paper: Shooter Wheel Speed Control

[Ether]

Originally Posted by kenavt

I'm also worried about adversely affecting the motors with this sort of harsh treatment (fast sequence of full and no voltage).

You do realize that with their PWM output, the Victors are applying full and no voltage at 150Hz to the motors all the time, right? ...I wouldn't worry about the motors.

But what about the controllers?

The switching in the Victors and the Jags is slightly different. The Jags short the motor leads during the OFF portion of the PWM cycle, whereas the Vics open the leads.

Since the Vic's switching method involves applying full voltage during the ON portion of the PWM cycle, and opening the leads during the OFF portion of the cycle, it seems to stand to reason that they are designed to handle that treatment. So commanding full volts and 0 volts alternately at 50Hz shouldn't be an issue. Anyone care to comment?

On the other hand, the Jags short the motor leads during the OFF portion of the duty cycle. The only time the leads are open (other than for a fleeting moment during the PWM cycle to prevent shoot-through current) is if they are in coast mode and a zero command is given. I am assuming the Jags are built to handle that condition repeatedly. Perhaps someone with intimate knowledge of the design could comment.

Because of the Jag's switching method (shorting the leads during the OFF portion of the PWM cycle), using a voltage ramp (for decreasing voltage) creates a problem for the bang-bang control method. If the voltage is ramped down (instead of being allowed to be commanded immediately to zero), it may cause dynamic braking when the wheel speed (and thus the motor speed) is high and the voltage is low but not zero. For the bang-bang method, you do not want dynamic braking.

I might tune the voltage ramp to prevent this occurrence primarily, as well as preventing the Jags from shutting down.

Adding excessive voltage ramping may adversely affect the bang-bang's dynamic response and accuracy.

This will be something I discuss with the mechanical side of my team.

I think it's an electronic issue, not mechanical.