Newsgroups: comp.robotics
Path: brunix!sgiblab!sdd.hp.com!portal!arioch
From: arioch@shell.portal.com (Kip J Mussatt)
Subject: Re: Driving Stepper Motors
Message-ID: <CMs63G.I1@unix.portal.com>
Sender: news@unix.portal.com
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Organization: Portal Communications Company
References: <94031506310019@comedy.com>
Date: Wed, 16 Mar 1994 23:18:49 GMT
Lines: 36

robert.bierer@comedy.com (Robert Bierer) writes:

>Tim,

>I've just received a book on robotics that includes a chapter for
>driving stepper motors (dc motors and speed control of.  In chapter 14
>of "ROBOT BUILDER'S BONANZA, 99 inexpensive robotics projects" by
>Gordon Mccomb (c)1987 (ISBN:0-8306-0800-1).  It cost me $25Cdn and has
>an abundance of information and tips on building robots.

>Chapter 14 shows several circuits to drive stepper motors and goes into
>explaining how they work.  I've got as much knowledge (or less) as you
>do about this stuff and this book explained quit a few things.

Be wary of some circuits in this book.  There are some very obvious things 
wrong / not totally correct with a number of the circuits.  One involving
the stepper motor controller (utililizing j-k flip flops; both cmos and ttl)
was one that comes to mind.  The JK's described have a !clr and !preset on them.
However, (very important) these must be tied high (+5v) or the cicuit may not
function as expected if that pin floats low.  The author failed to mention
this and from experience is *very* important if you want to circuits to 
behave.

Another example is his use of MOSFETs (or JFETs) to drive a normal DC motor
in both forward and reverse directions.  The voltage to the Gates must be equal
relative to the Source pin.  However, the Vg (gate voltages) are all referenced
to the ground.  This causes a difference in biasing and results in one of two
FETs not turning all all the way, therefore, the motor doesn't spin as fast
as it could or is described as spinning.

I am not trying to knock the author.  I have the book and for the $ it is good,
but just be careful when using it and if something looks odd, question it.  At
the very least you will learn something more.

-Kip
arioch@shell.portal.com
