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FAQ

4926 Questions and Answers about Combat Robotics
from Team Run Amok
Ten Years of Ask Aaron


Team Run Amok receives a lot of email asking about the design and operation of combat robots. In 2003 my son and team member Aaron Joerger (then 12 years old) requested a question and answer page to document our responses.

Got a question? We welcome combat robot questions. Check the Ask Aaron Archives first to see if your question has already been answered, then click the blue button.

The Ask Aaron Archives Click to browse thousands of previously answered questions by category, or search for specific topics. Includes FAQ

Caution   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.
In Memorium: 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   


Welcome to my website Recent Questions
 
Not all the questions we receive at Ask Aaron are serious. Some are odd, some misdirected, and a few are incomprehensible. Aaron enjoyed dealing with these questions, and I've collected some of his best responses in a in a special page:
Aaron's Greatest Hits
Aaron's Greatest Hits




Q: I've heard that you can anodize metal to change to change it into cool colors. How do I avoid making it weaker when I do so? [Massachusetts]

A: [Mark J.] Anodizing is a process that thickens the natural layer of oxidation on the surface of certain metals. The thickened layer of oxide can reduce surface wear and improve corrosion resistance, but it does not effect the physical properties of the metal beneath the surface. You don't weaken the material by anodizing it.

The effects of anodizing vary with the metal:

  • Anodizing titanium can produce color effects on the surface of the metal;

  • Anodizing aluminum does not directly produce 'cool colors', but the oxide layer can absorb dyes that create bright colors.
Ferrous metals (iron, steel...) cannot be effectively anodized because the iron oxides created do not have properties that improve surface wear resistance or corrosion protection.
Anodized Aluminum - Color Dyed



Q: How long is a piece of string? [Internet Node TCA]

A: [Mark J.] Just long enough - if you're lucky.



Q: What would be better as armor in 30 kg and 60 kg category: 202 stainless steel or 304 stainless steel? Any other suggestions? [India]

A: [Mark J.] Stainless steels are not commonly used for robot armor. Stainless alloys are fomulated for corrosion resistance and high heat performance -- attributes not valued in robot armor. Both of your suggested alloys are relatively 'soft' and deform easily (low yield strength), and neither can be heat treated for improved hardness. Of the two alloys, 202 would be my choice for armor due to its slightly greater hardness and yield strength.

I don't know the full list of materials available to you, but other Indian builders are using EN24 'chromoly' steel. EN24 is much better suited to use as robot armor and should be considerably cheaper than the stainless alloys.

Q: hi .... I would like to add to the 202 armour question . can u plz suggest some good options for armour. So i can see if the material is available to me . I have used 202 and it worked good . Titanium is out of budget . any other Bite proof (lol) good material ? [India]

A: See FAQ #17. Although I'm pleased to comment on specific materials, I don't think it's reasonable to ask me to list and evaluate all possible metal alloys, polymers, and composites so that you can pick thru them. It's better if you do your own homework on this.

I suggest that you read Chapter 3 of the Riobotz Combat Tutorial for an extensive listing of robot structural materials and for guidance on evaluating the specific materials that are available to you. Read the rest of the tutorial while you're at it.

Tip: don't rely purely on the properties of the material. Great armor depends as much on design and mounting as it does on the material itself. I built two champion robots armored with wood.



Q: Hi Aaron,i have a starter motor,and i use it to power my vertical spinner weighing around 6 kg .I am a bit confused about it's performance.so i need your help to know whether i should switch over to E30-400 or continue with the starter [India]

A: [Mark J.] There are LOTS of different automotive starter motors with a very wide range of performance, and none of them come with the type of specs a robot builder needs to calculate their suitability for a spinning weapon. Also, starter motors are designed to operate intermittently for a few seconds at a time, not continuously for several minutes. I can't think of any champion robots that use starter motors to power their weapons -- can you?

I really can't give you any advice on the unspecified motor you plan to use. It might work well, it might be completely unsuitable. Personally, I recommend using components that have full specifications and a proven record in combat robots. Let other builders research new motors and risk failure in combat conditions.



Q: can a hollow pipe be used as a dead shaft for drum? [India]

A: [Mark J.] Can a wooden boat carry an elephant? Depends on the boat -- depends on the elephant. The hamburger is bad.

The Hamburger is Bad



Q: How do I wire BotBitz 85A ESC to wheelchair motor? [Canton, Georgia]

A: [Mark J.] They didn't send you the user manual? Download it: BotBitz 85A User Manual -- wiring instructions are on page 3.



