Joe,

 I too have a few (3-4) motorized pots around that were used in DELCO
radios for GM cars.
 I'll look at them tonight to see if I can tell how it's done for sure,
but IIRC, there are two disks. =20
 One is attached to the pot shaft.  The other is a slip fit over the
shaft, and has a rubbery substance
 coating the inside surface. This one also has a gear tooth wheel
attached to it.  These two disks are=20
 contacting each other by a slight spring pressure.  The motor is
mounted above the pot and engages with=20
 the toothed wheel.  As the toothed wheel turns, it being in spring
loaded contact against the disk attached
 to the shaft, therefore turns the pot.  At the end of the travel, the
pot stops, but the disks now slip so
 no damage occurs.  Reversing the voltage source to the motor turns the
pot the other way, and at the end of
 the travel there, it slips again like at the other end.  If you want to
manually adjust the pot, you turn
 the knob and the disks slip by each other allowing the pot to turn, but
the motor doesn't turn, therefore
 it doesn't offer any resistance to movement.  I hope you can follow
what I'm trying to say here. =20

 Basically, it is similar to a manual transmission car clutch, except
instead of it disengaging by pressing
 the clutch pedal, this one doesn't really disengage.  It just slips
like the clutch was only partially
 engaged.  The teeth on the flywheel is engaged with the motor to drive
the shaft CW or CCW, and the pot
 shaft is like the transmission input shaft.

 Boy, a picture here would have saved a lot of dialog.  I'll see if I
can get some good photos of the pots I
 have at home.  That should help you out in understanding my description
above.

 Regards,

 Jim

> -------- Original Message --------
> Subject: [EE] Clutch for motorising a potentiometer
> From: ivp <joecolquitt@clear.net.nz>
> Date: Wed, November 10, 2010 4:13 pm
> To: "Microcontroller discussion list - Public." <piclist@mit.edu>
>=20
>=20
> Hi all
>=20
> could I have suggestions please for a long-lasting material that
> can act as a clutch between a motor and a pot shaft
>=20
> Or suggestions for a different construction method perhaps
>=20
> I've found (a) a range of inexpensive pots with access to the back
> end of the shaft and (b) that other types aren't very difficult to dis-
> assemble anyway to make access. There is a variety of cheap 3V
> to 12V motors I can use
>=20
> I'm DIY-ing because pots aren't available in either the value or
> configuration (eg stacked) I want, or are infrequently available
> or are tres expensive
>=20
> The material would have to be grippy enough to transfer motor
> drive to the shaft but not so grippy as to make the shaft hard to
> turn by hand against the gearbox. And also not wear down of
> course, although the clutch would be (lightly) spring-loaded
>=20
> I used to have a cheap motorised pot around here somewhere
> and have a sneaky suspicion it used some sort of direct drive
> that dis-engaged when the shaft was turned by hand or when
> the shaft reached the end of its travel
>=20
> TIA
>=20
> Joe
>=20
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