Questions and Answers about Combat Robotics from Team Run Amok.

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7547 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.

A Simple Indicator
Q: Hi, I want a power indicator for my combat bot, but I am not sure which one to use, can you suggest some good LEDs or strobe lights? Also while researching on protective cases for leds in order to not damage the LED during battles, I found polycarbonate cases for LEDs meet my needs but I am not sure where to get the stuff? Can you help me with this? [Ryerson University, Toronto]

A: [Mark J.] The requirement for a power indicator is typically something similar to the SPARC ruleset section 8.6:

8.6. All Robots must have a light easily visible from the outside of the robot that shows its main power is activated.
In small robots this requirement is often met by an existing small LED on an ESC or receiver positioned such that it may be seen thru a transparent top panel. The light does not need to be visible from all angles and it certainly does not need to be a strobe light.

If you want a discrete power LED you do not need a protective case, just mount it out of the way.

You can certainly construct your own indicator light but the components (plug, cable, resistor, LED) are difficult to purchase in small quantities and some calculation is needed to select the correct resistor value. Itgresa.com offers Robot Power LEDs with a cable that can be plugged into an unused port on your receiver. Six colors, easy to mount, wide voltage range, cheap. Buy a couple and keep one as a spare.


An Italian Dinner
Q: Greetings! I hope you're doing well, I did a bit of searching and wasn't able to find anything so I figured I'd go ahead and ask, do you have any tips for creating wiring harnesses to not be spaghetti messes / hard to cram into bots? It's a habit I've had for years now that I finally want to take the time to address to work on overall build practice and cleanliness. Any advice is greatly appreciated! [a Starlink Server in NYC]

A: [Mark J.] Thank you for your kind greeting. All is well for us here at the Run Amok homestead, and I hope the same for you.

Until recently my general advice on fighting spaghetti was to get your soldering skills up to where you weren't afraid to cut all those wires down to their shortest possible lengths. That helped clutter and also saved a surprising amount of weight.

But now you can take that up another level. Just 'Cuz Robotics produces a wide range of custom power distribution boards for small robots that range from simple connector organizers to full "motherboards" with BECs, power switches, power lights, servo support, and receiver integration. If you crave clean and neat you'll find all you need there.

Note: I have no connection to Just 'Cuz Robotics and I receive no compensation in any form from them or from any manufacturer or distributor of robot components or services.

Fishing for Bolt Heads
Q: Magnets: specifically, electromagnets

from what I know, there are no rules against using electromagnets as part of your weapon, IF it doesn't interfere with opponents' electronics. would it be possible to have a toggleble electromagnet on a lifter arm, and be able to have a more secure hold? and then turn off when over hazards. I know very little about magnets, and wondering if you had any advice.

Thanks! - Backyard Bots [Close to Raleigh, NC]

A: [Mark J.] Let's get you a little magnet knowledge. Here's a 9 minute video that will give you a crash course in magnetism. Go ahead and watch it -- come right back.

Great! I just needed a few minutes to make a fresh pot of coffee. Where were we? Magnets? Right.

Magnets in combat robotics have a long history of being difficult to control well enough to get the expected and desired results. On problem is that magnetic attraction decreases quite rapidly with distance. A magnet that has 50 pounds of attractive force when directly in contact with a thick steel surface might have only 5% of that power from half an inch away. You can play around with this Magnet Pull Force Calculator to see this effect. The calculator is for permanent magnets, but electromagnets have the same properties.

For the electromagnet to be useful it needs to be VERY close (direct contact is best) to a magnetic surface.

  • Unfortunately, not a lot of a combat robot is made from magnetic materials. Most of the 'bot is made from materials that are not magnetic (aluminum, titanium, magnesium, plastic, rubber...)
  • Worse, the parts that are magnetic are not generally surfaces that are easy to line up with your electromagnet.
  • Still worse, as soon as your opponents notice your electromagnet they can swap out or pad steel parts needed to deflect spinner weapons with non-magnetic materials to further limit areas vulnerable to your magnet, leaving you fishing for a little bits of attraction to small screws and bolt heads.
Can you use a small electromagnet on your lifter? Sure. Will it do you much good? I wouldn't think so.
Hero of the Revolution
Q: HHEEEEELLLLLPPPP!!!!!!! I signed up for Australian Robowars thinking it was a protest against Taco Bell... BUT IT WASN'T!! I’ve never seen a robot fight before! My friend told me to come here and ask what I should do?!?!?!?!?!?!
- Mistro Deb Hamper

A: [Mark J.] Make yourself a nice cup of herbal tea and take a deep breath. I'll get you thru this.

