5049 Questions and Answers about Combat Robotics
from Team Run Amok

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

Q: If thick walled drum weapons are not effective, why is the 'snail drum' on the heavyweight champion 'Touro Maximus' built to this design? [India]

'snail drum' weapon for heavyweight combat robot 'Touro Maximus' A: [Mark J.] Team RioBotz know what they are doing. They fight in large arenas and their attack plan is to charge at high speed into their opponent -- much higher speed than Indian robots can use in their small arenas. If the attack speed is high, the drum can rotate at a higher speed and still retain good energy transfer ('bite') into the opponent. Double the attack speed allows double the weapon RPM -- and double the RPM gives four times the energy storage in the weapon!


  • A specific robot with an attack speed of 3 MPH finds that it must the limit weapon to 2000 RPM in order to maintain good weapon bite. At 2000 RPM its weapon can store 1500 joules of energy.

  • If the attack speed of the robot is increased to 6 MPH, the weapon RPM can be raised to 4000 RPM and still retain the same 'bite'. At 4000 RPM this same weapon can store 6000 joules of energy.

  • If the attack speed of the robot is increased to 12 MPH, the weapon RPM can be raised to 8000 RPM and still retain the same 'bite'. At 8000 RPM the weapon can store 24000 joules of energy.
So, at 4 times the attack speed, the weapon can store 16 times the energy and still have the same ability to bite into the opponent without 'skittering' off. When you have the capacity to store that much energy in the weapon, you can afford to decrease the storage capacity a bit to make the weapon more durable and better able to survive the massive hits it will deliver.

Recap: the snail drum on 'Touro Maximus' is a thick-walled small-diameter drum in order to better survive the ultra-high energy impacts it delivers because it spins at very high RPM. It is able to spin at such high RPM because 'Touro Maximus' has a very high attack speed, which gives the weapon good 'bite' even at such high RPM.

This works in arenas that are large enough to allow robots room to accelerate to high speed. In a small arena it's much better to conentrate on larger, thinner walled drums to store high energy at lower RPM due to their greater rotational inertia. Don't blindly copy the snail drum if you're going attack at low speed!

Q: hello aaron can i use 304 [stainless steel] as drum tooth???? if yes then it should be hardened or not because i heard that [stainless steels] are not hardened.... [India]

A: [Mark J.] The 300 series stainless steels are Austenitic alloys that CAN NOT be hardened by heat treatment. They are soft and ductile: not what you want in an impactor for your drum weapon.

Impact tooth material has been discussed many times here at Ask Aaron. There is general advice on impactor material selction in the Spinner Weapon FAQ and there are several discussions of specific materials in the Ask Aaron Materials and Components Archive.

Q: what is "Demonic Teeth" in india most the bot uses it for drum tooth. [India]

A: [Mark J.] Unknown. Ask an Indian robot builder, and then scold them for making up 'cute' names for materials.

Q: i am having drum of 110dia (OD) and thickness is about 40mm and length is 20cms and using bearing caps at end i want to participate in a 60kg robowar dose it store enough energy at 3000 rpm [India]

A: [Mark J.] Have you been asleep in the back of the classroom?

There are at least four other posts on this page asking me to calculate the energy storage of drum weapons. My answer to all of them has been the same. Take a look at this post which makes the same error of data omission you have made.

Read the Ask Aaron Spinner FAQ. It will tell you how to calculate the energy your spinner weapon should store, and it gives you three options on how to calculate that figure.

Q: ...and also in your spreadsheet how can i give detail of tooth...thankyou

A: Ahhh! So you have been paying at least a little attention -- you know about the Run Amok Excel Spinner Weapon Spreadsheet. Good.

Impactor teeth and bars come in all shapes and sizes. Calculate the mass of the teeth (volume * density of tooth material) and increase the value for the drum radius until the mass is increased by the mass of the teeth. This will give you a good estimate of the contribution to energy storage the impact teeth will make.

Now, stop being lazy and run the numbers for your drum. You'll find that your drum is too small in diameter to store a reasonable amount of rotational energy. A larger radius and a thinner wall will greatly improve energy storage with the same mass.

Q: Thank you for i am making a new drum 15cm DIA and 25 cm length with thickness 35mm for 60kg weight limit ...but i am little bit confused about the diameter of dead shaft can you suggest me the dia of dead shaft

A: Is this a steel drum? Have you noticed that the drum will weigh nearly 25 kilos? That's a very heavy drum for a 60 kilo class robot, and it doesn't store a lot of energy for its weight. You may wish to work on the design a bit more. Here is your current design:

Wall Thickness
3000 RPM
24.7 kilos
Energy Storage
4420 joules

Reducing the wall thickness to 20mm and increasing the speed to 4000 RPM will significantly reduce weight and improve energy storage:

Wall Thickness
4000 RPM
15.9 kilos
Energy Storage
6074 joules

Better still, increase the diameter to 20cm, reduce the wall thickness to 11mm, and keep 4000 RPM:

Wall Thickness
4000 RPM
12.7 kilos
Energy Storage
10,063 joules

Thick walled, small diameter drums simply aren't effective at energy storage. Think bigger!

Back to your question -- the required diameter of the dead shaft depends on many factors:

  • shaft material
  • solid or hollow
  • energy storage capacity of the drum
  • distance from drum bearings to shaft support
  • strength of shaft mounting to chassis...

Assuming solid hardened steel alloy shaft and the drum design you've mentioned, 20mm to 25mm is a good starting point.

Q: I am trying to find a compact drive motor that can move 100+ easily do you have any ideas (Of cores high torque). [Moultrie, Georgia]

A: [Mark J.] Sorry, but 'move 100+ [pounds?] easily' does not give me enough information to recommend a motor. The hamburger is bad. See this post in the Ask Aaron archives for an explanation of the problem and a list of the information needed. There are also a great many posts about motor selection in the Motors & Controllers archive.

If you write back with complete information about your robot and the performance expectations you have, I may be able to make a motor recommendation.

Q: I'm expecting it to go at least 3 mph and be somewhat small and good for a battle bot competition in the USA not UK.

A: That doesn't really qualify as 'complete information' -- but I'll do what I can.

If you want to build a competitive combat robot for US competition you're going to need better than 3 MPH. You're also going to need enough power to accelerate to that speed quickly and provide good pushing power. Just how much speed and acceleration you need depends in part on your attack strategy; a ramming or wedge robot will need more speed and power than a robot carrying a large destructive weapon.

There's also the matter of how many motors your robot will use. Most have two drive motors: one on each side of the 'bot. Some have 4-wheel drive with four motors. A few have more.

