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CG5 GT Drift Problem

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#1 asteroid7



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Posted 01 June 2009 - 09:06 AM

My Celestron CG5 GoTo Mount is having a drift problem.
A star will drift to almost the edge of the fov and
suddenly snap back to the center of fov. This seems
to happen quite a bit but not every time.
I do balance the telescope and fooled around with the
backlash settings. But this doesn't cure the problem

Thank you for any help.


#2 Eddgie


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Posted 01 June 2009 - 09:27 AM

What backlash settings did you adjust?

Are you keeping the scope in balance or pre-loading it?

If the mount is "Sticky" in Right Ascencion, it might be better to slightly pre-load the mount, usually on the east side, so that the weight holds all of the slack out of the gears and keeps the worm engaged positivly to the worm wheel.

Did you check the worm engagement? This is the mesh of the worm to the worm wheel.

You should also check the end float on the worm gear. When you remove the worm housing with the worm gear in it, see if the worm gear moves back and forth in the little housing (this is end-float). As I recall, the busing on one end is threaded so that if there is end float, you can screw the bushing in a bit to take the end float out.

Have you checked the gear lash of the spur gears on the motor and on the worm gear shaft? The motor can usually be moved a bit and you should loosen it and move it so that the lash between the gear teeth is almost completly gone. In fact, I personally would tighten is so that ALL lash is removed between these gears, or at worse so that only the TINEST amount of lash exists.

While you are there, check the set screws that hold these gears to their shafts. Often these back out a tiny bit so that they are not making contact with the flat on the shaft. Tighten. Better yet, remove them and put a tiny drop of locktight (non-hardening) on the threads and re-install them.

Oh, and on the worm wheel, ensure that the worm is not bent. This is pretty simple to check.. Just mesh the worm fully into the worm gear (again, to me almost no play is best) and turn it one full revolution by hand. The pressure should be exaclty the same. If it feels tighter during the revolution in one place and much slacker in the other, then the worm is bent. This could cause your problem.


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