12vdc servo motor control from 5vdc signal

Discussion in 'The Projects Forum' started by dingy, Aug 12, 2011.

  1. dingy

    Thread Starter New Member

    Oct 25, 2010
    4
    0
    I have a 12vdc servo motor (locked rotor 1.6 amp) 7.5KΩ pot on shaft.

    I would like to build a circuit to control the position of this servo motor with a 5vdc output signal. The 5vdc output has the ability to ramp up its voltage from 0-5 on a 10 point user input curve.

    At 0vdc out put from 5v system I would like servo fully retract, as voltage increases to 5vdc output servo motor increases to fully extend.

    Looking for somewhat low cost, $20 or less if possible.

    I have 5vdc & 12vdc power available.

    What would it take to do this?

    Gary
     
  2. Bernard

    AAC Fanatic!

    Aug 7, 2008
    4,083
    385
    My take is that servo is a linear push-pull, moror is brushed 12V DC, the 7.5k pot wiper tracks the full length of plunger travel.??
    Basic set-up is a window comparator, invertor, & H-bridge. In addition an operational amplifier could be used to give an absolute V for differential input to allow speed control, [ PWM ] & a dead zone to inhibit hunting- would eleminate need for "window" on comparator. Anothet thought: use 2, single V supply OP-Amps, gain between 10 & 100, with inputs paralled but inverted, outputs diode ORd to give an input to a V controlled PWM speed control. Est $ 5.00 in parts.
     
    Last edited: Aug 13, 2011
  3. dingy

    Thread Starter New Member

    Oct 25, 2010
    4
    0
    1st picture is of new control modules program screen that I want to control servo motor from.

    2nd & 3rd are of servo motor. 12vdc motor on servo unit.Resistor is tied to end of output shaft.

    The motor RPM causes the control module to output a configurable voltage when a configurable RPM is attained.

    5V is maximum possible setting in software.

    Gary
     
  4. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    Is the output shaft allowed to make more than one revolution?
    Is there something like a rack & pinion to convert rotary motion to linear motion? " retract & extend"
     
  5. dingy

    Thread Starter New Member

    Oct 25, 2010
    4
    0
    The output shaft makes about 270 degree rotation full travel.

    The output shaft has a spool on it that retracts a small cable, which then operates another mechanism. The other mechanism is spring loaded to keep cable tight as servo moves back & forth.

    Gary
     
  6. Bernard

    AAC Fanatic!

    Aug 7, 2008
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    385
    The simplest version that I can think of is a comparator & H bridge [ Alegro UDN2962W, 4A, up to 45V, only $1.49 @ The Electronic Goldmine SN: G18502 ]. Additional cktry can be added to limit hunting & control speed.
     
    dingy likes this.
  7. xavierpereira

    New Member

    Sep 8, 2011
    8
    1
    I have Written a code to controll servos but I used Dspic 30f4011 ..
    its works fine ..just holla if u need it ... now I working on a different project ..Photovoltaic charge controller ..
     
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