Then there is the drivetrain. You can't just bolt a wheel directly to the shaft of a motor without gear reduction. The gear reduction ratio needed depends on the motor characteristics, the wheel diameter, and the weight of the robot. Since you're looking for a 'compact' solution, I'll assume you want a gearmotor that needs no external drivetrain components.

Using the Tentacle Drivetrain Calculator to model performance of a 100 pound robot with two motors:

  • The DeWut 3 Speed Gearmotor provides a compact and durable package ready to accept a drive wheel directly on the gearbox output shaft. With 4" wheels, a 100 pound robot powered by two of these motors will accelerate to a top speed of about 7 MPH in seven feet. That's good performace for a general purpose combat robot.

  • The AmpFlow E30-150 motor with speed reducer is another compact and durable gearmotor with enough power for your application. Top speed with 4" diameter wheels would be a bit over 7 MPH, with top speed reached in eleven feet.
That's as good as I can do with the info you've given me.

Q: I am joining the new battlebot competition in the middle white class so most likely it will be 115 pounds and i will be using five motors in all four for the drive and one for the weapon. the weapon consists of a fly wheel and steel bars with padlocks used as hammers. My design is some what like Mauler's but my body will be square. The wheel diameter will most likely be 3-5" tall and 2-3"wide all of the armor will be steel. The wheels will be boxed in. All of the armor will be 1/8". 18v motor. This is all of the information i have for now.

A: You haven't done your research -- BattleBots has changed:

  1. The 'new battlebot competition' (2015) has no middleweight class. It's a single class with a 250 pound weight limit.

  2. The 'new battlebot competition' is no longer an 'open' tournament. Competitors are invited by the show producers. If you aren't already a successful, established combat robot competitor you don't get to 'join'.

  3. Steel 1/8" armor and padlock hammers were OK twenty years ago, but they won't do at all for current competition.
Read thru the Frequently Asked Questions for some help in finding and competing in local/regional combat tournaments. You'll do well to start in a lower weight class and work your way up to the 'Big Time'. Write back when you have a new plan.

Inside Sewer Snake Q: hllo sir..
would you tell me how to calculate the motor specification to use it as lift motor like that is used in sewer snake..
thankyou.. [India]

A: [Mark J.] You may have noticed that there are VERY few electric lifters like 'Sewer Snake'. The problem isn't the motor -- lots of motors have the power needed to hoist your opponent off the floor. The problem is finding a gearbox that can take the huge torque loading without exploding! 'Sewer Snake' uses an AmpFlow A28-150 motor connected to an industrial 25:1 gearbox that feeds a 3:1 chain reduction [photo at right]. The torque available at the lifter axle is a whopping 10,650 kg-cm!!!

Here's the formula for the torque needed for a simple single-pivot lifter like Sewer Snake's:

Torque Required (kg-cm) = Weight of Opponent (kg) * Distance from Pivot to Tip of Lifting Arm (cm)

So, for a 60 kg class robot with a 50 cm lifting arm the torque required is:

60 kg * 50 cm = 3000 kg-cm

Now, your motor has to provide that much torque while still spinning at a reasonable speed, so you can't use motor 'stall torque' (zero RPM) as a starting point. A PMDC motor develops max horsepower when loaded to 1/2 stall torque, so we use 1/2 the motor stall torque in the next calculation.

Required Reduction Ratio = Torque Required / (0.5 * Motor Stall Torque)

Example: an AmpFlow E30-150 motor has 51 kg-cm stall torque. If you require 3000 kg-cm output torque at half motor stall torque, the reduction ratio required is:

3000 kg-cm / (0.5 * 51 kg-cm) = 118:1

When loaded to 1/2 stall torque, PMDC motor RPM is 1/2 the free-running speed. So the output RPM under load is:

Lifter Output Speed (Loaded) = (Unloaded Motor RPM / 2) / Reduction Ratio

The E30-150 motor has a free-running speed of 5700 RPM @ 24 volts, so:

(5700 RPM / 2) / 118:1 = 24 RPM = 2.5 Seconds per Revolution

You need less than 1/4 of a revolution to lift your opponent, so that's reasonable lifting speed. So the motor is suitable, but the problem is finding a 118:1 gearbox that can survive 3000 kg-cm of torque! A BaneBots P60 gearbox is rated for less than 500 kg-cm.

Q: how can a material be hardened like tool steel A-9 like hrc 50 because in india most the people don't know about hardening process [India]

A: [Mark J.] Heat treatment of metals is a highly specialized process best left to commercial facilities. The details of the process vary from alloy to alloy and often involve very high temperatures, controlled atmospheres, and carefully monitored heating and cooling rates. Attempting to do your own 'back yard' heat treatment will very likely yield warped/distorted parts with unknown properties. I HIGHLY recommend that you find a commercial heat treating facility to do your hardening.

Read the FAQ! Q: in your spreadsheet it shows the weapon has 109 joules of energy is it sufficient for a drumbot of length 22cm, 11cm dia and 30mm thickness and it is hollowed so that a dead shaft is inserted and bearing at end plates....if the energy is not enough then what should i do so that it can stores more energy i am using ampflow e30-400 [India]

A: [Mark J.] The Ask Aaron Spinner Weapon FAQ answers all of these questions. Read it.

Q: hello aaron, please suggest some ways how to make a drivetrain with chain and sprockets or some links may be..
motor - ampflow E30-150
gear reduction - 20:1
robot category-50kg [India]

A: [Mark J.] A chain drive at a 20:1 reduction requires a two-stage reduction thru an 'idler shaft'. The idler shaft is supported by bearings and has sprockets of differing size fixed to the shaft. To get a 20:1 reduction, the 'first stage' from the motor to the idler might be a 5:1 reduction (9 tooth sprocket on the motor to a 45 tooth sprocket on the idler, for example) with the 'second stage' from the idler to the wheel a 4:1 reduction (maybe 10 tooth on the idler to 40 tooth on the drive wheel). The overall drive reduction is the product of the first and second stages (5:1 * 4:1 = 20:1).

The upper diagram at right shows a two-stage chain and sprocket reduction with two idler output sprockets driving two wheels on one side of the robot.

The lower diagram shows the two-stage chain reduction in a BattleKit Modular Drive Unit with the idler shaft in-line between the motor and wheel.

Two stage chain reduction diagram

BattleKit modular drive unit

Q: is NPC-41250 Motor is good for wedge robot(25-30KG) for 60kg events having following specs
4 wheel drive with 1 motor each channel
6inch wheel
arena size (5X5)m
thanxx in advance [India]

A: [Mark J.] First, why are you building a '25-30KG' robot for '60kg' events? That's like showing up with a knife at a gun fight. Give yourself a chance and build to the weight limit.

