Continuous Polarity Switching dc motor

Discussion in 'The Projects Forum' started by itsjimbo, Apr 14, 2014.

  1. itsjimbo

    Thread Starter New Member

    Apr 14, 2014
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    (I am new, First post)
    I have a similar project that is a continuous nodding/tilting head which uses a 24vdc motor and two 3 pole limit switches. As the unit tilts, a limit switch is eventually triggered momentarily, and the motor should reverse direction until the other limit switch is triggered. I have read many posts on the subject, are there any readily available (retail) pwm controllers that can take the limit switch pulse and continuously reverse the direction?
     
  2. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    This is something that I assume is an animatronic? This type of movement is better done mechanically, with a crank and lever. Reversal of an electric motor is not needed at all. Look at how windshield wipers work. With the correct geometry there can even be a pause between nods or a different speed to each direction.

    Changing the direction electronically with a motor needs the motor to come to a complete stop. At least for a brushed motor. But a stepper motor can be reversed without the complete stop. But a stepper needs a logic circuit to drive it.
     
  3. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    DC motors can be reversed safely if you include a constant current limiter between the PSU and the motor.

    That limits the reversing (changeover) current, and if you set the current limit lwo enough you even get a nice decel/accel effect upon changeover.

    It only requires a LM317 and one resistor.

    Re the limit switches; you could use a DPDT relay as a reversing relay.

    But the best solution is like Brownout suggested which is used in most toys etc; use a continuously rotating motor and a crank. No switches or electronics are needed.
     
  4. shortbus

    AAC Fanatic!

    Sep 30, 2009
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    Shortbus and Brownout are not the same person. He's way smarter about electronics than me. :)
     
  5. THE_RB

    AAC Fanatic!

    Feb 11, 2008
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    Whoops! How's that for brain fade? :eek:

    These days I'm in the habit of typing replies with less care and less error checking. That has good and bad points.

    My sincere apologies Shortbus, I'll try not to call you by someone else's name again!
    :)
     
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