Mounting a Skywatcher focus motor to an Esprit 80

[Stu_2011]

Hi

I wanted to mount my Skywatcher focus motor to my Esprit 80 mm so had a play around with bits lying around and after various different combinations I found a good setup.

Parts needed:

Skywatcher focus motor - £50

Celestron dovetail - £40

85 mm ring O-rings - £3

Drive wheel of some sort for the motor, I modified a plastic focus wheel from a old Skywatcher focuser but you can buy similar wheels for not much money. The drive shaft on the motor is 6 mm

The pictures explain it best - it all went together really well and it seems to work very well. The holes on the Celestron dovetail match the holes on the Esprit dovetail perfectly. Apart the drive wheel I didn't have to modify anything, it just all bolted together.

The O-rings pop off really easily so you can get close on manual focus and then attach the O-rings.

I have one of the HitecAstro PC driver kits so can control focus from my PC now.

Thanks

[Bizibilder]

A nice neat set-up.  Just one thought is that O rings can snap (usually on a clear night / bank holiday!!) so it may be worth getting a small timing belt like these:  http://www.motionco.co.uk/timing-belts-timing-belts-c-25_38_27.html  They have ample grip on the knobs you are using and last forever in the application.  They only need to be "just" tight and will drive without slip.  They can also be easily slipped on and off if you want to "twiddle" manually - especially useful for coarse focussing when changing eyepieces/cameras etc.

[Stu_2011]

A nice neat set-up. Just one thought is that O rings can snap (usually on a clear night / bank holiday!!) so it may be worth getting a small timing belt like these: http://www.motionco.co.uk/timing-belts-timing-belts-c-25_38_27.html They have ample grip on the knobs you are using and last forever in the application. They only need to be "just" tight and will drive without slip. They can also be easily slipped on and off if you want to "twiddle" manually - especially useful for coarse focussing when changing eyepieces/cameras etc.

Thanks, I will look at the drive belts. I got a pack of 20 O-rings so have spares. They are cheap nitrile rings of eBay so yes I'm sure the long term durability wouldn't be great. The O-rings aren't tight at all, maybe a 5 mm stretch. How much stretch do the belts have? This arrangement doesn't have much height adjustment so went for O-rings that could be stretched slightly to compensate. I guess the belts are pretty rigid but I could be wrong??

I work near a proper O-ring shop so I might get some Viton or other fluro-polymer rings, much better life than nitrile.

Thanks

[Bizibilder]

The belts don't stretch at all but you need zero tension - just enough to stop them falling off will do!  You have more than enough adjustment in the motor mounting slots - once set up there should never be any need to adjust things.

[JamesF]

Looks suitably neat

There are lots of variations on this theme depending on how complex you want to make it.  I used a timing belt for mine and incorporated a "clutch" mechanism (not my idea originally so I don't have to remove the belt to turn the focuser by hand.

James

[Stu_2011]

Looks suitably neat

There are lots of variations on this theme depending on how complex you want to make it. I used a timing belt for mine and incorporated a "clutch" mechanism (not my idea originally so I don't have to remove the belt to turn the focuser by hand.

James

Thanks James, I have a mill and lathe and was drawing up a more complex design with belts and adjustable brackets etc, then one day I was sorting out stuff and realised that a simple approach might work - something satisfying about bolting a bunch of bits together in non standard way and finding that it just works.

Not everyone has access to milling / turning tools and the advantage of this approach is that you could buy all the bits and bolt straight on without having to make or adapt anything..

Stuart

[Sp@ce_d]

I still haven't got around to fitting a stepper to mine so was looking around for ideas & google found this thread.

Not wanting to put a damper on it Stuart but I take it you wont want to rotate the focuser at any point?

That's the problem I came across so it has to attach to the focuser or be light enough to hang directly off the end. All the motors I have are a bit heavy for that. I've been putting off stripping the focuser down hoping someone else had cracked it first

[Gina]

The stepper motors I use are very light - just 35g (I've just weighed one ).  Type 28BYJ-48 available in either 5v or 12v versions.  I find them ideal for focussing   And they're very cheap.

[Sp@ce_d]

The stepper motors I use are very light - just 35g (I've just weighed one ).  Type 28BYJ-48 available in either 5v or 12v versions.  I find them ideal for focussing   And they're very cheap.

Hmm does this mean I have to do the Arduino learning curve now then Gina..

Have you fitted this to your Esprit?

[Gina]

Hmm does this mean I have to do the Arduino learning curve now then Gina..

Have you fitted this to your Esprit?

You can copy someone else's sketch if you don't want to learn Arduino.

Yes I have fitted one to my Esprit.  The Arduino sketch is the one that uses 5 push buttons to control it.  I'll see if I can find the thread.

[Stu_2011]

I still haven't got around to fitting a stepper to mine so was looking around for ideas & google found this thread.

Not wanting to put a damper on it Stuart but I take it you wont want to rotate the focuser at any point?

That's the problem I came across so it has to attach to the focuser or be light enough to hang directly off the end. All the motors I have are a bit heavy for that. I've been putting off stripping the focuser down hoping someone else had cracked it first

Hi

I thought about this issue but for the Esprit it's not a problem in my view. The Esprit has both focuser and camera rotators.

The focus rotator is so that you can move the focuser into a more convenient position for manual focusing when on an EQ mount, as it's now motorised I'm not so worried about access to the focus controls. The camera rotator is on the end of the focus draw tube so I can still frame easily.

I was testing this last night with the Hitec Astro USB focus unit and it seemed to perform flawlessly. FWHM tweaking within Artemis capture was so easy. I did a test where I found a good FWHM focus, drove the focus right out and then back again and it came back to same FWHM value.

It's not a stepper motor but as I had all bits lying around I'm pleased with the result.

Cheers

Stuart

[fondofchips]

Thanks to Stu_2011 for the pictures and Bizibuilder for the information on motionco pulleys and belts.  http://www.motionco.co.uk/cd_calc.php?submitted=2&tooth_type=2.032&pulley_one=16&pulley_two=36&length=120

My arrangement here, very similar to the one above, except using a motionco pulley and belt and a 40mm x 6mm flat aluminium bar mounted in the gap between the dovetail and the AZ EQ6.  

This nicely finishes off my Video Astronomy setup. I have used the HitecAstro DC Focus controller with it. FLO do a bundle pack with the SW focuser and HitecAstro controller, £5 off the pair. The belt still slips off easily to allow quick changes of focus travel.

Cheers & Clear Skies.

Fondofchips.