NPC-41250: heavy (7.5 pounds), slow (3 MPH @ 24 volts w/6" wheels), awkward mounting, cast aluminum gearbox housing is weak. Suggest that you use the Team Tentacle Drivetrain Calculator to evaluate motors for your application.

Q: hi sir
whether12V 5310 RPM "CIM" Brushed DC Motor
  • 2.5-inch CIM brushed DC motor
  • Stall torque: 2.42 N-m
  • No load RPM: 5,310
can be used for combat if it is shall i buy this to run my 4kg drum [Tamil Nadu, India]

A: [Mark J.] The CIM motor has been used for years in the FIRST robotics program, and is certainly capable of being used in combat. However, it weighs a lot (46 ounces) for the amount of power it produces (about 1/2 horsepower). Compare that to the RS-775 motor That weighs 12 ounces and produces 3/4 horsepower.

Should you use the CIM motor for your 4 kg drum weapon? You didn't tell ne enough about your weapon for me to answer that question (see the Spinner Weapon FAQ), but YOU can use the Team Run Amok Spinner Excel Spreadsheet to model the weapon performance with the CIM motor to see if it meets your needs. This is the same solution I offered to the two posts immediately below. I'm sensing a theme here. Maybe that spreadsheet is useful?


A: [Mark J.] See post immediately below.

If you are unable to use the Team Run Amok Spinner Excel Spreadsheet, you do have other options:

Q: my drumbot length is 20cms and OD is 100mm and ID is 75mm and dead shaft is inserted in drum and at the ends bearings is mounted how much is energy it is storing ar 3500 rpm [India]

Ask Aaron is not a free engineering service! A: [Mark J.] 'Ask Aaron' is not a free engineering service. We provide tools and information to assist combat robot builders in the design, construction, and operation of their machines. We don't do your design work for you.

I spent a good deal of time and effort to create the Team Run Amok Spinner Excel Spreadsheet to assist builders in modeling the performance of spinner weapon designs. The spreadsheet is mentioned prominently several times on this page, in the Frequently Asked Questions, and in the Ask Aaron Robot Weapons Archive. Just a few questions farther down this page is a detailed example of the use of the spreadsheet in calculating the energy storage of a drumbot.

I will occasionally work thru the process of calculating some performance factors for a specific robot as an educational example. However, having already performed that exercise and having provided you with the tools required to calculate the energy storage capacity of your drum weapon, it does not serve the purpose of 'Ask Aaron' to perform that calculation for you.

I will point out that you failed to mention the material from which your drum is constructed. Without that information it is not possible to calculate the mass of the drum, and without the mass it is not possible to calculate the energy storage. I could not answer your question if I wanted to. Be so kind as to run the numbers yourself -- you might learn something.

Q: hi sir considering single teeth drum and snail drum two different drums which one will give best hit? [India]

A: [Mark J.] There is a previous post about the 'snail drum' -- search the Robot Weapons archive for 'snail' to find that post.

The snail drum does not store more energy or deliver a better 'hit' than a single-tooth drum with comparable dimensions running at the same speed. The snail is tremendously difficult to design and construct, and the primary benefit appears to be the durability of the integrated impact tooth. The only real reason to build a snail drum is to impress your opponents with your machine shop skills. Avoid the temptation.

'snail drum' weapon for heavyweight combat robot 'Touro Maximus'

Q: Dear Mark,How to attach two pieces of PC(Polycarbonate) sheet in T shape(one piece's side attach to another's face)?I tried self tapping screw but it is difficult to tight and damage the sheet.Should I try ordinary screw?(I think team Hurtz did so) Another question, can I disassemble the attached PC and attach them with no damage? [China]

A: [Mark J.] Team Hurtz's preferred method of joining polycarbonate was to chemically weld the parts together with a methylene chloride solvent, although other specialized adhesives are available. This spreads the load evenly over the entire area of the joint and minimizes local stress -- a key in joining polycarbonate.

If you require a joint that can be disassembled, you should use course-thread machine screws. The fastening holes should be pre-drilled and the piece to be joined should be tapped with a proper thread cutting tool. You didn't mention the plastic thickness, but in general the screw diameter should be no greater than half the thickness of the plastic. Use plenty of screws.

Do not over tighten the screws! Tighten only enough to pull the pieces together. Polycarbonate absorbs impact forces by flexing, and areas of high local stress will develop around the fasteners. If the screws are already creating strain by being over tightened, the risk of fracture failure at those points is increased. A large thin washer under each screw head is a good idea to help spread the fastener loading.

Q: Hi Sir, I am making a combat robot with specs: Diameter Of Wheels: 12cm, 2 motor for drive, 1 for weapon- rotating heavy weapon, Arena= 10*10 meters, Twin Weapon System- Lifter wedge and rotor on piston controlled arm like cutt-off saw machine, External AC power supply 220V - 10A. Max Weight of Robot =60Kg.
My question is :
What are specifications of all motors we should use?
What kind of drive we should use: four wheel or two wheel? [India]

A: [Mark J.] External 220V - 10A AC power???

  1. Re-check the rules for your competition. I'm told that AC power was outlawed in Indian robot combat years ago. I don't believe it's currently allowed in robot combat anywhere. Far, far too dangerous! The Robot Fighting League caps voltage at 48 volts DC without special permission.

  2. My experience in motors for robotic operation is entirely limited to Direct Current Permanent Magnet (PMDC) motors. The torque and power curves for AC induction motors are quite different and I am unable to comment on AC motor selection.
Beyond suggesting that you not participate in such a needlessly dangerous activity, I can't help you.

Q: Sorry Sir but I want to correct the previous question about AC supply in competition. I'm pretty sure about the rules. We can use either AC or DC supply. We wanted to use AC so that we can save the cost of Batteries as will be using Hydraulic pistons for our weapons that are quite costly and we have to outsource it. We will be using simple on off switches for driving (Wired Control). What we have planned is to convert AC to DC and all the motors will be DC so I Want to specifications of motors like Horse Power, Torque and rpm for the same above conditions stated in previous question? and the type of drive(four wheel or two wheel)?The robot will be 70*50 cm size and maximum height can be 1m. We want to use a heavy rotor, so motor must be powerful.

A: [Mark J.] Several problems:

  • Combat robots use batteries for good reason. A one horsepower PMDC motor -- typical for drive motors in your weight class -- will require about 65 amps of current at 24 volts to produce that one horsepower, and twice that current to produce maximum torque. Two drive motors at max horsepower = 130 amps of current @ 24 volts. How do you plan to convert your 220V 10A AC to 24V 130A DC?? And that's just for the drive motors.

