Re: ATM gear backlash in Alt. drive

[behambu@teleline.es (Berthold Hamburger)]

On Sat, 17 Jul 1999 00:18:05 -0400 (EDT), you wrote:

>I accept the fact that a generic surplus gearbox may have lots of play
>and periodic error.  Mel's software would hopefully handle any PEC
>needed.  

Hi Adam,

Mel's software handels backlash perfectly. Still it's kind of annoying
and you should look for a gearbox which has as little backlash as
possible.

PEC is a different topic with a small gearbox that consists probably
of 3-5 small wheels. My box has a 250:1 reduction and some wheel in
the box has a PE of some sort. The problem is that the wheel with PE
turns once per ~100 motor rotations.

The effect is that guiding works perfectly for let's say 40 motor
turnings until the PE of the wheel shows up. 
The effect is that after tracking for a few minutes you might think
the scope tracks the guidestar well and you turn away from the
eyepiece to rest your eyes, just to find out that suddenly your off by
several arcseconds.
The problem is that it is quite unpractical to build a PEC array over
100 motor rotation cycles to account for that error.


Then again it depends on what you want to do. For piggyback
photography it should be fine as guiding tolerances are very high.
Long prime focus exposures could become a bit stressfull I imagine,
but I have not tried it, since my focuser does not (yet :-)) rotate.

Berthold

                        -------------------
Berthold Hamburger - Cellist
InterNet: b-hamburger@teleline.es
Homepage: http://www.geocities.com/CapeCanaveral/9601