Re: ATM Friction roller drives

[andydtg@phoenix.net]

Adrian Peterson wrote:

>   How do I construct the 10" diameter wheel, I would like to have a plywood
>disk faced with Al, but how do I made a 'seemless' facing, this is needed on
>the Atz wheel to allow full sky coverage. Also how well would a 1/2" roller
>work with a 10" wheel? From the archives it seems like this would be pushing
>the limit. Andy made a comment in one of the messages that a smooth wheel with
>a chain drive would also allow manual movement, how is this accomplished?

I use plywood disks wrapped with 20 gage steel strip with my roller
chain drives, aluminum is a bit too soft. The 3/4" plywood disk is routed to
have a 3/8" deep by .4" wide groove on its edge, the steel strip is RTV'd
to the bottom of the groove, the edges serve to keep the 1/4 pitch roller
chain located on the steel strip. The ends of the strip are nailed
down with countersunk paneling nails.

The chain on the disk acts as a clutch by adjusting the chain tension
with an idler sprocket or by mounting the drive sprocket/motor on a
lever which allows adjusting the tension. The disk can slip
relative to the chain allowing manual motion, if the friction is set right 
the drive will rotate the disk for tracking or slewing.

Roller chain drives work ok for visual tracking but have too much slop
and quasi-periodic error for precision tracking for imaging.

PS I have been off the air for a week due to lightning damage
to my PC, modem, Fax machine, and Al Kelly's prototype alt-az-fp drive system
processor & encoders for his 17.5" scope. We got it running again, this
time with a double roller/disk drive, it works well enough
to take 2 minute unguided images with his CB245.

Andy Saulietis / DTG Alt-Az-Fp Drive Systems
HDPE Worm Gears, Custom designs & Machine work
12617 Harriet Ln
Santa Fe, TX 77510 USA
409-925-8854 Voice/Fax
e-mail: andydtg@phoenix.net