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Re: [Electronics_101] Re: motor controller help (VEX)

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  • Howard Hansen
    A word of caution. PWM by itself does not provide any directional information. Varying the duty cycle will not change the direction a motor rotates. Because
    Message 1 of 13 , Jul 3 9:33 PM
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      A word of caution. PWM by itself does not provide any directional
      information. Varying the duty cycle will not change the direction a
      motor rotates. Because the output on pins 1 and 2 of a NXT motor port
      come from a H bridge the polarity of the signals on pins 1 and 2 change
      when the NXT Brick wants the motor to rotate in the opposite direction.
      It is also the key reason the Bipolar Mosfet Amplifier uses optical
      isolators.

      I don't know what type of signal a VEX controller uses to control a
      motor. Seeing as you haven't had any responses from this mail group to
      this subject I suggest you try the VEX Forum. See:
      http://www.vexforum.com/

      However, if a VEX controller uses a method similar to a NXT Brick for
      controlling a motor then the same type of Bipolar MOSFET Amplifier
      recommended for use with a NXT motor port is recommended for use with a
      VEX controller. You could use a H Bridge IC instead of 4 separate MOSFET
      transistors to reduce the number of parts. But you will still need 4
      optical isolators.

      Howard



      Chuck Merja wrote:
      >
      > Thanks for all the help!
      >
      > Anyone have experience or resources for adding bigger motors to a VEX kit.
      > I think the VEX controller actually puts out a PWM, then I'd need some
      > (easy
      > and cheap to build H bridge?)
      >
      > Chuck Merja
      >
      >
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