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From: Tony Williams
Subject: Re: Speed control for small d.c. motors
Date: Wed, 25 Sep 2002 07:37:13 +0100
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In article <3D906E21.F2F50C98@webaccess.net>,
Chuck Simmons wrote:
> Sorry, Tony. I reread your post and you are saying the same thing I am.
I wondered if we were at cross purposes.
> I use a circuit that is the same in principle but is more complex
> because it is configurable for torque, speed or voltage control. It uses
> (1/2)LT1215 and all of an LM1877. The application is really position
> control but there is often no feedback so dead reckoning is used (since
> desired position is always known). I currently use voltage control
> because it is the best behaved of the three modes.
I've only done two or three dc motor controllers,
all analogue, one with a tacho. So am no expert.
> I would prefer speed control in the high friction situation
> but cheap motors have very poor commutators which introduce
> unpredictable behavior at low speeds with BEMF control.
One of those 8-ohm motors had an Ra that was much
higher (>50 ohms) at low current. Which is why I
noted the measurements as being "at stall". It
was as though the commutator needed a significant
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