Re: ATM Roller position, Teflon bearings

[Aplanatic@aol.com]

Shane LaPierre wrote:

> As a follow up to this question, has anybody ever tried to use the standard 
> dob components for this axis on a split ring (teflon on  ebony star) instead
> of rollers?  It's something I've been thinking about trying, and the same
for 
> the
>  southern end, with additional teflon "thrusting" the axis towards Polaris. 
> The only drawback I can see immediately is it takes the easy of attaching a 
> stepper without reverting back to rollers, but it seems it would be 
> inexpensive and easy
>  for anybody to do.

On my split-ring equatorial, I first tried Teflon on Aluminum as the bearing.
In my opinion, there was way to much "stiction" in this arrangement.  I
changed to a roller bearing before trying to drive this with a motor.  I
spaced the rollers 80 degrees apart on this mount and it worked very well.  

When I made a similar style mount for my Slevogt camera, I spaced the rollers
70 degrees apart and this seems to work very well also.  I have recently been
performing tracking tests on this mount using an ST-4 autoguider and have
found no problems at all in this approach.  I used very small rollers (5/16"
diameter stainless steel, precision ground) to achieve a large final reduction
ratio.  If there is slippage in this design, it doesn't affect the performance
at least at the level that can be detected by tracking studies.  However, I
would not use the drive shaft roller to make RA position measurements but
would favor using the polar axis itself to drive an encoder.

Dave Rowe
Torrance, CA