Re: ATM Earl of Crawford mount - HELP

[astrojoe@erols.com]

Thanks Dwight,

As I supected, wrong altaz design for this type of drive. I guess it
should work in a normal (axis over axis) design.

Thanks to all who helped out.

Joe Castoro





Dwight Elvey wrote:
> 
> astrojoe@erols.com wrote:
> > Any ideas as to why it is not working right ? One design difference is
> > that my DOB mount is for a refractor and has it's altitude axis in back
> > of the azimuth axis by 7". Could this be why it is not tracking on the
> > proper sideral arc ?
> >
> > Joe Castoro
> 
> Hi Joe
>  In order to work right, a line from the center of the
> altitude bearings to the arm that hangs out from the base board
> must be right on the celestial pole ( assuming the
> azimuth bearing is right under the altitude axis ). Without
> some kind of alignment scope, I doubt one could get the level of
> accuracy needed to track a 0.7 degree spot across the sky ( typical
> size of 70X image). If the altitude axis wasn't right over
> the azimuth bearing, I don't think this method would work
> correctly.
>  Try changing the length of the extension arm on the
> base board slightly to see if you are just slightly off, long
> or short. Also look at stars on the East and West side. If
> they drift the same way, you are not pointed right in azimuth.
> Dwight