Issues pointing far to the north

Thursday, February 4, 2021 4:59 AM

Problem(s) Encountered:

Telescope errors occurred pointing at DEC > 74 degrees. The telescope would not slew from JSkyCalc even though the object was east of the meridian and away from the West limit. As a result of the slew error the telescope seemed to lose its encoder positions.  Telescope was then pointed to the zenith and the tip/tilt sensors were used to zero the telescope. At a later point in the night the telescope slewed to DEC +73 but was not pointing at the correct field, slewing the telescope to lower DEC found the correct field without needing to reset the telescope 
using the tip/tilt sensor. 


For lack of better explanation, error had built up in the home position registry for the dec drive encoder.  Although the encoders are zeroed to the appropriate values at home (zenith) position, this incremental stack error appears to, somewhere low level, add error to where the telescope thinks it is.  I don’t quite understand this as it does not impact telemetry.  But it does end up impacting how far north the system will allow the telescope to slew.  Again, this only sort of makes sense to me, but working from a previous instance, I was able to zero out the error in the registry for the encoder and the telescope appears to once again go much farther north.