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BlueAstra

C8 SCT Motor Focusser

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I had a SW motor focusser that I used to use on my first scope. Since I sold the scope the focusser has been in its box waiting for a new home. After walking backwards and forwards from the computer to the scope to check focus for the 1000'th time I decided that focus should be integrated into my computer control system.

First was the mechanical attachment to the scope. I have a microtouch focusser replacement on the C8 main focus, so I made a small bracket to fit round the shaft. You could mod one of the brackets that come with the SW focusser, but I didn't want to spoil the supplied bracket. I went to a website www.motionco.co.uk to get a pulley wheel and belt, they have a useful calculator for belt length. I decided on a smooth belt so that I could use the focusser manually if necessary. This all fitted quite nicely on the scope with tie wraps, and the belt is taught enough to move the focusser and doesn't come off.

Next was computer control. I decided to use a Shoestring FCUSB module, which gives you power and USB control of the focusser. A range of cables are available for different focussers. I got this from OpticStar. This was recognised by the computer straight away, and the supplied FocusPal software controls the focusser, and there is an Ascom driver for Maxim, Focusmax, etc. I hooked it up and was quickly moving the focus from the computer! No more walks to check focus.

The total cost was about £80 for the USB module and cable, and the SW focusser was about £40 I think, about £8 for the pulleys, etc. So about £128 in total. Probably about half the price of a commercial motorised focusser. But the main advantage is way it has made setup much more easy.

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Continuing my quest to motorise the focus on both my scopes, I now turned to the Meade ED80. This time I found an old motor and gearbox assembly that looked ideal for the ED80. I checked it ran from the SW focus motor control box and set about making a curved Al bracket to hold it. A couple of stand offs were used to located the motor, and a shaft coupler fabricated with a couple of grub screws. I then got an old modem cable, cut it and soldered the wires to the motor, wires 1+2 to motor +ve, 3+4 to motor -ve. I removed the knob on the Meade focus shaft, and it now works a treat! Its connected to the computer by a Shoestring FCUSB module that gives me computer control of the motor focus. So I now connect this to whichever scope is on the mount.

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Edited by BlueAstra
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Well, you've inspired me Blueastra.

Armed with your enthusiasm I've bought a SW motor and rigged it up in a similar way to your original picture. I've used the shaft attachment that comes with the motor and a Dyson vacuum cleaner belt. It fits.

The movement is a touch coarse at the moment so I'm looking into dropping the voltage or using a Shoestring.

A couple of questions. Is the SK shaft 6mm ? Does the knurled shaft attachment eventually come off ? I've tried but it seems stuck fast. Did you prise it off without damage ?

Dave.

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Not entirely sure I understand your setup, but I assume you are using the SW focus motor to drive the original focus knob on the C8 SCT, similar to my original photo. The shaft of the SW autofocusser is 6mm. The motor speed can be slowed by a hardware mod, see this thread:

http://stargazerslounge.com/equipment-discussion/127471-skywatcher-autofocuser.html

There's also a video here on removing the knob from the C8 (not sure if thats what you refer to):

Feathertouch

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Hi again.

Thanks for the shaft size. The bit I'm referring to is on the SW shaft as it came in the box. I need to get it off before I can fit a smaller toothed wheel. The allen screw inside comes out but the knurled wheel won't budge. I think the shaft must be gnarled up, so short of getting a large screwdriver behind it, and risking damage, I'm as stuck as the Shaft is.

I don't have a C8 so I've attached a photo to show you what I've got out of this thread.

I'm going to try dropping the voltage but can't test until the cloud goes. Later in the year then :)

Dave.

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Ah, I see. The sw shaft sticks out about 10-15mm and I think it has a small flat on it. If you have removed the grub screw you should be able to force it off.

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Cheers for that. I think a Silver Back was employed to tighten mine up. I'll have another go once I've tried out the low voltage solutions.

For those that may be interested...... 9V rapid move. 8.4V no change. 6V seems good. 5 V seems better. 3 V doesn't want to move. Remember that's with a camera lens not a telescope.

Thanks once again for the ideas and links.

Dave.

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Nice mod, got a sw af and this gives me a chance to use it and still keep manual control, thanks.

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This is a great thread, I'd like to do this for my C8. Where do you get the SW motor from?

Pete

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I have the Skywatcher and a Lakeside, Both great, although the lakeside is much better.

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