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DIY Motor focus

fwm891

By fwm891
in DIY Astronomer

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fwm891

fwm891

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I spent today building a pulley / belt geared drive for my MN190 focuser. It's an old style focuser having only one speed.

One of the focus knobs was removed and a replacement sleeve made to take a small bearing and the larger pulley. Theres also a friction clutch arrangement allowing me to disengage the motor drive and use the focuser manually to get an approximate focus before re-engaging the drive.

The pulleys (15T & 60T) give a 4:1 reduction from the 0.9º step stepper motor.

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DIYASTRO

DIYASTRO

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Very neet!

May I ask where you obtained the belt pulleys etc. (Motionco or HPC gears perhaps)

Also what stepper Motor driver you are using would be helpfull?

Nice neet little job though and I am sure you will get the benifit from your labours. Its never as easy as the photo looks is it!

Kind Regards

Boyd

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Gina

Gina

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I'm doing much the same myself, also with a Maplin Motor/gearbox but without the worm drive. I like your hinge and spring arrangement to disengage the motor drive for manual focus - very clever :icon_salut:

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fwm891

fwm891

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The pulleys and belts are from Motion Co.

Thanks for the comments

As for control I'm working with someone else on the group (who likes electronics!) with the intention of using an arduino and Easydriver stepper driver board then focusmax or similar

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FrankieValley

FrankieValley

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As for control I'm working with someone else on the group (who likes electronics!) with the intention of using an arduino and Easydriver stepper driver board then focusmax or similar

Please let us see the results.

I'm doing much the same myself, also with a Maplin Motor/gearbox but without the worm drive. I like your hinge and spring arrangement to disengage the motor drive for manual focus - very clever :icon_salut:

Gina, in case you're interested, I upgraded the manual control box to use this, which gave me variable speed in the direction selected by the toggle switches - Panel Mounted Speed Regulator Module : Motors & Gearboxes : Maplin Electronics

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chrisshillito

chrisshillito

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Theres also a friction clutch arrangement allowing me to disengage the motor drive and use the focuser manually to get an approximate focus before re-engaging the drive.

Very nice Francis

If you want manual focus can't you just disengage power to the motor coils? I have a button (both physical and on the PC driver interface) that tells my focuser firmware to do that.

Chris.

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fwm891

fwm891

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Very nice Francis

If you want manual focus can't you just disengage power to the motor coils? I have a button (both physical and on the PC driver interface) that tells my focuser firmware to do that.

Chris.

Chris,

The idea was two fold: one, to have a quick-n-easy focus adjustment at the scope. Two: was more from a cautionary point of view in that by leaving the belt/motor engaged physically, any manual rotation of the focuser would rotate the stepper four times as fast! Rotating the stepper motor causes a voltage to flow back into the stepper driver board which may cause damage there. So by disengaging the belt drive I avoid the voltage generation back into the driver board.

I suspect it won't get used very often but its there if needed and didn't entail much extra machining (just the fancy brass knob rather than a machine screw and washer).

Francis

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Merlin66

Merlin66

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I think what you've achieved in your set-up is inspiring!

Just shows what can be done....

I, like many other, have re-used the DC SW focus motor to provide excellent remote control of focusing.

Well worth considering, for those on a budget.

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fwm891

fwm891

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Hi Neil, There's nothing much to the design. I replaced the original focuser knob with a sleeve that clamps to the focusers friction roller shaft (as per original), a little bearing to isolate the sleeve from the mounting panel, the large pulley and something to push (force gently!) the pulley against the inner half of the bearing and that against the sleeve. Once tight everything rotates together. Slacken the brass knob and you release the large pulley and any rotation of the manual side of the focuser is not transferred to the motor...

Once I knew the position of the motor relative to the the focuser body and the plate fixing points it was simple job of drawing round the component parts and cutting the mounting plate to shape.

I have used existing fixing points on the focuser where possible and only had to drill and tap one extra hole in the focuser's base plate.

Virtually everything was done on a small lathe with minimal tooling.

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