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The list of sources of confusion and their resolution came about through my own struggle to understand the principles of these machines amid all the confusion and misinformation that is out there, and was the result of some months of reading, corresponding, discussing and experimenting to get to the bottom of how they worked.
Richard Feynman's Lectures on Physics Volume II was most helpful. As was this website for a build-it-yourself: http://www.scitoys.com/scitoys/scitoys/electro/railgun/railgun.html You can see my improved version here: http://www.scitoys.com/board/messages/8/1257.html?1128906028 -- Dave Keenan
I've added a new photo that might replace the existing one; it's at http://commons.wikimedia.org/wiki/Image:Homopolar_Motor_Large.jpg oskay 9 August 2006 6 PM PST
Neat! :)) Technically this might be called WP:OR; however, it may be argued that everyone can easily verify it. ;-) - and BTW, I surely plan to do so! Harald88 21:03, 10 August 2006 (UTC)
I've changed my mind about the merge. No other elecrical motor and generator articles are merged on Wikipedia. Hopefully I've made it unnecessary by adding a brief description at the start. The existing material I've now put under the heading "Sources of Confusion" that I've seen used in other Wikipedia articles. I've also restored or rewritten some deleted material that I hope you agree now makes sense under this new heading. D.keenan 02:03, 1 December 2006 (UTC)
You will note that in the photo the magnet rotates with the nail. This violates at least two laws of physics: Newton's third law of motion and the conservation of angular momentum. The linear version of this motor would seem to constitute a reactionless drive, suitable to levitate and propel a flying saucer or spaceship. Mike La Moreaux ( talk) 21:56, 10 October 2011 (UTC)
I'm a bit new to talk pages, but what's POV and where is the equivalent discussion of "Reactionless Drive" on Talk:Faraday's law of induction 68.5.67.232 ( talk) 18:34, 10 July 2020 (UTC) New user
Duracell is proud sponsor of this article! — Preceding unsigned comment added by 94.133.55.75 ( talk) 23:56, 19 June 2012 (UTC)
Despite our well cited history section that says "The homopolar motor was the first electrical motor to be built. Its operation was demonstrated by Michael Faraday in 1821", IP editor 85.222.223.193 keeps inserting a claim that it was invented by Serbian electrical engineer Andrija Radović" in 2004. And, naturally, he is edit warring to push this POV. -- Guy Macon ( talk) 15:47, 12 August 2012 (UTC)
For possible inclusion in this article:
Homopolar motor with winding having multiple turns: US Patent US5144179 1992-09-01 [ http://www.google.com/patents/US5144179 ] and EP0507726 1992-10-07 [ http://www.google.com/patents/EP0507726 ]
Superconducting homopolar motor: [ http://www.ga.com/superconducting-dc-homopolar-motor ]
-- Guy Macon ( talk) 03:23, 1 October 2012 (UTC)
I disagree from what I've read on the homopolar motor that it is low current because it is only a one-turn loop. While multiple loops would require multiple sliding contacts, and that would increase voltage, that is not the point. The point is that it is a HOMOPOLAR generator/motor, in that there is no crossing of any magnetic field gradients, at all. The loops spin within the same polarity, axially, and therefore this effect should not exist per common electrical theory. No doubt they exist, and have been built in up to 1.5 megaAmpere versions at the University of Texas at Austin, used to power rail-gun experiments with extremely high current requirements. There are also megawatt superconducting homopolar motors contracted of late by the navy. However, it is HOMOPOLAR and a mystery to modern electrical engineering without abandoning traditional theory and adopting a fringe theory that is contended by someone somewhere. —Regards, DonEMitchell ( talk) 05:55, 3 January 2011 (UTC)
per [1]
This is pretty simple, nor is it cold fusion science, as the Tesloids sometimes like to portray the homopolar motor.
All it means is that the flux is (from the rotor's viewpoint, or more specifically from the viewpoint of some abstract point on the rotor's surface) always pointing in the same direction. Electric motors work by the cross product of the electric and magnetic fields. To be a continuously rotating motor, we require this product to always point in the same direction (at least if we work simply in polar coordinates). Motors are thus either commutated: where the magnetic field reverses for each pole, and so we need to commutate the electric field to reverse that too. Or else they're homopolar, where the magnetic field remains constant and so the electric field can too, not requiring commutation.