Just because Robowars didn't think they were a protest doesn't mean they couldn't become one. Pop out and buy yourself an R/C trailer truck, paint "Taco Bell is Murder" on the side, and stuff it full of those little Taco Bell hot sauce packets. Go back to the robot fight and toss the truck into the arena. Some nasty spinner robot will vaporize the truck and coat the inside of the arena with bloody red hot sauce and burst plastic packets. Nobody there will ever go to Taco Bell again and you will be a hero of the revolution.


Q: Hey Mark, just wanted to let you know my video editor said she was having trouble relating to combat robots, so I sent her here. She has a history of blowing up in peoples faces (you should see the credits of the IceyBots pilot episode!) so I told her to keep it down a notch. She goes by "Mistro Deb Hamper", by the way.
- sincerely, Iceywave [West of San Antonio ☆]

A: No problem, Icey. She totally took your advice and was entirely calm and collected by the time she got here. I think I solved her problem. Thanks for the referral.

You wouldn't happen to have an actual combat robot question, would you?

Q: In response to your question, yes I do!

I’ve heard from various sources that in sometime in 1998 (during the severe dry spell of American combat robotics) an obscure event was held under a bridge(?) that included the likes of S.L.A.M., Ginsu, and a few others. Do you have any additional information on this?
- sincerely, Iceywave☆

A: Someone as interested in the early days of combat robotics as you are really should own a copy of "Gearheads: The Turbulent Rise of Robotic Sports" by Brad Stone. You can buy a nice used copy for less than $8 shipped.

In the early nineties, a visionary special-effects guru named Marc Thorpe conjured a field of dreams different from any the world had seen before: It would be framed by unbreakable plastic instead of cornstalks; populated not by ghostly ballplayers but by remote-controlled robots, armed to the steely teeth, fighting in a booby-trapped ring. If you built it, they'd come all right....

In Gearheads, Newsweek technology correspondent Brad Stone examines the history of robotic sports, from their cultish early years at universities and sci-fi conventions to today's televised extravaganzas -- and the turmoil that threatened the whole enterprise almost from the beginning.

By turns a lively historical narrative, a legal thriller, and an exploration of a cultural and technological phenomenon, Gearheads is a funny and fascinating look at the sport of the future today.

"Gearheads" has a nice section on the obscure event you mention, but while you're waiting for your copy to arrive I'll point you to a couple of other sources:
  • This archived post discusses the canceled 1998 Robotica event, the 1998 San Leandro Parking Lot event, and the 1999 Underground Robot Street Fight which literally took place under an overpass in Novato, California.
  • Even better, RobotCombat.com has a write-up, photos, and videos from Novato event. I will warn you that the videos are black and white, very low resolution, and in antiquated formats for which you may need to find specialized players to view.

Three Designs and a Bowknot
Q: I was wondering if any of these designs were viable for a combat robot. [West of San Antonio ☆]

A: [Mark J.] Wow! Click Here for a full analysis of your designs.

Q: Will you also give me step by step instructions on how to bind my model airplane to its transmitter? Thank You!

A: Sure.

  1. Cut off about a yard of twine. If your airplane is large, you may need a little more. Cotton twine is good, but I prefer a good quality jute.
  2. Set your transmitter in top of your airplane, near the wing.
  3. Wrap the twine snugly around the airplane fuselage and the transmitter. Watch out for the propeller, if present.
  4. Tie the twine in a bowknot. Your airplane is now bound to the transmittter.
  5. Should you later wish to bind your airplane to a different transmitter just untie the knot.

Tossing the Caber
Q: I am designing an antweight (1lb) brushless lifter that I would like to be able to throw opponents (not into the ceiling or anything). I am planning to use a Flash Hobby 1204 2500Kv motor, connected to an 135:1 planetary gearbox. The lifting arm is 6.22in long, and the robot will be powered by an 11.4V LiHV battery. At 211.11 rpm, do you think that this would be too fast? Would it provide enough torque to not be too slow under load? (The manufacturer does not give stall torque.) Also, I know that brushless motor torque depends on the ESC, so I am planning to use AM32. Would you say that this is necessary? Thanks! [Outskirts of Madison, Wisconsin]

A: [Mark J.] The unsensored brushless motors and ESCs we use to build small robots are borrowed from the model aircraft hobby industry. They are designed to spin-up lightweight propellers to about 80% of their free RPM and run at that speed for several minutes. That task is far different from being bogged down against a heavy load right at zero RPM and being asked to develop enough torque to accelerate that load upward against gravity fast enough to toss it into the air. It's like asking a chicken to toss the caber -- they aren't made for it.

