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

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

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

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

You also might want to checkout these two links:
http://www.stepperstuff.com/
http://www.sscnet.ucla.edu/geog/gess...s/steppers.htm

"larry d clark" wrote in message
. com...

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

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

Be careful sizing your steppers. The biggest drawback to designing with
steppers is that if you exceed their available torque they'll quietly
fail, and your system will do Very Bad Things. So you want to
over-specify your stepper motors by quite a bit.

You'll need to consider two things when doing this: the amount of
torque it takes to turn your inductors, and their rotational inertia
(which will determine how fast you can accelerate them without causing
grief). You can determine your necessary torque experimentally with a
lever arm and weights, and you can determine your torque available from
a 'mystery motor' in a similar manner -- there's even a web page out
there to tell you how to do it, if you look for it.

Once you have selected steppers that are big enough, you'll know their
other drawback: they take up a lot of space compared to DC motors with
feedback.

But it's easy to understand how to control them, and you don't need to
figure out complicated position feedback schemes, so maybe steppers are
the right choice for you. If I were you I'd just use a stepper and a
pair of home switches -- one to tell me that the roller is at one
extreme of travel, and another to tell me that the drum has passed by an
index mark. If you 'and' these two signals together you'll get a
reliable home. Then each time your system starts up you just run the
steppers down to the home position, and back to where you want them.

--

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

Posting from Google? See http://cfaj.freeshell.org/google/

"Applied Control Theory for Embedded Systems" came out in April.
See details at http://www.wescottdesign.com/actfes/actfes.html

Be careful sizing your steppers. The biggest drawback to designing with
steppers is that if you exceed their available torque they'll quietly
fail, and your system will do Very Bad Things. So you want to
over-specify your stepper motors by quite a bit.


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

There is a way around the initial high torque, like friction loads etc. You
can use torsion spring/shaft to delay the application of torque to the step
motor. Had that problem back at IBM and solved it with torsion shaft spring
(Allen key), had invention disclosure on it and it was the only way to get
around the problem due to limited space/size of the motor.

Yuri K3BU.us
www.computeradio.us

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

Why using stepmotors.

Try to get syngons ( or synchrons ) instead. These are motor-alike things
that you feed with AC and when you turn one of them, the other reciproces.
It's like a radio controlled servo but without the usual QRM from the
motors.

Cheers


Dan / M0DFI