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Walk into Home Depot
Q: Hi Mark,

I was watching an NHRL stream and was interested in a beetleweight (3 lb) overhead saw robot called "Mako". I was having trouble figuring out how exactly the circular saw was mounted to the weapon motor, as it appears to be held on only by a TPU hub and lock nut (no screws or fasteners threaded directly into the motor. Any feedback is greatly appreciated. [Zanesville, Ohio]

A: Mark J. Mako's weapon is not the usual hobby brushless outrunner with a printed hub like 'Cheesecake'. As disclosed in this video Mako's saw is "...a literal off-the-shelf circular saw that you could walk into Home Depot and buy." It's likely a 4.5" cordless framing saw torn down to just the motor and hub.

Circular saws have blade mounts that look just like what I see in the photos. What appears to be a TPU hub in one photo is likely a polished version of the metal retainer that is catching yellow reflection from the printed chassis.
Rediscovered SOZBots
Q: Hi Mark. I met you way back at the 2002 Botbash tournament in Tempe, Arizona. I was with a friend who had a robot in the antweight tournament and I remember that you were one of the event judges. I've found some videos of the bigger Botbash robots from that tournament but nothing from the ant fights. Did you happen to take video of any of the ant matches? [An iCloud Server]

A: Mark J. That was a great event. My flight got in too late to register 'Rat Amok' for the antweight tournament, but I did get a couple of pick-up matches and I was able to sneak into the ant rumble. I did also sit in as a judge for the SozBots ant tournament.

Although I didn't shoot any video, a search of my robot combat archive turned up a CD with twenty ant combat matches from the SOZBots 1.4 tournament at BotBash! I have no idea where the videos came from but they are so nicely captioned and edited that they may have come directly from SOZBots.

I've uploaded this set of videos to my YouTube channel as a playlist titled "SozBots 1.4: Antweight Combat Robot Tournament". I also found a bracket tree for the event: SOZBots 1.4 brackets.

My favorite fight from SOZBots 1.4? One Fierce Beer Coaster vs. Tsunami -- it has a very suspenseful ending.

Not a Gyro Walker
Q: Was Tip-Top (RW S5) the first gyro-walker? Tip-Top had no powered wheels. It used actuators to tilt a petrol-driven disc which would cause gyro, causing movement. Suprisingly, it was not considered a walker at the time. [Social Media]

A: Mark J. Tip-Top was not a gyro-walker -- the description at the Robot Wars Wiki is misleading:

The disc's axle was rounded on both the top and bottom, and long enough to touch the arena floor, which enabled the disc to balance on the floor like a spinning top...

When the disc was spinning at full speed, the actuators could be fired to tip the disc mechanism, and the resultant gyroscopic forces from the dome pressing against the ground would move the robot. This form of locomotion, nicknamed in the modern day as "gyro-walking".

'Tip-Top' and others of its ilk gain motion from the rounded end of the disc live axle rubbing on the arena surface. The tilting determines what part of the rounded end is in contact and thereby the direction and speed of travel. This method would work even better if the disc were removed and only the axle remained -- gyroscopic forces play no role in locomotion and actually impede the propulsion response.

Gene Burbeck's beetleweight One Fierce Low Ryda used this propulsion method quite successfully -- racking up a six-win/two-loss record at the 2008 Motorama tournament. Gene calls this style of propulsion 'wackerdrive'.

The earliest combat true gyro-walker I know of is Team Misfit's antweight 'Gyrobot' which first fought in 2009.

Jumbo Can-o-Worms
Q: One of the more common lifter setups in insect classes is a rear hinged lifter arm with some sort of 2 part linkage further down the arm providing the lift (Compared to the servo horn providing torque right at where it's hinged). This allows for a greater range of movement for a longer arm.

However my maths is failing me (See bad drawing attached for definitions of symbols). For calculating the force on the lifter arm from the servo in the setup is it as simple as x*sin(theta)? However isn't that just the force transmitted between the servo arm and the arm of the linkage? What about transmission of force between the arm linkage and the lifter arm itself? Are there further losses there?

