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## pwdDuty

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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
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
• 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
• 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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