Re: Altitude going haywire #tickmanagement #oscillations

Rob Brown



Thanks for responding! Here’s what I have:


From Controller in current state:

Alt Motor Ticks 6,891,738

Alt Scope Encoder Ticks 765,361

Az Motor Ticks 3,640,499

Az Scope Encoder Ticks 1,214,385


From working calibration file (May 2018)

Alt Motor Ticks  6,813,919

Alt Scope Encoder Ticks  2,239,383

Az Motor Ticks 3,640,499

Az Scope Encoder Ticks 1,214,385


As you can see, the big change is in the Alt scope encoder. But it’s definitely not slipping. In fact, it can’t, because it is on a separate shaft from the drive and slip clutch and that shaft is free-running (idling).


I was going to try swapping the encoders to see if the problem followed them, when I noticed that the Alt encoder was actually wobbling on the shaft! It turns out that the brass shaft of the encoder was ever so slightly bent. I gently pushed it back, checking the wobble until it looked good. I then ran the Ticks Determination routine again, and Voila! Fixed! The average of three runs for the Alt Encoder is now 2,268,068. That’s very close to my last calibration, so I will now try re-loading the old cal and see if GoTo works.

Done! Problem solved!


Lesson learned: Protect your encoders! Both of them are highly exposed, and I simply must have banged it loading the scope (40 pounds) into the cradle. I’ll build enclosures.


-Rob Brown


From: Don W
Sent: Monday, November 4, 2019 11:42 PM
Subject: Re: [Sitechservo] Altitude going haywire #tickmanagement #oscillations


Hi Rob,

Do you have a record of the tics per rev for you mount and the servos?  Check using ServoConfig.exe to see that the tics per rev for all the encoders are correct.  If your mount uses friction drives, slippage might be your problem.  You can check the tics per rev by carefully moving the mount axis through a measured angle (Azimuth can go 360°, Altitude maybe 90°).  Check ALL the encoders.

What version of SiTech are you using?

Don W


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