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[DPRG] Researching Robotics Design Tools

Subject: [DPRG] Researching Robotics Design Tools
From: jeffrey loper jcloper at yahoo.com
Date: Tue Jun 12 12:17:09 CDT 2001

--- "R. Bickle" <rbickle at swbell.net> wrote:
> I was not planning to run the PWM at anywhere near
> that speed. I have my
> system running now at 250Hz. The Motor Mind Module
> that many people are
> using runs at 100Hz. Is there any advantage to
> running the PWM faster for
> motor control? Seems to me you will just get more
> MOSFET switching losses in
> the H bridge.
> Rick

The advantage is less velocity ripple about your
desired speed.  If that is not important (which is
definately true for hobby projects) then 250Hz is
fine.  But unless you have a well tuned, high gain
controller your gonna have some ripple.  That's
because the motor will slow down slightly when the PWM
is off and speed back up slightly when it is on for
any cycle.

I generally use PIC's for my robot brains and other
projects.  And they have the nice counter/capture/pwm
modules that can be set off the base clock (up to
20MHz these days).  With them I can use 15KHz PWM

If your module is all analog then maybe you could
generate a PWM signal with a comparator between your
control voltage and a triangle wave oscillator.  That
will create a square wave based upon your voltage,
that can then be fed into your H-bridge.

-Cameron Loper

Jeffrey C. Loper
jcloper at yahoo.com

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