Add to this handicap your choice of a brushless motor that weighs 6 grams 0.21 ounce and puts out about 50 peak watts of power maybe 10 watts at low RPM on a 4S lipo and you're running 3S. A typical antweight brushless spinner weapon motor that has a couple seconds to come up to speed against its load weighs perhaps 30 grams and pumps out more than 200 watts of power (see Brushless Motor Selection). With that tiny motor you're not going to be tossing opponents into the air, and the strain of moderately quick lifts may drive the motor into thermal failure.

As noted in FAQ #17 Ask Aaron is not a free engineering service - I'm not going to model the performance of your weapon for you. However, we do supply design tools like the Team Run Amok Electric Hammer Spreadsheet that can be used to model flipper designs. A lifter/flipper is effectively an overhead hammer with a very heavy hammer head (your opponent's 'bot) that traverses a small arc.


Two Days Later... My curiosity got the better of me, so I broke down and modeled your flipper performance.

I brought up the Electric Hammer Spreadsheet and plugged in the numbers for your flipper. Rather than make guesses about the torque curve of that tiny brushless motor I put in the specs for a brushed RF-370 motor that has comparable output wattage. The brushed motor has low-speed torque better suited to lifter duty than the brushless motor, so calculated performance will be a 'best case' model. I ran multiple simulations to determine the optimum gear reduction for the RF-370 motor:

Performance:

  • Energy = 1.00 joule
  • Time to 45° = 0.11 second
  • Terminal Speed = 1.04 m/sec
An object launched at a 45 degree angle with a velocity of 1.04 m/sec will reach a calculated height of... 2.76 centimeters.

I need help finding out which module I need to purchase for my jumper T18 transmitter. I’m running the Malenki nano dual + esc HV and have no clue what I need for my T18 to be compatible with it. -- The JP5in1 Module built into your Jumper T18 transmitter includes the FlySky AFHDS 2A protocol used by the Malenki. You need nothing more. -- There is no module in the bay of my T18. -- They call it a module, but it is internal to the transmitter -- it does not occupy the module bay. Just select "Internal Module / FlSky_2A" when setting up the model.
Walking Distance
Q: Will you be attending any competitions in the next few months? (Of interest specifically to me is Robogames.) And if you've been to Robogames in the past whether you have any recommendations of places to check out while in San Jose. [Ohio-ish]

A: [Mark J.] There are no events on our calendar, but Team Run Amok has spent some time in San Jose.

  • I'm a sucker for a good science museum, and the Robogames site is a five-minute walk from The Tech Interactive - a place that I think any robot builder would enjoy.
  • When you get hungry, you're also a short walk from Kukar's House Of Pizza - a San Jose institution which comes with my highest recommendation. Eat there, don't take-out.

Mathematically...
Q: mathematically (not realistically, I do not want to know if it is realistic or not, just want to know your take) what is the best combat robot design for a combat robot, with a combat robot being 1, 100, or 250 lbs, and best is the greatest advantage of the following:
  • drivetrain: wheel material, motor type, amount of wheels, and type of wheels (mecanum, omni, standard, swerve etc)
  • weapon: size, material, type, speed, profile etc. etc.
  • armor: material, thickness, and most importantly, angle.
  • assume that you can hold a very precise RPM, and traction is not an issue.
  • assume that you are using a common transmitter, receiver, ESC that do not have a chance of falliure.
  • assume as well that any type of battery is allowed and that it goes perfectly.
what would be your design? - Backyard Bots [Close to Raleigh, NC]

A: [Mark J.] Mathematically:

Philosophically:

A combat robot is a tool for defeating other robots. The best tools are simple, reliable, and easy to use.

See Also: What is a 'scale factor' and how does if effect combat robot design?


