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.
Solutions:
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.