  • Gear reduction from the example drive motors and your wheels should be around 8 to 1 for a balance of acceleration, speed, and pushing power.

  • Weapon calculations require more specific descriptions than 'heavy rotor' in order to determine an effective motor and gearing. Suggest you start your design thinking by reading the Spinning Weapon FAQ.

  • The switches for your 'simple' wired control are going to need to handle very large currents. You might be interested in reading the Solenoid Guide for some ideas on drive and weapon control options.

  • Hydraulic pistons to control your weapon position are expensive, heavy, add complexity, and are not needed. Recommend using a fixed position weapon and adding the weight saved by scrapping the hydraulics to the weapon mass. In my experience 'complex' and 'first time builder' do not go together well, plus simple robots win tournaments.

  • Robots with large, destructive weapons do not rely on four-wheel traction and pushing power. I would suggest two-wheel drive to avoid adding additional complexity.

Would you be so kind as to give me the contact information for the organizers of this event? I'd very much like to have a safety discussion with them.

Q: i was looking for alloy steels and which one will be good for drum teeth
en 18 ,en24 vs h12 ,h13(hot worked tool steel) [India]

Ask Aaron is not a free engineering service! A: [Mark J.] The topic of steel for impact teeth has been discussed MANY times previously -- see the Materials and Components Archive.

'Ask Aaron' is not a free engineering service. I'm not willing to compare every possible subset of materials on a 'which of these is best' basis. Here are guidelines for impactor material selection:

  • Desirable properties for impactor teeth are hardness and impact resistance. Both are required.
  • These properties vary with the heat treatment (hardening, tempering) applied to the material.
  • Heat treating is mandatory, but do not sacrifice impact resistance for great hardness.
  • Look up and compare the properties (Rockwell hardness, Charpy impact score) of the materials available to you.

Equally important to material selection is the design of the impactors. The teeth must be attached to the drum in a way that minimizes localized stress on the impactor or they will fail. I'd much rather have a well designed impactor made of mild steel than a poorly designed impactor made of the finest tool steel.

Q: I read through your page but could not understand clearly how to build a hollow drum.
Could you please tell me the processes involved and how to build the drum? [India]

A: [Mark J.] Most of the examples of drum construction in our Weapon Archive come from the Team Cosmos site. Suggest you read the Team Cosmos build log for 'Solaris' for photos and a description of the process. There are build logs for other drumbots on their site as well.

Q: hi mark
making 2 teeth drum materials
(mild steel)
(teeth- en18)

od 150mm
id 20mm
shaft -15mm to 20mm

bearings- shall i go for needle or tapered one's??
and my drum rotates @5700rpm at 24v can you tell me the energy stored in it
whether high horse power motors plays the role in storing the goodenergy in a drum orelse a high RPM ed one's [India]

A: [Mark J.] You've designed your drum weapon without knowing how much energy it will store? That's a critical element in the design, not something you save to find out about after the design is fixed. The Team Run Amok Spinner Excel Spreadsheet can calculate the mass, moment of inertia, energy storage, and spinup times for rotating weapons given their dimensions, construction material, speed, and motor specifications. I strongly suggest that you learn to use this tool to assist in your weapon design.

Bearings: drum weapons typically use radial ball bearings. They are economical, tolerate a little misalignment, and are available in sizes and ratings adequate for the purpose.

Energy storage: you have failed to include the length of your drum, so I cannot tell you anything at all about your weapon -- even if I were in a mood to do your design work for you.

Horsepower vs. RPM: this has been discussed previously here at 'Ask Aaron'. Take a look at this post on drum power in the Weapons Archive. You'll benefit from reading thru the Spinning Weapon FAQ as well -- you might learn something that you didn't even know you didn't know.

Q: length of the drum -150mm could u say me the energy storing capacity for it

A: [Mark J.] I'll do much better than that -- I'll show you how to use the Team Run Amok Spinner Excel Spreadsheet to calculate the mass, moment of inertia, energy storage, and spinup time for your weapon. You'll most certainly need to use the spreadsheet to evaluate new designs once you see the performance of the proposed weapon!

  • Download the spreadsheet on a computer with Microsoft Excel installed.

  • Select the 'Calculations' tab and fill in the specs for your motor. I've assumed that your 5700 RPM motor is an AmpFlow E30-150.

    • No-Load Speed: 5700 RPM
    • Stall Torque: 5 N-m
    • Gear Reduction: 1:1

  • Fill in the specs for your drum tube.

    • Material Density: 7800 kg/m2 [steel]
    • Length: 0.150 Meter
    • Outer Radius: 0.075 Meter [half of 150 mm]
    • Wall Thickness: 65.0 mm [(150 mm OD - 20 mm ID) / 2]

  • You didn't provide dimensions for your impactor teeth, so we'll assume they're small in comparison to the drum and disregard their mass.

The output from the spreadsheet will tell you that the drum is quite heavy, and that it does store a lot of energy. It will also tell you that the spinup time is ridiculously long -- it takes a one horsepower motor a very long time to store that much energy in a spinning weapon. I suspect you'll want to re-design your weapon to weigh less, spin slower, and store a more reasonable amount of energy. Now you have a tool to help you do that, so go use it!

Team Run Amok Spinner Spreadsheet input fields

Q: Hello,
I want to build a hollow drum of id- 25mm and od-70mm .
How am I supposed to build the drum ?
The length of the drum is 250mm.
What materials should I choose and how much energy will it store at 5700 rpm?
- Siddharth [India]
Read the FAQ!

A: [Mark J.] You're approaching this backwards. You don't start with the weapon dimensions and speed -- how did you decide on those values? You start with the weapon requirements and work toward a combination of dimensions, speed, materials, and components that will meet those requirements. Here is the correct sequence of events in designing a spinning weapon:

  1. Determine the performance parameters needed to achieve an effective spinning weapon in your weight class. Consult the Ask Aaron Spinner Weapon FAQ for guidance.

  2. Download the Team Run Amok Spinner Excel Spreadsheet and model the performance of a trial weapon design to determine the weapon mass, energy storage, spin-up time, and battery power requirements of the weapon.

  3. Modify the design parameters of the weapon (dimensions, materials, motor specifications, drive reduction ratio...) and observe the effect of the modifications on the modeled performance of the weapon.

  4. When you have a design that provides a good combination of performance parameters, evaluate the design for construction practicality. There are many posts in the Ask Aaron Weapon Archive that discuss drum weapon construction. Read them.
I can tell you that your current design (if constructed from steel) would weigh 6.5 kilos and would store only 810 joules of energy at 5700 RPM. Minor changes to the weapon design could greatly improve your weapon performance. Start over.

