Re: Big Wooden Circles (Was Re: ATM: Regarding new ATMs)

[Brad Davy <bdavy@bigdog.fred.net>]

At 03:13 PM 2/25/97 -0800, Matt & Belinda Tarlach wrote:

>Regarding the suggestion of closet flanges as altitude bearings,
>experience with my 8" suggests using something with larger diameter
>would be well worth the trouble.  My scope uses these and has a
>persistent wobble in altitude that takes 4-5 secs to damp out, compared
>with less than 1 sec damping in azimuth.  I've been over the entire
>mount and have to blame it on the skinny flange altitude bearings.

I'll be curious to see if I have this same problem.  I used the PVC flanges,
and they seem quite robust, with no apparent wobble in the flange itself.  I
cut 90 degree V's in the rocker box and mounted two "Magic Glide" teflon
pads in each V to rest the pipe portion of the closet flange on.  When
balanced, the entire assemble moves very smoothly, with no apparent wobble.

Something to think about on the wobble.  Weights at the end of the tube are
more likely to cause wobble due to inertia.  We used to fight this problem
on Submarines.  If the sub was ballasted to heavily toward the end, it was
more difficult to counter angular movement.  I think its probably useful
when adding counter weights to add heavier weights near the balance point.
You might try that to help damp out your wobble.
Brad
bdavy@fred.net               http://www.fred.net/bdavy/home.html
bdavy@nox.cs.du.edu