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Best motor for DIY DC motor focus unit

Astroboffin

By Astroboffin
in DIY Astronomer

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Astroboffin

Astroboffin

Posted
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Hi,

Am looking to build my own motor focus unit, and there are many different mini 12v DC motors available and some are already geared down with there own Mini gearbox fitted, so what RPM do I need, I have found one that is 5 RPM, but seems very slow.....

Does anybody know the actual specs of the Skywatcher DC motor, including RPM at 12v and power draw in amps..

Also I plan on fitting directly to my focus shaft with no extra gears or belts in between, so one turn of the motor will be one turn of the focus shaft, and the one I have seen at 5 RPM will mean one revolution every 12 seconds at 12v, does that seem either too slow or too fast.......I can't make my mind up, bearing in mind that the controller will be using a PWM to power it, so at say half speed of 6v that will be 24 seconds per revolution...and so on..

Any info much appreciated

Regards

AB

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faulksy

faulksy

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Have you looked at servo drives, might be a good option, you can link 2 together, if you get the same potential Thelwall drive each other. Excuse the speeling as um ok n hols and a bit drunk. If you turn 1 out put the other will turn with no Ower needed. 1 will generate power from emf and power the other. If non of thjs makes sense, pm me and I will be happy to help

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Astroboffin

Astroboffin

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Have you looked at servo drives, might be a good option, you can link 2 together, if you get the same potential Thelwall drive each other. Excuse the speeling as um ok n hols and a bit drunk. If you turn 1 out put the other will turn with no Ower needed. 1 will generate power from emf and power the other. If non of thjs makes sense, pm me and I will be happy to help

Hi,

I have seen this option while surfing the net, maybe it was your website or blog I saw it on

Anyway enjoy your hols....

Regards

AB

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r3i

r3i

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I used one of these when building a motorised focus unit for my Skymax180:  http://www.ebay.co.uk/itm/New-DC-6V-12V-8-16RPM-Long-Shaft-Turbine-Worm-Gear-Motor-Slow-Reduction-Gear-Box-/161634173562?pt=LH_DefaultDomain_3&hash=item25a225c27a - not sure if it will be suitable for directly driving your focus knob.

I used it together with a couple of pulleys and a belt and I reckon the focus knob turns at something like 2-3rpm.  I control it using a Shoestring FCUSB Controller though I'm sure there are cheaper ways of controlling it, especially if you're a dab hand with electronics (I'm not).

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Astroboffin

Astroboffin

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Im about to attempt the same thing - just waiting a couple pulleys and a belt. The motor i went for is 3.5rpm, but i got a speed controller as well for fine focusing.

This is the motor i got - http://pages.ebay.com/link/?nav=item.view&id=390993664036&alt=web

That motor looks practically identical as the one used in the Sywatcher auto focusers that are available, interesting thanks

Regards

AB

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Dr_Ju_ju

Dr_Ju_ju

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Have read through this thread http://stargazerslounge.com/topic/218975-arduino-ascom-focuser-mark2/page-1?hl=+arduino +focuser in which TekyDave uses a simple Arduino Nano that drives an eBay cheepo driver\motor configuration (http://www.ebay.co.uk/itm/High-Quality-5V-Stepper-Step-Motor-Driver-Board-ULN2003-28BYJ-48-For-Arduino-/381292009597?pt=LH_DefaultDomain_3&hash=item58c6c6587d). 

If you plough through the thread, there are links to a second one by RBrown that also uses a Nano, but has different layouts\drivers for different types of motors e.g. bi-polar driven by different drive boards e.g. 8825 A4983 etc...

Edit:

Forgot to add that the motors I'm using for my focusers are these http://www.omc-stepperonline.com/nema-14-bipolar-stepper-54v-08a-18ncm255ozin-14hs130804s-p-93.html

with pulleys and belts from http://beltingonline.co.uk/

hope this helps

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