Hi,

I'm actually using method 2 to study torque and speed of a small.
I've had some references on the following application note from
National semiconductors:
http://www.national.com/an/AN/AN-694.pdf#page=3D1

However it doesn't really gives much mechanical info on the subject,
so that's what I'm trying to do as my graduation project. But so far
I've had no luck in measuring torque.


-- =

[]=B4s
Felipe Baldner
fbaldner@gmail.com


On 10/9/07, Gerhard Fiedler <lists@connectionbrazil.com> wrote:
> Hello,
>
> when controlling a brush DC motor with PWM (bidirectionally, thus H
> bridge), there are basically two different methods. Method 1 has one leg =
of
> the bridge always on and PWMs the other. The motor gets pulses of supply
> voltage and in the intervals it freewheels through one of the switched off
> legs (B in this case):
>
> + ------+-------+
>        |       |
>       A=3DOn    B=3DOff
>        |       |
>        +---M---+
>        |       |
>       C=3DOff   D=3DPWM
>        |       |
> - ------+-------+
>
> Method 2 PWMs all legs, which means that 50% duty cycle means standing
> still (-PWM means inverted PWM):
>
> + ------+-------+
>        |       |
>      A=3DPWM   B=3D-PWM
>        |       |
>        +---M---+
>        |       |
>      C=3D-PWM  D=3DPWM
>        |       |
> - ------+-------+
>
> Does anybody know the differences between the two methods in terms of mot=
or
> behavior? I'm mostly interested in the mechanical aspects like torque and
> speed. Are there any good sources of information?
>
> Thanks,
> Gerhard
>
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