Re: [ATM] Worm mounting

["Don Clement" <clement.focuser@verizon.net>]

> I have currently finishing a large gem and am at the point of mounting the
> worms. I'm trying to decide whether to mount the worms in a fixed (but
> adjustable) mount, or on a carrier that is spring loaded to minimize
> backlash.

IMO, the worm would be best spring loaded against the worm gear. Worm and
worm gear are extremely sensitive to bearing runnout and form a single point
contact on an angled surface. Any runnout (and misalignment) will cause a
drive ratio change. Spring loading may help with this. My belief is that a
worm-worm gear is not the best mechanism for the final reduction of a
telescope drive. Other final drive mechanisms such as band drive, cable
drive or flexible rod drive offer more than single point contact (averaging)
with more immunity to runnout and manufacturing artifacts. See:

 http://mysite.verizon.net/res0owmd/id4.html Periodic drive errors from
bearing runnout and misalignment can be somewhat compensated for, but random
manufacturing artifacts (and/or dirt contamination) are much harder to
compensate for in an open loop drive. Closed loop systems require some
detectable error for compensation, so it is best to start with most linear
error free drive possible.



Don Clement

Running Springs, California

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