To a first approximation, Voltage determines speed and current
determines torque.  If you drive the motor from a current source you get
approximately constant torque.
Beware that if you have constant torque and no load the motor may
accelerate till it literally and lethally explodes!!!
        It is worth reading a book on motors befor actually implimenting this.

Sherpa Doug

> -----Original Message-----
> From: adastra [mailto:foster@ADASTRAN.COM]
> Sent: Monday, August 06, 2001 3:28 PM
> To: PICLIST@MITVMA.MIT.EDU
> Subject: [EE}: DC-PM motor, speed vs torque?
>
>
> We are working on a (PIC driven) application which uses a 90
> Volt DC-PM
> motor. In some circumstances we want to lower the speed to
> about half of its
> full-scale value, but we still need the torque we get out of
> the motor at
> its full speed. Of course we can lower the speed by lowering
> the DC drive
> voltage, but it seems that the torque also falls off
> proportionately to the
> lowered voltage.  Does anyone know of a control technique
> (PWM maybe?) that
> allows lowering the speed while maintaining the torque?  I am
> obviously not
> a motor expert.  Am I trying to break the laws of physics here?  Any
> suggestions welcome. Thanks very much,
>         Foster
>
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