I might tune the voltage ramp to prevent this occurrence primarily, as well as preventing the Jags from shutting down.Īdding excessive voltage ramping may adversely affect the bang-bang’s dynamic response and accuracy. For the bang-bang method, you do not want dynamic braking. 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. Perhaps someone with intimate knowledge of the design could comment.īecause 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. I am assuming the Jags are built to handle that condition repeatedly. 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. On the other hand, the Jags short the motor leads during the OFF portion of the duty cycle. So commanding full volts and 0 volts alternately at 50Hz shouldn’t be an issue. 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. The Jags short the motor leads during the OFF portion of the PWM cycle, whereas the Vics open the leads. The switching in the Victors and the Jags is slightly different. 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. I’m also worried about adversely affecting the motors with this sort of harsh treatment (fast sequence of full and no voltage). If you’d like a second set of eyes to look at your code, PM me and I’d be more than happy to take a look and provide feedback. I might be able to get some data on this precision with various execution cycle times by the end of the week on our practice robot.Įxcellent. The paper discusses how to do this for speeds typical of shooter wheels. The key is getting a noise-free speed signal. I’ve been told of similar results using a Victor. Does anyone have data about how precise this speed control method can be? That would obviously depend on the “small overshoot” Ether talks about due to execution cycles only being ran so fast. My only question would be the precision of the “Bang Bang” speed controller over a well-tuned PID loop (how close one is the target speed). Seems like this should have been the first thing our team thought of, over the glamor of PID!
An ingenious way of shooter motor control, definitely.
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