Why does the magnetic field reverse? In the absence of magnetic monopoles, and thus the need for the flux to form closed loops, the typical design with radial flux uses loops that are arranged circumferentially and are cut twice per revolution, once per phase. The homopolar motor typically (but not always) avoids radial flux in favour of axial flux. Downsides of the homopolar layout (and why they're rare) are largely those of engineering. They tend to rely on one single large field coil, and a single core that has to carry the entire field flux without saturating. This core usually needs to be longer than for most other motor layouts, thus heavier, more costly and with higher losses. Andy Dingley ( talk) 15:55, 8 May 2013 (UTC)
There's a wee bit of a problem here.
The discussion (and the Definition of the Lorentz Force) cheerfully talks about the force produced without ever discussing whenceforth the reaction to that force comes. Newton's third law has yet to be repealed.
The point is that there has to be the possibility of relative motion between the current carrying conductor and the magnetic field orthogonal to the current. It's the reaction between the current and the magnetic field that produces the force. With the various configurations of the "one-turn motor" (homopolar might be a bit of an exaggeration) it may not be very obvious exactly what is producing the reaction to the force, but it is there nonetheless. Trainforrest ( talk) 07:50, 13 January 2014 (UTC)
Another problem is that there is more than a little supposition that there is only the possibility of a single turn with this type of motor, but there does not appear to be a corresponding list of citations that prove the point. In fact, it may not be certain that there are any citations that prove the point. — Preceding unsigned comment added by Trainforrest ( talk • contribs) 05:30, 14 January 2014 (UTC)
Multiple current loops are possible in both homopolar motors / generators (and railguns too!). But there are practical difficulties in making them work reliably. — Preceding unsigned comment added by Knobeeoldben ( talk • contribs) 09:57, 8 November 2015 (UTC)
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It would be nice if the explanation shows an example of the direction it moves depending on current direction and magnetic polarity, as these facts are actually hard to find. — Preceding unsigned comment added by 2001:8003:E40F:F700:4C6:81B2:7C37:561C ( talk) 13:24, 14 November 2020 (UTC)
![]() | This article is rated C-class on Wikipedia's
content assessment scale. It is of interest to the following WikiProjects: | |||||||
|
The list of sources of confusion and their resolution came about through my own struggle to understand the principles of these machines amid all the confusion and misinformation that is out there, and was the result of some months of reading, corresponding, discussing and experimenting to get to the bottom of how they worked.
Richard Feynman's Lectures on Physics Volume II was most helpful. As was this website for a build-it-yourself: http://www.scitoys.com/scitoys/scitoys/electro/railgun/railgun.html You can see my improved version here: http://www.scitoys.com/board/messages/8/1257.html?1128906028 -- Dave Keenan
I've added a new photo that might replace the existing one; it's at http://commons.wikimedia.org/wiki/Image:Homopolar_Motor_Large.jpg oskay 9 August 2006 6 PM PST
Neat! :)) Technically this might be called WP:OR; however, it may be argued that everyone can easily verify it. ;-) - and BTW, I surely plan to do so! Harald88 21:03, 10 August 2006 (UTC)
I've changed my mind about the merge. No other elecrical motor and generator articles are merged on Wikipedia. Hopefully I've made it unnecessary by adding a brief description at the start. The existing material I've now put under the heading "Sources of Confusion" that I've seen used in other Wikipedia articles. I've also restored or rewritten some deleted material that I hope you agree now makes sense under this new heading. D.keenan 02:03, 1 December 2006 (UTC)
You will note that in the photo the magnet rotates with the nail. This violates at least two laws of physics: Newton's third law of motion and the conservation of angular momentum. The linear version of this motor would seem to constitute a reactionless drive, suitable to levitate and propel a flying saucer or spaceship. Mike La Moreaux ( talk) 21:56, 10 October 2011 (UTC)
I'm a bit new to talk pages, but what's POV and where is the equivalent discussion of "Reactionless Drive" on Talk:Faraday's law of induction 68.5.67.232 ( talk) 18:34, 10 July 2020 (UTC) New user
Duracell is proud sponsor of this article! — Preceding unsigned comment added by 94.133.55.75 ( talk) 23:56, 19 June 2012 (UTC)
Despite our well cited history section that says "The homopolar motor was the first electrical motor to be built. Its operation was demonstrated by Michael Faraday in 1821", IP editor 85.222.223.193 keeps inserting a claim that it was invented by Serbian electrical engineer Andrija Radović" in 2004. And, naturally, he is edit warring to push this POV. -- Guy Macon ( talk) 15:47, 12 August 2012 (UTC)