Q: hi sir (india)
s7 tool steel is mostly manufactured in rolled bar forms how it can be converted into plates for my drum teeth

A: [Mark J.] S7 tool steel is generally shipped in an annealed (soft) condition. In this form it can be machined with conventional tools and processes. Before use the steel must be hardened and tempered to achieve its desirable properties.

Although S7 steel is a very fine impact tooth material, other locally available steel alloys that come in plate form may be good substitutes. The attributes required of impact teeth are a combination of hardness and impact resistance. There are many posts discussing the merits of different steel alloys for weapon teeth in the Ask Aaron Materials Archive -- I suggest that you read them.

Q: Hi Mark, I am the dual Sabertooth guy running 4 drill motors guy. aka Mr. Land of Opportunity aka Joe H. Thank you so much for answering my question, when I checked the site and saw you answered, I refreshed the page a couple times to make sure it was really happening!

I made a couple errors (of omittance) by not giving more details of the robot. My sincere apologies for that. Quoting you...

"I'm assuming that in your diagram the two 'M1' motors are on one side of your 'bot and the two 'M2' motors are on the other side."

On the diagram I submitted to you, each M1 & M2 represent the sides of the bot (M1 & M2 on left run together, M1 & M2 on right run together). But to clear up any confusion (again, my apologies!) I spent last night making up a diagram that is a little easier on the eyes and more clear. I also clearly labeled the motors this time!

Two ESCs and four motors - don't do it like this!

"I'm also assuming that you have channel 1 and 2 mixing enabled on your FlySky transmitter. On most transmitters this is called 'Elevon' mixing but the FlySky seems to incorrectly refer to this as 'V-tail' mixing (channels 2 and 4 on other transmitters)."

I was using the regular mixing, which was a mistake that led me to contacting you, how confusing! I did a factory reset before trying anything you suggested. When I go into Elevon, it looks like that controls CH1 and CH2. V tail has CH2 and CH4 listed. When I hooked everything back up and ran through the tests you suggested, I was getting some really sporadic results, some of which resulted in the red error light flickering. I decided to call it quits at that point so I didn't damage anything. I tossed my batteries on the charger (thinking that could be a problem if they are low.)

But that makes me wonder if I do actually have this wired incorrectly. I say that because when you said my wiring was correct, you did that with the assumption that both M1s were on one side, and M2s were on the other side.

On page 5 of the Sabertooth 2x12 manual it says:

"If you are using multiple Sabertooths running from the same radio receiver, only one should have the 5v line connected. You can either take the red lead out of the connection housing or just clip the wire with a pair of cutters."

I am assuming when they say "only one" they mean "only one Sabertooth" should have the 5v line connected. The image they use as the example in that document is small and bad quality, so it's difficult to see what's going on there. That might explain the sporadic results and the red error light. I will make another attempt to hook everything up after work tonight, and I will report back. Thank you so much for your time and expertise.

A: [Mark J.] The updated diagram helps a lot, Joe. I had to make a few assumptions that turned out to be incorrect. We'll have you running in no time.

Yes, you do have the 'bot wired incorrectly for the way the motors are positioned:

  • Usually a 'bot with twin ESCs like you have is wired so that each ESC controls one motor on each side of the 'bot. That way if one ESC completely fails the other ESC can still control both forward/reverse motion and left/right turning -- albeit somewhat limited by dragging two inoperative wheels around. This was the set-up I assumed you had.

  • The way your 'bot is wired has each ESC controlling both motors on the same side of the 'bot. This can certainly work, but if one of the ESCs fails you'll be limited to driving back and forth in an arc. Your bot isn't working because each ESC is receiving signals for both the left and right side motors instead of just the signal for the side it controls. We can fix that...

...but let's clear up a couple of other things first:

Mixing: early versions of the FlySky transmitters had problems with mixing and had some of the menu options miss-labeled. It sounds like they've fixed that issue. Yes, Elevon mixing is the correct mix to use if it is now correctly implemented on the FlySky transmitter.

Sabertooth 5v lines: this isn't what's causing your main problem, but running 5 volt feeds from both of the Sabertooth ESCs to the receiver can cause some glitchy behavior. I wanted to fix your main trouble without inundating you with tasks, but since we're already on the topic: disconnect the red receiver pigtail wire from one (and only one) of the Sabertooth ESCs. Fold it back and wrap it with electrical tape. Problem avoided.

Charging the battery: it was a good idea to charge the battery. A low battery can cause all sorts of difficult to diagnose trouble. Nice call.

Now the main fix. We can do this two ways:

  1. We can re-route the motor power wires to have each ESC control motors on both sides of the 'bot; or
  2. We can re-route the receiver signal wires so that each ESC gets only signals for the side of the 'bot it controls.

Since I don't know how large a pain it would be for you to re-run the motor power wires, I'm going with #2. You've already got plenty of receiver pigtail length to accomplish that fix. If you'd rather implement solution #1 write back and I'll walk you thru that process -- but for now let's just get your 'bot running.

Take a look at the new receiver wiring diagram below:

Correct receiver wiring for ESCs controlling right/left sides of the robot
There is no need to split the channel 1 and channel 2 signal leads and run both signals to both ESCs. The left side ESC will get signal and ground from channel 1 (no 5v connection) and the right side ESC will get signal, ground, and 5v feed from channel 2. Note that the S1 and S2 connections on each ESC are 'jumpered' so that they both get the same signal input.

Prop the 'bot up off its wheels and power it up.

  • Give it a little forward throttle. Check that the two wheels on each of the sides of the bot are spinning in the same direction.

    • If one wheel spins one way and the other wheel on the same side spins the other way: switch the motor power leads for the backward spinning motor at the ESC power output terminals.
    • If the wheels on each side of the robot spin the same direction (both forward or both backward), move on.

  • Now go back to our earlier post (a couple posts down) and work thru the steps to get both sides to spin forward on forward throttle, and turn correctly in response to response to turn commands.

I went thru that pretty fast. If something doesn't make sense just drop me a note.

Q: my team is designing a pneumatic robot like ziggy. our budget is 30000 INR=approx 500$
  • 4 wheel drive with chain reduction method (20:1)
  • weight- around 75 pounds
  • chasis material- Steel
  • Motors- 2 X amp flow E30-150(79$ each+74$ to India)
  • ESC- out of budget
  • wheels- 4 wooden wheels with tires (custom made)
  • contol system- wired or wireless (depend upon the event)
My queries are-
1) Is there alternative methods for ESC for wired control bot
2) In India arenas are about 6X6 metres, so which motor is suited best to get 6-7 MPH speed and also provides high torque
3) Suggest the amperage for the ESC for our bots
thanxx in advance. [India]

A: [Mark J.] 'Ask Aaron' gets many questions from Indian builders about alternatives to Electronic Speed Controllers (ESC), drive motor selection, and ESC selection. I suggest you start by reading Frequently Asked Questions #21.

