Revelation/Skywatcher SCT dual speed R&P motor drive conversion

[JamesF]

Last week I finished modding the Skywatcher motor drive kit to fit my Revelation dual speed crayford that I'd previously modded to fit my PST.

Part of the reason for doing that was as a trial run for doing a similar mod  to the Revelation dual speed R&P focuser that I have on my C9.25.  This is a little more awkward to fit the motor to because there's nowhere on the bottom face of the spindle housing to bolt a bracket to.  The mounting points are in recesses in a part of the housing that is stepped back from the base.

I've seen ChrisLX200's mod to fit a motor to this same focuser by using a U-shaped bracket and grub screws to pinch on the sides of the spindle housing, but I decided to go slightly different route, using the existing housing mounting points with some longer allen screws and spacers to mount a simple L bracket.  In fact the spacers probably aren't absolutely necessary but I decided to make them because I could.

So, first steps were to make up the motor mounting bracket from 2mm steel plate, buy some 35mm button-head allen screws from ebay and make up three spacers from 8mm aluminium round bar:

This fitted nicely using three of the four existing mounting points just by replacing the screws.  The new screws protrude about 4mm into the focuser housing and don't appear to obstruct anything:

The two motor mounting holes were drilled and tapped to M4 which meant I could use the existing fittings to mount the motor:

And from this point on it was pretty much the same as the crayford mod.  I bought a 90mm MXL belt and matching 25mm timing gear from motionco, dug a 6mm wingnut out of my odds-and-ends boxes and turned up an extension for the motor spindle from brass:

The grub screw in the brass extension holds it in place on the 6mm motor spindle though it was quite a snug fit anyhow.  I removed the grub screw from the timing pulley so it's free to spin on the smooth part of the extension (also 6mm diameter) unless the wingnut is done up right, thereby creating a clutch mechanism that allows the focuser to be moved by hand if required.

Here's the everything completely assembled:

All I need now is an end to the weeks of cloud so I can actually get out and use it.

James

[rob0971]

Well done James, very good write up. Might have to do something similar. Thanks for sharing.

[ChrisLX200]

Good job James. I still haven't tried mine out yet due to lack of clear skies, a clear night is so rare I don't feel like 'wasting' it playing around so I use the refractor to capture image data. When the lighter nights unsuitable for imaging arrive I'll be able to test the setup.

ChrisH

[JamesF]

That's the really galling thing at the moment, isn't it?  If you could be reasonably sure there'd be another clear night along in a few days time then spending the odd one or two experimenting and tuning would be fine.  When the weather is so awful that even once a month seems like an unrealistic target it's tempting just to leave things as they are and get the most use out of what you already have.

James

[Tinker1947]

Nice job James, and yes the weather got my modded 600D and used it once in 3 weeks....

[sbj]

Fantastic James, just what I need.

When are they going into production?!

[kingboya]

Here is my effort. I went for the direct drive method because the focuser is only used for final fine focusing. The bracket was made from a piece of 4mm thick aluminium plate, and measured precisely to fit. I then bent the 90 degree in a vice, with quite a tight bend, so was pleased. <br />

Lastly, I tapped M4 threads in the bracket so I could use the originally supplied thumb screws for attachment. <br />

<br />

All I need now are replacment bolts to secure the bracket to the focuser. It works like a charm! <br />

<br />

[JamesF]

Excellent

I seem to recall the bolts I used for mine were 35mm stainless M3 domed hex screws that I bought from boltbase or someone similar on ebay.  Unfortunately the order confirmation doesn't give anything but the thread size.

James

[ChrisLX200]

Well done. I used mine for the very first time last night and it also works great for autofocus. With the gearing I have there are 50,000 steps for full travel of the focuser allowing plenty of lattitude for fine focusing.

ChrisH

[kingboya]

Thank you both very much for your help and inspiration in this little project! I love the astronomy community for the diy jobs and help we give each other!

[Stargazer33]

Very neatly done James.

Much better than using ty-raps like I did to secure my motor housing bracket!

[kingboya]

Very neatly done James.

Much better than using ty-raps like I did to secure my motor housing bracket!

Cable ties have their uses! Out of interest, is that a homemade dessicant cap in your SCT? If so, what is it made from?

[JamesF]

Very neatly done James.

Much better than using ty-raps like I did to secure my motor housing bracket!

It's certainly not the easiest of focusers to fit a motor bracket to.

James

[Stargazer33]

Cable ties have their uses! Out of interest, is that a homemade dessicant cap in your SCT? If so, what is it made from?

It is indeed. Believe it or not it is a screw top tub that contained mixed nuts I think and a 35mm film container. Original post here:

[kingboya]

The completed job. The stainless M3 bolts came today, but were not hex head, but no probs. The motor is free running, so fine wobble free focus is here. Just for the clouds now!

[kingboya]

The completed job. The stainless M3 bolts came today, but were not hex head, but no probs. The motor is free running, so fine wobble free focus is here. Just for the clouds now!

And now for the photos!

[michael.h.f.wilkinson]

Just found this page. Just what I need to convert my Revelation SCT R&P focuser. Should really make life easier for planetary imaging