Quote:
Originally Posted by nebulosity.
originally the idea was to use the usual timing belts and pulleys but I thought that if the camera is hanging down under the focuser it would try and slide the draw tube out and the motor (if not under load) will let it happen.
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hi Jo
This doesnt have to be the case.
if the roller pressure on the drawtube is sufficient, it would hold the weight. Id suggest testing this.
worm is a good idea but I think the mounting hardware to hold the worm in mesh might get bulky although I won't be surprised if you come up with an elegant solution.
Have a look at Steve's excellent clutch idea for his motorized focuser.
http://www.iceinspace.com.au/forum/s...stepper+clutch
I think a clutch is a very useful addition to the focuser.
you'd also need to think of the motor and controller.
will it be a motor with a gearbox, if so reduction would have to be quite high to keep the output revolution rate very low to allow fine focusing.
you'd have to use pwm to control the speed of the motor but may not have much range.
you could use a modded servo that has a gearbox built in, is very small and slow enough with an external worm or timing reduction, but quite noisy.
ideal option is a stepper either with a gearbox like the mclennan ones, or a 1.8deg stepper with your own reduction. you could use 1/16 microstepping to get a fine resolution but will require a reasonably sized motor to provide sufficient torque with microstepping.
printers have steppers that are ideal. look for bipolar ones.
finally, will this controller be ascom compatible for autofocusing or simple with just forward, reverse, fast, slow.
as for the focuser mounting, I'd strongly suggest to keep the profile as low as possible. you've got the focuser on the square brackets. that adds about 10 or 12mm to the distance to the secondary. the further you push the focal point, more the chances of vignetting. you'll also need a larger secondary.
keeping the focal point closer to the secondary allows for a smaller secondary, reduces loss of light at the edges.
Is there any way you could mount the focuser base behind the square tubes? that'll keep your focal point close.
Cheers
Alistair
is a cold night going to warp the scope or just move the focus? I was relying to the aluminium baffle to give some extra strength to the upper cage, but I do have some 1mm plastic sheeting that would probably be just as good and not expand as much?
I did have a wooden one that worked alright once but I need something a bit more solid for imaging 
Oh well, we will see how it go's.
