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PWM and Servo Motors

  1. Oct 31, 2011 #1
    Hi everyone,

    I am really trying to get the concept of Servo Motors and am sort of stuck on something, particularly how the motor gets its Pulse Width Modulation.

    I understand the 0 to 5V with a period of about 20ms and different pulse widths generate different angular positions. What I am unfamiliar with is how the motor's controller knows the desired position? Is it as simple as a certain voltage input into the controller generates a corresponding PWM for that voltage and thus varies linearly?

    Any help is greatly appreciated!
     
  2. jcsd
  3. Oct 31, 2011 #2
    Different pulse widths (duty cycles), generate different torque (0-100%), not angular position. The desired position/torque/speed is commanded by something or someone, the actual position/torque/speed is measured with a feedback device: angular encoder/load cell/tach/etc.
     
  4. Nov 1, 2011 #3
    Thanks for the reply!

    I basically get that the duty cycles dictate the position/torque, what I am unfamiliar with is how I command the driver to do so. I cant just stand next to the motor and say "turn 90 degrees please." what electronically does the driver receive to generate the PWM?
     
  5. Nov 1, 2011 #4
    It depends on the controller, some are a 0-5V analog input, others are digital command ("clockwise, 50%" ) e.g. over USB, ethernet, RS232 etc...
     
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