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.