Newsgroups: comp.robotics
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From: bouton@IASTATE.EDU (Chad E Bouton)
Subject: Re: Motion Controller -- LM629
Message-ID: <1993Nov23.121013@IASTATE.EDU>
Sender: news@news.iastate.edu (USENET News System)
Reply-To: bouton@IASTATE.EDU (Chad E Bouton)
Organization: Iowa State University
References:  <CGxJo5.M68@ucdavis.edu>
Date: Tue, 23 Nov 1993 18:10:13 GMT
Lines: 45

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LM628/9 
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From my experience, the LM 628/9 is more useful when controlling mobile
robots that have a little more substantial weight and/or where the user wants to
control the dynamic response more tightly.  Controlling toy robots is usually
easier and they tend to start and stop easily without much strain on the motor
amplifier.  If you want more accuracy you can add encoder feedback and use a
simple circuit with a 4046 phase-locked loop.  I have even used this on a robot
that weighed about a 100 pounds (Here I played with dividing the frequency from
the encoder to get good results).  The drawback here is that the motor will
operate at different PWM frequencies depending on the encoder feedback signal
and reference freq. that are put into the PLL. (If you want
more about this PLL scheme email me directly.)

Currently I am controlling a robot that weighs over 200 pounds with two
independent drive wheels, each controlled by a 629 (the 629 is the PWM version)
and MOSFET H-Bridges.  I am finding that it is tricky to tune up this system. 
To tune the system the PID constants have to be selected and also a couple of
other parameters in the 629. For those who have had some control theory, you
know that the object in tuning is usually to minimize settling time, overshoot,
and final error.  In other words with a PID controller like the 629 you can have
more control on how the robot reacts to what you tell it to do.

There is a good article that discusses tuning the 628/9 and it is:

*************************************
Closing the Loop on DC Motor Control
by Tom Dahlin and Don Krantz
ISSUE #28 August/September, 1992
The Computer Applications Journal
*************************************

One more note:

I have found that under certain PID parameters, I can run the robot over a piece
of carpet or push it from the front (rather hard) and a motor (or sometime both)
stop and make a funny sound like a water faucet running!

Have the 629's gone into wild oscillation? Has anyone else run into this?

--
Chad E Bouton
bouton@iastate.edu