Q: i have made chassis for my robot which is around 15-20kg.which motor would suitable for it? [Maharashtra, India]

A: [Mark J.] You made a chassis before you decided on motors??? All the components of a combat robot must work together, and stuffing motors into a chassis not designed to match their requirements and capabilities is a poor start.

See Frequently Asked Questions #21 for general motor guidance and a link to a tool that is very useful in evaluating possible motors.

I don't know what motors are available to you, and and you haven't given me enough information about your robot for me to be able to make a recommendation. If you would like to send the specifications of a motor you are considering I might be able to evaluate its performance in a 20 KG robot -- but I can't blindly recommend a motor.



Q: will aluminum pulleys work for transmitting power from motor to drum? i mean will the keyway expand wid the jerk created [Maharashtra, India]

A: [Mark J.] The hamburger is bad. There are various grades of aluminum, various designs for hubs, and assorted sizes of pulleys. A properly sized aluminum pulley with a well designed hub made from a good quality aluminum alloy should be fine.



Q: hey my ampflow A series motor shaft is bent, could you offer any suggestion to deal with it.It was damaged during a match. [Tamil Nadu, India]

A: [Mark J.] You bent a 1/2" hardened steel motor shaft? I'd carefully evaluate the weapon/drive design to better isolate the motor shaft from such high loading. AmpFlow motors have a nice long shaft, but you should mount the pully/sprocket/gear as close to the motor bearing as possible to keep excessive loading off the shaft.

Straightening a large diameter shaft is unlikely to yield useable results, and it isn't practical to attempt a shaft replacement in an AmpFlow. I think you mark it 'bad' and save it for parts. Combat robots are an expensive hobby.



Q: I m making a drum bot having ID 120mm,so i will fit bearing housing to end caps as i cannot get 120mm OD bearing having smaller bore. my question is, will the bearing housing sustain impacts caused by drum? [India]

A: [Mark J.] Short answer - yes. The force of the impact will be borne by the impactor, the drum, the endplates, the bearings, the drum shaft, and the shaft supports. Each of these elements must be strong enough to withstand the full force of the weapon backlash. Don't skimp on the bearings!



Q: Hi I have been kicking some robot ideas around for a while, and I am interested in the DeWalt motors. However, the gearbox seems to be the weak point, and it has a nonstandard output. Do you know of any examples of the motors being used without the gearbox? The Robot Marketplace says the output pinion gear is unique, and it appears to be permanently mounted.

Thank you from San Diego.

p.s. I just rediscovered your site after a few years, and I am sorry about Aaron's passing.

A: [Mark J.] Thank you for your mention of Aaron. He is always on my mind, and I miss him terribly.

Dale Hetherington has used DeWalt motors mated to his own gearboxes in several of his projects. He offers advice on removing the nonstandard pinion using a custom gear puller. I suspect you could also carefully grind away one side of the pinion with a Dremel tool and more easilly pop the gear off. The motor shaft is 5mm and can be adapted to a variety of power transfer options.

You also may be interested in the DeWut?! 3 Speed Gearmotor Kit which adapts the 'new-style' DeWalt motor and gearbox to a strong package with a standard output shaft.



Q: Hi, we are using a Hitec Giant Scale HS805-BB Servo motor in a mechanical engineering senior design project. We hoped to have a shaft coming directly out of the spline, but all the Servo Shaft Couplings I can find online are for a C1 size spline, and ours is D1. Do you know of any vendors with D1 size, or at least any vendors that might have a D1 to C1 adapter? Thank you! [New Jersey]

A: [Mark J.] You've just learned a valuable engineering lesson:

In any mechanical design project there is one vital part that should be available off-the-shelf but isn't.

Suggestion: tear apart an old servo and extract the final drive gear that has the C1 splined output shaft. If you don't have an old servo send me your address and I'll send you the output gear. Center the C1 output gear on the output horn of your Giant Scale servo and sink a couple screws thru the gear and into the horn. Presto, you've built your own adapter.

Q: I would appreciate that part! We are on a very limited budget, and do not have a servo to spare. Could you send the part to [address redacted]. Thank you!

A: I'll have it in the mail tomorrow. All my junk servos are Futaba, so if you order accessories make them for the 1/4" Futaba 3F Standard Spline (25 tooth).



Q: hi mark lucky here thanks for ur precious guidance in yr 2014 because of which my team won 3rd prize at ITT B robowars,
again I have one question that upto which hrc I should heat treat the EN24 material? [India]

A: [Mark J.] Glad to hear of your success at Robowars, Lucky.

