Motor advice please

Discussion in 'The Projects Forum' started by beth88, May 28, 2009.

  1. beth88

    Thread Starter New Member

    May 28, 2009
    1
    0
    Hi.

    Im working on a project at the moment that requires a lightweight alluminium sheet on a small drawer runner approx 200gms in weight to be pushed out and pulled back in via a motor running with a rack and pinion and remote control, (Same action as a drawer)

    I also need it to stop at a pre determined distance so that the motor doesn't keep running when the drawer runners are extended and closed. The motor needs to be as small as possible and have a slow running speed. If anyone can point out a particular motor that might be suitable that would be great.

    Thanks
     
  2. beenthere

    Retired Moderator

    Apr 20, 2004
    15,815
    282
    While it is possible to use a control scheme to slow a motor, your application might do well with a gearmotor. That is a motor that has a set of gears to reduce RPM (and increase torque).

    You could search for surplus gearmotors - http://www.sciplus.com/category.cfm/subsection/18
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
    5,435
    1,305
    Sounds a bit like a CD drive drawer? Maybe you could adapt a gearmotor and rack/pinion out of an old CD drive or DVD drive? They usually have limit switches too.
     
  4. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Another solution would be to employ a Linear Actuator. It is a bit pricey but it is simple and most such actuators come with built in adjustable microswitch detectors for setting the travel limits.

    hgmjr
     
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Electronic Goldmine has some gear-head DC motors, like G15492 @ $ 12, .2 in dia shaft.; Gears & timing belt, G15973, $ 5.95, 2 gears & timing belt. Belt cut, makes a good rack, sugest attaching with contact cement.One problem ,willneed a bushing to match gear to motor. Not sure what type of remote control that you need; long cable, IR, RF, etc.
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Forgot the reed relays, G17100, 2 ea. did not find a small bar magnet to go with.
     
  7. Mike Mandaville

    Active Member

    May 27, 2009
    81
    1
    Beth88, you have gotten some good answers so far, and here is another one which I hope you will find useful. Model airplane servos which are designed specifically for lowering landing gear employ a rack-and-pinion gear configuration, and such servos are available in a wide range of sizes. There also is a circuit which is available on the internet which will enable you to operate such a servo independently of any radio-control receiver.
     
  8. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    I modified this drawing from an earlier one for another thread, but it might work to control the "drawer". When push button,OUT, is pressed, RY is energised via diode,motir starts via other diode , causing limit SW C-D to close, allowing motor to continue. When limit SW A-B opens at full extention, motor stops.As NC pushbutton IN is pressed, Ry is un-latched, motor reverses and drawer closes untill closed limit SW C-D opens. At least that is the way it's suposer to work.
     
  9. jpanhalt

    AAC Fanatic!

    Jan 18, 2008
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    I have never seen a model aircraft servo that used rack and pinion. Landing gear servos which which I am familiar (mostly Hitec) simply go to preset positions once "triggered." That is, their movement is not proportional to stick movement.

    EMS makes an add-on to convert servos to linear motion ("EMS Linear Servo Conversion Kit"). One simply replaces the gear case of a standard servo (Futaba S148) with its device. It is not rack and pinion, but rather a flexible strap wraps and unwraps around the pinion. The servo arm attached to the other end is constrained in a groove and gives rectilinear movement.

    At this point, it would be nice to hear from Beth88 about whether s/he wants to go with a servo approach or a motor with limit switches or other type of end-travel detectors. A third choice would be a stepper motor.

    John
     
  10. Mike Mandaville

    Active Member

    May 27, 2009
    81
    1
    Sorry about that. My memory must be fading.
     
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