RA Tracking Drive Failure

Wednesday, December 10, 2014 10:31 AM

Problem(s) Encountered:

I followed a target far to the west and around 2:30, near an

HA of 5:30, the tracking stopped.  I figured the telescope had

hit a limit, though I had thought it would go to 6h west at this

dec (+26 degrees).

I slewed out of the limit and when I got to the next position

the telescope never settled.  The HA was not moving, and I

couldn''t get it to move; the telescope responded to the paddle,

but not to set rate in the E-W direction.  

After turning the tracking on and off, turning the drives on

and off, and cycling the power on the black box several

times, I took the dangerous step of restarting the TCS computer.

I didn''t power it down, but rather hit the reset button, and it

did come up, but had lost pointing entirely.  This didn''t

cure the problem.

Finally I went out and looked at the RA drive assembly.  The

tracking motor was spinning but the small toothed drive belt

that connects it to the mechanism was slipping. I had Erek

flip the motor on and off, and it started and stopped as

expected but the drive belt was still slipping.  By exerting

gentle pressure on the belt I could get it to move, but it would

slip as soon as it came back to the same bad spot on the belt.


Replaced drive belt for HA stepper system.  Pulled pulleys and cleared grunge and grease from them as well.  Decided to also check the dec stepper drive belt.  While it looks fine, I went ahead and replaced it as well.  Since the telescope tracks in HA and not dec, it is expected that the HA belt would go quicker.  Reset pointing by the tilt sensors and successfully tested all motions/speeds.

Regarding the rotator encoder setting:  There is an old detent/switch assembly above the rotator plate that was used to trigger a light when the rotator hit “0” on the old system.  This was not implemented with the new system.  I peaked in and set the zero-point by allowing the switch to settle into the detent.  This aligned nicely with the “fiducial”.  An upgrade to be performed when time permits would be to find the end of the old wire from the switch and hook it to a multimeter to more accurately find 0.