Re: [TASS] Inexpensive drive idea

[Tom & Lou Krajci <krajcit@3LEFTIES.COM>]

From: Tom Droege <droege@WWA.COM>


>Very nice.  I am curious about how well you can do.  It has been a struggle
>for me to get down to a few seconds of arc.  I do not do periodic error
>correction.  I have a 12" machined radius.  This is then driven by strings
>from a lead screw.  The break through to get down to a few seconds was to
>use a follower on the lead screw made from chamois.  I engage about 3" of
>the lead screw, so the chamois averages the errors in 60 turns of the
screw.


Sorry for the delay in response, I had some other mechanical drive issues to
work before I could do PEC analysis.

My azimuth worm gear requires about 45 arcseconds of PEC.  (Why so large?
Probably because I've taken no steps to make sure the worm is
accurately/concentrically coupled to the motor shaft, also the worm is a six
inch length of nylon threaded rod...that is not perfectly straight.)
Residual drive error at the eyepiece is between 5-10 arcseconds peak-to-peak
after PEC is applied.  (I suppose if I made more mechanical adjustments to
the worm I'd have less initial error to deal with, and could probably get
even better with the software corrections.)

The elevation sector's performance?  Without PEC it's error is about 5-10
arcseconds peak-to-peak.  I have not yet tried to fit a PEC curve to this,
but might do that the next clear night.

Not bad for JB-Weld molded worms and nylon threaded rod worm gears!

Tom Krajci