From: "Chuck Shaw" 
To: 
Reply-To: "Chuck Shaw" 


Murray,

Nils Olof's advice is correct.

If you are planning on driving your platform with a threaded rod, and your
scope is not REALLY heavy, having the CG a bit away from the virtual polar
axis will not be a problem.  The threaded rod tangent arm drive has a lot
of mechanical advantage.

Balance only starts to get important for heavy scopes or if you are using
very low torque motors

Chuck

Chuck Shaw
cshaw{at}ghg.net (home)
cshaw{at}ems.jsc.nasa.gov (work)
http://www.ghg.net/cshaw (S4: Stars, Sailing, Spaceflight & Stuff)


>
> Date: Mon, 9 Dec 2002 23:35:58 +0100
> From: "Nils Olof Carlin" 
> Subject: Re: ATM Equatorial platform
>
>  Murray wrote
> > Newbie here...
> > I am attempting to build an equatorial platform for my 8" homemade
> > truss-tube dob. I am basing my design on Chuck Shaw's excellent
> article, as
> > well as the designs on Jan van Gastel's site.
> >
> > I have encountered a design problem: the azimuth/ground board pivot
> point is
> > not in line vertically with the scope's optical/altitude CG. It's my
> first
> > homebuilt attempt, what can I say :)
> .......
> > => Altitude/azimuth bearing offset = 3.5"
> >
> > So, rotating my scope through azimuth looks like it will move the CG
> away
> > from the polar axis...what will this do to the way the scope tracks?
> Or is
> > this even going to work? Should I just give up now and move the
> azimuth
> > pivot on my scope?
>
> My suggestion is try now, give up later ;-)
> Hard to tell for sure, but in my limited experience balance isn't
> supercritical, and your setup *might* work.
>
> Nils Olof
>
> ------------------------------

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