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pwdDuty

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  • phattran2001
    Hi! I have problem understanding the pwdDuty for AIBO, Is there a way to calculate it. Is it possible to get minus value? I tried one of the Sony samples
    Message 1 of 3 , Jul 5 8:17 AM
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      Hi!

      I have problem understanding the pwdDuty for AIBO, Is there a way to
      calculate it. Is it possible to get minus value? I tried one of the
      Sony samples PIDControl, but it is hard to understand the connection
      between pwdDuty and PID. Any suggestion would be a great help.

      /Phat
    • Ethan Tira-Thompson
      I ll take a shot at it: Let s say you have the position you want your joint to be at, and the current position it s at now. In rough terms, you can pass these
      Message 2 of 3 , Jul 5 3:28 PM
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        I'll take a shot at it:
        Let's say you have the position you want your joint to be at, and the
        current position it's at now.
        In rough terms, you can pass these values through the PID control
        equations, which will output the power to be sent to the motor.
        However, typically it seems that motor control circuitry doesn't
        support variable voltages for controlling motor power. Instead, they
        switch the full voltage on and off at some frequency - the more power
        that is needed, the more the motor spends with power 'on'.
        This fraction of time with power 'on' is the duty cycle, as read from
        the pwmDuty variable.

        So it is possible to have a negative value as well - just depends which
        direction the motor is trying to turn. I think with the AIBO, a
        positive duty means it's trying to move in a positive direction, so you
        can think of the duty as kind of a derivative of position (sort of,
        with some scaling factor). I don't think you'll ever see magnitudes
        larger than 1 however (because 1 is full power on all the time) Let me
        know if I'm misremembering any of this.

        -ethan


        On Jul 5, 2004, at 11:17 AM, phattran2001 wrote:

        > Hi!
        >
        > I have problem understanding the pwdDuty for AIBO, Is there a way to
        > calculate it. Is it possible to get minus value? I tried one of the
        > Sony samples PIDControl, but it is hard to understand the connection
        > between pwdDuty and PID. Any suggestion would be a great help.
        >
        > /Phat
      • Phat Tran
        Hi! OK, thanx Ethan, I think I understand a bit now. PID give the power and to get that power the PWM take over. Is the pwmDuty in 10^-6 (micro)? It is hard to
        Message 3 of 3 , Jul 6 5:27 AM
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          Hi!

          OK, thanx Ethan, I think I understand a bit now. PID
          give the power and to get that power the PWM take
          over. Is the pwmDuty in 10^-6 (micro)? It is hard to
          tell in the OPENR document. I know that duty cycle is
          in procent. What is the period for PWM, is it the same
          as the processor period.

          How is it meant to controll the speed of the motor,
          with PID or pwmDuty? It very confusing for me.

          /Phat

          --- Ethan Tira-Thompson <ejt@...> skrev: >
          I'll take a shot at it:
          > Let's say you have the position you want your joint
          > to be at, and the
          > current position it's at now.
          > In rough terms, you can pass these values through
          > the PID control
          > equations, which will output the power to be sent to
          > the motor.
          > However, typically it seems that motor control
          > circuitry doesn't
          > support variable voltages for controlling motor
          > power. Instead, they
          > switch the full voltage on and off at some frequency
          > - the more power
          > that is needed, the more the motor spends with power
          > 'on'.
          > This fraction of time with power 'on' is the duty
          > cycle, as read from
          > the pwmDuty variable.
          >
          > So it is possible to have a negative value as well -
          > just depends which
          > direction the motor is trying to turn. I think with
          > the AIBO, a
          > positive duty means it's trying to move in a
          > positive direction, so you
          > can think of the duty as kind of a derivative of
          > position (sort of,
          > with some scaling factor). I don't think you'll
          > ever see magnitudes
          > larger than 1 however (because 1 is full power on
          > all the time) Let me
          > know if I'm misremembering any of this.
          >
          > -ethan
          >
          >
          > On Jul 5, 2004, at 11:17 AM, phattran2001 wrote:
          >
          > > Hi!
          > >
          > > I have problem understanding the pwdDuty for
          > AIBO, Is there a way to
          > > calculate it. Is it possible to get minus value?
          > I tried one of the
          > > Sony samples PIDControl, but it is hard to
          > understand the connection
          > > between pwdDuty and PID. Any suggestion would be
          > a great help.
          > >
          > > /Phat
          >

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