How does a homopolar motor work?

[lalbatros]

How would you explain this homopolar motor seen on youtube?

https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/3aPQqNt15-o&hl=en&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/3aPQqNt15-o&hl=en&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

Thanks

 

[Bob S]

Faraday built a similar motor in 1821. See http://www.sparkmuseum.com/MOTORS.HTM
for a picture of it (see image attached). Faraday used mercury as a contact, and he used a Volta pile instead of an AA battery.

Basically axial and radial magnetic fields interact with radial and axial current in the wire to produce a tangential force (vector cross product, Lorentz equation F = I x B ).

 

[lalbatros]

Thanks Bob S,

I now realize that I chose a wrong illustration as well as a wrong title for this thread.

My motivation was this paper:

http://www.fjp.org.ar/AJP-Homopolar.pdf​

where figure 1 represents the simplest form of a Faraday motor (better named so).
The interresting point is that the system will also rotate when the rotor and magnet are attached together.

This other youtube video illustrates somewhat better what I wanted to discuss:

https://www.youtube.com/watch?v=<object width="425" height="344"><param name="movie" value="http://www.youtube.com/v/w2f6RD1hT6Q&hl=de&fs=1"></param><param name="allowFullScreen" value="true"></param><param name="allowscriptaccess" value="always"></param><embed src="http://www.youtube.com/v/w2f6RD1hT6Q&hl=de&fs=1" type="application/x-shockwave-flash" allowscriptaccess="always" allowfullscreen="true" width="425" height="344"></embed></object>

The disk below the screw is a magnet.

 

[Phrak]

Hey, thanks guys. Both for the drywall screw motor--surely the simplest possible, and the early motors--the brushless DC motors were the best.

I've got to make one when I find a small Neodymium magnet.

I don't have some spare mercury about, so I can't make one of the original brushless DC motors, but using a magnet to preform the task is ingenious. How do these guys come up with these ideas?

 

[Bob S]

I don't have some spare mercury about, so I can't make one of the original brushless DC motors, but using a magnet to preform the task is ingenious. How do these guys come up with these ideas?

I panned about 10 pounds of metallic mercury from abandoned mercury mines in California about 1950, and have given most of it away. I cannot find anyone who wants it any more. I cannot even mail it.

Faraday built his little motor in 1821, about 50 years before Lorentz wrote down his famous equation, and he didn't even get a Nobel Prize for it (Alfred Nobel (1833-1896) was born in Stockholm, Sweden, on October 21, 1833.

 

[Gnosis]

As Bob S stated, Michael Faraday first demonstrated his invention, the “Homopolar Motor” back in 1821, which was 10 years prior to the birth of James Clerk Maxwell, so Maxwell is totally undeserving of credit for Michael Faraday’s invention.

Unfortunately, there are a number of websites that continue to perpetuate in error by referring to Michael Faraday’s Homopolar Motor as “Maxwell’s Motor” or “Maxwell’s Homopolar Motor”.

Michael Faraday was a brilliant individual and deserves the credit that he is due in many areas.

The following video is neat in that it demonstrates a number of unique wire forms to use to form a Homopolar Motor…

http://www.metacafe.com/watch/504644/homopolar_motor/

 

[Phrak]

I made a jumping coil. At one place where I worked there was a 5V, 30 amp power supply looking unused. I made a coil of #12 wire, two feet long and about 1-1/2 inches around. I suspended it a little less than 2 feet from the top of a thick sheet of aluminum. Everytime it shorted to the sheet it would contract. It looked very much alive, jumping around in an erratic manner, leaving burn marks where it went.

 

[Relay]

I have build the dangling drywall screw homopolar motor. Yes it works, it's no trick. I don't know why it works but here's one of my quesses. The electron flow through the plating of the neo magnet creates a magnetic field same as through a copper wire. The magnet's magnetic field pushes this electron generated magnetic field clockwise or counterclockwise. The electrons then enter the wire that is touching the neo magnet and establish a magnetic field around the wire. The magnetic pole on the neo plating is opposite to the pole on the wire touching the magnet. They will therefore attract each other. As the wire moves or the magnet moves to close the distance between the poles, the affect will outrun the mechanical motion and continue to accelerate the motor. This also works if the magnet and wire repel each other. Lenz's law, Maxwell's equations, and Faraday's work don't explain the homopolar motor to me.