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how would you define/quantify backlash?

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#1 Myles


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Posted 27 May 2009 - 12:32 PM

I am selling a SVP and do really know how to accurately describe the level of or lack of backlash.

I know if I move the drive contoller to center an object there can be alittle tendancy to overshoot at higher powers. I'd that backlash?


#2 Eddgie


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Posted 27 May 2009 - 01:15 PM

Backlash is "Slop" in the gears. Usually it is when the worm isn't fully mated with the worm wheel.

It can show up after slewing or it can show up when you are doing fine adjustments to the field. For example if you are using slow speeds to center a star and when you stop pressing the button, the star drifts in the field for a few seconds.

First, if the backlash is in Right Acension only, then to approximate how much, just get everything as perfectly balanced as possible.

Now, point to a bright star, then use the handset to drive the object into the center of the feild of view so that the telescope is coming FROM THE WEST. This will preload the gears to the west. If you have any significent backlash, you should see that for a brief interval the star will drift from the center of the field in the eyepiece while the motor drives the gears to the west until the slack is gone, and when the worm catches up, the scope will start moving again.

You will have to know the field of view of the eyepiece. For example, suppose the field of the eyepiece is 20 arc minutes and the star drifts half way to the field stop. That would be 5 arc minutes of backlash. Of couse this doesn't have to be exact. I mean no one is going to buy an SVP and expect you to nail the backlash error within a few arc seconds.

Also this. It might not be gear backlash. Could be something else loose in the mount.

And it MIGHT not be the worm engagement to the worm wheel (though it is a 50/50 chance that it is). It could be that the spur gears that go on the motor and the RA shaft coming out of the mount have loosened.. This is VERY common. If the little Allen screw on either shaft has backed out some and not making contact with the flat on the shaft, that can cause the same problem. It may even have come this way. This is an EASY fix if you have Allen wrench.

Good luck.

#3 Myles


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Posted 28 May 2009 - 07:03 PM

Thank you,
that helps alot to put a definition on it and how to evaluate my mount.

- Myles

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