Re: (Just gotta gloat) Where there's a will, there's a way...
- From: "Chris" <cfoley1064@xxxxxxxxx>
- Date: 22 Apr 2006 06:19:15 -0700
Don Bruder wrote:
So I've been doing some dinking around with stepper motors on and off
over the last year or so, trying to come up with a way I can drive them
to do various things.
I've done the "scavenge an ancient floppy drive board" and
"frankenstein" it, "scratch-build a custom circuit around an oscillator,
counter, and various other chips", and a whole bunch of other things,
some with greater or lesser success, but none of them turning out
*QUITE* the way I hoped they would.
Yesterday, I finally came up with something that seemed like a
positively brilliant idea - But it's GOTTA be too simple to actually
work - You can't run a stepper THAT easily - Can you???
If I take a center pin and make it "+V", then arrange a circle of pins
around it, wired together so as to give me what amounts to several
"1-2-3-4" sequences appearing on 4 wires (Each one feeding one phase of
a stepper) then run a "wiper" out to the pins from the "hot" center pin,
and give it a spin, I should get "motor goes 'round and 'round" action,
right?
Put together a very small-scale version (4 pins) to test the theory, and
I'll be dipped... It works! No fancy electronics needed. No worrying
about cooking off a drive transistor. No worries about back-EMF.
So this morning, I set out to construct a "sturdier and more useful than
brainstorm-test" version, and ended up cooking myself up what amounts to
a single-pole-36-throw rotary switch out of a chunk of plywood, a
handful of finishing nails, a chunk cut from a tnua can, and a few
pieces of wire.
Lo and behold, this version works too! With a semi-beefy power supply
(scavenged out of a dumpster-dived, smashed-keyboard Apple IIe) behind
it, spinning the "wiper" spins the stepper exactly as planned, and has
enough "oomph" to drive a fairly impressive amount of weight (as well as
holding the position properly)
Prior to this widget, I'd been having lots of trouble getting enough
juice to the motor to make it useful without cooking things off in the
process. Now, I could (at least in theory) hook up multiple amps worth
of power and never have to worry.
Hooray for me! :)
Now to make a few refinements to the prototype...
--
Don Bruder - dakidd@xxxxxxxxx - If your "From:" address isn't on my whitelist,
or the subject of the message doesn't contain the exact text "PopperAndShadow"
somewhere, any message sent to this address will go in the garbage without my
ever knowing it arrived. Sorry... <http://www.sonic.net/~dakidd> for more info
Congratulations, Don -- you've won the Angus MacGyver award for the
month. That's a good demonstration of the motor winding switching
principle using household materials. But I'll bet you'll eventually
see that you can do more with a stepper motor if you can electronically
switch the windings, and then you'll have to go back to figuring out
how to use those transistors. It's not all that difficult, even with
many amps of switching current. Feel free to post again if you need
help.
You will eventually have to worry about back-EMF, though, because the
coils are going to arc as each switch is opened, pitting and burning
your contacts.
Is there any duct tape in there? ;-)
Cheers
Chris
.
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