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10375Re: [SeattleRobotics] Johnny5 head control

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  • Mark Medonis
    Mar 1, 2002
      That works, sure. However I found that method too slow for my own
      animatronic head. In fact, you can buy stepper motors with a threaded shaft
      running straight thru them. Marlin P. Jones & Assoc. catalog usually has a
      couple for sale. http://www.mpja.com

      A linear solenoid or true linear motor would be preferable for another
      reason, too. In direct drive, under PID control, you can have compliance. So
      if you push against the head, it has a certain amount of give. Much more
      similar to human muscle control, and also aids in shock absorption. This
      compliance is under software control automatically because of the nature of
      PID, just as the compliance in your neck varies depending on how tense your
      neck muscles are.

      The Honda Humanoid robots P2, P3, and Asimo don't use linear motors, BTW.
      They use rotary motors, but have torque sensors on the output shaft for
      force control.

      Mark Medonis

      > How about putting a long bolt on the end of a motor shaft. Attach
      > motor to collar bone and nut (threaded rod coupler is better) to head. A
      > linear pot for feedback and you have a linear servo. (A string wrapped
      > around the shaft of a ten turn pot could also substitute for the linear pot.)
      > If your computer has analog input, you can use it to directly drive an H
      > bridge.
      > Just a thought
      > Pherd
      > Somers, CT
      > [Non-text portions of this message have been removed]
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