  1. DPDT switch wired as an 'H Bridge' motor reversing switch.The Solenoid Control of Robot Weapon and Drive Motors FAQ has multiple posts and a discussion of alternatives to ESCs that will work for "system-wired or wireless" control systems.

    If you are looking for a very simple switch control box system that runs full voltage and current thru the long control wires and switches, you can use a pair of high-current Double-Pole Double-Throw (DPDT Center Off) toggle switches wired as 'H Bridges' (diagram at right) to control the right and left side motors in forward/off/reverse. There is some considerable power loss in running the primary robot power thru such long wires, but this has been commonly done for robot control in India.

  2. The Team Tentacle Drivetrain Calculator is a valuable tool for motor selection that all robot builders should learn how to use. I don't have performance specifications for all of the motors available to Indian builders, but a pair of the AmpFlow E30-150 motors you mentioned would provide adequate performance for a robot with the specifications you've given. Equipped With 8" diameter wheels and a 20:1 chain reduction, the Tentacle calculator gives the following performance estimates for a 75 pound robot powered by two E30-150s at 24 volts:

    • Theoretical top speed: 6.76 MPH
    • Acceleration distance to top speed: 5.98 feet
    • Acceleration time to top speed: 0.83 second
    • Time to cross a 6 meter arena (side-to-side): 2.23 seconds
    • Current per motor to spin wheels (maximum pushing): 18.9 amps
    • Estimated battery capacity required for 5 minute match: 2.210 amp-hours

    Wheels of a different diameter will require re-calculation of the performance numbers.

  3. Wait, didn't you say that an ESC was "out of budget"?

    The E30-150 motor at 24 volts can draw 125 amps of current when stalled, but your gear reduction will provide enough torque to break traction and spin the wheels long before the motor stalls. With 8" wheels and a 20:1 reduction, the Tentacle calculator estimates a maximum sustained current draw of 18.9 amps per motor. I like to add a little for unexpected conditions, so I'd suggest an ESC that can deliver a minimum 25 amps continuous current per channel.

A couple of additional notes:
  • Pneumatic systems are not allowed at many Indian combat events. Make certain that your weapon will be allowed to compete in the events you plan to enter.

  • Have you priced the required pneumatic components? With more than $300 spent on motors you don't have a lot of budget left for an effective pneumatic flipper.

Q: hloo sir, Pnumatic guy again..
thanxx alot sir for active response..
I read the teamdavinci pnneumatic. it is very helpfull.
i have some queiries more-

1) So i can use Sabertooth 2 x 25 Dual 25A Motor Driver??

2) i read the whole solenoid sections last night. I think 4 40A relay switch for channel is good?? and i will use 2 30 Amp DPDT Switch for wired control. Any suggetions??

last questions according to our specification about bot: can we go for AME 226-series 12V 325 in-lb LH gearmotor(68A stall current) or RS775 12V(stall current 30A)? please suggest.

thanzz alot in advance sir. this askaaron site is heaven to me.

A: [Mark J.] I'm a bit confused -- are you planning on using an ESC, solenoids, or wired switches? You don't need all three!

  • For wireless (R/C) control, you can use either ESC or solenoids for motor control. As noted on the Solenoid FAQ, an ESC provides much better control.

  • For wired control you can use solenoids with a small control current thru the control wires, or you can run full current thru the control wires and use high-current switches in the control box to control the motors. Using solenoids will prevent power loss thru the long control wires.

1) The Sabertooth 2x25 ESC has sufficient current capacity to control a robot with the specifications given in your earlier post (75 pounds, E30-150 motors, 20:1 reduction, 8" wheels). You may wish to consider alterative ESCs, as some combat related problems have been identified with the Sabertooths. See recent posts in the MOTORS archive for some ESC recommendations.

2) You can get away with a 25 amp ESC, but switches and relays are another matter. Instantly switching high current DC loads with contacts can cause arcing and may even weld the contacts together! This is a particular problem when attempting to reverse a rapidly spinning motor. I wouldn't be comfortable using a switch or relay with a direct current rating any less than half the stall current of the motor being controlled -- and even then I'd be very cautious about reversing a spinning motor. In your case, that would be 65 amp DC ratings.

If you're using relays/solenoids to control the main current flow to the motors, the switches that activate the solenoids will only carry a small current -- typically about one amp. Circuit diagram for forward/off/reverse control of a DC motor with twin DPST solenoids and a wired switch.

I've been reluctant to provide a circuit diagram for a wire controlled solenoid drive 'bot because I didn't want to encourage builders to use this control method. However, I've decided that it's necessary to clarify the control issue. The diagram at right shows the two solenoids and single remote switch needed to control the drive motor(s) on one side of a 'bot. As noted above, the control switch has a very low current requirement since it only activates the coils in the solenoids.

Now, about those motors:

  • The AME 226 motors at their rated 12 volts have an output power of about 200 watts. Compare that to the 750 watt output for the AmpFlow E30-150 at 24 volts. With 8" wheels your top speed would be just over 2 MPH and the peak current draw when pushing is 28 amps. I can't recommend these motors for your purpose.

  • The RS-775 motors come in a couple versions:

    The 12 volt 30 amp RS-775 you mention has only about 90 watts of output power -- far too little for for your robot.

    The more powerful 18 volt 130 amp RS-775 has about 585 watts of output power and is more commonly used in combat robots. These are high speed/low torque motors that require a large reduction ratio. A 64:1 reduction would give you around 7 MPH top speed with 8" wheels, but acceleration would not be as good as the AmpFlow motors could provide. Peak pushing current is about 27 amps.

The AmpFlow motors are widely used for good reasons. If you want reliable speed and torque with easy drivetrain construction, the AmpFlows are well worth their price.

Comment: thanxx alot sir..
all my confusions are sortedout..
Neumatic guy [India]

Wiring diagram - two ESCs and four motors.' Q: Hi Mark. I have a question about running two speed controllers together. First a bit about my setup. I have 4 drill motors and want a "tank drive" setup using 2 2x12 sabertooth motor drivers. My transmitter/receiver is a FlySky FS-T6. I have searched high and low and can't seem to find anyone with a similar case, let alone a wiring diagram that is similar to my case. Most use 1 2x12 and drive only 2 motors.

My question is, is what I am trying to do possible? I have a photo of my wiring diagram [at right]. Can you suggest any changes? The problem I am having is the motors do not seem to spin the right direction. Moving the stick forward makes the left side motors go backwards and the right side go forward. Moving the stick backward does the opposite (the left side motors go forward and the right side goes backward).

