Victor Brakes
 

How do u hook a victor up so that you can reverse the polarity and cause the motors to stop. Could this cause a type of brake?Could there be a way to include it into the programming so that we can control it from the control board?

Re: Victor Brakes
 

All Victors except the SC (Spin Control) versions are capable of running motors forward and reverse. PWM values* of 128-254 run a motor forward, values of 126-0 run the motor in reverse. Yes, running a motor in the opposite direction that it's turning will rapidly stop the motor. Of course it won't just stop at zero speed, it'll start turning in the opposite direction unless you put it in neutral.

Also, if a motor is turning full power full speed in one direction, and you instantly change it to full power in the opposite direction, you run a good chance of blowing a fuse or breaker somewhere. This draws a LOT of current.

*There's a deadband of 12 or so around 127 where it's still in neutral, but I can't remember the exact size. It's probably actually 134-254 and 122-0.

Re: Victor Brakes
 

Also, the Victors have a Brake/Coast jumper (check the manual) when this jumper is set to Brake and the victor is in the neutral range, it will short the leads of the motor causing a resistance to motion. I believe you can somehow hook the brake coast jumper pins to the robot controller to have selectable braking.

Re: Victor Brakes
 

Yes, you can. Simply switch some of the digital inputs to digital outputs, and you're good to go. Just drive the pins.

Re: Victor Brakes
 

I believe there is something in the rules against this though... let me check.


Nope, guess I was remembering something else... but anyway... check this thread out?
http://www.chiefdelphi.com/forums/sh...906#post449906

Re: Victor Brakes
 

It should also be noted that there is a function called dynamic braking, in which the Victor shorts it's output creating a short across the motor windings. This causes drag on the motor that is proportional to the speed in which it is spinning. It only engages when the Victor receives a neutral signal.

It is controlled by a jumper setting, and there is round about method of remotely turning this on and off. It can't hold a motor stopped on it's own, but it will slow down a free spinning motor. Some teams use dynamic braking on the victors that control their main drive motors. It has the effect of eliminating any coasting a robot might otherwise have. Most teams, however, do not use dynamic brakes, feeling that the sudden stops produce more strain on the drive train and victors then is worth it. More common uses are for motors controlling long arms that otherwise 'droop' when no power is applied.

Could you describe what you want a brake for?

Edit- The method that I know of for remotely turning the dynamic brake on and off is to wire the jumper pins to a limit switch, and toggling the switch with a servo (or other mechanism). I don't know exactly how the pins function, so I couldn't say what the result of applying voltage from a digital out might be. Can you simply cause digital out to create a short? If so, that would be a much simpler way of doing it, although possibly illegal.

-Andy A.

Re: Victor Brakes
 

That would have been illegal under last year's rules I believe.

Re: Victor Brakes
 

This site shows how to control the brake/coast setting from the RC.
http://www.ifirobotics.com/forum/vie...956098 63b6c6

Re: Victor Brakes
 

It's also important to note that the retarding torque provided by dynamic braking is directly proportional to the speed the motor is rotating at.

Trick Question: Assume a frictionless CIM motor, with some internal resistance, spinning at, oh, 100 rpm. When does it stop spinning if you turn on dynamic braking? The answer should tell you why dynamic braking isn't necessarily useful.

Re: Victor Brakes
 

I don't know if this thought will help, but what about regenerative braking?

I figure(correct me if you see errors), put a single-pole, double throw contact switch between motor, victor and leads to diodes then to a battery. By switching to the leads with diodes the motors are turned into generators by the forward motion of the robot. The diodes are so the battery doesn't back into the motors causing them to run at full.

Re: Victor Brakes
 

Sounds interesting, but also illegal under 2006 rules. Per <R59>, custom circuits may not "[d]irectly alter the power pathways between the battery, fuse blocks, speed controller/relay, and motor." (Excepting voltage- and current-measuring devices.)


Per <R70>, "[d]igital outputs of the Robot Controller may be connected directly to brake/coast headers on the speed controllers to permits [sic] 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."

Re: Victor Brakes
 

I think that the intent of the rule here is to be using a relay
to replace the jumper, and control the relay with the RC.

Re: Victor Brakes
 

I don't think you need the switch. There's some diodes in the transistors that will do the job. If all of the transistors are off, spinning the motors forces current into the supply.

Re: Victor Brakes
 

IFI actually approves of the direct method, with one conductor betwen the signal pin on a digital output and the centre pin on a Victor, without any intervening circuitry. It's just a matter of feeding the B (centre) pin a high or low signal for coast or brake, respectively—and the A and C pins on the Victor just happen to correspond to those levels when using a jumper. See here for some more information.

As far as I know, this rule was uniformly interpreted as written during 2006 inspections, meaning that the use of a Spike or other relay to trigger the brake/coast settings would not have been permitted.

Re: Victor Brakes
 

I agree with Tristan. We researched this last year, and found the same postings he notes. We were surprised that IFI did not recommend a method similar to what Sciguy and EugeneBrooks suggested. At the Palmetto Regional, we built and successfully tested a wiring harness to switch our drive train Vics between Brake/Coast modes, from the Digital I/O pins of the FRC. Afterwards we decided not to use it in the competition, since it did not provide the type of braking effect we were looking for.

Eric