Check this previous post that addresses hardening EN24 (chromoly 4130) steel. The full answer on hardening depends on the use you will have for the material. If you plan to use it for a weapon impactor you should consider other options.



Q: hi aaron,from india
i need to know the rating of motors which used in cordless drilling machine,whether those motors are good when compared to bane motors ?? [Tamil Nadu, India]

A: [Mark J.] A very wide range of motors are used in cordless drills. Many drills use motors that resemble the BaneBots RS-550 motors (225 watt output), but they are made by differing manufacturers to differing voltage and power specifications. Performance varies greatly: power output runs anywhere from sub-100 watts to more than 900 watts.

The cordless drill gearboxes also vary a great deal:

  • Nearly all have plastic housings;
  • Some have plastic gears in one or more of the reduction stages;
  • Many are held to the motor by the drill case and come apart when removed;
  • All come in odd shapes that are difficult to properly mount to a chassis; and
  • A few have strange output shafts that are a challenge to adapt to a wheel hub.
If you do decide to use cordless drill motors, make sure they are a brand that can be easily adapted to robot use. Check what brands other builders are using successfully. Tips for adapting drill motors for robot use can be found by a websearch for "drill motor hack".

In contrast to drill motors, the BaneBots gearboxes:

  • Are all metal inside and out;
  • Adapt to a variety of small motors;
  • Attach directly to the motor with machine screws;
  • Come in a wide selection of gear reduction ratios;
  • Have a strong standard size output shaft with a keyway; and
  • Are designed for simple and secure mounting to a robot chassis.
Note: motors and gearboxes in more expensive contractor-grade drills are often custom-made to the specifications of the manufacturer and offer superior performance compared to consumer-grade drills. In particular, the powerful and reliable DeWalt 18 volt drill motors have powered a great many combat robots, but they too require extensive modification to be converted to robot use. See Equals Zero Designs - DeWut?! 3 Speed Gearmotor Kit.
Harbor Freight 18 volt drillmotor.

BaneBots P60 gearbox and motor.



Q: Hey Mark,

My robotics program at my school is going smoothly, students are currently modifying existing Fingertech Viper kits to modify them with basic weapons. One student, a senior, wants to build a Hazard style overhead bar spinner (except he will use a saw blade for convenience purposes. These bots will never compete outside of the classroom so Massive KE impact is not needed.) What do you think would be the best way to go about doing this? We do not have a machine shop at the school but we do have basic tools: Access to a drill press, vise, reciprocating saw, Dremmel and tin snips. Shall I say it's the good old fashioned way?

All the best,
New York

A: [Mark J.] Good to hear from you, New York.

An overhead spinner weapon looks like a nice simple option for an 'old school' antweight robot -- until you start in on the design details:

  • You need to keep the height low enough to actually hit your opponent and inflict damage;
  • You need a strong shaft and an accurate hub assembly; and
  • The entire structure must be well supported.
Given the lack of machine tools and my own appreciation of simple design, I'd model the weapon after the existing Viper Spinner Addon kit and turn the 'bot upside-down. Using a low-profile outrunner brushless motor direct-driving the FingerTech blade hub solves most of the critical design issues. The blade will spin too fast for best bite, and the spin-up time may be a little long -- but it is a simple and fairly rugged solution.

Shouldn't you guys be working on more 'Sportsman Class' style weapons? Spinners are going to cause a lot of damage. I'd make him spin a Popsicle stick.

Q: The bots will actually have a weight of 2 pounds allowed to reduce the weight constraint. The kid wanted to do a hazard style where the bot has to go up the wedge for contact (though hazard did not actually have to have his bots go up into the blade). With this in mind, do you think he could still stick to a overhead bar or should we tell him to go for the under cutter from finger tech?

As a matter of fact, he will be required to spin a piece of balsa wood before hand so he will indeed be spinning something like a popsicle stick!

A: By all means encourage the student to construct the weapon he wants -- that's the best way to learn.

My concept is to mount a small brushless outrunner motor to the chassis in the holes provided for the undercutter weapon, then flip the chassis upside-down to put the weapon in an overhead spinner position. If your opponent happens to be more vulnerable to an undercutter you can turn the 'bot back rightside-up.

You can order the whole undercutter kit from FingerTech, but it may be less expensive to buy the blade hub from them and order the motor and controller direct from Hobby King.

If you really want to mount the weapon to the top panel you should either replace the Lexan with something sturdier (aluminum, garolyte, carbon fiber, plywood...) or construct a mounting bracket that attaches to the base chassis. Lexan doesn't do well with high loadings and small bolt holes.



