Can a permeable but non-magnetic rotor be used in an electric motor?

[ksh93]

TL;DR Summary

can a permeable but non magnetic rotor be used in an electric motor?

Let's say, the disc has a circumference of 1m, made of steel, or copper if you like.
The stator has a north and a south pole facing the surface of the disc, let's say at the perimeter of the disc, one perpendicular to the left and one perpendicular to the right ie opposite sides of the spinning disc. The offset between north and south at the circumference is 1cm, or perhaps variable - and as close as practical without touching the surface of the disc (or, touching but frictionless perhaps).

What speed at the perimeter, where these poles are placed 1cm rotationally from each other, does the disc need to spin for the inducted field in the disc to peak just as it passes the next stator pole, and give propulsion to the disc?

 

[Baluncore]

Welcome to PF.

I think we need a sketch or a diagram.
Are the magnets permanent magnets or electromagnets?

Do you mean something like a homopolar motor with slip ring(s)?
https://en.wikipedia.org/wiki/Homopolar_motor

Or a disc motor without slip rings?
https://en.wikipedia.org/wiki/Electricity_meter#Electromechanical

 

[ksh93]

for this let's say permanent magnets
and let's say the disc has no friction and is not connected in any way other than the inductance
let's imagine the disc is 3 million meters thick - so the propagation I guess from one side to the other is 1/100th of a second? so 1 revolution per second would cause propulsion?
at 1 million meters thick propulsion would be at 3 revolutions per second?
at 1 metre thick at 3 million revolutions per second?
at 1cm thick at 300 million revolutions per second?

 

[Baluncore]

at 1cm thick at 300 million revolutions per second?

You are new to magnetics.

A magnetic field takes time to enter or depart a conductive material because it generates an eddy current that opposes the initial field. A conductor is therefore, more like a reflective mirror, than a welcoming medium to the magnetic field.
The disc will be braked by the field from the permanent magnets.
Read and understand all this article.
https://en.wikipedia.org/wiki/Eddy_current

The speed that the magnetic field propagates into solid copper is only about the same as the speed you can run, which leads to the skin effect.
https://en.wikipedia.org/wiki/Skin_effect

 

[Vanadium 50]

I think we need a sketch or a diagram.

I agree. Apparently the OP does not. Hopefully our telepathic abilities are up to the task.

The answer to the question in the title, as asked, is yes. I am not sure the OPs question is in fact, he question in the title. I also question how serious a moon-sized motor really is. I suspect "not very".

 

[ksh93]

You are new to magnetics.

A magnetic field takes time to enter or depart a conductive material because it generates an eddy current that opposes the initial field. A conductor is therefore, more like a reflective mirror, than a welcoming medium to the magnetic field.
The disc will be braked by the field from the permanent magnets.
Read and understand all this article.
https://en.wikipedia.org/wiki/Eddy_current

The speed that the magnetic field propagates into solid copper is only about the same as the speed you can run, which leads to the skin effect.
https://en.wikipedia.org/wiki/Skin_effect

super! thanks :-)

 

[ksh93]

yes clearly your visual imagination is

I agree. Apparently the OP does not. Hopefully our telepathic abilities are up to the task.

The answer to the question in the title, as asked, is yes. I am not sure the OPs question is in fact, he question in the title. I also question how serious a moon-sized motor really is. I suspect "not very".

yes clearly your visual imagination is lacking
"moon size" is an edge case, conveniently rounded to an approximation of the speed of light
a spinning disc. two poles not quite opposite each other on either side of the disc draw your own diagram.

 

[ksh93]

super! thanks :-)

ok how about if the disc were copper? Lenz's law means there should be a corresponding magnetic field right? but not instantaneous right?
so, how to harness it? variations welcome and happy to be corrected and given further direction - physics, not engineering.

 

[ksh93]

yes clearly your visual imagination is

yes clearly your visual imagination is lacking
"moon size" is an edge case, conveniently rounded to an approximation of the speed of light
a spinning disc. two poles not quite opposite each other on either side of the disc draw your own diagram.

here you go

 

[Baluncore]

ok how about if the disc were copper? Lenz's law means there should be a corresponding magnetic field right? but not instantaneous right?
so, how to harness it? variations welcome and happy to be corrected and given further direction - physics, not engineering.

Tens of thousands of motor and generator designers, have considered every conceivable combination of components, over many years.

