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CGEM jerking in R.A. with tapping noises

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#1 Michael Covington

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Posted 15 August 2019 - 09:58 PM

This evening, while videoing Saturn, I noticed the image irregularly jerking about 5" in R.A., as often as two or three times per second, and then noticed I could hear a faint tapping noise from the mount whenever a jerk occurred.  (This might be quite audible in a place without so many crickets and tree frogs.)  The power consumption, normally 0.8 amp, was 1.1 to 1.2 amps, apparently fluctuating faster than my digital meter could keep up with.

 

A few minutes earlier, I had videoed Jupiter with excellent tracking.

 

I looked for a dragging cable, but there was none.  I looked for a balance problem, but it was in balance (a tiny bit east-heavy) and slightly changing the balance didn't alleviate the problem, though it did make the taps a bit less frequent.

 

I slewed to several other areas of the sky and the problem disappeared; there were no taps, and power consumption was 0.7 to 0.8 amp.  (I didn't evaluate tracking.)

 

What's going on?  Until this, the CGEM had served me very well, and I was thinking of having it hypertuned simply because I'm the 3rd owner and it has never had any maintenance.  A few years ago I had a tapping problem with my AVX that ended up being a bad gearbox.  If this is going to be a multi-hundred-dollar repair I'll have to seriously consider getting a different mount.   (And the advocates of CEM40 and GM811G can fight it out, giving me advice.)  Or is it a freak problem that will never come back?

 



#2 EFT

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Posted 17 August 2019 - 01:05 AM

It could be something that is not out of the ordinary.  It is hard to say remotely, but the fact that it was a one-time occurrence in one part of the sky certainly doesn’t suggest a significant issue.  Since the mount has gotten some use from a few different people, it’s possible that the grease is getting pretty contaminated at this point and you just hit some stuff caught in the gears that was creating the jerking or even that you were in just the right position that the balancing of the axis was close enough to perfect that it allowed the axis to bounce around backlash between the worm and ring gear.  If it was something in the grease, it’s possible that the debris was scraped out and won’t cause a problem again.  It’s not very likely that it is a gearbox problem since you would likely see that more often if not all the time. 

 

While your mount might benefit from a tune-up, I would not say that it is something that must be done at this point.  Video astronomy is not particularly demanding and really doesn’t require the mount to be working at as high a level as imaging.  It’s probably worth using the mount some more to see if the problem becomes chronic.  At that point, you might have it tuned up.

 

Unless you plan on more rigorous imaging, there would not really be a good reason to spend money to change mounts since the mount seems to otherwise fit your needs.



#3 Michael Covington

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Posted 17 August 2019 - 09:03 AM

Thanks, Ed.  In fact I also want to use this mount for autoguided deep-sky work with my C8.  (My AVX does not seem to be *quite* up to that.)  So still thinking of having it hypertuned, mainly because it has never had any maintenance.

 

I did consider that it might be bouncing back and forth across its own backlash.

 

Could this possibly be a firmware issue?  If I recall correctly, it has beta firmware.  I'm going to look in on TeamCelestron and probably revert to production firmware.



#4 Michael Covington

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Posted 17 August 2019 - 10:27 PM

I used it for an hour of visual observing tonight and had no recurrence of the problem.  Maybe it was a balance issue.



#5 Michael Covington

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Posted Yesterday, 08:10 PM

Celestron Support says that if it recurs, I should try updating the firmware before pursuing mechanical problems.




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