2 Potentiometers cancel each other?

Discussion in 'The Projects Forum' started by Actuator, Dec 29, 2007.

  1. Actuator

    Thread Starter New Member

    Dec 16, 2007
    8
    0
    Can 2 potentiometers be used to cancel each other in the following manner?

    Pot 1 controls the speed of a motor which is connected by some form of linkage to Pot 2. As potentiometer 1 is opened, the motor turns in such a manner that Pot 2 is turned. As Pot 2 opens, it reduces the speed of the motor until Pot 2 is opened to exactly the same angle as Pot 1. At this point they cancel each other and the motor doesn't turn.

    The idea is that it's a feedback loop so that whatever angle Pot 1 is opened to, the motor opens Pot 2 to exactly the same angle and then stops. Pot 2 would be acting as a sensor.

    Thanks.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    What you have described is quite feasible. Of course, additional electronics would be required to complete the design.

    Did you have a particular application in mind for this feedback system?

    hgmjr
     
  3. thingmaker3

    Retired Moderator

    May 16, 2005
    5,072
    6
    One example would be to feed voltages from both potentiometers into an op-amp differential amplifier. Use the diff-amp output to control PWM duty cycle and polarity fed to the motor.
     
  4. Actuator

    Thread Starter New Member

    Dec 16, 2007
    8
    0
    Thanks Thingmaker, I'll investigate that idea.

    Hgmjr: I do have a particular idea in mind. Pot 1 would be physically connected to one of those mechanical 24 hour wall timers so that it opens at 15 degrees per hour. Pot 2 would be connected at a pivot between 2 arms that are driven apart by a threaded rod or linear actuator. If the idea works, then Pot 2 would work as a sensor so that the arms open at exactly the same angle as Pot 1.

    In more general terms, Pot 1 could be operated manually to open a gate or other thing to a desired angle.

    I was hoping there might be a simple way to directly connect both pots to each other so they'd cancel in the manner described.
     
  5. hgmjr

    Moderator

    Jan 28, 2005
    9,030
    214
    Here is an article (one of many) on the implementation of a servo-motor. This design uses an AVR microcontroller to monitor the potentiometer and drive the motor until the error signal indicating the difference in the position of the motor, as indicated by the potentiometer, relative to the desired postion is reached at which time drive signal is removed from the motor.

    hgmjr
     
  6. Actuator

    Thread Starter New Member

    Dec 16, 2007
    8
    0
    Thanks Hgmjr. I guess, in a sense, I just described a big servo. I might first investigate whether I could utilise an existing servo's circuitry somehow. Maybe I could remove the motor and connect the servo circuitry to the other motor driving the arms.
     
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