Dynaminc Braking on Victors

[Max Lobovsky]

I understand that one can short A and B on the jumper on the Victor to put it in "dynamic braking mode" As i have been told, this will have the speed control give enough power to the motor to prevent it from being backdriven. I have a couple of questions about this.

1. Does this affect normal speed controlling of the motor?
2. Does it work effectively in both directions of backdriving?
3. Is there a way to estimate about how much power it will draw to keep it still?
4. Will it be effective for a winch, as in will it have a quick enough response time to not let the winch slip too much before holding?

Thanks.

[Kevin Sevcik]

dynamic braking will NOT stop backdriving. This has been conclusively proven many times. Dynamic braking doesn't apply any power to the motor at all. It simply makes the motor more difficult to turn if you aren't already applying a voltage to it.
The way it works is that it shorts the leads of the motors together when the Victor isn't applying power to the motor. This creates back-EMF when the motor is spinning, but does absolutely nothing while the motor is at rest. Try it with a drill motor or CIM. Spin it by hand when the wires aren't connected, then have someone hold them together and see if it's harder to turn it.

to answer point by point:
1. No, it will not affect the normal operation in the slightest, though if you use it on drive motors, your robot will stop MUCH more quickly as opposed to coasting.
2. Yes, it work in both directions, but doesn't stop backdriving.
3. It draws ZERO power.
4. No, it will not stop your winch from slowly unspooling at the end of a match, AT ALL.

[Ian W.]

By itself, it may not stop a winch from unwinding itself, but if you use a Victor set in Brake mode along with a motor with a worm gear (Van Door motor, perhaps?) then it would be pretty hard to unspool itself (although not impossible).

We've done some testing with the brake mode on drive motors, and it makes the robot stop much faster than in coast, so it definitely has an effect, if the motor is spinning at high speeds. But anyone who knows the fun hand rules from physics can figure that out .

[Kevin Sevcik]

We tried van door + winch + braking on the 2000 chin-up bar. It didn't work terribly well and we had it geared down rather low. I'm not sure that there are any motors in the kit that don't backdrive, but that's a discussion that's already happened in atleast one thread this year.

[sanddrag]

Originally Posted by Kevin Sevcik

We tried van door + winch + braking on the 2000 chin-up bar. It didn't work terribly well and we had it geared down rather low. I'm not sure that there are any motors in the kit that don't backdrive, but that's a discussion that's already happened in atleast one thread this year.

Are you saying the van door motor IS backdriveable?

[kiracofe8]

Originally Posted by sanddrag

Are you saying the van door motor IS backdriveable?

Yes, the van door is backdriveable, and fairly easily too. Try it yourself. It only takes maybe 30 in-lb or so to backdrive it.

[Kevin Sevcik]

oh yeah. heck, van door motors are backdriveable by design. How else do you open a van door if the switch breaks or something?
Just because it's a worm drive doesn't mean it's not backdriveable by default. Take a look at what Martin Sprockets has to say:
Martin Sprockets

That being said, I only know that previous year's van door motors were backdriveable. That might not be true this year. I'll clamp one down tomorrow and go at it with a cresent wrench.

[UCGL_Guy]

Our 2000 van door motor winch would backdrive without power with a 130 lb. robot on it. Think about how a boat winch and it is an easy problem to solve