Quote:
Originally Posted by tnott
Bojan how accurate is your system? It looks a bit more heavily engineered than what I had in mind. Also the ALT roller would need to ride on the ebony star laminate of the ALT bearings - which is very slippery.
Tim
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It is quite good, I do not have more that 1-2 steps difference when going to and back 90 degrees couple of times.... The sensitivity I have is ~6000 steps per 360 degrees of the telescope axis rotation which is enough to give me reasonable accuracy for visual observations for the night.. If I need to have it more accurate, I can always point to the desired object and reset coordinates (in my Bartelized system) .
As you saw on the images, I am using al wheels as bearings on which the tube is riding, and the small grit-wheel is spring-loaded upwards onto the ALT bearing so I can remove or place the tube into cradle and ALT encoder is automatically decoupled or coupled.
In your case, you can have the slippery stuff covering only part of the thickness of the ALT bearing, and the rest (without ebony star laminate) can be used for riding a wheel... Or you can attach the bigger or smaller sector wheel on one of the bearings for encoder roller in parallel to the bearing.
I think the slippage errors they are talking about are inevitable with rubber wheels. Grit-wheel is different.. on the high pressure it will press-in its own path into softer material of the bearing and this will act as a gear... and no significant slippage.
You can make one by wrapping around the existing wheel the tape cut from sand-paper and gluing it on.
Or, you can apply the araldite on the wheel, then pour on this a sand particles obtained from sand-paper.. When the glue is set, simply remove the sand which is not firmly attached and you have a grit-wheel.
Have you considered chain option? There is no slippage here either... It may be a bit more fussy to assemble the scope for a nigh but worth a try...
Or, toothed rack, wrapped around the bearing (or additional sector). Then, you can have a gear on the encoder axis...