Re: [APML] Declination Drive problem

["Fred & Liz Lusen" <fl.lusen@verizon.net>]

Bill,

Have you determined if the problem is actually the motor or the gear train?
Also are you using an AC or DC motor?  My guess is that the slop is in the
gear train due to the inherent imperfections in gears themselves and the
pivot points they are on.  You may want to look into the arrangement that
Larry Meyers of Mountain Instruments uses on his MI-250.  This setup mounts
a cam directly on the motor shaft with the cam held in tension by a spring.
It would require you obtaining a motor that turns at 1rpm but that is not
impossible.  I have no backlash problems with this mount.  The only problem
with this type of setup is that you have to realize where the cam is before
you start an evening of guiding else your buttons may reverse in the middle
of an exposure.

Fred Lusen

----- Original Message -----
From: "William R. Mattil" <wrmattil@ix.netcom.com>
To: <astro-photo@seds.org>
Sent: Thursday, January 17, 2002 11:14 PM
Subject: [APML] Declination Drive problem


> Gentlemen,
>
> While probably Off-Topic I have a problem when guiding photographs that
> has me stumped. Situation is this, mount is a 1.5 inch shaft GEM with
> conventional RA drive and tangent-arm Dec driven by a Hurst 1 rpm motor.
> After being inspired by what I am seeing by lurking here I am trying to
> refine my guiding and have run into this. By definition I was told that
> tangent-arm Dec systems have "no backlash" and this seems plausable. But
> what I am experiencing seems to be just that. Backlash. When reversing
> directions there is a definent delay before the Dec reverses direction.
> After disassembling the Dec assembly and drive I have come to the
> conclusion that the "backlash" is present in the motor itself. Not the
> drive assembly itself. So I pondered this and cannot fathom a solution.
> I have three of these motors and they all exhibit the exact same
> behavior. I would imagine that constructing a new motor assembly would
> bear no fruit either since after adding the gears to reduce the speed to
> 1 rpm the backlash is introduced. That and the motor coasting. Can
> anyone point me in the right direction here ? I can guide in RA with
> *no* trouble at all, but this Dec thing is giving me fits.
>
> Perhaps superflouous information would be:
>
> 10" f/6 Newt. Guidescope is 90mm f/11 refractor. I am guiding at ~303x
> 9mm EP and 3X barlow. Flexure is *not* a problem.
>
> Trying desperately to get pin point stars .....
>
> Regards
>
> Bill
> --
> William R. Mattil | Fred Astaire wasn't so great.
> wrmattil@ix.netcom.com | Ginger had to do it all backwards
> (972) 399-4106 | and... in high heels.
>
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