And then to calculate whether you can lift something or not, is it (F * y) - (W * z) (Where F is the force from the lifter motor on the arm, W is the weight of the robot being lifted, y is the distance between pivot and lifting point and z is the distance between pivot and robot being lifted)?

Hope this makes sense

Thanks in advance. [Somewhere around Manchester, England]

A: Mark J. You've opted to open up the jumbo can-o-worms, eh? What you have is known as a 4-bar mechanism, and the calcs are especially nasty because the lever advantages keep changing as the lift progresses. In your sketch the initial advantage is poor and a good deal of torque is needed, but as theta increases the advantage improves and less torque is required. The general approach is to calculate the actual rise in the tip of the lifter for each change of say 1 degree of servo arm motion and convert that into a torque requirement for each progressive angle.

I know this because I wrote a pair of 4-bar Excel spreadsheets that perform these calculations for standard "Biohazard" style 4-bar lifters (movement up and forward) and for the servo linkage you describe (single pivot hinge motion). That is the good news.

The spreadsheet I wrote for the servo-powered single-pivot lifter has the correct geometry for your purpose, but the example layout has a hinge point much farther forward than your design. You will need to adjust bar lengths and angles to morph into your longer rear-hinge design. This may well take some time. Here are the spreadsheet link assignment letters as they apply to your sketch:

Give it a shot. If the calculations balk, you can wade thru the "Equations" tab on the spreadsheet and make adjustments as needed. Download the Team Run Amok Servo Lifter Spreadsheet from our Combat Robot Design Tools page.

Compress and Release
Q: Hi, I hope you are doing well! I am designed a featherweight combat robot for my senior design class. The competition winner is based on who is the last robot on the arena aka we have to push the opponents off to win. Our design for our active weapon right is a retracting spear/pusher mechanism. We are looking into doing a lead screw mechanism with a spring, but I am unfamiliar and have scoured the internet for examples or anything really and had no luck. Right now, my understanding is the very rough drawing I have attached.... How would we retract and load the spring? Would the spring be encasing the lead screw? [Baton Rouge, Louisiana]

A: Mark J. The reason that your internet search came up blank is that there is no simple and practical method to retract and then quickly release your spear with the lead screw mechanism you propose.

  • See my Ask Aaron: Spring Loaded flipper Mechanisms page for four designs that could be converted to compress and release a linear spring -- if you really want to pursue this weapon.
  • I will warn you that combat robot lateral spear weapons are ineffective. Newton's Third Law of Motion tells you that when you push against an object, the object pushes back on you with an equal and opposite force -- you might just as well smash into your opponent directly.
Doesn't Want Cleats
Q: I've heard of RC tire preparation - heating, chemically softening, scoring wheels, but it seems like that stuff when applied to cast urethane wheels on you hubs either does not apply or would provide only a limited benefit for the first few encounters in a 2 or 3 minute match on a wooden floor.

I was wondering if you have experience / recommendation for tire preparation beyond alcohol wipes / cleaning a cast urethane tire up. Cleats seem the primo option for max traction on wooden floors for beetles but I've had issues with opponents mangling mine so I'd like to look for advantages with urethane wheels. [Terre Haute, Indiana]

A: Mark J. The Brazilians swear by two methods to improve polyurethane tire traction:

  • Clean the tread surface with WD-40. It reacts with the surface to create a softer sticky layer without effecting the durability of the urethane core. Spray it on, wipe it off, fight. Repeat before every match.
  • Sticky treads collect dust, grit, and oil which smear around their surface. Casting or cutting lateral and/or diagonal grooves into the tire provides voids into which the tire can wipe collected gunk, allowing the tire to clean itself rather than just continuing the smearing. Diagonal grooves give a smoother rolling action than do lateral grooves.
The Force Products are Equal
Q: Battlebot 'Ripperoni' has a big vertical weapon disk but a much smaller counter rotating flywheel to cancel out gyro forces when turning. I thought that only worked if the two rotating disks were the same, like 'Counter Revolution'. How does Ripperoni get that to work?

