Filter Wheel Motion Failure

Tuesday, October 4, 2016 10:33 AM

Problem(s) Encountered:

Filter error occurred a few times in the MIS GUI.  Filter could not changed.

In the morning, when I took flats, it was OK...


Conversing with the observer via email last night, I suggested simple resets of things within the xmis2 GUI, but the problem persisted.  I then suggested they rotate the filter wheel in the opposite direction.  This seems to have helped out.

This morning, testing verifies that the filter wheel has issues turning, I believe CW when looking downward.  These problems appear to be limited to slot positions 2, 3, and maybe 4 (BV and maybe R).  The problem only occurs here, when trying to go upwards (eg U to V, slot 12 to slot 2, etc...).  Approaching the problematic positions from the other direction (eg slot 6 to slot 3) seems to always work correctly.  When the problem occurs, there is a sound as if the motor is binding, or not providing enough torque to start turning.  

I seem to recall this issue occurring years ago, although I believe it simply went away with time.  This time, it could be related to the recent drop in temp.  Also, this is the 2.4m filter wheel, mounted on the 1.3m.  This wheel has always seemed to take more effort to turn when rotation is performed by hand.  

My current plan, since the telescope is not scheduled to go back on-sky for a number of nights, is to pull the filter wheel and install the one typically used on the 1.3m (was out of service for a time due to a failed detent roller, which is now repaired) in the past.  Staff will then have time to open up the one that is having issues and see if there is anything obvious going on in there.  Interestingly, last time this filter wheel was opened, the wheel spun without issue, so the additional resistance to turning comes from somewhere other than the bearing or gear play.