Q: Hi Aaron, how I can build the remote control for a battlebot? ¿Tienes algún esquema del circuito? [Ecuador]

A: [Mark J.] I VERY STRONGLY recommend that you NOT attempt to build your own radio control for a combat robot. Commercial radio systems are rugged, reliable, loaded with features, and inexpensive. You aren't going to achieve any of those attributes by building your own system. Even a $25 Chinese R/C system would be far preferable to a home-brew radio. Don't do it!



I'd like to offer my sincere thanks to all who read and contributed to 'Ask Aaron' in 2014. It was a difficult year for me, and keeping busy with the website was a greatly appreciated distraction. Best wishes to you all in 2015.

 - Mark Joerger



Interlocking finger joint. Q: Hey Mark, I've got a few questions:

Right now I'm overhauling the construction of my primary antweight, my old design had horrible weight distribution due to the heavier material being shoved up front, so I'm going to a box with a hinged wedge, made from plastic cutting boards and garolite. My issue is how the the plastic is screwed together, should the screws be parallel with the wheels (with the front and back flush with the side panels with seams) or perpendicular (the front and back being all one piece with no seams)? The wheels themselves are internal and are mounted to the base plate. [Oregon]

A: [Mark J.] Why not have it both ways? If you cut the plastic sidewalls in an interlocking finger joint pattern (see drawing) you can hold the walls together with screws in both directions. It's a stronger joint with less chance of shearing a screw by an impact from either front or side.

Q: Another thought I had not having to do with the above question, how come there hasn't been more widespread use of multi-rotor motors? I ask this because they spin slower than similar motors of equal power and are flatter, which I think would make them more appealing to ant and beetle builders. If they were just as easy to use as normal brushless motors, then more builders would be using them, or am I just the first person to think of them? I even ran the numbers on one with a six and a half inch steel disk and the numbers were promising (over a hundred joules in half a second, surely that's a good speed and power for an insect arena). [Still Oregon]

A: There isn't anything particularly unusual about multi-rotor brushless motors. They are outrunner-style (rotating case) motors of large diameter for their power rating, which does give them greater torque and lower speed. There's no reason that they should be any more difficult to use than other brushless weapon motors, and the lower RPM and higher torque make them a desireable alternative. I suspect that builders are just using well-tested motors that others have had success with. Be brave and give 'em a try.



Q: Hi mark,I have two ampflow motors e30-400 for my bot weighing 66lb and I want to reduce motor rpm to400 rpm.in case I also want my bot to have 4 wheel drive and I want to use chains and sprockets.Is it a good idea? please also suggest the reduction ratio for running it to 400rpm [India]

A: [Mark J.] Chain and sprocket is the standard method to make a two-motor robot 4-wheel drive. Keep your sprockets well aligned, maintain proper tension on your chains and you should be fine.

Your E30-400 motors have a no-load speed of 5700 RPM at 24 volts. The formula for calculating gear reduction to obtain a desired output RPM is:

(Motor RPM / Desired RPM) : 1 = Gear Reduction

For the E30-400 motor, (5700 / 400) : 1 = 14.25 : 1 gear reduction. You didn't mention what size wheels you plan to use, but that should give good performance in a 66-pound robot with wheels around 6" in diameter.



Robot combat historian Nate Franklin has been very busy collecting videos from the 'Golden Age' of the sport. Check his YouTube Playlists for hundreds of videos.



Q: And a robot with this torque: 4.14 Nm can move 100Kg, because i need something similar to this sumo video, what gearbox is neccesary to achieve [Equador]

A: [Mark J.] Your pushing power is traction limited. If you require 100Kg pushing force from a 3 Kg robot, you will need a great deal of magnetic downforce. Assuming a coefficient of friction of 1.3, a magnetic downforce of 75 Kg, a wheel diameter of 10 cm, and two motors producing 4.14 Nm stall torque each -- you will need a gear reduction of 4:1.

Update: I recall from an earlier post that your two motors have a combined torque of 4.14 Nm stall torque -- so you'd need an 8:1 gear reduction to achieve 100 Kg of pushing force.



Q: I found a formula to calculate motor power from RPM and torque:

Power (watts) = RPM * Torque (Nm) * 0.105

When I enter the values for my drive motor (2500 no-load RPM, 4.6 Nm stall torque) I get a watt output number much larger than I expected. What's wrong? [India]

A: [Mark J.] You're getting a number about four times too large, right?