For possible inclusion in this article:
Homopolar motor with winding having multiple turns: US Patent US5144179 1992-09-01 [ http://www.google.com/patents/US5144179 ] and EP0507726 1992-10-07 [ http://www.google.com/patents/EP0507726 ]
Superconducting homopolar motor: [ http://www.ga.com/superconducting-dc-homopolar-motor ]
-- Guy Macon ( talk) 03:23, 1 October 2012 (UTC)
I disagree from what I've read on the homopolar motor that it is low current because it is only a one-turn loop. While multiple loops would require multiple sliding contacts, and that would increase voltage, that is not the point. The point is that it is a HOMOPOLAR generator/motor, in that there is no crossing of any magnetic field gradients, at all. The loops spin within the same polarity, axially, and therefore this effect should not exist per common electrical theory. No doubt they exist, and have been built in up to 1.5 megaAmpere versions at the University of Texas at Austin, used to power rail-gun experiments with extremely high current requirements. There are also megawatt superconducting homopolar motors contracted of late by the navy. However, it is HOMOPOLAR and a mystery to modern electrical engineering without abandoning traditional theory and adopting a fringe theory that is contended by someone somewhere. —Regards, DonEMitchell ( talk) 05:55, 3 January 2011 (UTC)
per [1]
This is pretty simple, nor is it cold fusion science, as the Tesloids sometimes like to portray the homopolar motor.
All it means is that the flux is (from the rotor's viewpoint, or more specifically from the viewpoint of some abstract point on the rotor's surface) always pointing in the same direction. Electric motors work by the cross product of the electric and magnetic fields. To be a continuously rotating motor, we require this product to always point in the same direction (at least if we work simply in polar coordinates). Motors are thus either commutated: where the magnetic field reverses for each pole, and so we need to commutate the electric field to reverse that too. Or else they're homopolar, where the magnetic field remains constant and so the electric field can too, not requiring commutation.
Why does the magnetic field reverse? In the absence of magnetic monopoles, and thus the need for the flux to form closed loops, the typical design with radial flux uses loops that are arranged circumferentially and are cut twice per revolution, once per phase. The homopolar motor typically (but not always) avoids radial flux in favour of axial flux. Downsides of the homopolar layout (and why they're rare) are largely those of engineering. They tend to rely on one single large field coil, and a single core that has to carry the entire field flux without saturating. This core usually needs to be longer than for most other motor layouts, thus heavier, more costly and with higher losses. Andy Dingley ( talk) 15:55, 8 May 2013 (UTC)
There's a wee bit of a problem here.
The discussion (and the Definition of the Lorentz Force) cheerfully talks about the force produced without ever discussing whenceforth the reaction to that force comes. Newton's third law has yet to be repealed.
The point is that there has to be the possibility of relative motion between the current carrying conductor and the magnetic field orthogonal to the current. It's the reaction between the current and the magnetic field that produces the force. With the various configurations of the "one-turn motor" (homopolar might be a bit of an exaggeration) it may not be very obvious exactly what is producing the reaction to the force, but it is there nonetheless. Trainforrest ( talk) 07:50, 13 January 2014 (UTC)
Another problem is that there is more than a little supposition that there is only the possibility of a single turn with this type of motor, but there does not appear to be a corresponding list of citations that prove the point. In fact, it may not be certain that there are any citations that prove the point. — Preceding unsigned comment added by Trainforrest ( talk • contribs) 05:30, 14 January 2014 (UTC)
Multiple current loops are possible in both homopolar motors / generators (and railguns too!). But there are practical difficulties in making them work reliably. — Preceding unsigned comment added by Knobeeoldben ( talk • contribs) 09:57, 8 November 2015 (UTC)
Hello fellow Wikipedians,
I have just modified one external link on Homopolar motor. Please take a moment to review my edit. If you have any questions, or need the bot to ignore the links, or the page altogether, please visit this simple FaQ for additional information. I made the following changes:
When you have finished reviewing my changes, you may follow the instructions on the template below to fix any issues with the URLs.
An editor has reviewed this edit and fixed any errors that were found.
Cheers.— InternetArchiveBot ( Report bug) 13:37, 4 April 2017 (UTC)
It would be nice if the explanation shows an example of the direction it moves depending on current direction and magnetic polarity, as these facts are actually hard to find. — Preceding unsigned comment added by 2001:8003:E40F:F700:4C6:81B2:7C37:561C ( talk) 13:24, 14 November 2020 (UTC)