that I sent you back in March. I figured it would be easier to use in this file format. If you ever need someone to help with any web graphics, just put "I NEED HELP!" in giant text at the top of the Ask Aaron homepage and I'll get to it! I work free of charge, just getting to help is enough for me. : )-sincerely,Iceywave A: [Mark J.] How very kind of you, Icey -- offering to help a doddering septuagenarian find his way around the mysteries of modern web graphics. Are you working on your "Aiding the Elderly" merit badge? Fun Fact Mark built his first computer - from discrete analog components - in 1963.
P.S. - I’ve already violated General Order #26, are there any other important General Orders I should be aware of?
A: Well, you're in danger of violating General Order #17, but if you give it a little thought I'm sure you can avoid it.
P.P.S. - I’m not working on a merit badge, I just like helping people! To be honest, I didn’t know what use the SVG for either. I just thought it looked cool! A: I may have found the perfect use for the SVG. How about a T-shirt? Reply: I love it! Just put the Ask Aaron logo on top and I think we have a bestselling product. Greedy Like a Snake
Q: I've changed my mind about what kind of robot to build, and I think going for a lifter/grabber/suplexer thing is probably a good way to go!
Please could you explain to me how the lifter-grabber combo mechanism works (particularly in UK bots) as I haven't been able to find any internal mechanism diagrams or gifs, or how to build the mechanism at all. Also, how would you recommend I mix the weapon system on my Flysky FS-i6 controller? Cheers! [Eton, England]
Fusion is Lying To You
Q: I'm having trouble with the JavaScript Spinner Weapon Calculator. I have a 2.5" asym disk press fit on to a Emax 2205 and the calculator is reporting almost 1000 joules of energy at full throttle at 3S which feels very high. The MOI according to Fusion is 17.7 oz-in2 across the rotational axis with a weight of 1.6 ounces. All the units have been converted correctly. Are these numbers correct?
Thank you. [Canton, Georgia]
A: [Mark J.] I think Fusion is lying to you.
A 2.5" diameter solid steel disk with a 28mm hole in the center weighing 1.6 ounces has a MOI of 0.000037 kg-m2 = about 2 oz-in2. Given that your disk is asymmetric, I figure your real MOI is 1.77 oz-in2 and you're off by an even order of magnitude.
Two Types of CAD
Q: I just finished my antweight after a redesign to give it more interior space: the issue was that the wires took up much more space that I anticipated, even after wire shortening. I put the sizes of the objects in my CAD and I saw they fit with tons of space to spare, and I had most of the electronics just in the middle, no specific parts to hold them. How do I properly plan around the amount of space I need for wires inside my bot? [Cambridge, Massachusetts]
A: [Mark J.] The amount of space the assorted wires take up in a small 'bot often comes as a shock to new builders. I suggest using both types of CAD to avoid the need for a redesign:
Reply: It turns out the phase wires disconnected on both my Repeat Brushless motors. I sent the video to Peter and he told me what the issue was, and sent me two replacement motors for free. Great guy. Slippery Dark Forces
Q: I am a relatively new builder, and I’m looking to build a beetleweight. My idea is that it will be a large, potentially curved wedge, with a small spinner at the top, perhaps similar to the attached picture. It will be 2.W.D and have a very low clearance to the ground, perhaps aided by some magnets on the underside. How would you recommend I accurately bend metal in this way to form a wedge, and do you have any other suggestions and things to consider? I am rather new to this and have never made a spinner before! (I will build a prototype out of HDPE/Polycarbonate first, and then make a proper shell out of aluminium.)
Cheers! [Eton, England]
A: [Mark J.] I see that you're a fan of 'Team Dark Forces'.
Your photo shows version 8 of Russ Barrow's antweight 'Dark Pounder'. You can see vertical lines along the length of the curved body indicating that the piece was hand formed. Thin metal may be formed to a curve by simply pressing it around a curved surface, moving it a bit, and repeating the process as the curve takes shape. Thicker metal will require a substantial curved form (tree trunk?) and a mallet. It takes time, patience, and a good deal of 'fiddling'.