You're entering the no-load RPM of the motor and the stall torque -- things that do not happen at the same time. Stall torque comes at zero RPM, and at no-load RPM the motor torque is zero. You need to enter a speed and torque that happen together.

The maximum power output of a Permanent Magnet Direct Current (PMDC) motor is achieved when the motor is loaded to 1/2 the no-load RPM, at which point the motor is producing 1/2 the maximum (stall) torque. To calculate the maximum output of a PMDC motor, the correct numbers to enter into the formula are the values at the maximum power point:

Maximum PMDC Motor Power = (1/2 no-load RPM) * (1/2 stall torque) * 0.105

= 1250 RPM * 2.3 Nm torque * 0.105 = 302 watts output



Q: Did you and your son ever hope that there would be a third season of Robot Wars: Extreme Warriors to enter? [Unidentified location, North America]

A: [Mark J.] We were looking forward to it! We had two heavyweight robots, twin European frequency R/C radios, a pair of shipping crates, and plans for upgrades. All we were waiting for was the word.

There were many rumors about a third televised season of Robot Wars: Extreme Warriors. Robot combat icon Dan Danknick was told by the Robot Wars production crew to get ready to organize the American competitors for a new series. There were also reports of a robot arena being built at Universal Studios for filming the future series. We thought it was a sure thing, but it didn't come to pass.

Our heavyweight lifter 'The Gap' still sits on a raised platform in a corner of the workshop, right next to our retired champion 'Run Amok'. 'The Gap' only needs a new set of batteries and a full tank of CO2 and it's ready to go -- but it wouldn't be any fun without Aaron.



Q: Hey mark what will happen if i overvolt 24v 300w 2500rpm pankmotor to 30v for drive system? I m bulding a 132lb wedge bot 2 wheel drive with 10" wheel and a gear reduction of 1:30 (too slow)...!

And one weird thing came in my mind that for wedge 600w is nt enough so i was thinking to use two of those motors on one wheel's shaft. [India]

A: [Mark J.] I don't know this 'pankmotor', so I can't comment on how well it will tollerate overvolting. See Frequently Asked Questions #25.

If the motor can survive a 25% overvolt, speed will increase by 25%, torque will increase by 25%, and current consumption will increase by 25%. Since power is the product of speed and torque, the power of the motor will increase by a factor of (1.25 x 1.25) = 1.56 -- so the motor will have a peak power of (1.56 X 300) = 469 watts. More power, but still slow.

Running two of these motors per wheel will generate double the torque for better acceleration, but will supply very little extra speed.

If you have full specs for this 'pankmotor', the Tentacle Torque-Amp Calculator can give you performance parameters for changes in gearing, voltage, wheel size, and number of motors. It's what I use to answer questions like yours.



Q: What is the torque and rpm that provide maxon 148866 with a gearbox of 2:1, of I supply 14.8V [Equador]

A: [Mark J.] OK, let's walk thru it. Here are the specs for the Maxon 148866 motor at it's nominal 12 volt rating -- assuming that you can supply the full stall current :

  • No load speed: 7500 rpm
  • Stall torque: 1.68 Nm
  • Stall current: 105 amps
Raising the supplied voltage from 12 volts to 14.8 volts will raise the speed, stall torque and stall current by a factor of (14.8 / 12) = 1.23:
  • No load speed: 9250 rpm
  • Stall torque: 2.07 Nm
  • Stall current: 129 amps
Then, using a 2:1 gearbox will decrease speed by a factor of 2 and increase the torque by a factor of 2. Stall current is unchanged:
  • No load speed: 4625 rpm
  • Stall torque: 4.14 Nm
  • Stall current: 129 amps
If your power supply cannot provide the full stall current, stall torque will be reduced in proportion to the reduction in current.



Q: when did 2.4ghz radios become popular? [Havertown, Pennsylvania]

A: [Mark J.] February 3rd, 2008 at 10:24 AM pacific standard time.

Q: that's very specific.

A: That's when RoboGames decided that tracking transmitter frequency crystals was too much bother and mandated spread-spectrum radios for their combat events. The 2.4 gHz radios would have taken over eventually, but RoboGames pushed the issue.

About that same time RoboGames also decided that the single most popular large combat class - Hobbyweight robots - was too much bother and dropped it. Superheavys and Feathers followed. Power corrupts.



Q: A builder on one of the forums claims that he spins his featherweight [30 pound class] drum weapon at 20,000 RPM and still gets bite. Is this possible? [Ohio]

A: [Mark J.] Usually, no way -- but I know the bot in question.

