Re: Disk brakes
 

That isn't how it works. In "brake" mode, a Victor speed controller isn't supplying any power to the motor. It's simply connecting both sides of the motor together, turning it into a dynamic brake.

Re: Disk brakes
 

another good source for brakes is here. The ones I would use are about halfway down the page. http://electricscooterparts.com/brakes.html


the 120mm is 4.72 in in diameter and with activation from a pneumatic cylinder they would be quite effective.

Re: Disk brakes
 

Hmm I wasnt aware of that, thanks for the info. However, a physical brake im sure can stop shaft movement much better than an electronic one.

Re: Disk brakes
 

Indeed it can--at the cost of extra weight and complexity. (Granted, they can be quite light if you design it right--look at 25's robot this year--but they still have mass.)

Re: Disk brakes
 

Just another one of those times when you have to take into account what you want more. :)

Re: Disk brakes
 

Disk brakes sound really inefficient for a FIRST robot. Why not just take the (+) and (-) wires and have them touch (I am not giving away any concept designs, just an ideal concept). Take a motor and spin the shaft. Now connect the two wires together and try it again. It would be a lot harder, and even harder when you have that going through a gearbox.

Re: Disk brakes
 

This is how the breaking feature on the Victors work.

Re: Disk brakes
 

However some people may want more braking power then that.

Another robot will certainly not have very much of a hard time pushing 2/4 motors on a transmission, especially if it already has the momentum going for it and it is using the same type of drivetrain.

Re: Disk brakes
 

Woah! Is it like a programmable thing? Has his been around for a long time? I never looked into detail about the Victors. :rolleyes:

Re: Disk brakes
 

I'm looking at the DeWalt transmissions. Does the anti-backdrive pin on these work well/reliably? Sounds like a good way to hold up an arm.

Re: Disk brakes
 

There's a jumper on each Victor that allows you to decide if you want to set it to brake or coast. Brake is as described, while coast is what most folks use.

Teams have, in the past, created a servo-driven mechanism that allows them to switch between the coast and brake modes in the middle of a match.

Edit: Also, apparently you can program it to switch back and forth. You learn something new every day :)

Re: Disk brakes
 

The brake/coast jumper has always been on the Victors. Just move it from one position to the other. I think it usually ships in the coast position by default so you may have never noticed it. If you connect the jumper back to the robot controller digital I/O (switches) then you can program the Victor to either brake or coast at will.

Re: Disk brakes
 

Last year IFI pointed out that the jumpers on the speed controllers could be wired to a digital IO port, allowing you to control in software the mode the speed controller was in. It made sense last year, as a team would have been able to enable brake mode, if the robot started to go in the direction opposite the one it was heading in as the match ended (WHILE DISABLED!). That is, you could have the robot coast up the ramp, and then not slide back down (if the dynamic brake was strong enough).

Re: Disk brakes
 

And you had enough traction.


The essential point that I was making is that the Victor brakes are almost always good for use in a drive-train in FIRST. I'm willing to bet that one of the robots involved in the pushing match (either yours or the robot trying to push you) will lose traction before the motors back-drive in brake mode. Especially considering a vast majority of pushing doesn't occur head on (a great deal of it is rotational in the world of FIRST, something that a braking mechanism that locks the wheels won't help with). If you want a system to prevent torqued out of position, it would have to be in contact with the playing field rather than the wheels.
Mechanical brakes (such as disk brakes) may be a valid solution for other aspects of the robot, such as arm and shoulder joints.

Re: Disk brakes
 

My post was a follow up to M. Krass's.

As for what you are saying about brake mode: it is not that strong. It does provide some resistance to motion, but not alot. Brake mode seems good for allowing the robot to stop on a dime, and also for helping to keep an arm stationary. Break mode may not help much in a pushing match.