Subject:
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stepper motors: choosing an approach
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Tue, 7 Jul 1998 12:43:52 GMT
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Original-From:
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K. F. MacDorman <KFM@GULL.ME.ES.OSAKA-U.ACsaynotospam.JP>
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Viewed:
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1167 times
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There appears to be much interest in using the handyboard to control
stepper motors. Choosing the right approach depends on what you want
your robot to do.
There are a number of specialized boards for controlling stepper
motors, but they are generally expensive and, from the hobbiest/
roboticist's perspective, over-built. For example, to control just
two stepper motors (typical for robot locomotion), you would need to
buy three boards from, say, Pontech (http://www.pontech.com) and spend
about $350. The boards also consume more than 200 mA (at 5-15 V) even
when the steppers are switched off (no sleep mode). Although these
boards have many features, they may not be versitile enough for your
application, especially if they are not programmable.
There are hacks that permit handyboards to be controlled with fd(0)
and bk(1) commands; the approach taken by Peter Harrison at
http://www.cctc.demon.co.uk/stepper.htm; the $10 EDE1200 unipolar
stepper motor IC from E-Lab (http://www.elabinc.com); etc.
The approach I was considering was to use a $49 Basic Stamp II in
conjunction with Darlington arrays ULN 2003A, roughly based on the
design in the Basic Stamp I Application Notes, No. 6, for unipolar
stepper motors at http://www.parallaxinc.com. The idea is that control
of the steppers should occupy as few cycles as possible of the Handy
Board's MC6811. So the MC6811 can give short simple commands to the
Stamp through a serial interface, which the Stamp buffers in memory.
Imagine this just being <motor number, direction, number of steps,
step delay>. The Stamp handles the rest, including acceleration
and deceleration if necessary (CurrStepDelay = StepDelay +
MinStepDelayFactory - [AccelFactor * Steps] ). If the signals sent
to the Stamp describe movement along a path, it is important to be
able to clear the Stamps memory buffer -- for example, if an object
suddenly appears in the path and a new path must be calculated.
I would be grateful to anyone who would point out what's wrong with
this approach.
Best wishes,
Karl
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