Slew Errors

Wednesday, October 31, 2018 12:57 PM

Problem(s) Encountered:

When we attempted to slew to a new target, the telescope repeatedly came back with a slew error. The error read:

ERROR point not converging dist=11.430 dra=8.641 ddec=7.483

(although the numbers at the end changed slightly each time.)  After driving the telescope by hand toward the zenith and then slewing the telescope again, the telescope pointed without a slew error. The error repeated itself again 2 slews later, but was fixed by just telling the telescope to slew again.

At the end of the night we encountered more pointing errors with the error code:

ERROR dome axis=m_az timeout

This time we managed to get the telescope to point the zenith without a problem, but then when we attempted to point to a target again, the telescope continued not the slew. We opted to the close the telescope at this point.


Telescope behaved like there was a preload issue in dec.  Movement was choppy and seemed to bind frequently.  This occurred most when changing the direction of travel.  Adjustments to preload however did not resolve the issue.  I also changed out the fluid in the preload’s hydraulic cylinder but the problem persisted.  At this point, I had Tony watch the system as I tried moving in dec.  It was quickly discovered that the flex coupler between the dec drive train and the encoder had failed.  This is a large coupler and we have no spares.  No spares on the summit either.  But we do have vinyl tape.  Considering this connects the encoder (low torque), tape is worth a shot.  Taped it up and all is well again.  I also tightened all hardware mounting the encoder to the telescope, which was all quite loose (cause of the failure—motion and play over time??).  A new coupler will be ordered and installed.