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

Re: Victor Brakes
 

Last year we did that. Then had a button the the joystick so the driver could turn it on or off depending on what they wanted. It worked pretty nice.

Re: Victor Brakes
 

We did this as well after one of our regionals. To prevent the possibility of tipping over, though, we took into account our current speed before engaging the brake (since our position tracking system already was measuring wheel speed). So, when the drivers would put the joysticks in neutral, the brake mode would be engaged once the robot's speed fell below a certain minimum. When in low gear this made our robot much more difficult to push around but avoided the nasty side effect of possibly tipping over if the joysticks were released while running at full speed.

Re: Victor Brakes
 

Hmm, assuming you had the braking feature of the victor hooked up to an IO pin, do you think a pulsed variable breaking system similar to ABS would provide varied levels of braking? :eek:

Re: Victor Brakes
 

Alex,
The speed controllers have this feature built in but using a slightly different method. The current supplied by the motor used as a generator is dumped into the transistors in the controller which are acting as a short. The controller is an "H" bridge design. Imagine the "H" with the motor connected from the center of the left vertical to the center of the right vertical. The top and bottom of each vertical is a set of power MOSFETs. The top of both upper vertical bars are connected to the positive battery connector and the bottom of both lower verticals is connected to the negative battery connector. To turn the motor on in one direction, the transistors in the upper left and lower right corners are turned on. To reverse the direction of the motor, the upper right and lower left transistors are turned on. To vary speed, you add a switching waveform to turn the transistors on and off, with speed determined by the ratio of the ON time to OFF. To provide braking, turn ON both of the bottom sets of transistors. Since they are both connected to the negative battery terminal, they are shorted together and that produces a short across the motor.
By varying the pulse that enables the brake you could vary the braking force. As pointed out by others in this thread, the braking is dependent on rotation. The slower the motor is turning, the less current is being developed in the motor, and the less effective the braking becomes.

Re: Victor Brakes
 

It could, but you can do it without pulsing as well. ABS doesn't pulse for the salke of pulsing, it does so to avoid wheel lockup, since only a spinning wheel has directional control. A locked wheel cannot steer. While optimally braked ABS wheels may have a slightly shorter stopping distance on some surfaces, that's not the point of ABS. Instead, it allows you to maintain heavy braking while steering around the potential crash.

Also note that the braking feature of a Victor is not all that powerful, since it is proportional to the motor speed. So, it would not be a good brake.

Don

Re: Victor Brakes
 

In the distant past (2000) we used a globe motor to rotate a set of forklift type arms from a stowed position. As the arms passed vertical, gravity would take over and the arms desended quickly. The globe motor was programmed to move foreward fast and then switched to a slow reverse to counteract the effect of gravity. The arms then continued to rotate forward but the action was less stressful on the mechanical parts. We have since learned that it is better to use springs to balance arms.

Re: Victor Brakes
 

When I tried hooking the SIGNAL pin of a Digital Output directly to the centre pin of the Victor Brake/Coast header (2006 Robot Controller) the red HARDWARE LED comes on (Master Reset), on the Robot Controller.

This can't be good :confused:

Shouldn't the Relay Outputs on the Robot Controller be used instead???

I have been unable to find a schematic for the Victor controller showing the Brake/Coast jumper.

Re: Victor Brakes
 

What? That definitely says that you *can* connect a digital output to a Victor.

Re: Victor Brakes
 

Sorry, I misread it.

Re: Victor Brakes
 

In my experience, that red light usually means something is drawing too much current from the RC's +5v output. Are you absolutely certain you got the connection the way you intend it to be? Might your connector be faulty and have a short between signal and ground? Did you perhaps accidentally also connect the +5 from the digital header to the ground (I think it's the Coast end, but I might have that backwards) on the Victor?

Re: Victor Brakes
 

Thanks Alan.

It is either something like that, or a short somehow via the chassis (unlikely - but I will be checking it).

Last night we did try using the Relay Out ports, which seem to work. However the rules state that only the Digital Output can be used.


We modified a standard servo cable so that it has one end normal (at the RC) and the other (at the Victor) routes the white (SIGNAL) wire to the centre conductor. The black and red servo wires are not connected to anything.

This assumes that the PWM cable going to the Victor supplies the ground return - however since I cannot find a schematic for the Victor (or the RC for that matter), I don't know if this is correct. But IFI Robotics FAQ for the Victors does state:

Re: Victor Brakes
 

mluckham,
I would check the operation of your wiring by removing the brake connection at the Victor and checking it with a VOM. It should not have voltage and should read a short to ground when Low and open circuit when High. You might be one pin off on the RC and feeding +5 volts to the jumper.

Re: Victor Brakes
 

If you are referring to the digital output from the RC, it will actually output 5V when high and ground when low. We used it in this configuration last year.

Re: Victor Brakes
 

Dave,
I thought this was not an active high. So if it is disconnected from the Victor, there is no pull up.

Re: Victor Brakes
 

No, it's just a standard digital output on the RC. When set to high it outputs 5V and when low it shorts to ground.

Re: Victor Brakes
 

There are pull-ups on all the io pins according to ifi. This will pull them up to 5V. This permits an normally open switch to be attached to an io line and not have it floating around electrically.

http://www.ifirobotics.com/docs/anal...al--i-o-rc.pdf

Bud