The Center Isn't Off
Q: I am trying to make a combat robot for the first time, and with the right joystick in the center resting position it reads as half power and turns the motor on. I have looked across the internet on how to make the resting position read as off and if I go down the motor reverses and forward it goes forward. I’m using the fs-i6s transmitter and a TOYTENSI 20A esc. [Social Media]

A: [Mark J.] Your radio is not the problem - the problem is your ESC.

All the TOYTENSI ESCs I can find are for model airplanes. An airplane ESC is uni-directional with the zero-throttle stick position all the way down. Some aircraft ESCs can be switched to forward/reverse response with center off, but the functions available on the TOYTENSI programming card do not include this option. You need a different ESC.

To keep things simple search for an ESC that specifies 'bidirectional' or 'forward/reverse', like the Repeat Robotics Brushless Drive ESC. ESCs that say 'thrust reversing' are different and will not give you the stick response you're seeking.


Just Point the Front Wheels
Q: With car-steering being obsolete in combat robotics for the past two decades, would you say there are any advantages to using it (as opposed to tank steering) in modern times?

While we're on the subject, was Run Away! the last combat robot to use car-steering?
-sincerely, Iceywave ☆ [West of San Antonio]

A: [Mark J.] Realtively few combat robots have used automotive-style 'pivot steering', but many fans are surprised to hear that Combat Robot Hall of Fame members 'KillerHurtz' and 'The Judge v1.0' had steered front wheels. Stability in a straight-line and the ability to hold a smooth turn radius remain good reasons to consider the design, although the development of solid-state gyro controllers has brought similar control to skid-steer 'bots. The last pivot-steered robot I'm aware of was Team ICR's middleweight 'Trainwreck' from Sandusky Ohio. They fought in Comedy Central BattleBots seasons 3.0 and 5.0, winning two matches at the latter event. The 'bot went on to compete at Michael "Fuzzy" Mauldin's Robot Club & Grille where they were the #7 ranked middleweight for the 2002/2003 season.


Anywhere But There
Q: I am part of a team that is brand new to combat robotics. We just completed and tested our very first robot and are ready to fight in our first tournament. Got any tips on how to find the right competition for our skill level? Thanks. [North American Comcast Server]

A: [Mark J.] The typical order of events to get into combat robotics is:

  • Find a nearby event;
  • Watch the tournament and talk with builders;
  • Pick a contested weight class that feels right to you;
  • Build a robot for the selected weight class; and
  • Return to compete at that tournament.
Your team appears to have skipped the first three steps and jumped right to 'build a robot' in (what I hope is) a commonly fought weight class, with no specific tournament in mind. Interesting.

The IP address attached to your question submittal has ties to servers in Maryland, California, Florida, New Jersey, and maybe other states -- so I can't provide regional advice on beginner friendly events. You aren't likely to find more than a couple of events within reasonable traveling distance, so your list of options will not be long. There are two websites that list upcoming events in North America:

Sift thru the listings to find events in your region that include robots in your weight class. Check their event-specific rules and contact the event organizer with any questions. Any tournament you select will be very happy to welcome new builders, but I advise novices to avoid the National Havoc Robot League (NHRL) events: their level of competition is VERY HIGH.

Plastic Traction
Q: dont know if you have any experience in the plastic ant category, but two things

first, what would be the best infill for high-impact hits with PLA plus

secondly, what would be your thoughts on our current design, and issues that you can spot (yes I know it needs a top-plate, and there are no screws) Ive had problems in the past with traction, so that's mainly what I'm looking for. [Close to Raleigh, NC]

A: [Mark J.] It's a very pretty design, isn't it.

First question: I claim no specific knowledge in 3D printing PLA, but I do know that more infill equals more strength. How much strength you need depends on your design and expected impact forces. There are two groups on Facebook that might provide more useful responses:

Second question: I don't know what your previous designs looked like, but if you build the current design I foresee continuing traction problems in your future. You've placed your wheels as far back in the chassis as possible to get chassis clearance in both upright and inverted modes. Doing so leaves a lot of the robot's weight supported by those long forks.

Take a look at successful two-wheeled insect spinnerbots. They have the motors as far forward in the chassis as reasonably possible, with battery and electronics hanging out behind to shift the 'bot center of gravity closer to the wheels. Unfortunately, unless you switch to much larger wheels you don't have room for much rear overhang. This is a serious flaw.

