Subject:
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Using Step-Motors
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Newsgroups:
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lugnet.robotics.handyboard
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Date:
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Sun, 20 Apr 1997 19:30:43 GMT
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Original-From:
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Patrick Cutts <patrick@#AntiSpam#surfari.net>
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Viewed:
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1701 times
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A couple people have expressed interest in how to use step-motors with their
handyboards. I
have used step-motors with my miniboard, and since both the handyboard and the
miniboard use
two L293D chips to run the motors, I am fairly confident that the procedure will
be similar if not
identical.
To begin with, I'm sure some of you will cringe at my methods, but they were
fast and easy, as
well as netting me an 'A' on my senior project and a second place finish at the
1997 Cal Poly
Computer Society robot contest (given that my program had to be simple enough to
fit into 2K
while the winner had 32K to play with and he STILL only beat me by 34 seconds, I
don't feel too
bad).
Anyway, If you take a look at the specifications for Motorola's MC3479P 2-phase
bipolar
step-motor driver IC, you will find that by locking the chip in either full or
half-step mode, you can
supply complete control to one step-motor using two bits from the
microprocessor. Now, since the L293D IC's also use two bits to control one
motor, all you have to do is build a circuit incorporating the step-motor
drivers and connect it directly to the bits of the controller that are currently
wired to the L293D IC's, and connect the step motors, and you are in business.
Almost.
There is still the problem of programming the robot to use step-motors instead
of DC motors.
This turns out to be a lot easier than it seems if you are willing to sacrifice
a few motor speeds.
I am using C to program my robot, and I use Chuck McManis' miniboard library,
which has 32
available speeds, 16 forward and 16 reverse. It turns out that if you try using
the library as
written, and control your motors as if they were DC motors, you will find that
there are 8 usable
speeds, 4 forward and 4 reverse. With the right drive train, you can make good
use of this, or if
you're smarter than I am, you might want to actually write software that makes
better use of the
step-motor's potential.
I simply soldered a ribbon cable to the miniboard traces between the 6811 and
the L293D and
left them on the board. It was handy to have the forward and reverse led's so
that I knew when
and in what direction my motors should be going.
If anyone wants me to, I can dredge up the schematic of the circuit using the
MC3479P that I
used in my robot.
-patrick
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