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From: arioch@shell.portal.com (Kip J Mussatt)
Subject: Re: PWM DC motor control
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References: <Mar18.181352.31507@acs.ucalgary.ca> <PJG.94Mar18132910@parint.esl.com>
Date: Thu, 24 Mar 1994 21:47:59 GMT
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pjg@parint.esl.com (Paul Gyugyi) writes:

>In article <Mar18.181352.31507@acs.ucalgary.ca> morrow@cns8.cns.ucalgary.ca (Bill Morrow) writes:
>   Is anyone trying to actually vary the driving voltage to the motor,
>   using some feedback from shaft encoders? You know, just like they 
>   taught you in that control systems course. It seems to me that this
>   type of control system would be more efficient, responsive and cover
>   a wider range of motor speed.

>From what I understand, while the ratio of voltage to speed is fairly
>linear, the tourqe from a motor increases greatly with higher voltage.
>That is, for a given speed, you get more torque by using PWM at the
>max voltage than you do by having a constant, lower voltage.

Where as this is somewhat true, 12 V of PWM (say 50% duty cycle) does not
give the same amount of average torque as 12V DC (100% duty cycle).  It will
give more impulse power to overcome start up/static friction, but the RMS
voltage of 12 V PWM at 50% duty cycle is 6 V.  So you get 6 Volts worth of 
average torque.

Again, my $.02

-Kip
arioch@shell.portal.com
