pulley and motor

I am thinking of creating a remote for my shades using an arduino or raspberry pi.  My shades are top down\bottom up, meaning there is a cord on each side.  Currently you need to pull the string to the side to unlock the string, then pull up and down like a regular shade.

My plan was to break the locking mechanism so that if you pull the string, the shade goes up (or down) and  you need to hold it.  I need a pulley and motor so that when it is at the proper setting, the pulley would stop and be able to hold without power.

If I could find a motor like that, I would simply have to go in one direction to pull up, in the other direction to go down, then stop when at the right height.
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dbruntonQuid, Me Anxius Sum?Commented:
You'll need some sort of brake on the motor.  This could either be a ratchet and pawl mechanism or a band brake.  Also see https://en.wikipedia.org/wiki/Electromagnetic_brake

Probably the easiest to implement would be the band brake as you could make it part of the pulley that does the winding.

See http://www.roymech.co.uk/Useful_Tables/Drive/Band_Brakes.html and http://www.knottbrake.com/bandbrakes.html for examples.
dbruntonQuid, Me Anxius Sum?Commented:
Hmm.  A worm drive might also do the trick.  You'd have to try it out.  Sometimes the gears can't turn the worm while the worm can turn the gear.  You'd be putting a load on the gear/worm mechanism though.

See https://en.wikipedia.org/wiki/Worm_drive and see the first graphic and associated text in the Application section.
jackjohnson44Author Commented:
Thanks.  I am looking for a specific part not a general category.  I am not sure if what I am looking for exists.  I need to buy a relatively cheap part.  I am not looking to spend a ton of money, or have the time to create anything myself.

Here is an example of an accessory motor for the arduino.  It is too small and won't fill my needs.

jackjohnson44Author Commented:
I believe that I am looking for something called a stepper motor that will have sufficient power to lift a 10lb weight.
would an oki 320 turbo printer model do? that is a rather strong motor

you could look for a used one, or on e-bay
dbruntonQuid, Me Anxius Sum?Commented:

If your suggested motor isn't powerful enough then you can gear it down.  See http://forum.arduino.cc/index.php?topic=50104.0  But those prices aren't exactly cheap.

nobus has suggested an OKI printer motor.  I suspect something like that could be done but that would probably be a long process to do.  I think you are looking for a quick drop in and bolt together project.

Also see http://www.instructables.com/id/Arduino-controlled-automated-blinds-with-Web-UI/?ALLSTEPS if you haven't already.  The forum there might be able to guide you better.

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