Alt-BEAM Archive

Message #02796



To: beam@corp.sgi.com
From: "grant mckee" gmbeam@hotmail.com
Date: Thu, 29 Apr 1999 15:46:24 PDT
Subject: [alt-beam] stepper motors


Ah forgive the lack of terminology, for my understanding is crude at
best.

I was looking at how to control a stepper motor without using a
computer, I believe it was Mark Tilden who used these in his robots
in the Yuma Desert due to the carbon sweeps oxidizing in the alklitic
air, this problem was solved because stepper motors have no cabon
sweeps, anyway If you want to control a stepper motor you can do it
with a microcore or a specialized IC, I did it with the microcore.
How to control the stepper motor depends on what kind it is just
cound the wires comming out of it, I think most disk drive motors
will have 5, one wire will be the common positive and the other wires
when connected to ground will energize certain coils in the stepper
motor. To find the common positive measure the resistance between
the 5 wires, the resistance will be half compared to the rest of the
wires.. if wire 1 is the common between that and all of the others
there will be lets say 75 ohms now between wires 2 and 3 there would
be about 150 ohms. I would recommend hooking the common to +5v and
systematically hooking each wire to ground and observing the movement
of the stepper motor. to get the microcore to run the stepper motor
I built a 4Nv loop with a PNC so it would go into a single process
state, the microcore itself cannot output enofe to power the stepper
motor I used so I drove it with a 74AC245. The order in which the
microcore powers the coils in the stepper motor is important (if
connected wrong it will probably just go back and forth). I
used .22uf caps with 2.2 meg resistors on the microcore, the stepper
motor moved slow but allowed me to see what was going on. Im not
really sure how to gear stepper motors and with my design you would
probably need a whole separate circuit to get them to reverse.(im
terriably sorry for being so vague but it would probably take pages
for a full explanation) A good page a found on controlling stepper
motors and getting some ideas was at
http://www.doc.ic.ac.uk/~ih/doc/stepper/

feel free to correct any errors Im sure i made alot, but this should
give a crude idea on how to controll stepper motors via a microcore

"Here I send this through thousands of miles of lines for the hope
that I don't get flamed.."



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