Team Dark Forces moved on from the large curved structure for the next version of this robot. The photo below shows version 9 of 'Dark Pounder' in front of version 8. Russ found that the fully curved structure of version 8 made it very difficult to slide an opponent up into the small weapon -- they kept slipping off to the sides. Version 9 concentrated on "delivering the opponent to the weapon".
How Many Can I Have?
Q: I am currently designing a bot with a chainsaw, hammer, etc, but I don’t know about any limits on the sheer amount. I’ve read through the rule book multiple times and cannot find anything about it. Am I blind or just straight up dumb? [Social Media]
A: [Mark J.] There is no limit to the number of weapons. Knock yourself out. As long as you stay under the weight limit you're golden.
Of course, hitting your opponent with a 10 pound hammer while your 10 pound chainsaw, 10 pound drill, 10 pound flamethrower, and 10 pound pincers all wait idly by for their turn isn't as effective as just hitting your opponent with a 50 pound hammer. Use your weight allowance wisely.
Virtual Robotica, Baby
Q: Hear me think:Robotica is back in YouTube again and I was thinking on having a Robotica day/Robotica Night/Robotica Week What would I need to prepare for a Robotica day/night/week and treat it like the NCAA tournament and NCAA championship and various other superbowl events and have you ever heard of Sling TV well Mech Plus is in Sling TV [Erskine, Scotland ☆]
A: [Mark J.] If you're going to have 'Robotica Week' you should have the whole experience. You need a week-long virtual tournament.
Robotica, Baby! (audio)
Day 1 Send me an application to be accepted to participate in Robotica Week. Include pictures of any mechanical devices you have made, any special dietary requirements you have, your blood type, your credit rating, and a 500 word essay on why you would make a good Robotica Week contestant. Wait around the rest of the day for my reply, which will arrive at 11:55 PM.
Day 2 Download the rules and construction requirements. Your robot design is due at midnight. Spend the day designing a robot to meet the challenges as described in the rule set. About 9:00 PM I will send you a revised rule set that will make your design unsuitable. Start a pot of strong coffee, revise your design, and send it in at 11:59 PM.
Day 3 Prepare a detailed parts list with prices and weights. Discover that two vital parts are no longer available and that your design is 40 pounds overweight. Your weapon for the 'Fight to the Finish' is changed from a hydraulic crusher to an electric screwdriver spinning a #11 X-ACTO blade. At 11:59 PM you send me the spreadsheet and PayPal me 10% of the total 'bot budget as your entry fee.
Day 4 Go to the airport and pretend to fly to a destination 1000 miles away. When enough time has passed, get a taxi and check in to a moderately priced hotel near an industrial area. Wander around in the industrial area and find an abandoned warehouse where you will spend Day 5 and Day 7.
Day 5 At 8:30 AM you may download the virtual version of your robot provided by a talented teenager in Texas. You have 30 minutes to learn how to drive it. At 9:00 AM qualifying starts on a previously unrevealed obstacle course. We didn't mention qualifying in the rule set? Really sorry. Top 24 qualifiers are paired off for the tournament. Everybody else goes home.
Day 6 You have the day off. Watch "The Big Cheese" episode of Dexter's Laboratory on the hotel TV. Go to an amusement park and eat greasy fast food. Get on a roller coaster and wish you hadn't eaten the greasy fast food. Get some take-out Thai food for dinner and return to your hotel room.
Day 7 The six finalists are paired off in any way I feel like pairing them.
Gotta Catch 'Em All
Q: Not a very important question, but would you like me to compile all of the 'Extreme Warriors' .bot files for Robot Arena 2 into one zip file? That way people can have the option of downloading all of them at once, or only specific bots.- sincerely, Iceywave
A: [Mark J.] Woah! It's already too easy to get a complete set. How about I remove the individual download links and put up a random and unspecified "Mystery Bot" to download each day? I could make a couple of them 'holographic rare' and only have them crop up every month or two.