A: Mark J. A flywheel will cancel the spinning weapon's gyro forces if the two spin in opposite directions and have equal products of inertia and speed:

Moment of Inertia (kg×m2) × Angular Velocity (rad/sec)
If the weapon has greater MoI, the flywheel must spin faster to achieve an equal force product. In the case of 'Ripperoni' the weapon has a much greater MoI than the compensating flywheel; perhaps four times the value. The flywheel must spin four times as fast as the weapon to offset the gyro forces.

A more complete explanation of calculating gyro forces is available here: Designing Around the Gyroscopic Effect.

It Launches Itself
Q: Would it be possible for a vertical spinner with a higher scalar tip speed to lose a head on engagement to a vert with a lower tip speed if less of the decomposed velocity vector at contact is actually going into vertical motion? E.g. A low profile drum spinner strikes a tall Deep Six style vert. The drum spinner hits at the middle of the arc where 100% of the motion is vertical. The Deep Six vert hits at the bottom of the arc where most of the motion is horizontal. Since the y-component of the drum spinner's velocity was superior, the tall vert gets launched up and back while the drum only slides backwards on the floor. The reason I'm asking this is because in many internet builder circles (Reddit, Discord) these days I'm seeing an upsurge in the sentiment that head on vert on vert contact is somehow partially decided by RPM (???) and not entirely by tip speed which does not really make much sense to me. This is generally supported by an anecdote and/or Youtube clip of a vertical with a measured ~200 mph tip speed launching a vert with ~250-300 mph tip speed weapon on weapon. Where I believe the RPM assumption originated is the fact that these videos tend to feature a low profile drum (inherently higher RPM to reach X tip speed) against a high profile large diameter vert (inherently lower RPM to reach X tip speed). What I think happened here is that the vector decomposition at contact resolved in the "lower tip speed" vert having a higher vertical speed at contact. Then the condition arose that RPM was somehow a determinant of engagement. Any thoughts? [Arlington, Virginia]

A: Mark J. Everybody likes to simplify a complex interaction: it's all about tip speed, it's all about RPM, it's all about bite, it's all about googly eyes...

I don't buy your analysis that the y-component of the impact is different for the two weapons. The line tangent to the point at which two circles of differing diameter touch provides an identical x-y vector to each circle (purple arrow in illustration below). We need to look elsewhere for an explanation. The whole "Tip Speed Rules" argument says that the impactor of the slower weapon cannot 'catch up' to the impactor of the faster weapon and will therefore inevitably be struck from behind and launched by the faster weapon. This assumes that neither weapon has enough 'bite' to get past the opponent's impactor and hit some 'meat'.

In your scenario: even though the large diameter vert has a higher tip speed than the small diameter drum it will have a considerably lower RPM which gives it much better bite. It may well avoid the impactors on the small drum and strike the drum itself. Here's where it gets interesting.

As the surfaces of the two verts are moving in the same direction, the impact vector magnitude is reduced to only the difference in tip speed rather than the full speed of the larger weapon. However, the 'kickback' vector (yellow arrow in the illustration above) is independent of the weapon tip speed difference and has a magnitude related to the displacement created by the impactor. This 'up and back' kickback may very well launch a high-energy large-diameter weapon under these conditions.

The smaller drum weapon does not launch the big vert -- the energy to launch the big vert comes from the big vert itself.
Somebody is Reading My Code!
Q: Is this a faulty conversion factor under bite1? Shouldn't it be times 25.4 rather than 24.2? [iCloud Private Relay in New York]

// bite depth calculator weapon-teeth-speed -- insert-bite
var insert1 = 1 / ((weapon.value / 60) * teeth.value) ;
var bite1 = speed.value * (5280 / 3600) * insert1 * 12 * 24.2 ;
insert.value = insert1.toPrecision(2) ;
bite.value = bite1.toPrecision(3) ;
A: Mark J. Congratulations! You have discovered the secret "Find the Twenty-Seven Javascript Errors in My Website" contest.

This particular error - in my Rotary Weapon Bite Calculator - undercalculated weapon bite by a tad less than five percent by screwing up an inches to millimeters conversion. The code has been corrected and I have attached a remark giving you full credit. As I don't know your name I have credited "Walter Codepoker".