I am also confused about the #4 dip switch (the one that controls mixing). Is it necessary to use the #4 dip switch if I plan on using mixing on my transmitter?

Thank you for any help you can provide. I'm a newbie and am now wondering if I got into the wrong hobby! I'm going insane! Bleh!! [The Land of Opportunity]

A: [Mark J.] Getting 'mixing' correct is one of the more difficult things for a newbie to figure out. Yes, it is entirely possible to use two Sabertooth 2x12 ESCs to drive four motors. Your wiring diagram is fine, your DIP switch settings are correct, and you're very close to getting it to work. All you need are a couple of minor programming tweeks to the transmitter.

I'm assuming that in your diagram the two 'M1' motors are on one side of your 'bot and the two 'M2' motors are on the other side. I'm also assuming that you have channel 1 and 2 mixing enabled on your FlySky transmitter. On most transmitters this is called 'Elevon' mixing but the FlySky seems to incorrectly refer to this as 'V-tail' mixing (channels 2 and 4 on other transmitters). This isn't a problem, but it is needlessly confusing. Just one of the annoying things you have to put up with on a cheap Chinese radio...

Here we go. When you move the elevator stick forward the robot spins to the left:

Step 1: Enter the 'Setup' menu on your FlySky transmitter and select the 'Reverse' function. Select Channel 1 and change it from 'Nor' to 'Rev'. Press OK to leave the menu and try the forward command again:

  • If both motors are now spinning forward, great! Go to Step 2.
  • If both motors are now spinning backward go back to the 'Reverse' function menu, change channel 1 back to 'Nor' and change channel 2 to 'Rev'.

Step 2: Check the turning response. Move the aileron stick a little to the right (spin right command):

  • If the robot spins right, your basic setup is complete.
  • If the robot spins left, swap the positions of the channel 1 and channel 2 plugs in your receiver. Check the forward command again -- you may need to re-do Step 1 to get correct forward/reverse function after swapping the receiver plugs.

That's it! You may need to adjust the V-tail response settings from the default 50% to 100% to get full throttle from the Sabertooth ESCs. See this video on FlySky mixing if you need help with how to do that.

Once you get your 'bot running, you may want to explore some of the other functions on your transmitter that may make the 'bot more comfortable to drive. The Team Run Amok Transmitter Programming Guide will give you some help there. It was written for Futaba transmitters, but the functions covered are similar on most transmitters.

Q: Hey mark ... I have some [RoboGames 2015] questions. [India]

How does the trap of original sin work for horizontal spinners?

A: [Mark J.] Search our Robot Weapons archive for 'bar spinner trap' to find a previous discussion and photo of the 'Original Sin' spinner trap. The device is intended to slow and stop the big bar spinner while keeping their opponent directly in front of them. Sometimes it works, sometimes not.

Q: How was last rites able to rip off polar vortex so strong wedge?

A: Massive power and a fortunate attack angle.

Q: And why was original sin smoking a bit at last times of the final match?

A: I could only speculate. 'A bit' of light smoke usually comes from overworked speed controllers or motors. Lots of dense smoke is often a battery failure.

Q: How do we beat last rites? Nothing survives that thing ... I bet touro couldent have survived those ruthless hits?

A: 'Last Rites' record stands at 44 wins 28 losses, and 12 of those losses are to 'Original Sin'. I'd suggest doing what Sin does.

'Touro Maximus' has faced 'Last Rites' twice: one win (2010), one loss (2011).

Heavyweight combat robot 'Touro Maximus' Q: And how come touro max was without an armour? It seems to be bare aluminium.

A: RioBotz likes to use very thick aircraft grade aluminum for armor. Suggest you read section 3.9.7 of the RioBotz Combat Tutorial to discover their reasons.

Q: And why does it have sort of cuts or folds on the side face? The metal seeems to be bent.

A: The side panels of 'Touro Maximus' are machined with a raised triangular 'peak'. A flat-sided robot can (and surprisingly often will) become immobilized by getting stuck balanced on its side. The peaked sides cause the 'bot to tip back onto its wheels. There is also a gentle curve to the side panel which allows it to clear the wheel while minimizing the weight of the robot structure.

Q: Hi Sir...I am thinking of making a combat robot with two weapons: Wedge and Vertical Spinner. How can I use motors to operate these two weapons? Thank you in advance ! [India]

A: [Mark J.] Both horizontal and vertical spinner weapons are typically driven by a belt and pulley system. See the photo of horizontal spinner 'Fiasco' at right for an example of a belt driven spinner weapon. There are many posts about weapon motor selection and calculation of the correct belt drive reduction ratio in the Robot Weapons archive.

A wedge is a 'passive' weapon that does not require its own motor. A wedge relies on a powerful drive train in the robot to ram and lift the opponent and break their traction, allowing you to push them with reduced resistance. There are many, many posts in the Motors and Controllers archive on selecting drive motors and calculating the correct gear reduction for your robot drivetrain.

Horizontal spinner 'Fiasco'

Search the Archives!' Q: Hi Sir..I am completely new to a combat robot making.....I wanna have flipper as a weapon in it...Would you please tell me how can we transmit power from cylinder to function the weapon?And also,what can be the effective orientation of cylinder [with respect to] weapon? Thanks in advance !!

A: [Mark J.] There are DOZENS of posts about pneumatic flipper weapons in the Ask Aaron Weapons archive. Search there for 'pneumatic'. A few notes:

  • The Team Da Vinci Robotics Understanding Pneumatics page has several animated examples of pneumatic weapon designs, and a thorough discussion of pneumatic components.

  • Many Indian robot competitions do not allow pneumatic weapons. Check with the specific events you plan to enter before you build your flipper robot to make certain that you will be allowed to compete.

  • Pneumatic flipper weapons place great loads on the robot chassis and can be extremely dangerous if improper components or techniques are used. I can not recommend that anyone 'completely new' to combat robots attempt to construct and implement a pneumatic weapon. Pick something much simpler for your first combat robot.

Search the Archives!' Q: hey mark .. any idea about botblitz esc? the 85amp version . and why do these esc look like brushless ones? are these combat suitable ? [India]

A: [Mark J.] Your questions about the 85 amp BotBitz ESCs have been previously answered here at Ask Aaron. Search the Ask Aaron Motors & Controllers archive for 'BotBitz' to find multiple posts.

BotBitz takes inexpensive Chinese brushless ESCs and installs new firmware for use with brushed motors. The '85amp' version is popular in Australia for featherweight (30 pound) combat robots, but these are very basic 'no frills' motor controllers. There seem to be some quality control issues with BotBitz controllers that may trace back to the original Chinese manufacturer.

