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Unread 30-03-2004, 15:25
Larry Barello Larry Barello is offline
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Re: PID control loops - closed loop feedback

Quote:
Originally Posted by TedP
...

Every year I always hear that... but I never pay attention to it... and I'm always too lazy to see the reason why. I figured that 255 was some special mode that the speed controllers got in... perhaps an OFF mode or something... and I THOUGHT one year I found out why there was so much commotion about it and that particular year they removed the reason for that commotion... but I don't remember. Anyway, I've never had a problem going full scale... but that's definitely something that could easiliy be fixed.
The 255 issue is a holdover from the old PBasic days. The packet sent between the the user processor and the control processor used two "255" in a row to delimit the end of a packet. If you sent out a bunch of 255 as PWM values the packet would be truncated. This happened to us in 2001: at stick extremes the two PWMs went to 255 and got the packets out of synch and all heck broke loose.

The current system still uses the 2x255 but hides it from you by "adjusting" 255 to 254 before sending it to the control processor. We discovered this when trying to send telemetry data back. We were using some of the unused PWM slots for the dashport, so we could get data back each cycle. Well, no such luck. So we limited the data to 7 bits and used two slots to pass 14 bits of data back. (it was gyro angle in .1 deg so it needed to be an int).

Now that IFI has given us a real processor, it is time to give a real radio without these limitations.
 


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