I'm surprised I didn't think of this earlier. This marketing strategy works great for collectable card games like Pokémon and Yu-Gi-Oh! I'll get to work on the code. Better hurry and download a set now if you want to do it the easy way!
Keep It To Yourself
Q: Do you like REDACTED? A: [Mark J.] That's rather a personal question. I'm not sure that I want the general public to know if I like REDACTED or not. The answer is a qualified "yes", but don't spread it around. It Almost Happened
Q: ROBOTICA IS BACK! Allright it's season 1 but it's back in YouTube at long last thanks to SomeRandomDude. I wonder what this really means? [Erskine, Scotland ☆]
A: [Mark J.] 'SomeRandomDude' has been very busy on YouTube. In addition to the playlist you found, there are additional playlists for:
Q: And since I have seen the Run Away model sheet I might create two sheets of Run Away v1.0 the spinning rotor blades to add to my Run Amok model to create... Super Run Amok!
A: I've added the 'Run Away v1.0' paper model and weapon detail sheets to the Run Amok Paper Model page to make them easy to find.
'Super Run Amok' came very close to reality. As you know, Team Run Amok received a VERY late invitation to compete in Robotica season three. We would have needed an active weapon to meet the rules for that event and given the very short notice that weapon would have been Run Away's "side wheel" weapon strapped to the top of Run Amok. We just couldn't find a way to pack up, travel the 900 miles to Hollywood in 18 hours, and arrive ready to compete. We had to turn down the invitation.
Too Puny by Half
Q: Can I use a simple 300 rpm torque N20 motor for a flipper on a US antweight instead of a servo? My flipper arm is about 3" long. Will this work well? [Social Media]
A: [Mark J.] Nope. A Pololu 100:1 N20 @ 7.4 volts puts out about 2 watts of power and stalls at 27 in-oz torque. With a 3" arm it will stall at a lifting force of 27 inch-ounce / 3 inch = 9 ounces. Not a flipper -- not even a lifter.
Note also that the N20 gearboxes are weak. Pololu recommends an absolute upper torque limit of 25 oz⋅in, so going to a higher gear ratio won't help. N20 motors are used as lifter/flippers in 150 gram UK ants, but they are too puny for this use in 16 ounce US antweights.
For lifter design guidance see the Ask Aaron Lifter FAQ.
Old Age and Titanium
Q: Could a Comedy Central era bot still be competitive in the modern Battlebots era assuming the overall design remains the same but the mechanical bits are modernized?
A: [Mark J.] Somebody hasn't been paying attention. Here's a fight between a spinner reportedly accepted to the 2024 BattleBots World Championship VIII and a veteran flipper from the Comedy Central era that should answer your question:
Twice Equals None
Q: I'm moving up from my FingerTech Viper antweight kit to a beetle, but I am having some issues controling my new robot with the Flysky FS-CT6B transmitter from the Viper. I have a Scorpion ESC wired to two motors. When I move my joystick up and down it only moves one motor, and then I move my stick left and right it moves the 2nd motor.
I read somewhere that my transmitter might be in "drone" mode and I need to program it into "robot" mode, but everything was fine with my antweight. Is there an alternative solution? [Social Media]
A: [Mark J.] The problem is that your old transmitter and new ESC are both providing the channel mixing needed for single-stick control:
Different models of Scorpion ESCs have different methods of disabling the MIX option:
One Hinge Leads to Another
Q: Are "double hinged" wedgelets more effective than regular ones? I’ve seen them used on 'RotatoR', but (just from personal observation) it doesn’t seem to out-wedge opponents any more than other bots with forks.- sincerely, Iceywave A: [Mark J.] I don't believe that double-hinged wedges as sometimes seen on multiple competitors are intended to directly win 'the ground game'. I believe their purpose is to allow specific wedgelet designs to glide more easily over imperfections in the arena floor while still presenting a ground game to match their opponents. The technique may be particularly useful on invertible 'bots. More Extreme Warriors for RA2
Update: Here are the last replicas of Extreme Warriors competitors, including husband and wife duo 'Black Widow' & 'Rocky-Bot-Boa', Team Raptor's 'Cyclone', undefeated loaner bot 'Tut-Tut', and Run Away's other tag team partner, 'General Chompsalot'!.
