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Martin
Thats a very pro and neat job, well done !.
Ok, PLCs aren't cheap but it will be a small one ($300-400). Im determined to use one because I know how, they are opto isolated in and out, built in relays so no extra hardware and utterly reliable. Ive seen them last >20yrs going hard 24/7 in harsh conditions. The one I used at itelescopes ROR has been going 24/7 for 9 years now without a problem.
Partly what will make the control simple is i will mount a small long range ultrasonic proximity sensor (ok, not cheap, $300-400) on the OTA rings looking at the dome slot edge. If the slot disappears, ill just nudge the dome a bit more till it comes back (basic closed loop). Then i dont have to deal with fancy software, geometry, alignment and horrendous math. Ive heard horror stories getting that right, even on commercial domes. I may be able to do initial sync and flips with this, havent thought about it yet, but i can do this manually at the start of a session anyway, its at home, not remote. Ive realised dome tracking speed is so slow I may have to use stop-start tracking after all, but with gentle acc/dec on the drive.
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