The rule-of thumb for two-wheel 'bots is to put ~65% of the robot weight on the wheels. More than that may let the 'bot raise the nose off the floor under acceleration -- see Section 2.2.7 of the RioBotz Combot Tutorial. Given the wheel placement on your design I'm guessing that less than 50% of the weight is on the wheels, which will give both poor traction and poor turning response. No amount of latex or silicon rubber coating on the tires is gonna help.

Q: this was our earlier design, and it had the most abysmal center of gravity possible, which was over the forks, we are currently using 2.25 inch wheels, what do you thing would be the best size option?

A: You're not trying to tell me that the little circle marker on the current design render is the calculated center of gravity, are you? I'm entirely not buying that. Nope. No way.

From a practical standpoint, I'm really not sure your design is salvageable. That very large and heavy spinner hangs so far out in front that it's going to take a lot of mass out behind the wheels to make the drive work:

  1. Flip the contents of the chassis box to move the drive motors to the front;
  2. Find the new location of the center of gravity (CG);
  3. Extend the chassis box rearward and shift enough mass aft to move the CG to a point about 1.5" ahead of the axle line;
  4. See how big the wheels need to be to get the new lump sticking out behind the 'bot off the floor.
Taking a fresh look at the design has me worrying about another problem. When (not if) the 'bot lands on its side it's going to be very difficult to get it back on its wheels. The upper and lower forks will provide a wide and stable base, and the weapon is going to sit very close to horizontal. You're going to be pretty well stuck.

As I said at the start, it's a pretty design -- I just don't think it's practical.

Q: for the forks, would having what basically is a plastic popsicle stick going perpendicular to the forks help us with that issue [of being stuck on its side]?

A: I'm sure you have an image in your mind as to where that stick would be placed and how long it might be, but my psychic abilities are quite limited these days.

  • You could construct a cardboard model of your design and experiment with adding various lengths of lateral 'spinner bait' to get an idea of how much help they might provide in righting.
  • You could decide that the design has too many flaws to fix by tacking on doodads.
  • You could Ask the Cheerleader.

Hitting a Wedgeless Brick
Q: My team just competed at NHRL over the weekend and we have a question about the results of our hits. In the attached clip we hit 'Beast' twice with the big beater bar on 'ARES' only to spin them backwards. What’s the most probable reason for ARES recoiling backwards instead of launching Beast? Could this be a result of rake angle (0 degrees), too much bite, or something else? [Cambridge, Massachusetts]

A: [Mark J.] It is my considered opinion that this is a clear case of something else. Here's the full 3-second clip: ARES and Beast at NHRL.

Both of the hits in the clip have your beater bar impacting hard vertical surfaces on the front corners of the wedgeless brick Beast. Nothing to grab, and no downward impact vector to press down onto your opponent as a multiplier for the poor steel-on-steel coefficient of friction. The hits are just gonna slide up the steel wall and tap the brick and ARES apart.

Things that would help:

  • Forward Speed - ARES was sitting nearly still and allowing Beast to come to her. A full-speed charge would improve bite and would add a horizontal vector to increase sliding friction along that vertical wall when the hit lands. It will also reduce backward recoil.
  • Friction Enhancement - No change in rake angle is going to add grip against that vertical steel wall -- but wrapping a length of 'friction tape' around the beater impactors for this special case may improve mechanical grip enough to launch.
  • Weapon to Weapon - Crank up the weapon speed and charge their drumette. If you have a tip speed advantage a chunky weapon is a prime launch target.
UPDATE: I finally located the full ARES vs. Beast fight -- 4 hours and 45 minutes into the 8 hour 46 minute long "NHRL 2024 March Rd 2 Qualifying Rounds" video. You did get a solid launch on Beast when you took a hard run at their side and slid them far enough up your forks to get a better impact angle. Speed is your friend.

Worth the Trouble?
Q: I was desoldering a FingerTech Silver Spark and the little metal tab that I solder to the wire to broke off. I tried adding some solder to the remaining visible metal but its not sticking well. Is there anything I can do to save it or is the motor just screwed? [Random Comcast Server]

A: [Mark J.] The photo shows what the inside of the Silver Spark motor 'endbell' looks like. The nylon that the metal tab disappears into goes down a fair distance and becomes the support for a motor brush. If you're REALLY determined to save the motor, you can carve away some of the nylon to reveal more of the brass tab, then use a good quality soldering flux (I use Rubyfluid Soldering Paste) to tin the exposed brass. It will then be easy to attach the power wire.

