RA Motion Issues

Wednesday, January 18, 2017 1:00 PM

Problem(s) Encountered:

The hour angle motion and east-west coordinate readout is showing some serious-looking symptoms - I''m wondering whether yesterday''s adjustments had some unintended consequences.  

The telescope will occasionally stop tracking altogether, though the drive keeps trying -- it''s as if the motion jams up.  This happened three times.  Also, the pointing drifts relatively quickly, necessitating a coordinate reset with nearly every slew.  The error appears to be entirely along east-west. As the telescope guides on an object -- so its true RA is really constant -- the indicated RA creeps upward at the rate of something like 20 seconds of time per hour.  

There''s also a fair amount of squealing, and they don''t sound like squeals of delight.  The last time the telescope jammed, I heard a short, rhythmic chirp coming from the dome that sounded for all the world like some kind of alarm.  I went out to investigate and found the RA drive pushing, then slipping, then pushing, then slipping -- didn''t look good!  

One possibility that occurred to me was that one of the support rollers on the main drive is going, but when that happened before the failure was more gradual -- the telescope developed a rhythmic slip/recover motion that would last for several minutes and occur at random, and which grew steadily worse over several months.  The present symptoms weren''t happening at all the previous nights -- in fact, the pointing was pretty good.


I found that when tracking was initiated, or when moving at SET speed (same motor), there were occasional, non-periodic high-pitched squeals accompanied by a slowing, and sometimes reversing of the drive train.  It is hard to hear exactly what was squealing, but my best guess is one of the clutch interfaces, designed to slip when running at non-slew speeds.  I lubricated this clutch interface and the occasional squealing has completely gone away, as has the odd drive anomolies (tracking drive belt slowing/reversing).  However, the RA continued to slowly climb over time when tracking is turned on.  This corresponds to the telescope drifting east if I’m correct, or tracking slower than desired.  I’ve tightened the cam that provides contact to the drive friction plate and have gotten that drifting to all but disappear.  Time will tell if this is a fix.  I’m wondering if this is temperature related.