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Windows Driven Stepper Motor Focuser

Shelster1973

By Shelster1973
in DIY Astronomer

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Shelster1973

Shelster1973

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Just wondered if anyone has come across one of these?

Saw a mod / hack where you can use two reolvers wired togetrher to give a battery-less focuser drive, but was wanting to go one step futher and be able to control the focus from laptop.

The ones that I have found so far seem OK, but not exactly what I am after.  They are all centred around running for a number of steps in a sequence...ideally I would like to be able to have the motor move one step on the press of a button in real time.

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Shelster1973

Shelster1973

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I have just made a PC controlled stepper motor addon for my C8 using one of these:

http://www.pc-control.co.uk/control/products/packs/mini-stepper-pack.php

I can let you have a copy of the ASCOM driver & test application if you want it.

James

Looks good...may have a look at getting one of those.

Did you use any reduction gearboxes to get a fine control?

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james_screech

james_screech

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Looks good...may have a look at getting one of those.

Did you use any reduction gearboxes to get a fine control?

The motor in the kit already has a gear box, so you get 2048 steps per revolution of the output shaft. I put a 35mm diameter wheel on the output shaft and used this as a friction drive onto the focuser (rubber removed) on my SCT. If the information I found on the web about the pitch of the thread on the SCT focuser is correct (0.75mm pitch thread) then I get about 1 micron mirror movement per step. As the main mirror is F2 it's critical focus range is about 12 microns so I get more than enough steps without further gearing.

James

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AstroAdam

AstroAdam

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I have just made a PC controlled stepper motor addon for my C8 using one of these:

http://www.pc-control.co.uk/control/products/packs/mini-stepper-pack.php

I can let you have a copy of the ASCOM driver & test application if you want it.

James

That looks good.  How did you mount it to the back of the c8?  As it's ASCOM controllable, I may be looking at investing in one of these.  Is it easy to get anything that's ASCOM focuser compatible to control it?

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james_screech

james_screech

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That looks good.  How did you mount it to the back of the c8?  As it's ASCOM controllable, I may be looking at investing in one of these.  Is it easy to get anything that's ASCOM focuser compatible to control it?

I mounted a piece of 0.8mm x 51mm strip brass on two of the three screws around the base of the focus control. Then mounted the motor on this using screws and nuts to lift it to the required height. When I get some time I'll take some pictures and write up the project and post it in the SGL DIY section.

The driver I wrote only supports the ASCOM relative focuser mode, unfortunately I had problems with an absolute driver. I'm not sure if the issue was my code to get around the 16000 step limit on the StepperBee card or the motor missing steps, one day I may try again.

The driver should work on any software that supports ASCOM relative focusers, it certainly works with my test application and APT. However it does not work with Nebulosity, but Nebulosity doesn't work with the ASCOM focuser simulators either, so I assume this is a Nebulosity problem.

James

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  • 5 months later...
Shelster1973

Shelster1973

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Just a quick update (well, quick for me I suppose)

Have finally got round to getting the StepperBee (actually is the + version which I got on here in the classifieds) and also the stepper motor.

All is working great and can control it fine from within BYN.

Many thanks James for the driver.

Next step is mounting the motor onto the OTA and running a band to the focuser.

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  • 2 months later...

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