A conventional drumbot has the drum well out in front of the rest of the robot and rams the weapon directly into the opponent. In this particular robot the drum is set fairly well back and rather tall 'wedgelets' lead the opponent up and into the drum at a height close to the drum axis. This gives the drum a good chance to impact the sharp leading edge of the opponent and provides a favorable attack angle.

This isn't 'bite' in the conventional sense, but it does allow a very fast drum to connect and release a decent hit IF the driver can coax their opponent up the wedge.



Two in one day. Must be a phase of the moon -- are the grunion running?


Q: how many people in iraq [Philadelphia, Pennsylvania]

A: [Mark J.] ...build combat robots? Not any, that I know of.


Q: 5. In what sense did the "Sixties" begin before 1960 and continue beyond 1970? What events might one choose to define the beginning and the end of a "long Sixties," and why? [San Francisco, California]

A: [Mark J.] I've got an uncle who took a bad fall on an icy sidewalk. He believes to this day that Nixon is still the President. It'll be 1969 for him until our robot overlords arrive to set us free. Does that help?



Q: Hey mark.. I have seen Robo Bacon in antweight matches in robogames 13 and I have decided to do that robot weapon for 35 kg bot ... What kind of weapon is that? How it differs from double teethed drum? Which produces more impact on opponent? please prefer some material to do that weapon.... [India]

A: [Mark J.] How can you decide on a robot weapon before you even know if it has any advantages?

Team Uai!rrior's antweight 'Bacon' has a single-tooth spiral drum weapon, similar to hall-of-fame middleweight 'Professor Chaos'. Go read section 6.3 of the RioBotz Combat Tutorial for an explanation of the advantages of an asymmetric single-tooth spinner.

See this post in the Weapon archive for some notes and a diagram on spiral drum construction. The machining is difficult, and balancing the drum is a real challenge. A spiral drum is typically made of aluminum with steel inserts for balance and a hardened steel impactor.

Antweight drum spinner 'Bacon'.



Q: Hi..mark..what is the range of hardening H13 and D2 material for tooth of drum.. [Pune, India]

A: [Mark J.] Six posts down this page is the post from a couple days ago discussing of D2, A2, and H13 tool steels. Read that.

General notes:

  • H13 is a 'hot working' steel designed to retain useable properties at VERY high temperatures -- not the conditions encountered in a drum impactor tooth. Room temperature hardness and toughness are poor. There are much better drum impactor materials.

  • D2 is a steel designed for high resistance to wear in prolonged use in dies and shearing blades -- not the primary property of interest for impact teeth. At HRC 60 hardness it has an acceptable blend of hardness and toughness. I would rate D2 steel as a fair impactor material.

  • A2 is a general purpose tool steel. At HRC 60 hardness it has much greater toughness than D2. It makes a good impactor material.
The preferred impactor material is S7 shock-resistant tool steel, but I'm told that it is not available fron Indian sources. Tempered to HRC values around HRC 58 it has several times the toughness of D2 or A2. It may be overkill, but if you have access to S7 you'll probably want to use it.



Q: hello i am preparing for techfest i need urgent guidance about how to use 2.4 ghz transmitter to move weapon and locomotion [India]

A: [Mark J.] If you're in need of urgent guidance you would be well advised to search the FAQ and the Ask Aaron archives to see if your question has been previously answered rather than wait for me to get back to you. In this case, it has been discussed and answered in great detail.

  • Start by reading thru the FAQ. Pay particular attention to question #19, but read the whole thing -- if you don't know how to rig your R/C transmitter to control your motors there's a whole lot more you're gonna need to learn about.

  • Many Indian robot builders use solenoids to control their robot motors, so you'll want to read the special Solenoid FAQ to see if that option will work for you.

  • There are many, many, many questions on this topic answered in the Ask Aaron archives.

    • The Motors & Controllers archive has answers to many questions on speed controller selection for drivetrains.

    • The Robot Weapons archive has answers about weapon motor controller selection.

    • The Radio & Electronics archive will supply details on programming your transmitter for intuitive control of the drive and weapon motors, as well as help on battery selection.
That should get you a start.



Q: Hi Mark...How we can use ampflow F30-400 motor effectively ?? Whether i can go for increase in voltage or increase in current ? What will happen if I use it with 24v and 150 amp suplly ? [India]

A: [Mark J.] There seems to be some considerable confusion about electric motor power requirements amongst Indian robot builders. The relationships between voltage, current, and motor performance have been discussed in many previous posts to Ask Aaron, but let me summarize them here.