I may consider revisiting this one day, but I think 12 robots is a good place to stop for now. I hope everyone else has as much fun with these bots as I did!
Reply: [Mark J.] Iceywave has been busy in the 'Extreme Warriors' arena. Icey's playable Robot Arena 2 'bot models for the following Robot Wars Extreme Warriors 'bots are now available for download from the Team Run Amok Virtual Robots page:
Q: Are your robots ready for the solar eclipse? A: Hacienda Run Amok was smack in the path of totality for the 2017 eclipse. I still have protective goggles for all the 'bots, so we'll be fine. A Minimal Shipping Charge
Q: My motor seems to be "twitching" and can barely spin up. When it stalls at a high power, the ESC beeps and beeps again when I return the stick to normal. I checked that all the solder connections are good and that everything is wired correctly. I have done no modification to the default ESC settings, and only cut the shaft on the motor. Any idea what could be causing the twitching, or how to fix it? Also, why is it beeping?
Setup:
A: [Mark J.] If only the one gearmotor behaves this way:
I Think I Know
Q: Why is Hypershock so good? Don't give me any of that "The robot is built by an experienced team" or whatever. I want to know exactly how it works!- Kevin’s Bots & Stuff
A: Either Complex or Inaccurate
Q: Remember the Run Amok model sheet?
Well I was wondering, what about a 'Run Away' model Sheet so that it can be recognised by any Extreme Warrior fans? [Erskine, Scotland ☆]
Q: Coincidentally, I actually tried brainstorming ways to make a 'Run Away' paper model several weeks ago, but to no avail. I've been working on paper model designs for your team's other robots, so they should hopefully be ready to share with the world soon! The Gap was wwaaayyyy too complicated, so I'll make a "Bonus Bot" as a replacement.
-sincerely, Iceywave 
A: All of a sudden my two most prolific contributors each have an interest in a paper 'Run Away' model.
Run Amok's design made it possible for me to create an accurate scale model in a simple cut-and-fold paper format. Run Away's top-mounted weapon for both the "long top" version from Robot Wars Extreme Warriors season 1 and the "bare top" version from season 2 creates a problem. I have to choose between "complex to construct" or "inaccurate".
The best I can do is to provide a detailed robot base 'bot that you might be able to set your own weapon mount (Lego?) on top to get an acceptable model:
That Side Wheel Weapon
Q: I like the paper model of 'Run Away' [post above] and I'd like to try to make a replica of the side-wheeler weapon to put on top. Do you have any drawings that might help?
Two Days Later...
A: [Mark J.] There never were design drawings for the version 1.0 weapon. My metal fabricator cut and welded the support cradle on the fly around my drive train and shaft. I went down to my workshop and found the weapon cradle from version 1.0 of Run Away and measured the components that had been scavenged for the version 2.0 weapon, which hangs intact on the workshop wall.
I gave the version 1.0 top armor to a local fan years ago, but the weapon mounting points were easy to estimate from photos. The weapon drive is a 4:1 sprocket and chain reduction with the lower portion of the large sprocket obtaining clearance from a cut-out in the top armor. Send me a photo when you're done.
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:
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A: [Mark J.] I believe you're looking for details of the "snatch weapon" developed by 'King of Bots' competitor 'Greedy Snake'. The mechanism is very clever and uses a single motor to both clamp and lift.
Aluminum is in general far too soft to make suitable armor for the current beetleweight level of competition. When they were made eight years ago, both versions of antweight 'Dark Pounder' shown used formed titanium for their bodies, and other 'bots from the team used 'spring steel'. Current wedge material tends toward thick flat panels of abrasion resistant steel. I don't think that "hammered around a tree trunk sheet metal" is a good bet in 2024.
If the transmitter and ESC both have mixing turned on 
I've provided a short dashed line across the wide red stripe to indicate the correct position for the weapon axle.
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]
We welcome combat robot questions. Please search the