One down, twenty-six to go. Keep up the good work.

Inside the Faraday Cage
Q: A question about antenna in a metal box. I've read here that it is best to put it outside the metal box or at least use radio transparent materials, but how do the heavyweights in battlebots still manage to receive signals? Does poking a hole help? [Central Luzon, Philippines]

A: Mark J. A continuous box of conductive plate or mesh forms a Faraday Cage that can block radio reception -- but most heavyweight robots have substantial gaps for weaponry or feature non-conductive cover plates. Very small holes are not effective at allowing radio signals to enter but gaps of 1/2" or more will allow a 2.4 GHz frequency wave to leak in.

It's also vitally important to position the receiver and antennae away from internal components that produce electrical interference. This comment from Team Monsoon at their Reddit AMA highlights that problem:

"We've never really had any major issues with this version of Monsoon, however when we first went through safety at BattleBots the robot wouldn't drive straight and we had very poor radio signal. The receiver aerials were routed underneath our motor phase cables and creating interference. After a bit of wire re-arranging it was totally fine."
See Also: Combat Robot Reception Problems
Alive and Well
Q: Can we even expect heavyweight robot combat to survive the collapse of BattleBots on TV? I'm thinking the entire class is gone for the most part now and watching the featherweight NHRL matches is the future of the sport. [Social Media]

A: Mark J. I think your prediction is premature. Heavyweight combat robots are still going strong in the UK many years after Robot Wars left the television networks. Both Robots Live! and Extreme Robots have live heavyweight show tours that draw large crowds.

You can watch UK live events on Extreme Robots TV -- a subscription is free.

The Return of YCOSV
Q: YCOSV guy back again with another question about engagement theory. Your breakdown of the moment of impact into a normal and tangential force vector -with the normal force vector being opposed by a kick back- was enlightening to me. However I'm stuck between two possibilities:

In idealized conditions (smooth non-wedged armor, constant closing velocity) at contact...

  1. The normal vector component is the ONLY force relative to the opponent that matters for damage- so the optimal speed value is some undefined amount below the "skate" threshold dependent on some math I don't want to do right now.
  2. If the normal force component exceeds the kick-back vector produced by the hard armor panel, then the weapon will be pressed or "engaged" with the opponent robot and then some of the tangential force can be dumped into the opponent - therefore the optimal speed is the highest you can go without skating, and energy transfer "cliffs" off after that point.

A: Mark J. Both of your scenarios are important to energy transfer, but which holds greater importance will be dependent on the weapon style.

  • A horizontal spinner will generally benefit from maximizing the forces you describe in your "A" scenario, so as to generate acceleration on a vector thru the mass center of the opponent rather than a tangential acceleration that would simply spin the them around.
  • A vertical spinner seeking to 'launch' their opponent will most greatly benefit from catching a sharp edge but, should none be available, the ability to engage as described in your "B" scenario comes into play.
Zorro Arcade
Q: I want to set up my Radiomaster Zorro for arcade stick style driving (throttle controls forward/back and steering is on the aileron). I have done single stick mixing before on a Flysky but I am still trying to learn the Zorro. I think I understand the steps in your EdgeTX Combat Radio Tutorial to set up a single-stick mix, but what would I need to change to make it dual-stick? [Somewhere in California]

A: Mark J. My new combat robot setup guide for EdgeTX uses a Radiomaster Zorro transmitter for its example. This Link will jump you straight into the single stick mixing section of the guide.

  • This is what the Mixes Screen looks like with a right single-stick mix using CH1 Aileron and CH2 Elevator:

  • To shift forward/reverse control to the left stick we will remove CH2 Elevator from the mix and add CH3 Throttle in its place:

You'll also need to adjust your left gimbal to be self-centering. Here's a video: Zorro gimbal adjustment.
Once you get the mix set on your transmitter it may still need to be tweaked if the robot is not responding correctly. Maybe a forward command causes the robot to turn left? My Combat Robot Mixer Fixer will ask three questions about your robot and will provide a quick correction.
Setting Up Zorro
Q: I want to set up my Radiomaster Zorro for arcade stick style driving (throttle controls forward/back and steering is on the aileron). I have done single stick mixing before on a Flysky but I am still trying to learn the Zorro. How do I set this up? [Somewhere in California]

A: Mark J. I always recommend downloading the manual for any transmitter you are considering purchasing to see if the instructions make sense to you -- before buying the radio. Setting up a Radiomaster transmitter is a whole different world from FlySky.

