I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

--Hmmmm. You might try asking that over at sci.physics.electromag...

--
"Steamboat Ed" Haas : A steaming pile of
Hacking the Trailing Edge! : obscure information...
www.nmpproducts.com
---Decks a-wash in a sea of words---

"_" wrote in message
...
I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

There is no way to stop a magnetic field. You can alter the flux path with
a ferrous metal however putting aluminum between a steel plate will do
nothing to increase or decrease the strength. Magnets lose their
attraction at 1/D squared.. in other words if we double the distance from
the magnet it will only have 1/4 the attraction
For many years Eddy Current clutches were used to do what you describe .

_ wrote:
I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

The only practical effect would be to isolate the steel from the magnets
for as long as the magnets move in relation to the aluminum. Any
paramagnetic effect of the aluminum will be negligible, if I'm even
correct in remembering that Al is paramagnetic at all. Strong magnets
working against aluminum _will_ generate eddy currents as a consequence
of motion, and you can use that to generate drag. Strong magnets
working against steel will generate an attractive force, eddy currents,
and some hysteresis force that'll work even when the relative motion has
ceased.

Without knowing why your clutch uses steel instead of something else,
and how you propose to mount the aluminum, I couldn't say what the
effect will be.

--

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

Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" gives you just what it says.
See details at http://www.wescottdesign.com/actfes/actfes.html

On Aug 1, 9:48 am, _
wrote:
I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

Seems to me it would WEAKEN the field. Conducting non-ferrous metals
actually provide some shielding of varying fields.

Tim Wescott wrote:

Any
paramagnetic effect of the aluminum will be negligible, if I'm even
correct in remembering that Al is paramagnetic at all.

It is. A bit. The right word to look for in wiki is susceptibility. You'll
find that Al has one of 22.2·10?6. And materials with a susceptibility
above 0 are paramagnetic.


Nick

Nick Mueller wrote:

It is. A bit. The right word to look for in wiki is susceptibility.

Just came to my mind:
Brass is halfway good for shielding magnetic fields, copper is better. But
you have to make a closed case. Not applicable in your case.
Materials out of my head, I might be wrong. Once made a shielding case for
measuring cellulars and researched a bit into that. In the case of radio
waves, things are a bit more complicated, because there are magnetic and
electric fields.

Mu-metal is best for shielding pure magnetic fields.

Nick

I've done a spring loaded clutch. Check my web site under builders
log. Might
be of some interest.

DOC

Have robots. Will travel. http://www.robot-one.ca

On Aug 1, 2:24 pm, Nick Mueller wrote:
Nick Mueller wrote:
It is. A bit. The right word to look for in wiki is susceptibility.

Just came to my mind:
Brass is halfway good for shielding magnetic fields, copper is better. But
you have to make a closed case. Not applicable in your case.
Materials out of my head, I might be wrong. Once made a shielding case for
measuring cellulars and researched a bit into that. In the case of radio
waves, things are a bit more complicated, because there are magnetic and
electric fields.

The magnetic field that represents a radio wave generates a
current in the shielding material, whether it's aluminum or copper or
whatever, and this current is grounded, effectively killing the
field's effect on whatever the shield is protecting. A common example
is shielded ignition wires used in aircraft to stop radio noise.
I would expect that a magnetic field passed through an aluminum
plate would have no loss of strength UNLESS the plate or magnet was
rotating, whereupon an eddy current would be generated that would
likely heat the aluminum somewhat. That heating would represent some
loss of field strength through the aluminum. The current generated in
a wire's shielding is created as a result of the AC nature of the
field, which has the same effect as relative movement between the
field and shielding.

Dan

On Wed, 01 Aug 2007 10:42:35 -0700, Don Stauffer in Minnesota wrote:

On Aug 1, 9:48 am, _
wrote:
I'm thinking of how to make a small clutch and was wondering if putting a
sheet of aluminium between a rotating magnet and a steel plate would
decrease the distance they would need to be separated for the same drag.

Seems to me it would WEAKEN the field. Conducting non-ferrous metals
actually provide some shielding of varying fields.

If the field is varying then a conductor will block the variation -- the
varying field generates eddy currents which set up opposing fields.

--
Tim Wescott
Control systems and communications consulting
http://www.wescottdesign.com

Need to learn how to apply control theory in your embedded system?
"Applied Control Theory for Embedded Systems" by Tim Wescott
Elsevier/Newnes, http://www.wescottdesign.com/actfes/actfes.html