Talk:Homopolar motor

Feynman's Lectures on Physics

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

Yes! Please add some photos and diagrams like this experiment: http://physics.usc.edu/demolab/em/em7/em7_2.html. oskay 9 August 2006

New Photo

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

Thank you, Windell. I've replaced photo and marked low-res duplicate for deletion. Though it would save some work if your just upload a new version to the same name in Commons, instead of uploading it by a new name. --M5 13:19, 9 August 2006 (UTC)

Nice picture yes but I don't understand it - why don't all parts just fall on the paper (except for the magnet which seems to be sticking to the srew's head)? Harald88 21:20, 9 August 2006 (UTC)

M5: Thank you very much for cleaning up after me. I goofed and I have learned my lesson. Harald88: The background is the wall in my kitchen, not a piece of paper; gravity points down in the picture. I will edit the caption to indicate that now. Hopefully someone (for example, myself) will provide a clear explanation of how this simple homopolar motor works in the near future. oskay 10 August 2006

Verify it yourself

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)

Harald88: The original research was done by Michael Faraday in, or shortly after, 1821. My photo is merely a demonstration of extremely well-established phenomena. - Windell Oskay

Ah right - that's why it looked so familiar! :-) Harald88 21:37, 10 August 2006 (UTC)

Merge?

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)

Reactionless Drive

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)

This assertion has been covered exhaustively on Talk:Faraday's law of induction. Please do not attempt to duplicate that long drawn out discussion here. One talk page full of POV pushing is one too many; we certainly do not need two. Guy Macon (talk) 22:48, 10 October 2011 (UTC)

I do not see where it has been mentioned, at all. Mike La Moreaux (talk) 23:33, 10 October 2011 (UTC)

Not going to take the bait. Advise others to do likewise, referring to Talk:Faraday's law of induction Talk:Faraday's law of induction/Archive 3#There are no "counterexamples" to Faraday's law for an example of what will follow if they do. Guy Macon (talk) 01:11, 11 October 2011 (UTC)

An easy enough theory to test. I confirm that the magnet spins with the screw. ;-) (talk) 19:24 UTC, 25 September 2013. —Preceding undated comment added 19:26, 25 September 2013 (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

It is at Talk:Faraday's law of induction/Archive 3#There are no "counterexamples" to Faraday's law (it was on the talk page when the above trolling was posted, but was later archived.) Bottom line: Reactionless drives are either pseudoscience or science fiction. Homopolar motors are not reactionless, nor do they violate any laws of physics.

As I said on that talk page, a homopolar motor does not violate Newton's third law of motion or the conservation of angular momentum. As the system gives the magnet and screw a rotational acceleration, it gives the wire and battery an equal and opposite rotational acceleration. thus conserving angular momentum. This can be easily demonstrated by hanging the homopolar motor from a string rather than holding it in your hand. Each component rotates in an opposite direction at an RPM inversely proportional to their mass, giving you a net angular momentum of zero. --Guy Macon (talk) 19:22, 10 July 2020 (UTC)

There are hompolar motors, where The conductor and Magnet rotates in same direction.

https://www.youtube.com/watch?v=rl9hXn2fseU 212.91.182.63 (talk) 20:10, 30 April 2023 (UTC)

The aluminium-floor is the conductor in that video therefore the floor is moving in the opposite direction to the magnet, the battery doesn't need to be considered. But there is truth in what you are saying regarding homopolar motors are able to be reactionless. Its so simple. You confine the magnetic field of magnet into a c shape piece of iron and the put the conductor on the side with no magnetic field in the air (hence no reaction of conductor) 2A00:23EE:2870:CC4:8CF1:1581:F845:864F (talk) 20:04, 16 May 2023 (UTC)

Duracell

Duracell is proud sponsor of this article! — Preceding unsigned comment added by 94.133.55.75 (talk) 23:56, 19 June 2012 (UTC)

You make a good point. I wouldn't mind if someone did a bit of Photoshopping so Duracell doesn't get free advertising. ---Guy Macon (talk) 19:41, 20 June 2012 (UTC)

I went to fix this, only to find that someone else had fixed the problem and then self-reverted. I reverted back to the no-advertising versions --Guy Macon (talk) 19:32, 2 February 2014 (UTC)

Sorry, but I've reverted you at Commons, as this was not covered by COM:OVERWRITE and as there were already "neutralized" versions of these 4 images since 2013. Use them instead, if your prefer. --Túrelio (talk) 20:08, 2 February 2014 (UTC)

Not a problem. I didn't realize we already had neutralized images. Thanks!

I just replaced the existing images with:

File:Motor homopolar neutral.png

File:Motor homopolar plane neutral.png

File:Motor homopolar flux force neutral.png

File:Homopolar Motor Large neutral.jpg

--Guy Macon (talk) 21:40, 3 February 2014 (UTC)

Invented in 1821 or 2004?

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)

You are obviously right to remove the absurd claim that the homopolar motor was invented by Andrija Radović in 2004. There's absolutely nothing new (or particularly useful) about the homopolar electric motor. It's basically a pedagogical curiosity. - Eb.hoop (talk) 16:49, 12 August 2012 (UTC)

Now now... It is also a great converter of live batteries to dead batteries! <smile> --Guy Macon (talk) 00:38, 13 August 2012 (UTC)

Superconducting? Multiple turn?

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)

Violates traditional electrical engineering theory?

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)

There's nothing written in physics about magnetic field gradients and movement. The way this works is by lorentz force. There's a current running through a wire, with a constant magnetic field. The lorentz force will work perpendicular to the direction of the current and the direction of the magnetic field. The current goes "down", the magnetic field points outwards, so the lorentz force will be . Not really a mystery. Ragnagord (talk) 17:49, 12 January 2013 (UTC)

It's not a question of fringe theories. It's just that the lines-of-flux model commonly used by working electrical engineers is a simplification that works just fine on most kinds of motors but not on homopolar motors. The physicists use theories (Lorentz force law and Faraday's law of induction) that work with any electric / magnetic circuit but are a somewhat difficult to visualize, thus the commonly used but limited lines-of-flux model used by EEs which leads to wrong answers in this limited case. A well-educated EE knows this and doesn't use the lines-of-flux model in situations where it breaks down. All of this is explained quite well in our Faraday paradox article. --Guy Macon (talk) 18:44, 12 January 2013 (UTC)

Unidirectional flux

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)

As I usually do, I agree with your improvement to my edit. Is there some page related to unidirectional flux that we can wikiink this to? A Google search turns up page after page about cell membranes and simulation Brownian diffusion. --Guy Macon (talk) 17:20, 8 May 2013 (UTC)

BTW, I found some patents that use phrases like "unidirectional magnetic flux":

http://www.google.com/patents/US4514653

http://www.freepatentsonline.com/4514653.html

http://www.google.com/patents/US3586894

http://www.freepatentsonline.com/3586894.html

--Guy Macon (talk) 18:02, 8 May 2013 (UTC)

Rankin Kennedy, circa 1900, seemed a fan of homopolar machines. It seems like one of those ideas that's a great idea at the start, from the principles, but then you get bitten by the engineering (it's hard to make a non-saturated core for one bigger than a lab bench) and so it falls by the wayside. I think they were a serious competitor during the era of the bipolar motor (which has much the same problems), but started to lose it once high-temperature wire insulation was available and coils could move internally, with less core loss. Andy Dingley (talk) 18:24, 8 May 2013 (UTC)

Except that....

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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Polarities

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)