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Control Unit for Home Built Rotator from Pitch-Prop Motor
Richard,
Agreed on the suitability of an analog solution... I certainly made some steps toward critically damped operation. My circuit design was bad, though. I didn't have a very analyzable problem; the rotator rotates one of those fiberglass surplus military masts with respect to another, so I get a lot of stick-slip, especially if there's a breeze (there are 12 feet of mast above this thing). This is not to say a suitable set of P, I and D couldn't be found, and it would have been pretty slick if I'd set up right for empirical loop tuning, but I hadn't done that. I got pretty close by soldering components in and out. I would have had a better time with a real multiple op amp circuit with a knob for each of P, I and D. I think you hit the nail on the head regarding too heavily dampened with too much gain in the antenna rotator case. I just couldn't really tune the thing. In my case, I just decided to throw up my hands and go to the simplest method so I could get on the air with a rotating antenna. I have a quite successful analog servo going every day with my remote antenna tuner (www.n3ox.net/projects/servo). That one is ever-so-slightly underdamped, proportional only, and works nicely. There's a little bit of hysteresis and it certainly could be improved, but I stopped at the good-enough-for-daily-operation level. I guess what I meant by "going digital" was that depending on whether you're more comfortable with programming than a soldering iron (not me!) you might think about having a simple motor drive circuit and implement the admittedly complex PID loop in software/firmware. You're absolutely right that you can't do this if you don't know how to do the analog... 73, Dan N3OX |
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