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Help with CG-5 mount tuning

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#1 zAmbonii

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Posted 11 April 2009 - 06:39 PM

A little over a month ago I bought a used Cg-5 ASGT mount and have been getting used to since then. When the mount arrived it seemed like it had been well taken care of/little used, but both the RA/DEC axes seemed quite a bit stiff. When I mean stiff, I mean that it was hard to tell balance because with the clutches open I could not get the axis to "fall" in either any direction (even when unbalanced). The RA axis seemed to loosen itself up a bit after my first couple of tries out, but the DEC axis was still way too stiff.

I had enough with the DEC axis when trying to autoguide, it seemed to have a stick/slip where small guiding errors would not be corrected until a large enough command could overcome the stickiness. So i decided to tear apart the DEC axis and relube. I left the RA axis alone until i saw if the DEC axis improved.

After putting the DEC axis back together, I am just unsure if I have tightened everything correctly or not. I am still running into two issues with the DEC axis and I wanted to run it buy those here to see if I got things too tight or whatever.

The two problems I have are these:
1) When I tighten and set the ring nut it is either too tight or too loose.

2) When trying to guide/move the DEC axis from + to - there seems to be a slight drift in RA direction before it moves completely in the DEC direction.

For deeper explanation:
1) I tighten the ring nut just slightly past the point where i start to get resistance. If I don't tighten the set screws the axis seems to be free but not loose. But as soon as I tighten the set screws, the axis becomes too tight to me. Tight as like I said above, it seems stiff even when I unbalance things. Thing is, if I loosen things to the point where everything seems loose enough even after I tighten the set screws, the axis seems to be too loose.

Just how far should I tighten the ring nut? I thought that moving the axis around when it is just slightly tight that it would loosen itself up a bit, but that doesn't seem to be happening. Any help here would be appreciated.

As for #2), I am not sure what is causing the slight shift when changing directions in DEC. Is it because the axis too tight or is it because it is too loose, or does it have something to do with the motor gear/worm gear mesh?

For example, when I looked at my PHD guiding logs from messing around last night, the RA angle the program measured was right about 1.00 degrees. The DEC axis though was something like 3 degrees. This causes problems in guiding because PHD guiding will translate a part of the RA movement into a false DEC movement and will try to guide that out, even though there is no real movement in the RA axis. Any help here would be appreciated also.

One final thing. I havent tore down the RA axis, because I haven't really had that much problem with it so far and wanted to get things straigtened out with the DEC axis first. I took a look at the PE last night (on Vega) and it didn't seem to be THAT bad. My PE from the peak to trough was a total of about 35 arcseconds. I am having a slight problem trying to guide that out.

One thing I noticed when adjusting the worm gear and regreasing the motor gears was that I cannot seem to get the motor gear to mesh enough with the gear on the worm drive. There seems to be too much space inbetween the gear teeth, and I can definitely notice a gap (and lag) when moving from RA+ to RA-. I cannot get the gear teeth to mesh any more because I have the motor as far forward as I can get on the motor bracket, and I cannot see a way to move the motor bracket any more forwards. Is this the way it should be? Should I be able to get the teeth to mesh better?

Any help on any of this would be greatly appreciated. Supposed to be clear tonight and I am going to get some imaging done, not sure how successful it will be though :)

#2 yock1960

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Posted 11 April 2009 - 07:33 PM

Have you been here?

http://www.astronomyboy.com/cg5/

Also, here is some info regarding endplay and backlash on the cousin mount, LXD75.

http://www.thestarde...enance_101.html

I've never taken my axes apart, so I don't have direct experience there. As far as moving the motor forward, if you are talking about the spur gears, I don't think they would have much to do with backlash unless they were not tightened on the motor axle (slippage from set screw loose), or they were way too far apart. It's the worm against the ring gear on the RA axis fit that determines backlash. That's my understanding at least.

It can be frustrating, but after enough taking apart and digging around online, you'll understand it better!

Good luck!

Steve

#3 zAmbonii

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Posted 11 April 2009 - 07:54 PM

Yup been to the site linked, and yea, I was talking bout the spur gear. I know it shouldnt be that important on the RA axis especially when guiding (because a -RA guide would really only make the gear move slower). But I would think that how well the spur gears mesh would also contribute to PE somewhere in the chain. Just wondering how tightly or how loosely they should mesh.






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