If your soldering skills are not good, I'd suggest buying a new Silver Spark and saving the gearbox as a spare.


Fifty-Six Megabytes
Q: I had a video planned to celebrate Run Amok's championship anniversary, but it said "only 8 megabytes may be sent at a time". The video file is 56 megabytes, and I can’t decrease the file size to the desired amount without a severe decrease in quality that I’m not willing to sacrifice. Hopefully I can post it to YouTube sometime.

Happy Anniversary! -sincerely, Iceywave ☆ [West of San Antonio]

A: [Mark J.] Thanks, Icey! We can't let a few megabytes come between friends. Let's try this:

A Secret Portal Opens. A Large File Passes Thru. The Portal Fades Away.

There, that wasn't so hard. Let's see what we've got here... Whoa, thanks, Icey! I've embedded your video recreation of the Robotica 'Fight to the Finish' below, and tossed a copy onto my YouTube channel.

Reply: I'm happy to hear you enjoyed my video! Turns out the file I sent was actually 59 megabytes. The original recording was 56 mbs, but I had to put it through some editing software to add fade in/fade out on the video. The models of Juggerbot and Ram Force were built by myself, in case you were wondering. I also have a big surprise coming April 1st, so be prepared!
-sincerely, Iceywave


Bang Bang Bang Thud - Again
Q: Hi there, I've been playing around with the hammer calculator v2.2 spreadsheet and believe I've found two errors in the methodology that throw off the results by a very large amount:
  1. (more minor) The integration done on the Calculations tab assumes that gravity is a constant resisting force, when it's a varying force that resists by cos(angle) (peak at horizontal in a standard 180 degree swing), but by the impact at 180 degrees it's fully adding to the system energy. Not accounting for this throws off the spreadsheet's optimal gear ratio recommendation by 5-20% based on playing around with a fixed version.
  2. (more *impactful*) The total system energy is KE + Torque, not just KE (Since 1Nm = 1J). For spinning weapons, Torque can usually be ignored since it's minor, but since hammers without an energy storage system (flywheel/pneumatic spring) are so inefficient in terms of motor weight to impact energy, it's actually a massive factor. For example a 1Nm torque motor output at impact speed, 0.25m arm, 10:1 reduction has a motor energy of 1*10/0.25 ~= 40Nm of applied torque at point of impact = 40J in addition to the KE. I'm assuming most real systems will have a clutch or the impact would risk damaging the system too much, but the limited torque could be substituted post clutch quite easily.
The net result in the configurations I've been playing with is that the optimal setpoint for the gear reduction is typically a slightly higher reduction, and the actual impact energy is 2-2.5x what the existing spreadsheet suggests. This raises hammers from ~1/10th the impact energy of an equivalent weight allocation traditional spinning weapon, to maybe 1/4, which is still atrocious but closer to viable given the typically weaker top armor and lack of reliance on relative velocity that hammers can take advantage of.

Since this is a Q/A, any errors in my math/methodology? Cheers, Joseph Duchesne [Ontario, Canada]

A: [Mark J.] I appreciate your effort to "keep me honest" by digging through the code in my Hammer Spreadsheet, Joseph. Few people make that effort.

Given that I authored the spreadsheet eight years ago, my working memory of the calculation details is not terribly good. I would appreciate corrections to my comments below should your recent review prove them to be in error.

  1. Cosine correction exists: In the spreadsheet there is a hidden tab named "Data Table" which you may or may not have discovered. If you 'unhide' this tab you will find in cell M4 the following formula that corrects the gravitational force in the manner you suggested above: =Calculations!D10×9.8×COS(RADIANS(M3)) The cells beneath M4 adjust available motor torque based on this correction.
  2. N-m comes in two flavors: A newton-meter is used to describe both a unit of work (energy) and a measure of torque (force) -- but the two are not interchangeable:
Flavor #1: Multiply the weight of of an object in newtons by the height the object is lifted to get the unit of work: a newton‑meter (N‑m). In this context 1 N‑m is a measure of energy equal to 1 joule.
Flavor #2: When measuring torque, a force of 1 newton applied at a radial distance of 1 meter equals a newton-meter (N‑m). In this context a N‑m is a measure of force rather than energy. Equating this flavor of N‑m to joules is fallacious.
We could resolve any confusion on this issue by building a miniature "Test Your Strength" carnival machine for a robot hammer weapon to strike. The height reached by the known weight could be quickly translated into a measured value for the hammer energy. I'm betting on my calculations.

