troque

[XXShadowXX]

What is maximum troque (prior to gear ratios) 2-1/2" CIM motors ( part #FR801-001 and or M4-R0062-12)?
thnxs (thanks)

[XXShadowXX]

well I found it,

if anyone else wishes to know its 343.4oz/in squared

[Iceman1330]

"torque"

[jee7s]

While your number is correct (300 or so ounce inches), that's the stall torque, at which point the motor is drawing 110-120A. Your breakers will pop well before then.

That does however give you the Torque Constant of the motor. For a DC motor like the CIM, we can assume that torque output is linear to current, so just divide the stall torque by stall current and you'll get the torque per amp.

Typically, we've designed for 1 N*m of torque from each CIM.

JEE

[danshaffer]

Originally Posted by jee7s

While your number is correct (300 or so ounce inches), that's the stall torque, at which point the motor is drawing 110-120A. Your breakers will pop well before then.

I've been told that the breakers aren't instant, so you might be able to run for a very short amount of time at that current/torque, but you probably want to design to pick a pretty small percentage of it (10-25 should work ok, correct me if i'm wrong) and try to operate generally around there (driving your robot or whatever, but without obstacles, or driving your arm with a ball but not into the wall or with someone hanging on it...!)

[jee7s]

When it comes to popping breakers, there's actually a time dependence related to current. A small overage takes a longer time to pop than a large overage. 100+ Amps would pop that 40A breaker almost instantly. Maybe it could be tolerated for something on the order of milliseconds, but not much more.

Also, on a side note, the breakers pop more slowly with repeated usage/popping. I suppose it would be a "gentle" workaround the rules to deliberately pop the breaker a number of times to draw extra current. This isn't in the spirit of the competition, but it would be literally legal.

JEE

[Alan Anderson]

Originally Posted by jee7s

Also, on a side note, the breakers pop more slowly with repeated usage/popping.

I'd have expected it to be the other way around. Since the breakers are tripped by heating up, shouldn't they be faster to trip if they're already running hot due to repeated overcurrent events?

[jee7s]

The slowing was an observation made by one of my fellow engineers/mentors during a motor test. Over repeated breaker trips in a short period the breaker slowed its trip time.

Our best guess is that it has something to do with deformation of the metal strip in the breaker. Heat may make it more malleable, which would reduce the "snap action" of the breaker. The difference is small, but could be significant.

JEE

EDIT: I got some clarification on this, and I misstated the concept. The slowing isn't in the tendency to trip, but in the reset. As was previously stated, the heat makes the trip more sensitive, but it also makes the reset time slower. This means that popping the breaker causes slower reset, disabling the motor for a period of time. AKA...bad idea. My mistake in interpretation.