Re: ATM Re: Worm Fabrication

[PFAFF2@delphi.com (Robert C. Pfaff)]

>
>Here's what we came up with & invite comments/criticisms,
>even flames :(
>
>Build a 1 axis platform with a *long* known radius sector
>on it & drive it with a *good* leadscrew/tangential thin metal belt with
>an accurate crystal controlled stepper, with << 0.1 arc sec steps.
>At most it would only have to move about 5-10 degrees. The rate would be
>about 10x sidereal. This would produce an accurately known angular rate with 
>virtually zero periodic or scale factor errors.
>
Andy Saulietis / DTG Alt-Az-Fp Drive Systems

Hi Andy
I not sure I follow the scenario but here is a tip on
how I made accurate lead screw drive to pull a thin steel belt
to drive a telescope. I  cut the lead screw into, rotated  1/2 of the lead
screw 180 deg. with respect to each other. The screws were built into
a frame asm. parallel to each other. They were loaded against a single
balls on there ground ends. A nylon block that acted as a double nut
would run up the parallel lead screws. The lead screws were driven
by a gear that drove a gear on each lead screw. the lead screws stayed
in sync. Now the steel tape was attached half way between the lead
screws in the center of the nut block.

This drive had a differential action. The center of the nut block would
 null out. Any lead advance error in one screw
would be canceled by the retarding action othe other screw. This
is assuming the lead error in the screw is constant:-(

I guess you could use 3 section of a lead screws 120 deg. out of phase
and be even more accurate :-) A triangle nut block with the steel tape
attached at the center of the triangle.

This whole thing is probably over kill but just thought I would
throw it out for thought.

Good luck
Bob Pfaff