Now please pardon me, I must take my medication and lay down for a bit.


Q: Thanks for pointing me in the right direction with regard to torque vs. energy. I got tripped up since most times when the units check out, the physics does too. The missing part was that the actual unit of torque is best described as Joules/radian, but since radians are unitless, this misleadingly appears to just be Joules.

A: It's a trap. Using the same units for two different measures will cause reasonable minds to make the same assumption you made. The usage really should be clarified and/or replaced.

Q: Intuitively, I still feel like there would be a slightly harder hit if the motor torque is applied beyond impact, vs. becoming disconnected the instant before impact, but this is likely a very small fraction of the additional system energy I had been hoping for.

A: Yes, small.

  • Up to the moment of impact all torque is being used to accelerate the hammer; and
  • Following impact the force of motor torque will be limited to the amount needed to lift the front of the hammerbot off the arena floor -- which has likely already been raised by impact rebound.
Q: With regard to the cosine correction: Yes, the correction is there for the starting condition, but it needs to be integrated across the whole hammer swing, since the newtons of downforce (adjusting the effective torque of the system) "swing" from resisting the hammer at 0 degrees, to not resisting the hammer at all (90 degrees) to aiding the hammer swing (180 degrees). The correction in the spreadsheet applies to the starting condition. ~Joseph D.

A: You're killing me, Joseph. Why would I have written that nice column of equations and then failed to spread them across the full swing? Now I have to dig thru the code of an eight-year-old spreadsheet to look for the place where I dropped that thread...

I woke up with a clear head, determined to sort out the evolution of my Hammer Spreadsheet.
  • Over my first cup of coffee I was able to trace the origin of the "starting condition only" gravity correction. Let's just say that it served the original purpose of the spreadsheet.
  • By the start of my second cup of coffee I had determined that your suggestion to integrate gravitational effects across the whole hammer swing had undeniable merit.
  • Half way thru my third cup of coffee I settled on implementing a varying time constant as the method by which I might implement your suggestion.
Some hours later, I had beta version 2.5 of the Electric Hammer Spreadsheet with gravity correction that shows a reduced optimum gear reduction and models slightly improved energy and time-to-strike curves.
A couple of weeks passed before I noticed some very odd results when modeling a hammer with an undersized motor. Tracing this problem revealed that my decision to use a varying time constant in the model created a progressive error in motor torque that over-estimated hammer performance by a factor several times greater than the understatement in the earlier version. Rats!

I now recall the full reason I had front-loaded the gravitational correction in the model. From a standstill, a hammer with a 180 degree swing may spend half of the total strike time pulling up thru the first 45 degrees of arc where the retardation by gravity is greatest. The last 45 degrees where gravity is assisting the swing flashes by in about 15% of the swing time.

I've withdrawn beta version 2.5 of the spreadsheet. Version 2.2 does slightly understate the theoretical performance of an electric hammer, but it is closer to real-world values than is the flawed version 2.5.

The link to download the most current version of the Hammer Spreadsheet is always on the Ask Aaron Combat Robot Design Tools page.

Unspecified
Q: I know what I said about not being back until April, but I just remembered something. I heard a rumor that a specified team was asked to leave a specified event because they committed a specified offense. Is that true?

-sincerely, Iceywave☆ [West of San Antonio]

A: [Mark J.] I have removed the names of the team, event, and offense from your question. If I can neither confirm or quash a rumor of this nature from personal knowledge I don't care to spread it. Here is what I can tell you, based on reliable sources:

  • The specified team was expelled from the specified event after the competition began.
  • There were multiple reasons for their removal, but my sources do not confirm the specified offense you mentioned.
I prefer to leave it at that.
Just Keep Fighting
Q: Hi, when building battle bots which temperature sensors/ impact sensors do you recommend using? [Parts Unknown]

A: [Mark J.] It is the nature of combat robotics to push components well beyond their design limits.

  • Temperature sensors are seldom found in robots below the heavyweight class. In heavyweights they may be used to identify design problems during testing, but during a match you can't back off just 'cause something overheats.
  • Given that the magnitude, angle, and location of impacts in combat are unpredictable, the data from impact sensors is effectively useless. When a part fails, replace it with a stronger part.
All of our robots include a non-structural piece of wood. If the wood bursts into flame we know that it's getting hot in there.
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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