VEX motor control

[LockheedJoe]

We recieved a Vex motor (393) and a vex PWM (29) motor controller.in the KOP. However, the Motor open and power set vi's don't control it. Is there a way to controll it with LabVIEW? I tried the victor setting but that didn't work. How do we control it?

Thank you

[sciencewhiz]

It needs the servo jumper installed, so that it gets power.

Based on the PWM specs on the vex robotics website, I think victor would be the best choice.

[LockheedJoe]

I had the jumper installed. Using the "victor" open, it moved but slow and REALLY jumpy. Any other ideas?

[sciencewhiz]

It's possible that the vex motor can't handle the the faster update rate that the victor can handle. The servo VIs use a 20ms update rate, so you could try that.

Another option is to use the PWM Vis in IO->PWM. Use the set period multiplier vi to set the period multiplier to 4x.

I wonder if NI's tested with the vex motor.

[sciencewhiz]

In WPI_Default_PWMConstants.vi, there's the following comment on the front panel

Taken from WPI LabVIEW C code PWM.h

/**

     * kDefaultPwmPeriod is "ticks" where each tick is 6.525us

     * 20ms periods (50 Hz) are the "safest" setting in that this works for all devices

     * 20ms periods seem to be desirable for Vex Motors

     * 20ms periods are the specified period for HS-322HD servos, but work reliably down

     *      to 10.0 ms; starting at about 8.5ms, the servo sometimes hums and get hot;

     *      by 5.0ms the hum is nearly continuous

     * 10ms periods work well for Victor 884

     * 5ms periods allows higher update rates for Luminary Micro Jaguar speed controllers

     *

     * This is the 1x period (5ms).  In hardware, the period scaling is implemented as an

     *   output squelch to get longer periods for old devices.

     * Set to 5.05 ms period / 6.525us clock = 774

     */

I guess that confirms my guess that the update rate is causing a problem.

[LockheedJoe]

I found the vi that had this informaiton in it but it didn't look like that vi had the inputs for the information it says it needs. Is there an example of how to do this? What vi's would I need to do this?