Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook