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Direct control of a Servo for Halloween?

Discussion in 'Electronic Basics' started by WantonZoo, Oct 12, 2006.

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  1. WantonZoo

    WantonZoo Guest

    Hi all - I want to use a servo to move a model for a small head on my
    shoulder. You know - my evil - attached to my shoulder twin? Anyhoo - is
    there a way/simple circuit to control a servo without using RC reciever,
    etc. Just a direct push button a it turns left then button b it turns
    right?
     
  2. Chris

    Chris Guest

    Hi, Wanton. You and your evil twin will appreciate this hobbyist
    circuit for making a servo control pulse from an LM556 (or two LM555s):

    http://www.seattlerobotics.org/encoder/200210/servoex/ServoExcerciser.htm

    A servo accepts a control pulse every 20ms. or so. The active-high
    pulse width is the position control (the wider the pulse, the more
    angle).

    Just use a 10K resistor instead of the 10K pot on the 2nd 555, and
    place your switch contacts across the 10K resistor. When the switch is
    closed, the pulse will be short (and the head will move toward you).
    When the switch is open, the pulse will be long (and your evil twin's
    head will move away). This circuit provides two position control,
    where the servo will travel end-to-end.

    Simple circuit, runs off your servo's power supply, and all components
    are commonly available at any hobbyist source, including Radio Shack.

    Good luck
    Chris
     
  3. Bob Masta

    Bob Masta Guest

    Heck, why not skip the servo and just have a reversible DC motor
    (geared down appropriately)? Think of all the cheap kids' toys that
    do all sorts of antics with nothing more complex than that (plus maybe
    a few clever linkage arms, etc).

    Best regards,


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
  4. WantonZoo

    WantonZoo Guest

    Exactly smackly. Instead of building a circuit I could hack a cheap RC
    something and animate the head that way. Or simply take one of those heads
    in a ball they have in the stores right now and stick it to my shoulder.
    Thanks -
     
  5. jasen

    jasen Guest

    yup. you need to generate a pulse width modulated signal.
    one way to do this is using a chip called a 555 (which is cheap),
    an a few other cheap parts. have you encountered this chip before?

    if you don't have a servo yet, consider using a central-locking
    actuator as they are cheaper easier to drive.

    Bye.
    Jasen
     
  6. Si Ballenger

    Si Ballenger Guest

    The "DollarTree" store has little wire controlled battery powered
    cars for $1 that have foward and reverse buttons on the 2 AA
    battery control. Easy hack to have the axel move a light head
    left and right.
     
  7. Bob Masta

    Bob Masta Guest

    The car wheels probably move a lot faster than you want the
    head to move, so you can gear down the wheel motion and
    have plenty of torque to turn the head. In fact, skip the gear
    reduction: Pop the wheels off and use a bare axle as the
    drive, and put the head on a shaft that can take the wheel
    (assuming it is soft rubber). Now the motor shaft drives the
    rubber wheel by friction, giving a huge "gear" reduction and
    having an automatic clutch action. The slower speed will
    make it a *lot* more creepy!

    Best regards,


    Bob Masta
    dqatechATdaqartaDOTcom

    D A Q A R T A
    Data AcQuisition And Real-Time Analysis
    www.daqarta.com
    Home of DaqGen, the FREEWARE signal generator
     
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