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Motorized screen help

  1. Jul 27, 2006 #1
    Im trying to build a device that would alow me to raise or lower a rolled piece of fabric a set distance with the use of a switch. for example flipping the switch down would cause the motor to spin the spindle one direction, lowering the fabric to say a distance of 4 feet and stopping, then flipping the switch up would cause the motor to turn the spindle the oposite direction pulling the fabric up and stopping. I was thinking of using a stepping motor. any ideas?
     
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  3. Jul 28, 2006 #2

    FredGarvin

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    Something like this wouldn't really need a stepper motor. You could do it with a regular motor, a couple of limit switches and a bit of cirucuitry.
     
  4. Jul 29, 2006 #3

    NoTime

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    Most stepper motors won't be able to generate enough power to do this. having done this arrangement I will say it takes more power than you might think.

    You will probably need to look for a "gearhead" motor.
    This is a small motor with an attached transmission for reduceing shaft rpm and increasing output shaft power.

    And as Fred said a couple limit switchs and a bit of circuitry.
     
  5. Jul 29, 2006 #4

    Danger

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    While NoTime is accurate in his appraisal, I would say that a gear-head motor is not required. You can achieve the same result, more cheaply, by simply using a pulley or gear train to create the output rpm that you desire. Depending upon your supplier, that might be less costful than buying a motor with the gearbox built in.
     
    Last edited: Jul 29, 2006
  6. Jul 30, 2006 #5

    NoTime

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    I made mine for free out of bits and pieces in my junk box :smile:
    But, I have the tools to make a support for all the gears necessary to slow the rpm down to the point where the screen(in this case vertical blinds) didn't just get ripped to shreads.

    Pulleys worked out to take up way too much space for what I had in mind and the supporting structure is more complicated as rubber drive belts arn't strong enough.

    Sutible gearhead motors can be had for $16 to $26 from a place like http://www.jameco.com/. Which one depends on how big your screen is and how fast you want it moving.

    Connecting the motor and limit switch to my screen proved to be a bit tricky also.

    I tried to find somplace that sold the complete works, but was unsucessful.
     
  7. Jul 31, 2006 #6

    Danger

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    Ahhh... I wasn't aware of the space limitations. My approach to something like this would be to fasten a chunk of 1/8" threaded rod to the motor, with a matching nut on the side of the screen. (Maybe with a parallel guide bar on the other side to keep it straight.)
     
  8. Jul 31, 2006 #7

    NoTime

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    I have used this idea for many things :smile:
     
  9. Jul 31, 2006 #8

    Danger

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    Yeah, it's amazingly simple, cheap, and efficient. The only problem is that hardware-store rods aren't exactly straight. I avoid problems with that by leaving some flexibility in the driveline, such as connecting it to the motor shaft with a piece of gas-line hose or shrink tubing. You couldn't build a holography stage that way, but it works fine for opening closet doors or whatnot. :biggrin:
     
  10. Jul 31, 2006 #9

    NoTime

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    Fair enough.
    Try rolling one on a flat surface and giving it a tweak here and there. Helps a lot with the bends.
    Also double bearings or using an inch or two of the right size tubing as bearings at each end helps reduce induced wobbeling.
    Old "rabbit ear" extendable antennas are a great source of odd size tubing.
     
  11. Aug 1, 2006 #10

    Danger

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    Good idea with the tubing. I never thought of that. I usually just straighten the rod by eye. (I got used to checking bar timber that way when playing pool without access to my own stick; it's more accurate than rolling. You just sight down it like a rifle and slowly rotate it to see which way it bends.)
    I've never needed bearings for anything that I've done with these set-ups. Usually, I'll just use a matching nut and drill the internal threads out of it. If more support is needed, I just drill the hole in a piece of steel or aluminum instead.
     
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