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Old 31-05-2018, 03:37 PM
skymuster (Mike)
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Autfocussing on a budget with Skywatcher motor focus

I'm exploring the option of adding a motorised focuser to my Skywatcher 250 newtonian. I currently use Sequence Generator Pro for my imaging and would love to be able to explore its autofocus feature to keep it in focus during an evening's imaging session.

I see Skywatcher sells a cheap DC motor add on kit, and you can add the Shoestring controller to allow you to control it via ASCOM however I'm keen to hear people's thoughts from anyone that has this setup and how successful it has been. From reading up on SGP's autofocus feature it looks like it's designed to run with the more expensive stepper motor focusers however with FCUSB I understand that pulses sent to a DC motor can be used, albeit not so accurately.

So, long way to get to my question, but will I be able to use the $99 Skywatcher motor focus unit plus the Shoestring focus motor controller be able to perform autfocussing in Sequence Generator Pro?

Thanks,
Mike
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Old 31-05-2018, 05:49 PM
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xelasnave
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I have a cheap electric focus which is a little better than manual focus but not always strangley..sometimes manual works better fir me...but if you have to come back it suffers from what I guess you would call backlash.

ITS probably good to try one out but it seems the reality is if you are going to get serious you need to set your sights higher.

And be lrepared to pay more for the real deal focuser than you paid for your ota and maybe your mount...

However I get resonable focus but if you want to have it respond to temp change well all I can say is have a look of what you can spend.
Alex
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Old 31-05-2018, 06:30 PM
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redbeard (Damien)
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I think you will need a stepper motor if you want precision. And precision is what you need for autofocus generally.

Good luck
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Old 01-06-2018, 07:02 AM
tim.stephens (Tim)
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Try this ascom project:

https://sourceforge.net/projects/ard...?source=navbar

I did this about 2 years ago and it works brilliantly. Bought a 400 steps/cycle stepper motor from a local supplier and it's sufficient to get critical focus on my scope with half stepping. Having said that, I would suggest getting a geared motor for the extra torque and resolution. They are a little more expensive but worth it if you have a fast scope and/or small pixels to achieve critical focus.

You'll have to make a bracket for your focuser. I just made mine out of some aluminium L brackets and bolts from the local alu supplier. Also, you'll have to work out a way to attach the stepper motor to the craford. I used a 5mm axle connector to directly drive the craford mechanism from the motor - it seems to be the most secure and backlash free option.
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Old 01-06-2018, 10:28 AM
Russj (Russ)
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+1 for https://sourceforge.net/projects/ard...?source=navbar

I've built 2 of these now, total cost with a geared stepper is around $120.
But..... you will need some basic experience in assembling circuitry and wiring.

Rob has an excellant 100 page manual for assembly and setup d/l here
https://sourceforge.net/projects/ard...2.pdf/download

If your are interested in building one I have a spare circuit board.

The focusers works flawlessly, best addition I've made to my setup.
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Old 01-06-2018, 03:36 PM
skymuster (Mike)
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Thanks for responses guys. It sounds like a stepper motor solution is going to be the way to go rather than kluging together a DC motor solution to look like a stepper motor…

@Tim, Russ - I recently made my own dew heater controller so embarking on a project like this could be a lot of fun! I’ve been looking for an excuse to get into Arduino stuff 😊. Just need to hone my engineering skills so I can get a nice smooth mechanical connection with maximum precision / minimal backlash….

@Russ – I would definitely be interested in your spare PCB. I’ll PM you!

Do you have any suggestions on where to source an appropriate geared stepper motor?

Cheers,
Mike.
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Old 01-06-2018, 04:05 PM
Russj (Russ)
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[I]Do you have any suggestions on where to source an appropriate geared stepper motor?

IThe manual I mentioned has links to most items you will need on ebay, this manual is one of the most complete documents I've ever built off, Bob updates it every month or so.
He also has links to Youtube on setting up the focuser.

Cheers Russ
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