My understanding is you want no fuse-like failsafes during a combat robot competition because anything is better than your robot dying and being torn to pieces by the other robot (though you might be able to end the match early and save yourself some money). The way to limit stall current IS to gear it down so the loads applied never make the motor stall and to pilot the robot intelligently. I think one point you can start from is to select a gear and wheel size combination so that the robot produces a force double to it's own weight at the edge of the wheel. There are weight limits for the classes of combat robots so you know the maximum weight of the other robot and your robot. You just have to choose the tradeoff between excess torque and speed and hope that it will be enough to overcome the torque of the other robot, but still be fast enough to catch it.

As a rule of thumbs for DC motors:

-The point of maximum power output 50% of stall torque or 50% of no-load RPM (they are the same point on the efficiency line on the torque-RPM graph). You generally do not want to apply more torque than this so that the motor slows down more than this for any continuous operation.

-Maximum efficiency is 1/7th of stall-torque or 6/7ths of no-load RPM.

As you're planning to use a commercial speed controller, check with the manufacturer, presumably a controller suitable for those motors will be able to handle the problem, or current limit accordingly.

Originally Posted by Russ Hensel

dknguyen makes some good points, but I would say monitor the current with your microcontroller and if current is too high give it some strategy for resolving the problem, reversing direction, rocking, off-rest-on, grab the other robot and set both on fire.

The vast majority of combat robots aren't automated so it's up to the pilot. The only thing worse than 500lbs of kill-bot running around with a crappy AI is 500 lbs of kill-bot running around with a smart AI.

Originally Posted by mech king

Good points, as far as i know, the vantec speed controller has no current limiting Built into it, but i wanted to use it because its very good for a 145kg bot with differential steering. I will email the manufacturer to confirm this though

How could it not? It's so expensive.

Also, here are alternatives
http://www.roboteq.com/brushed-dc-mo...-selector.html

Sorry, the RDFR47E has some current limiting feature, but its expensive - $800.

The Roboteq ESC seem alot more reasonable and appear more robust and user friendly. Going to scan over the manual and see what the crack is with these.

I think my ESC will end up being expensive, no matter which one i go for, because i live in England and we dont really have any good ESC over here for differential steering applications - well none that are simply plug and play type.

4QD is based in the UK.

Just returning to the ESC topic,

My design uses two Magmotors at the moment, but in the future i may use four motors, if i have enough weight allowance left. All of the ESC i have seen can accomodate 2 motors for tank style differential steeing, but can four be used also? Would you have any suggestions as to this arrangment? I gues i will obviously need more batteries or a higher rated Ahr battery?

Thanks

Originally Posted by mech king

Just returning to the ESC topic,

My design uses two Magmotors at the moment, but in the future i may use four motors, if i have enough weight allowance left. All of the ESC i have seen can accomodate 2 motors for tank style differential steeing, but can four be used also? Would you have any suggestions as to this arrangment? I gues i will obviously need more batteries or a higher rated Ahr battery?

Thanks

I don't see real point...you might as well use two larger motors instead of 4 smaller motors (simpler, more reliable, morepower, less weight). The only real reason is if you wanted 4 driven wheels.

But in either case, it does not change the fact you are likely to get slaughtered if you try don't have differential steering. You need that maneuverability.