Blowing the 120A breaker?

[colt527]

OK, well here is the deal. We are planning to use 4 CIM's to drive the robot using the gearbox that FIRST supplied us, and 1 motor, probably a window motor to raise a pulley system. To move our main arm, we have 2 designs:

1.) Use a series of pistons that has the ability to raise the arm to various different levels.
2.) Use motors (Probably 2 Taigene motors) to raise the main arm.

We have ran into some road blocks with the pneumatic approach, and I personally would like to go with the motors to raise the arm. But, here is my biggest concern. Let's say we are just plain moving around, lifting the main arm, and using the pulley system, will the main 120A breaker pop? Has any team successfully used 7 motors running at the same time to operate their robots? If so, did you ever experience this problem, or any other problems for that matter.

PS: Do the Taigene motors back drive if you apply 100 ft-lbs of torque to them? I have to test that out one of these days.

Thanks for your time =)

[Cory]

First off, you should not have trouble with breakers blowing. Your drivetrain should have the wheels slipping before you reach the stall current, so you'll never be pulling that much. Many teams have used 6 motor drives successfully in the past, and that's with all 6 running the entire match. If you have a total of 7 and are only driving 4 the majority of the time, you should be fine.

Second, the van door motor can be backdriven if you apply enough force to it, if I remember correctly.

[sanddrag]

Also, there is only one Taigene Van Door Motor in the kit. You may not use two. As far as backdriving, I would say yes. Do this, take your motor (not hooked up to anything) and put an adjustable crescent wrench on the flat spots and crank it. It is not too hard to backdrive. You can reduce the effect by setting the jumper on the speed control to "brake" but this will only reduce it a little. To try that by hand, do the same thing as above but touch the two wires from the motor together while cranking. It should be a little harder.

The concern of tripping the 120A breaker does not directly relate to the number of motors but how much current those motors are drawing. You could probably run 30 motors at the same time on that breaker if they didn't have any load.

Theoretically it would be easily possible to do under an intense pushing match but in reality that breaker can sustain much more current for a substantial amount of time. The only time we've tripped ours was in 2003 when we were practicing for a long time and driving with lots of binding in the drive system and the "suckers" were deployed and dragging on the carpet for a long time. But beyond that I've never heard of anyone trip it.

[Ali Ahmed]

There should not be a problem with using 7 motors at the same time. Last year we had 6 motors and the compressor running at the same and we didn't trip the 120 breaker.

[sciguy125]

If you look at the specs, you'll see that you can draw a lot of current without blowing it for awhile. 120A takes 500s and 240A (200% of rating) takes 10s. You'll probably be fine unless something really bad is happening.

Last year, however, we had serious problems with our drill motors in the drive train constantly blowing the 40A breakers....

[Al Skierkiewicz]

Originally Posted by colt527

OK, well here is the deal. We are planning to use 4 CIM's to drive the robot using the gearbox that FIRST supplied us, and 1 motor, probably a window motor to raise a pulley system.

Ken,
The First supplied gearbox has been designed for efficient driving using two Chalupas for each box. The 120 amp circuit breaker should not trip in a two minute match with those motors and a normal array of other motors. It is unlikely that you will be running all the motors at the sme time, and a two minute match should keep you under the trip charachteristics of the breaker.