Re: How to make speed of DC motor match speed of another?

On Mon, 12 Jun 2006 07:58:57 -0000, Jasen Betts <jasen@xxxxxxxxxxx>
wrote:

On 2006-06-11, Eric R Snow <etpm@xxxxxxxxxxx> wrote:
I have a situation where a dc motor drives a wheel which pushes an
aluminum wire at variable speed through a 15 foot tube.

Gee, that sounds a whole lot like a MIG welder :)

I would like
to be able to pull this wire also at the tube exit at the same time to
avoid jams.

I won't suggest oil as that's no be real useful in a mig welder,

can you get a teflon coated liners for your tube?

When the speed of the pushing roller changes the speed of
the pulling motor must change with it. I can think of several ways to
sense the push motor speed but not how to use this to make the pull
motor spin at the same rate. Is there a simple and cheap way to do
this?

one way would be use a stepper motor with the coils switched by an encoder
on the pushing motor.


Thanks,
Eric
Gee Jasen, it seems like you may be reading my mind. It's kind silly
maybe but it's a small welder and the weld shop says that even with
the teflon liner the wire tends to tangle. With larger MIG welders
there are pull systems, like the Cobra, that work great. I could even
adapt one to my small unit. But they are expensive and heavy. So I'm
trying to think of ways to make a cheap one. Mostly just for my own
pleasure. Stepper motors could work. US Digital sells a chip that
accepts signals from an encoder and outputs step and direction. I have
one of these, an encoder, and a chip that accepts step and direction
and will drive steppers up to a couple amps at 24 volts. But stepper
drives are sensitive to electrical noise. And the encoder is slated
for a different project. It looks like a slip clutch just may be the
way to go.
Eric
.

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