You should consider the Talon SRX ESC as an alternative. The Talons have been well tested in recent US competition and have proven themselves reliable in the lightweight (60 pound) combat class.

Q: Dear Mark,

By now, I have read at least 85% of your forum, which has become like a bible to me. Thank you for this, and for keeping Aaron's dream alive. I'm sure it hurts in an unimaginable way, no parent should ever experience it and it is so easy to give up, but you did not.

What's cool about what you guys have done, combat robotics and robotics in general is the cumulative nature of the learning experience, the more you learn, the more there is to learn and your site is like a never ending stream of fresh info.

I built a 2 wheeler bot with 2 CIM motors with 16:1 P80 gearboxes and 12" wheels, 2 Victor SP speed controllers. This will eventually become a self balancing ride-able scooter for my kids (after I figure out my IMU / Kalman filter issues), but for now I added some casters (kids call them 'training wheels' lol) and it is an R/C experimentation platform to figure out how things work in combat robotics. My kids want a battlebot and I decided to do it, but I'm taking steps and experimenting with some smaller scale stuff, like this 2 wheeler and a 4 wheel hockey bot that's in the works (thanks to the Tentacle calculator, which is an invaluable tool).

I have 2 questions:

  1. For my 2 wheeler with Victor SPs, I tried using the IMX-1 mixer (from Robot Logic). I like it a lot, it is very simple (just plug and play) the steering feels good and the reversing channel works like a charm. I use a Spektrum DX6i, just because that's what I have. The issue I'm having is the fact that I have no idea how to fine tune this system. Basically what I'm noticing is that one of my motors is a bit slower. I also notice that when I push the Elevator stick all the way up, the LEDs on the Victor on the faster motor light steady, which tells me it is at its max, while on the slower Victor, the LEDs are rapidly blinking and never reach the steady max state. I tested the Victors separately (without the IMX-1) and I can reach full speed at full stick throw without issues, the motors have no binding, everything feels pretty equal. When I try to calibrate them with the IMX-1 board, I get a consistent result, one motor is always slower. I know I can probably offset the Victors separately “by eye” then plug the mixer and at some point I might achieve similar speeds, but this is very annoying. Is there anything I'm missing, any other trivial way to trim things with this system? I'm thinking in the heat of the battle, it's slightly awkward to not being able to make fine adjustments. Maybe something I can do within the DX6i? I can't wrap my brain around it because any adjustment I try in the TX, makes a mess after it gets mixed through the board.

  2. Kind of related to 1., I read most (if not all) posts related to transmitters and I noticed you have a preference for the Futaba T6J as an entry level (~$200 and under) TX for combat. Right now, this is what I do to get mixing done through my DX6i [when not using the IMX-1 mixer]:

    ELEVON > ACT (makes 50% throws)

    Then I apply the D/R & EXPO settings as you recommend in your posts.

    For the most part it is very usable, but I can't figure out a way to add flipping/reversing (for driving inverted or with the rear) and there's that diamond shaped throw pattern best described in the IMX-1 mixer's manual:

    "Unlike our mixer, some RC transmitters and mixers use an “add and clamp” algorithm that reduces the controllability of your robot. This "simple" way to do tank/elevon mixing will cause your motor outputs to clamp to their maximum everywhere outside an inscribed "diamond" in your joystick's range of motion. This means that when your stick is anywhere within a triangle in each corner of its range, your robot is trying to spin as fast as it can. Our algorithm gives you smooth proportional control all the way to the corners of your stick's travel. The only time your robot spins at its maximum speed is when you jam the stick all the way to the corner."

    I drove with and without the IMX-1 and there is a noticeable difference, the IMX-1 algorithm is indeed nicer. But I don’t like the lack of fine tuning options, I think doing all the mixing and flipping inside the TX is much more elegant and simple (and less points of failure in combat).

    My question is: Will the Futaba T6J allow more control over the mixing compared to the DX6i? Will it allow me to assign a button/switch for inverted mix (inverted/backwards driving)? I looked all over and could not find any info on how to program the 6J for combat. Does your guide for the 6XAP (or the older Battlebots-era guides for the 9C series) apply to the 6J at all?

Sorry for the many words, so many questions to ask... Thank you in advance for your time and for your great service to all the noobs.

New York, USA

A: [Mark J.] Thank you for your kind comments about 'Ask Aaron'.

Question #1 has a fairly simple solution, once we find the right component to adjust:

  • The IMX-1 mixer - A very nice unit, and as you note it's completely 'plug and play'. Its simplicity is a strength, but it also prevents any fine tuning of the outputs. Nothing to be done there.

  • The DX6i transmitter - It has lots of tweeks, but nothing that can balance the throttle output after it's already gone thru the mixer. That leaves us with...

  • The Victor SP speed controllers - Take a look at page 6 of the Victor SP Quick Start Guide and follow the calibration procedure for each of the two speed controllers with the mixer in place. After calibration both of the Victors should give full throttle in both forward and reverse.

Question #2 [a cluster of three questions] is a little trickier to answer. As you've noticed, the Elevon mixing in the Spectrum transmitters is not optimized for robot use. You've implemented the standard work-around in order to get full-range PWM output. Unfortunately, this fix takes up not only the mix option but also both of the programmable mixes!

Among the reasons I prefer Futaba radio systems is their superior mixing implementation. With a Futaba transmitter you do not need a 'work-around' to get full PWM output, and their mixing does not use the “add and clamp” algorithm -- you have full response all the way out to the far corners of the stick travel, just as you do with the IMX-1 mixer. The 6J transmitter also has 'sub-trims' which allow trim adjustments on individual receiver outputs rather than just on the transmitter stick inputs. This is very handy for adjustments to individual channel outputs after transmitter mixing has taken place: if one motor is a little slow, or if it 'creeps' at neutral.

More good news: programming the Futaba 6J for robot use is nearly identical to programming the Futaba 6XAPs. The menu layout is a little different, and a couple of the function abbreviations have changed, but the Team Run Amok Futaba Programming Guide should walk you thru the 6J with very little trouble.

Now the bad news -- I've never found a method to assign an invert function to a switch on any of the commonly used R/C transmitters. Full-function hobby R/C systems are built for model aircraft, and there isn't an instance where an aircraft needs to reverse the response direction of a channel in flight. Even using the programmable mixes won't get the job done.

My advice: re-calibrate the Victor SPs to work properly with your IMX-1 mixer and continue to use its invert function. You'll need an on-board mixer anyway when you get around to experimenting with piezo gyros.

Q: Am I cool [Pennsylvania]

A: [Mark J.] If you have to ask me, no.

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.

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