Your assumption that the field has not been explored, demonstrates your lack of experience and exploration of the field.

You cannot expect us to show you the way to your dreams. You must explore the literature, and find that path for yourself.

 

[berkeman]

Thread closed temporarily for Moderation.

 

[berkeman]

Thread is reopened provisionally...

TL;DR Summary: can a permeable but non magnetic rotor be used in an electric motor?

What speed at the perimeter, where these poles are placed 1cm rotationally from each other, does the disc need to spin for the inducted field in the disc to peak just as it passes the next stator pole, and give propulsion to the disc?

@ksh93 -- What do you mean by "give propulsion to the disc"? Do you mean rotational torque like a motor, or do you mean translational propulsion like you are trying to convert the rotational motion to linear translational motion?

If the latter, we do not allow discussion of "Reactionless Drives" at PF. From the PF Rules (under INFO at the top of the page):

EMDrive and other reactionless drives
See https://www.physicsforums.com/threads/nasas-em-drive.884753/

 

[ksh93]

Tens of thousands of motor and generator designers, have considered every conceivable combination of components, over many years.

Your assumption that the field has not been explored, demonstrates your lack of experience and exploration of the field.

You cannot expect us to show you the way to your dreams. You must explore the literature, and find that path for yourself.

You are making the assumption that I am developing a product, or attempting to - I thought this was a physics forum, not an engineering forum?
This scenario is the best way I could define a circumstance where I have no understanding of field phenomena - perhaps you don't understand it either?

 

[ksh93]

Thread is reopened provisionally...


@ksh93 -- What do you mean by "give propulsion to the disc"? Do you mean rotational torque like a motor, or do you mean translational propulsion like you are trying to convert the rotational motion to linear translational motion?

If the latter, we do not allow discussion of "Reactionless Drives" at PF. From the PF Rules (under INFO at the top of the page):

No, not reactionless - yes, rotational torque (imagining the simplest "at the circumference, being 1m"), just wanting to understand propagation of EMF - it must take time, and the fields should propagate at the speed of light, but it's still time.

So I suppose the question could be rephrased as "does the EMF in copper (or choose a medium aluminium or if demonstrates something steel) move through the medium at the speed of light?" , and can that quanta of time over distance theoretically be used to cause the induced magnetic field to interact with another magnetic field?

Or perhaps, what does the "downstream" fixed pole see of the induction from the "upstream" pole?

I don't have the language or terms to find the right place to learn - thanks if you can point!

 

[ksh93]

maybe take an AC generator, supply single phase to a 1,000,000m copper wire (I guess it's pretty thick and voltage high enough!) that returns to the site of the generator - how far out of phase is the source and target ends of the wire?

 

[ksh93]

50hz
about 3 microseconds
1/(6666) out of phase?
[edit]
oops missed a few zeroes, 3 milliseconds, 1/(6.666) out of phase?
so if our wire was 3.333 times longer, ie 3,333,333m long, it would be exactly half a phase out?

 

[Vanadium 50]

What is this? "Can you stump PF?"

My suggestion - take a step back and work on clearly stating your question. When you posit planet-sized motors, people will conclude you are not serious. Write complete sentences, using capital letters and punctuation. Spend more than a few seconds per message (we see the posting times). Otherwise, people will again conclude you aren't serious.

If what you talking about requires a drawing, make something more enlightening than confusing. Scribbles are not helpful.

Respect the time and effort of the people whose assistance you are asking for.

 

[berkeman]

Thread is closed again pending Moderation...

 

[berkeman]

My suggestion - take a step back and work on clearly stating your question. When you posit planet-sized motors, people will conclude you are not serious. Write complete sentences, using capital letters and punctuation. Spend more than a few seconds per message (we see the posting times). Otherwise, people will again conclude you aren't serious.

If what you talking about requires a drawing, make something more enlightening than confusing. Scribbles are not helpful.

Respect the time and effort of the people whose assistance you are asking for.

Agreed.

@ksh93 -- Please check your PMs and work more on your formulation of these questions. As you have stated and illustrated them so far, they are very haphazard and not supported by any work on your part on the math of the propagation of signals in wires and in media.

If you can draft a new and much better thread start about this question of yours, please send me a PM with that draft and I can try to help you tune it up for posting in the forums. It will need to incorporate a much clearer explanation and include quality drawings and detailed calculations.

Thank you. This thread here is done.