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SN 102 refractor: Alt gear slips after nav keys released


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#1 tbransco

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Posted 21 June 2013 - 12:46 PM

My StarNavigator 102 refractor has begun to slip down whenever I release one or other of the direction/navigation arrows on the AudioStar handset. For example, a target star will "fall" about half the field-of-view at 110X. There is a small bit of motor noise associated with this movement, so perhaps 'slip' is not the best description of what's happening. At any rate, I'd much appreciate any advice from those with more experience, or better mechanical acumen.

Thanks, all.
Terry
Current Location: 123° 21´ 56´´ W,  48° 28´ 23´´ N

#2 MistrBadgr

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Posted 21 June 2013 - 01:37 PM

Hi Terry,

Welcome to the forum! The mostly likely cause of this is the characteristics of the gears has changed some with a bit of wear. Try retraining the drives.

I have slept a few times since I did one of those, and I do not have the AudioStar handset. I have the older version of the 497. But, the drive training setup should be the same or very nearly so from one handset to another. If you are not familiar with this, and cannot figure it out, let me know. I will look it up to make sure about what I tell you and then give you steps to follow.

Best Regards,

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#3 tbransco

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Posted 23 June 2013 - 02:48 PM

Thanks, Bill.

I re-trained the drives as you suggested, and I also re-balanced the OTA in the mount. It had been a bit back-heavy due to the mounting plate of a telrad I had attached. Unfortunately, the scope still wonders a bit after I release the navigation buttons. In my first post I described the scope as slipping down, but that's actually what the stars do. The scope, of course, wonders up. :unsure:

I also disassembled what I could of the altitude gear housing to see if the worm gear was engaged with the main gear, and I took a snap of what I saw:

Posted Image

Hmm. Inserting an image with a Dropbox URL doesn't seem to have worked. Here's the same URL, but in a link: https://www.dropbox...._1238176_tn.jpg

To my eye, the gears looks well engaged. Not sure how to get this any further apart, though. Would you happen to know how I can get at the main gear wheel itself?

Thanks again,

Terry
Current Location: 123° 21´ 56´´ W,  48° 28´ 23´´ N

#4 MistrBadgr

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Posted 23 June 2013 - 04:34 PM

Terry,

If you remove the mount ring from the mount by unscrewing the four bolts on its inside, you will see a keeper nut and under that a compression nut that looks like a three-legged stool, when you get it out. If you have already removed a long bolt that goes all the way through the altitude drive, which I think you have, judging by your picture, you should be able to pull the whole drive unit out of the other side from your picture.

The whole big end of the altitude drive, after you remove the mount ring is the drive shaft that you see poking out with threads on it in your picture.

They are probably way back in the posting files now, but in the DS section of the forum, I have some posts describing how to get into and out of the various sections of the mount. The mount I was describing was the older Generation 1 mount, while you have the Generation 2, much of the description works well. There are a few changes that were made that have made the mount more robust in most cases, but the mount generally comes apart and goes back together the same. The biggest obvious difference is the top bushing in the azimuth drive section was changed to a radial pin bearing.

Have fun!

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma

#5 tbransco

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Posted 02 July 2013 - 12:47 PM

Bill,

I just wanted to thank you for your help on this, and report back that the altitude gear on my SN 102 appears to be working just fine once more. There was nothing visibly worn on the gears, so I think the problem I was having can be attributed to either my misbalanced OTA (now corrected) or to the tensions I had placed on either the lock nut or the aluminum 'spacer` on the opposite side of the gear housing. Whatever it was, it's now under control and I can spend time viewing the stars, rather than chasing them around my field of view.

Clear skies, everyone.
Current Location: 123° 21´ 56´´ W,  48° 28´ 23´´ N

#6 MistrBadgr

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Posted 02 July 2013 - 06:35 PM

Hi Terry,

You are most welcome! That is one of the main reasons for this forum, to share knowledge when things go wrong.

Have fun with your scope!

Bill Steen
Bill Steen, Sky Hunters' Haven Observatory, Broken Arrow, Oklahoma




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