About current: an electric motor will consume current based on the voltage supplied and the work load placed on the motor.

    PMDC motor torque/speed/current chart
  • The AmpFlow F30-400 motor operating at a supplied 24 volts under no-load will spin at 4800 RPM and consume 2 amps of current.

  • Any work load placed on the motor will decrease the RPM and increase the current consuption in proportion to the load as the required torque increases. Double the load = double the current consumption.

  • If the load placed on the motor is so great as to stop the rotation of the motor completely, the motor is 'stalled'. When stalled, a Permanent Magnet Direct Current (PMDC) motor like the AmpFlow will consume the maximum current it is capable of drawing (stall amps) and produce the greatest torque it is capable of producing (stall torque). Note that it is inadviseable to design a drivetrain or weapon that will risk stalling its drive motor.

  • If the power supply is incapable of providing the full stall current to the motor, the maximum torque available from the motor will be reduced. At 24 volt stall, the AmpFlow F30-400 motor can draw a bit more than 370 amps of current and produce 2500 ounce-inches of torque. If your power supply can provide only 150 amps of current, the maximum torque of the motor will be reduced to: (150/372) * 2500 = 1014 ounce-inches of torque.

  • Using a power supply that can provide more than the stall current of a motor will provide no increase in motor performance.
About voltage: changes to the voltage supplied to the motor will impact both the speed and the current draw.
  • Doubling the supply voltage will double the motor speed. The AmpFlow F30-400 motor has a no-load speed of 2400 RPM at 12 volts, and 4800 RPM at 24 volts.

  • Doubling the supply voltage also doubles the torque and doubles the current demand. The AmpFlow F30-400 motor has a stall torque of 1250 inch-ounces at 186 amps at 12 volts, and 2500 inch-ounces of torque at 372 amps at 24 volts.

  • Power is the product of torque and speed. Since doubling the voltage doubles both the torque and speed of the motor, doubling the voltage increases motor power by a factor of four (twice the RPM * twice the torque = four times the power). The AmpFlow F30-400 motor has a peak power output of 0.75 horsepower at 12 volts, and a peak power output of 3.0 horsepower at 24 volts.

  • At 48 volts the motor would have a theoretical peak output of 12 horsepower -- but it would also have a VERY short life expectancy. Overvolting motors will reduce their longevity and should be done with care and moderation. Search the Motors & Controllers archive for 'overvolt' for additional information.



Q: Hi Mark, Sage here. I was thinking of making the bot such that the plow could be interchanged for a wedge in the pits (I'm thinking about a hinged plow and wedge) because I kinda have a bad feeling that a wedge could get underneath my plow. I'm really not sure which would get underneath which, so right now I'm just guessing!

I saw the Combots V Breaker Box vs Sewer Snake fight and noticed that the plow could lift the forks easily. Also in the fight with Great Pumpkin it could get underneath easily but I think that may be partially due to the fact that when GP accelerates it's nose lifts up a bit making it easier to get under.

What do you say would a low wedge (somewhat like one on Original Sin) get under a plow or not?

Should I try interchangeable weapons or stick with the hinged plow?

Are there any specific advantages for the wedge over the plow (like flipping vertical spinners over, for eg. Terminal Velocity vs Pipe Wrench, which I think couldn't have been possible if PW used a plow instead of a wedge) and for the plow over the wedge so I can change my strategy against different bots?
Thanks a lot! [India]

A: [Mark J.] There is no advantage in design between a wedge and a scoop (plow) in a contest of who gets under who. The difference comes in construction skill and attention to detail. Lowest edge wins, whether it's on a wedge or a scoop.

The advantage of a scoop is that the gentle curve allows it to better fit the radius of a vertical spinner/drum and prevent the weapon from obtaining 'bite' on the scoop surface. The curve is also useful in preventing an opponent from driving 'up and over' your 'bot.

You can get into trouble with a scoop if its radius is smaller than the radius of the vertical spinner weapon you face -- such as the large radius weapon on 'Terminal Velocity'. A change from a direct frontal attack to an angled attack in such situations can help to overcome that disadvantage.

In general, I'm not a big fan of interchangeable weaponry -- particularly if it's just swapping out a scoop for a wedge. The pits can get hectic between matches, and trying to squeeze in time for a weapon swap may result in some critical item being overlooked. Also, your 'quick change' fittings are unlikely to be as strong as more permanent mounts. I'd build a good, strong, shallow scoop and run with it.

