Installed SharpSky auto-focuser on my SCT

[ChrisLX200]

I bought the SharpSky kit to motorise the focusers on my 10" SCT and my (as yet undelivered) new refractor. The kit consisted of one controler and two motors, the assumption being that I would never be using both those scopes at the same time - simply not possible on my current mount anyway due to the weight - so I only needed one controler rather than two. Dave can supply a second controler with modded firmware if two controlers need to be run simultaneously. Anyway, this is the first scope: a 10" Meade LX200 classic fitted with a Revelation add-on rack & pinion focuser.

I really wanted to avoid having the motor mounted as a direct drive which would necessitate the motor sticking out of the side of the scope by a long way. Also, by using a toothed belt drive the torque could be increased by gearing down using different sized pulleys, this offers increased torque and hence robustness of the focusing action. 'Lost' steps are the bane of stepper motor systems without an encoder to physically indicate rotary position. For the motor mounting I milled out a simple bracket to attach it to the underside of the focuser, I avoided drilling holes in the focuser by having it clamp to the sides of the focus spindle housing. A total of six grubscrews holds the bracket in place as seen in the photos.

The pulleys needed to be bored out to suit the motor shaft (5mm) and a split-collet arangement made for the thin 10:1 fine focus shaft to mount the second pulley (this shaft was 3/32" diameter - the imperial dimension because it was of American manufacture I think). I still intend to make a quick-release clutch mechanism to aid rapid manual focus adjustment, at the moment there is an electronic 'manual' adjustment via a small handset but I like the idea of quickly disengaging the motor drive as needed. This will be another collet arrangement with a closing screw - working very much like a milling chuck. At the moment though I just want to get the thing up and running.

This is the complete motor and focuser assembly mounted on the scope, I'm pleased it turned out to fairly compact - the motor was a little larger than I expected!

The controler box I attached to a short pier extention I made a long time ago (it houses a 12>18 volt converter and  batteries for the illuminated reticle of the polar scope). The extention also has a couple of brackets to hold the Gemini control box. For the SharpSky I just milled out a block of alloy to a radius to fit the side of this extention, bolted it in place, then used a couple strips of industrial Velcro to hold the box onto it. It's neat, out of the way of other stuff, and convenient to attach cables to (the SharpSky also offers 4 channels of Dew Heater output, all remotely controled via the PC).

Naturally I can't test the auto-focuser in anger due to the unending awful weather, but everything seems to work in simulator mode. I'll update when I get chance to test the automatic focusing routien via SGPro.

ChrisH

[sbooder]

What you need there is some more cables!

[ChrisLX200]

What you need there is some more cables!

You think that's bad - you can't see all the USB cables coming out the Hub mounted on the back of the Gemini controler! 

ChrisH