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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.
Left Weapon Spins Clockwise
Q: Hello. I was examining a previous question about the successful 3 lb robot Droopy regarding how it produces motion through torque reaction and gyroscopic precession. I have some questions:
1. Let's say my layout uses a two-blade system akin to Droopy's that spins the left blade counterclockwise and the right blade clockwise. Would the body spin clockwise (right) due to the conservation of angular momentum when the left blade is given more power than the right, and the body counterclockwise if the right is given more power? I want to make sure my understanding of the post is correct before continuing.
A: [Mark J.] I think I may be responsible for your confusion. My original description of Droopy's locomotion had an error in the direction of weapon spin. I promptly corrected that description in the Ask Aaron Design and Construction archive, but I suspect you were reading a copy of the original version that I had overlooked in the 'Ants, Beetles, and Fairys' archive. I corrected that version today.
Here's the correct description as given to me by Droopy's builder Tommy Wong:
Acceleration of the blade on the left side (clockwise rotation) causes the right side to lift up and pivot due to the simultaneous effect of two variables:
2. If I were to program this robot such that I could flip a switch or push the throttle to make the weapons spin in the intended directions (at say, a constant 50% power), and use the aileron to shift the power from (50% left, 100% right) to (100% left, 50% right), how would I set it up/go about doing so? Is this even remotely possible?
A: Most transmitters are capable of this type of multi-channel mixing. It is essentially a simple(?) modification to the standard robot Elevon mix. A transmitter using OpenTX or EdgeTX firmware would have a very different setup than say a FlySky FS-i6, but such a control scheme is entirely do-able. If you tell me what transmitter you have and where you want the controls located, I can assist.
Sorry if the hamburger is bad. Thank you for your time. The hamburger is fine and you are welcome. My apologies for causing your confusion. Q: Hi, gyro walker person from yesterday here. 1. I originally had the spin direction opposite that of Droopy's (left CCW & right CW rather than left CW & right CCW), but in hindsight there must be some merit to spinning the blades in the latter directions given Droopy's success, so let's use that as a reference. A: There is considerable merit to spinning the blades in the directions used by Droopy. You can try the reverse directions to see the result but I don't think you'll like it.
2. While I don't have the transmitter on hand, I plan on using the FlySky FS-i6. This is a rough idea of my proposed control layout:
A: I feared you would want to do this with a FlySky FS-i6. The available pre-programmed mixes assume reversing ESCs with "off" in the center, but you'll be using single-direction ESCs that interpret the output from a spring-centered joystick as 50% throttle. For safety purposes we can't have your 'bot snap to 50% throttle on two spinner weapons as soon as the transmitter is turned on. To safely attain the precise controls you've specified we'll need to use with custom mixes. The FS-i6 has only three custom mixes -- that may not be enough.
Three Hours Later...
OK, I think I've got it. I don't have a FS-i6 in my workshop at the moment so I'm unable to test, but it works on paper. Suggest you read thru my FlySky FS-i6 Combat Programming Guide to become familiar with navigating the FS-i6 menu system and the processes for entering new values into the function fields.
This limits the "throttle" stick input to 50%.
This prevents unintentional "rudder" input from impacting the motor speeds.
This mirrors the "throttle" stick output to receiver ports 3 and 4.
This adds throttle to the left motor when the "aileron" stick is moved left of center.
This adds throttle to the right motor when the "aileron" stick is moved right of center.
Reply: Hi. Thank you so much for answering my torque reaction walker inquiries. I know it was probably a hassle, but I greatly appreciate your help and commitment to this website.
Response: You are very welcome. I enjoy a good challenge, and I have a need to pay back the combat robot community for the help given to me when I needed assistance.
I've received a bit of feedback on my proposed mixes that confirms the approach is correct. I've annotated the mixes above with possible improvements. Still waiting on actual confirmation from someone with an FS-i6 in hand -- stay tuned.
The Small One Goes in Front
Q: I have a gear ratio question. My son started designing his first Beetle and wanted to have big wheels in back and small wheels in front. The back wheels are direct driven by the motor. What is the formula for calculating the timing pulley sizes on the front and back wheels to match the overall outer diameter rpm's of each. My assumption is a smaller pulley in back and larger pulley up front on the smaller wheel.
A: [Mark J.]
The smaller wheel requires the smaller pulley. When driven by the larger pulley it will spin faster to 'keep up' with the larger wheel.
The ratio of the pulleys is the same as the ratio of the wheel diameters. Here is an example calculation for 2.5" diameter rear wheels and 1.5" diameter front wheels with a 30 tooth pulley on the rear: Teeth on Front Sprocket = 30 Teeth × 1.5" ÷ 2.5" = 30 Teeth × 0.6 = 18 Teeth I'm Told they Smell like Roses
Q: Somebody's probably already asked this, but how practical would this asymmetrical drum-spinner design be? (The blue stick is the axle)
A: [Mark J.] Not at all practical, Icey. Although the offset drum is "statically" balanced, the drum is not even close to being "dynamically" balanced. It would shake the 'bot violently -- see: The Difference between Static and Dynamic Unbalance (video). I've added arrows depicting centrifugal forces and a symbol showing center of mass. Repositioning the mass as shown below would solve the problem.
Q: Also, I just wanted to say thank you for all the great time I’ve spent on this website. This past month has been a large self-reflection for myself, and it’s made me realize that I don’t have the passion or drive to participate in this sport anymore. My true passion lies within animation and video editing, and even though I sorta-kinda knew that for the past year or so, it became extremely apparent after my BattleBots 25th anniversary contest. In a way, it feels like I’m throwing away a piece of myself, but at the same time, it's a fantastic lift of weight off my shoulders. I now know exactly what I was made to do with my life, and I couldn’t be more excited!
Q: I still have one more BIG post I want to share, plus another batch of RA2 bots to celebrate the one year anniversary of my enormous CRHoF ballot. See you there...
- sincerely, Iceywave : ) A: Please tell me that you aren't building a Robot Arena 2 virtual robot for each of the one-hundred-seventeen 'bots listed on your 2023 Combat Robot Hall of Fame ballot. I swear that I'll go buy local goats to avoid that. 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?
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:
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.
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.
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.
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?
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 doubtful. 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.
I don't need ten commandments to keep robot combat events safe. I can do it with three:
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.
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.
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.
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 :) 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. 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.
A: [Mark J.] Aside from price, the main differences are:
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:
I know that other builders use this receiver. What am I doing wrong? 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.
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:
"Turn on the transmitter and receiver."
"Move the transmitter sticks and switches to the desired failsafe positions and hold them there for the next step."
"Hold down the receiver bind button 'til the LED flashes, then stays steady."
"You're done."
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?
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.
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? 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.
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?
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.
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
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.
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.
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.
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: Best luck to you in your chosen path, Icey. In an odd coincidence, I've just recently realized that I have never been a good fit with mechanical and electrical design. I've always known in the back of my mind that I was cut out to be an animal herder. I've ordered a crook from Etsy and I got a good price on some goats from Temu. I hope the instruction manual is readable. Shipping the goats from China will take a while so I plan to keep Ask Aaron active until they arrive. Looking forward to my new life. I wonder what a goat smells like? I've heard good things.
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'.
Q: What do your combat robots think of the current COVID-19 pandemic? [Kansas City, Missouri]
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