Rotator Motion Failure

Wednesday, November 11, 2015 3:12 PM

Problem(s) Encountered:

The main problem I encountered was that the rotator hit the limit and stopped working.  I was observing a target where the parallactic angle was near -77 deg, which should be within the limits of the rotator.  I was out in the dome rotating from a PA near zero to that angle and I heard a sound and was then unable to rotate back any more (i.e., back towards PA=0 deg, not the direction I was going). I tried going back and forth in both directions but all that did was to move up to the limit of -85 deg.

This was near the end of the night, so I just used PA=-85 for the remaining objects and I left the telescope in that rotated position.  


The hint in the report was the statement “...I heard a sound…”.  That sound was the connector for the CCW limit cable snapping apart and subsequently disconnecting.  This is why the rotator could only be moved in one direction—it assumed it was in the CCW limit.  

A cable wrap that is mounted to the mirror cell and routed around the rotator snagged or came free or something.  Hard to tell what happened first.  But included in that wrap is the CCW limit switch cable, along with a number of other cables.  When it came free, it snagged the cable wrap that rotates with the rotator and pulled taught, resulting in the CCW limit cable connector ripping out.  Overall, we’re lucky.  The connector itself is in good shape, as are the pins.  I’ve reconnected it to the electrical panel and duct taped it into place until I can order some spare connectors (206429-1 4-pin Male CPC plug) and perform a real fix.  Also luckily, no other cables were damaged.  Almost surprised about that.

The offending cable wrap has been connected to the mirror cell in a much more rigid manner and where possible, cables exhibiting a potential to snag were shored up as much as allowable.  All systems test out functional.