  • FlySky uses a menu-driven system where you just check boxes and move some sliders to setup your transmitter. Simple.
  • Radiomater employs the EdgeTX/OpenTX firmware which is essentially a programming language. It's flexible, but challenging.
Fortunately, I've written a combat robot setup guide for EdgeTX/OpenTX that will walk you thru setting up single-stick control. The guide uses a Taranis Q-X7 transmitter for its example, but for the purpose of single-stick setup the Radiomaster differs only in the buttons used for menu navigation.

Once you get the mix set on your transmitter it may still need to be tweeked if the robot is not responding correctly. Maybe a forward command causes the robot to turn left? My Combat Robot Mixer Fixer will ask three questions about your robot and will provide a quick correction.

If you get stuck I'll be happy to assist with specific problems.

NOTE: The Zorro actually has a "Delta Wing Mix Wizard" that will do a quick automatic version of the single stick for you. You'll still need to go in and adjust the elevator settings to +/-100 to get full forward/reverse thottle response, so I personally find it easier to just set-up the mix by hand. If you want to give the wizard a try, here is a video: RadioMaster Zorro Setting up a Delta Wing in EdgeTX - Model Wizard.

Are you sorry you gave up on your FlySky yet?

Q: Hey! It's the guy with the Zorro. I'm actually looking for help with mixing to two sticks, where the left stick up/down would be forward reverse and right stick left/right would be steering. I think I understand the steps in your tutorial but what would I need to change to make it dual stick?

A: Sorry for the misread; you said "throttle" but then later mentioned "single stick" on the FlySky. My bad. I prefer throttle on the left stick and steering on the right stick as well. You have your choice of two easy ways to accomplish this:

  1. You can modify the Mix Screen to use CH1 Aileron and CH3 Throttle instead of CH1 Aileron and CH2 Elevator. The new screen looks like this:

  2. Alternately, you can use the standard delta wing mix as given but switch the transmitter "Mode" from the default "Mode 2" (throttle on left/aileron on right) to the Euro standard "Mode 1" which moves CH2 to the left stick and CH3 to the right stick:
    • Power On: Turn on the RadioMaster Zorro.
    • Enter System Setup: Access the main menu and go to the System Setup.
    • Navigate to Radio Setup: Scroll to the "Radio Setup" menu.
    • Change Mode Selection: Select the desired "Mode" and change it to "Mode 1".
Whichever method you choose, you'll also need to open up the transmitter case and adjust your left gimbat to be self-centering. Here's a video: Zorro gimbal adjustment
Flashback: an archived post from 2021
Like Frozen Pizza
Q: Isn't there anything we can do about those stupid kit bots? They're ruining the insect weight classes! I really hate to see some guy show up at a tournament with a kit they put together in an afternoon and beat up real robots that real builders took a lot of real time designing and fabricating. Can't they just compete in a class for kit bots only? [Everybody on Reddit]

A: Mark J. Complaining about kit bots is like complaining that frozen pizza is ruining dinner because it tastes better than what you cook. If you can't beat a kit bot you need to up your game.

Buy a Better Battery
Q: Went to set up my new Viper V3 antweight kitbot today. Followed all the instructions but can’t get it to work.

I made it to testing with the 9V battery. When I power it on the ESCs lights are bright red but then instantly shut off, and the receiver slowly blinks red. No inputs do anything. Now after several tries no lights turn on at all. I checked all connections. [Social Media]

A: Mark J. How long has that 9 volt been in your battery drawer? The LED signals you see and the sudden complete electrical failure all point to a weak battery. Try a fresh battery.

Q: That got it! The 4th 9V I tried fixed this. Charging up a Lipo battery now.

No Steering Wheel
Q: drive train [Madhya Pradesh, Bharat]

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.

 
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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