First External Rotor Electric Motors

[BretCahill]

When were external rotor electric motors first conceived?

Patents for "exoskeletal" or "inside out" gas turbine engines only appeared a
few years ago.


Bret Cahill



All conservatism is based on censorship of
economic information.
-- Bret Cahill

 

[Zak]

BretCahill wrote:

When were external rotor electric motors first conceived?

Papst had asynchronous motros like this. I think they were used in Revox
A77 tape decks.

http://www.theimann.com/Analog/A77/Versionen.html

Sold since 1967. In the bottom two pictures on that page you can see
what looks like the capstan motor. Internal coil, external rotor.



Thomas

 

[Zak]

BretCahill wrote:

When were external rotor electric motors first conceived?

Also see http://home.freeuk.com/revox/a77diag/ for the spooling motor. A
very clear drawing.


Thomas

 

[Watson A.Name - "Watt Sun]

In article <20030924125128.03047.00000161@mb-m07.aol.com>,
bretcahill@aol.com mentioned...

When were external rotor electric motors first conceived?

ISTR seeing such motors decades ago. All of the brushless DC fan
motors I've experimented with have a similar design. I believe those
designs have been around for several decades. But when you think
about it, a regular DC motor, with brushes, is no different. The
magnets are around the outside, and the armature is ineide the
magnets. All you have to do is affix the commutator shaft to the
mounting point, and let the outside of the motor revolve. And since
the commutator is no longer moving in relation to the mounting point,
the brushes can be eliminated. But you still have to keep the
magnetic field moving inside, so that's where the electronics comes
into action. Seems like eliminating the brushes is a fair tradeoff.

Patents for "exoskeletal" or "inside out" gas turbine engines only appeared a
few years ago.

Does one need to point out that gas turbines are not found in consumer
equipment?

Bret Cahill

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[Richard Crowley]

Brett Cahill wrote...

When were external rotor electric motors first conceived?

Most of those ceiling fans use external rotors.
Many (most?) of the designs are approaching 100 years old.

 

[Mjolinor]

"Zak" <Zak@spam.invalid> wrote in message
news:80lcb.6661$P51.10742@amstwist00...

BretCahill wrote:
When were external rotor electric motors first conceived?

Also see http://home.freeuk.com/revox/a77diag/ for the spooling motor. A
very clear drawing.

Is there a reason why (or why have I never seen) this type of motor used in
power situations. The reason for asking is that I hired a big belt sander to
sand a maple floor and it was ridiculously convoluted in design because of
the need to drive a wide drum from a shaft and it seemed so obvious to make
it with the rotating part of the motor on the outside.

 

[Michael A. Terrell]

Mjolinor wrote:

"Zak" <Zak@spam.invalid> wrote in message
news:80lcb.6661$P51.10742@amstwist00...
BretCahill wrote:
When were external rotor electric motors first conceived?

Also see http://home.freeuk.com/revox/a77diag/ for the spooling motor. A
very clear drawing.


Is there a reason why (or why have I never seen) this type of motor used in
power situations. The reason for asking is that I hired a big belt sander to
sand a maple floor and it was ridiculously convoluted in design because of
the need to drive a wide drum from a shaft and it seemed so obvious to make
it with the rotating part of the motor on the outside.

Why? It would require a custom motor design that is heavier, and
would cost more. By using an off the shelf motor, they save on initial
design cost, they can change brands, series, or other specs without a
full redesign, and they are easier to repair in the field.
--


Michael A. Terrell
Central Florida

 

[Mjolinor]

Is there a reason why (or why have I never seen) this type of motor used
in
power situations. The reason for asking is that I hired a big belt
sander to
sand a maple floor and it was ridiculously convoluted in design because
of
the need to drive a wide drum from a shaft and it seemed so obvious to
make
it with the rotating part of the motor on the outside.

Why? It would require a custom motor design that is heavier, and
would cost more. By using an off the shelf motor, they save on initial
design cost, they can change brands, series, or other specs without a
full redesign, and they are easier to repair in the field.
--

Normally I would agree but in this case the motor was made by the maker of
the sander and was a totally custom thing, I tried talking to the guy that
made them and he had never seen or heard of a motor where the outside
rotated. I would have thought that for this type of application there are
advantages that would out weigh the disadvantages though as the motors do
exist that must not be the case unless there is some reason that they can't
be made to produce enough power and still be a reasonable size. I don't see
why it should be heavier or bigger for a given power, its only a case of
which bit you denote as being stationary.

 

[Mark Fergerson]

BretCahill wrote:

When were external rotor electric motors first conceived?

I'm almost certain Tesla did something with the idea but
can't find a reference.

Patents for "exoskeletal" or "inside out" gas turbine engines only appeared a
few years ago.

I don't think a Tesla turbine could be turned inside-out. ;&gt

Mark L. Fergerson