Dec. Drive Motion Failure

Saturday, November 28, 2015 12:41 PM

Problem(s) Encountered:

At about 21:00 the telescope became unable to move in Dec. We tried restarting the TCS (telescope stop/start, restart/initialize the GUI) a few times, with no success. We verified that it would move in HA, and then moved it to HA=0.

We found a trouble report from Oct. 23 where a similar problem was encountered and solved by changing electrical connections in the TCS box. We did not mess around with the electronics, but we cycled the power to the TCS box in the computer room. Upon restarting the system, everything worked normally but the Dec drive could not be homed or talked to at all.

We did home the focus and dome, so the focus is now at a value of 0.

We then called Eric at 21:50 and he suggested power-cycling the Dec drive in the telescope mount. Previously we had looked at the status of the OMRON display and found it was normal, but we cycled the power and nothing changed. Eric suggested a visual inspection of the drive belt, which appeared fine to our untrained eyes.

Finally, we shut down/put the e-stop on and killed the TCS GUI and did ''telescope stop''. The telescope is close to zenith by coincidence (prior target had Dec ~ +30).


Found that the two set screws holding the motor shaft to the pulley were missing, allowing the motor to turn freely from the telescope.  Installed a couple cap screws with toothed ends to grip the shaft a bit better and will place a drop of blue loctite on each screw to keep them from walking out again.  Homed axes and needed to power cycle the TCS in order for the dec to properly home.  What it was doing was returning an error that it timed out.  Still, it also returned a value of ~40 degrees, even though it appeared to be pointing more or less to zenith.  After power cycling, it seemed to home correctly.

One last thing I noticed was that the four wires that had to be directly connected due to a broken connector (10/23 trouble report) appeared to be coming slightly loose.  I reseated them and verified they are indeed tightly connected.  I take this as well as a hint to send out a reminder to have a replacement of this “special” connector sent to us.