Power of Victor Brake

I have seen that many teams are deciding that they need to have brakes so that they will not roll down off of the ramp.

What is the effectiveness of the Victor brake…is it really that bad that you need to have a manual brake?

It depends on the friction in the rest of your drive train, but yes, it is probably that bad. The brake in the Victor is a dynamic brake. That means that the two leads of the motor are essentially connected together. When you try to turn the motor, it acts as a generator and produces a voltage which gets fed back and tries to prevent the motion. Try it yourself by just connecting the leads of a motor together. It’s useful in many situations, but maybe not enough to keep you from rolling back down.

Does the Victor break work when the robot controller is disabled?

Last year, Ockham had a lift made of 80/20 lifted by a belt system powered by a van door motor. I’m not sure of the exact weight of everything together, but it would backdrive with the Victor braking even without a tetra.

Hope this gives you a bit of a gauge on how effective it is–if you really want it to stay in one place, I’d suggest a mechanical brake.

If you want to see what the effectiveness of the victor break is, power one of your motors directly off a battery, and while it is still spinning, take it off the battery and short the leads together. The motor will stop pretty rapidly. This is what the victor brake does. It Won’t do much at all as far as locking your wheels from moving while your robot is stopped or at a very slow speed, but it will bring things to a stop pretty rapidly. The force it exerts is porportional to the current speed of the motor. It relies on using the motor as a shorted out generator.

It’s as effective as the speed in which the motor is turning. As the motor gains speed it generates a higher voltage with slows it down. As it slows down, the voltage drops which lowers the effective braking effect so it speeds back up. This roller coaster gets averaged out of course, so in effect the brake produces a speed in which all the forces balance out.

As for keeping a robot on the ramp, it probably won’t be enough. It will slow a robot down, but the robot will keep moving until the force of gravity can not overcome the friction of the drive train. Since scoring of objects on the ramp won’t happen right away, the bot will probably hit the carpet before being scored.

The dynamic brake can slow down a motor. It can not ‘lock up’ a motor because as soon as the motor is not moving, it is not generating a voltage.

-Andy A.

The dynamic brake in a Victvor will not keep a robot on the ramp. It effectively is a method where in converting mechanical energy to electrical energy being delivered to a dead short provided by the brake, causes a similar load to be applied to the motor. Energy is generated only when the motor is moving.

Is a shorted motor not harder to turn though?

Also, does the braking still work when the RC is disabled?

Al,

While I agree that the Brake function in the Victors will not hold a robot still in the ramp, it does help a bit. According to the Victor manual,

So, some resistance to turning will be achieved, even when the robot is disabled:

For the students that never played with it, the best motor to try it on is the FP with the gearbox attached. Try turning it with the leads connected and you’ll see exactly what the Victor does when it is set to Neutral (a pwm output of 127) or has no signal while the Brake jumper is selected.

Sandrag,
I believe the brake jumper is still active when disabled.

Manoel,
I agree but the brake is still only effective when the motor is turning, so with it active you will still roll down the ramp, just more slowly than without the jumper.

OK, yes… The break does still work when the RC is disabled… AND if there is enough friction in your drivetrain (probably with 6 or 8 wheel designs) the victor brake will be enough to slow your motion off of the ramp down, but it will be the friction that stops you. Basically, If you have to exert a “good amount” of force to push your robot on the groud while it is not powered up, then you have a chance at staying on the ramp with the Victor brake.

as long as your off the ground when the buzzer sounds, you should count as being on the ramp. The victor break may help you, but don’t count on it.

The main use for the victor brake is when you are driving, when you let go the robot slows quickly, if you don’t have the Victor break on the robot tends to coast for a few feet. We did some tests to see if the break eats the battery more than if it wasn’t on, but it didn’t seem to make a difference, at least in the 2 minutes and 15 seconds that we drove with them on (several times).

The brake is most useful when used on a motor whose position you are depending on. For example, our turret motor uses the Victor brake to keep from overshooting.

If you are just on the cusp of being able to stay on the ramp, the brake might help, but it’s not going to be able to hold that much by itself.

Brake-ing your victors can also assist your drivetrain to position a bit more accurately.
My question is (and I know this has been brought up before) what is the legality of flipping between brake and coast mode in-match, and how can this be done (I recall threads where people were talking ideas for this. )
I would assume you could build a custom circuit to do this easily…
The reason I ask is because our drivetrain is amazing with braking mode on. Very precise, fluid movement, etc.
But, we’ve been discussing the whole strategy debate of giong for the ramp when we remembered our strategy in '03.
In '03, our bot was set to coast by default, and at the last seconds in te match, we had the system such that we gunned it for the ramp, and coasted up into position, sometimes even after the buzzer. (just by a bit)
We’ve been talking of doing this this year, but would like to switch between coast and brake. Any ideas?

There’s a rule this year prohibiting that.

Hmm. Well, I guess we’ll just have to set her to coast and see how she does…

A rule prohibiting what exactly? Costing onto the ramp or switching between coast and brake with a custom circuit?

<R70>Digital outputs of the Robot Controller may be connected directly to brake/coast headers on the speed
controllers to permits programmable control of this speed controller function. The brake/coast header on the
speed controller may NOT be connected to any other circuit or input.

Wait a sec, that allows controlling the brake/coast as long as you use digital outputs. You just cant use a custom circuit. So, this is awesome, we can do it this way.
All you need to do is map a switch to two digital outputs to control whether you brake or coast. Cool…

Oh my. I must be tired. I could have sworn I read “may not” Thanks for catching my goof. Looks like I get my brakes afterall. :slight_smile: