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Originally Posted by Doug G
We do the same thing with our shooter, but just simply use a couple of encoders connected to the RC and Watson's velocity PID code with some tweaking of the constants and are getting pretty good results. So why use the separate PIC?
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2 reasons to use the PIC
1) The student who did it had some PIC experience and wanted to add a bit of interesting control circuitry. This also provides an example for future robots.
2) We were worried about the interrupt overhead from the impellers spinning at over 2000rpm. We did do a pass through mode so that (if there was a problem with the sensor PIC) we could hook the sensors up to interrupts 5 and 6 and do everything in the RC.
The off board PIC can determine the speed on every revolution by measuring the pulse width. The sensor
sees one high and one low every revolution.
We also thought about routing the GTS signals (from our robot drive system) through the PIC (or a similar device) to get the drive rotational direction since measuring the GTS pulse width is difficult to do in the RC. However, we ran out of time to do that.