Wedge and Scoop



Q: Hi Aaron, excuse my writing mistakes because I do not speak English but want to build the robot battle Ziggy. What materials do I need ?, How I can build it? [Ecuador]

A: [Mark J.] Where do you plan on fighting a superheavyweight combat robot in Equador? See Frequently Asked Questions #2, and read thru the rest of the FAQ while you're there.

Superheavyweight 'Ziggy' is a very complex combat robot with a great many custom made parts. You might as well ask me how to build an automobile. It also uses high-pressure pneumatic components that are far too dangerous for a beginning robot constructor. Build something simpler.

There are many posts about 'Ziggy' in the Weapon archive that may give you some insight into its design and construction.

Ziggy's flipper.
Click for larger image



Q: hey Mark., what are the merits of using chain drive and belt drive in LAST RITES ?? what would happen if we use belt drive instead of chain drive ., [India]

A: [Mark J.] The 'Last Rites' chain drive has been previously discussed. See this post in the archives.

Note: 'Last Rites' still has the chain drive, but now has a mechanical clutch mechanism to provide a little 'slip'.



Q: i am using EN24 metal for my weapon teeth ,what is maximum hardness mark ? please tell in HRC . 50 hrc is good for great impact [Tamil Nadu, India]

A: [Mark J.] EN24 is the European designation for SAE 4340 chromoly steel. This alloy is a general purpose low alloy steel, but it is not commonly used for weapon impactors. Weapon teeth require a combination of hardness and impact resistance, but EN24 looses impact resistance rapidly with increasing hardness.

EN24 can be hardened to HRC50, but at that hardness it would be VERY brittle and have a very high risk of fracturing on high-energy impact. For comparison:

  • At HRC 45 hardness, EN45 steel has a Charpy impact score of 21 -- quite poor.

  • At HRC 55-58 hardness, S7 tool steel has a Charpy impact score of 171 -- excellent.
That's why tool steels are the preferred impactor materials. If I had to use EN45 for impact teeth I wouldn't harden beyond HRC 40 (Charpy impact 45), and I'd make the teeth extra wide and deep.

Q: hello mark . can u suggest drum teeth metal for us . here s7 tool steel is not available and its imported price is high , can u suggest some other steel for drum teeth impact , if any other tool steel can replace s7 tool steel means please mention all listed the above with hrc rating ?

A: I'm not going to look up the properties for all the possible alloys since I don't know which are available in India. Commonly available impact-resistant tool steels include O1, A2, D2, S7 and W1. Find out what your suppliers offer and look up the properties for those steels. Don't assume that the greatest HRC is best -- you want an alloy that is both tough and hard.

Q: gud eve ,in India available H13 , A2, D2 tool steel alloy , from this three which is good impact for drum weapon ?

A: From my answer above -

  1. "Find out what your suppliers offer..." - Well done.

  2. "...and look up the properties for those steels." - FAIL.
Any of the three available alloys would be acceptable for impactor use. There are differences in expense, workability, ease of heat treating, and hardness/toughness blend. I know which I'd choose, but your priorites may be different. To make your choice I again suggest that you look up the material properties of the alloys.

Here's a link to a site with data sheets for all three of your alloy options: Simply Tool Steel.



Q: hi mark is there any tutorial or blog which could guide us about driving of our bot means any tips or guidelines that can we follow or from u as well? [Maharashtra, India]

A: [Mark J.] Aaron listed his favored driving exercises in this archived post.

Equally important to getting your driving practice is to tweak the transmitter settings to make the radio interface comfortable for the driver. In combat your nerves will be on edge and a too-responsive robot will become impossible to control. See our transmitter set-up tips in the Run Amok R/C Transmitter Programming Guide.



Q: hello mark,could you suggest me a motor to hit a badminton smash for robocon.Since we are starting from scrach we have poor knowledge about motors.hope you respond me positively. [India]

A: [Mark J.] A few problems:

  1. This isn't about combat robotics;
  2. The hamburger is bad;
  3. The challenge of building badminton playing robots is HUGE!
Best I can tell there is exactly one badminton playing robot in the world (Video). It travels left/right on a beam (no forward/back motion), it has a room full of computers and at least two technicians controlling it, and it can return shots within only a very limited range of trajectories. It can't serve, it can't play drop shots, it can't cooperate with a robot partner, and it can't play in a court the size proposed by the Robocon challenge.

I really can't see the competition being a success. I recommend spending your time on a more reasonable challenge.

Badminton racquet and bird





Remembering Aaron... 

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's Minecraft High Dive Video
Aaron's World of Warcraft New Player Guide

Killer Robot drawing by Garrett Shikuma




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