K7ITM wrote:


On Oct 15, 3:00 pm, larry d clark wrote:

i have always wanted to build a step motor driven
balanced tuner. i have acquired an excellent tx air capacitor
and 2 matched 28 uh roller inductors. next step is
to acquire 2 step motors with some kind of positioning
indicator, either optical or a pot.

any have any recommendations for a company site, or for
anyting else related, pulleys, belts, encoders etc

larry
kd5foy


Some places you'll find surplus steppers:
Marlin P. Jones Associates, www.mpja.com
Surplus Center, www.surpluscenter.com (usually not many steppers,
though)
Herbach & Rademan, www.herbach.com
There are plenty of others. Some of these also have other drive
components. You may also find just what you need in an old printer or
pen plotter. I have a friend who has a bunch of big old printers and
keeps talking about cleaning out his garage. He'd probably give you
one for free, but you'd have to ship it. You may have someone like
that near you.

You may need to gear down (or otherwise step down the speed) of the
motor to get enough torque to drive the capacitor and inductors.

Especially if you use steppers, you may only need to detect a "home"
position, since you can count steps from there and know where you are
(or rather where the capacitor and inductors are). A continuous servo
system may only need to know the ends of travel, to know that it can't
go beyond those points.

If you want it to auto-tune, you may find it easier to just use DC
motors, though doing so successfully would probably take some
understanding of servo control systems.

Cheers,
Tom

If you decide to use DC motors, and if you decide to drive them from a
microprocessor (which would be indicated if you're planning on tuning it
under computer control or auto-tuning), this may help:
http://www.wescottdesign.com/articles/pidwophd.html.

But I'm not sure that it would be necessary -- as long as you've got
_something_ that'll locate the variable components where you want them
and does so reliably it doesn't matter whether they're DC motors or
steppers.

--

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

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"Applied Control Theory for Embedded Systems" came out in April.
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