Within A Non Magnetic Metal Torus

Possibly the best way to create and locate the supermagnets in a permanent way may be to have the magnets manufactured with a threaded central internal hole right through from north pole to south pole. This would require only one type of special magnet.

If the magnets are 10mm long x 25mm diameter, then 2 magnets with like poles facing would be forced together by screwing them onto a 20mm length of threaded rod, and retained with Loctite.

The diameter of the threaded rod in this case may be ok at 6mm, which would be a very small loss of magnetic strength compared to a 25mm dia solid magnet.

The material choice for the threaded rod may need some testing.

Steel is strong but will interfere with the magnetic field. This may be beneficial or detrimental.
Aluminum will be lighter, and will not theoretically alter the magnetic field. But who knows.

I would suggest making 3 supermagnets using steel and 3 using alum.

These could be tested for time taken to drop down an alum tube about 30mm ID, and also by lifting them while attached to a sensitive scale. These should be spaced apart with solid magnets to maintain the distance apart they would be in a rotor, and held together in a plastic tube or similar. The best choice will have the greatest drag, or fall time. Perhaps.


I have been making the supermagnets by retaining them inside an alum tube about 4mm longer than 2 magnets. The ends are turned over to hold the magnets in place. This means that there is a gap between magnets. I have been using smaller diameter x 2mm long magnets to get the magnets to contact each other. This is less than ideal.

Any magnets used between supermagnets can be solid and the same diameter as the supermagnets, or maybe the same diameter as the alum retainer,so should enhance the field strength of the rotor.

Which magnet type ? Everything is guesswork for me. There are no textbooks. Funds are always scarce. Neodymium  are probably best. But there are sintered or bonded varieties. Sintered are stronger flux but more expensive. The only way to correctly test magnets is to install them into a machine. This requires much tedious coil winding and unwinding. I am testing (Feb 2025) my number 3 rotor. The magnets are 15mm diameter x 10mm long N50 ? Neo retained within AL tube. At the ends of the supermagnets are 10mm dia x 2mm long packer magnets N35 ?. In between are 12mm dia x 5mm long N50 ?. These should have been 15mm dia but none were available.
This rotor has changed to 72 poles. This should put more flux into the torus wall, and the rate of change of polarity will double. This has required the outer torus shell coil positions to be doubled to 54. The coils may now be too close together and interfere with each other. The coils are also narrower and higher with the same amount of copper wire as the previous setup. I think the coils are not as powerful now. It is possible to double space the coils.

It may be possible to force fit the magnets into alum tube. This would be the same length as the 2 magnets. Fitting packer magnets between would be easier.

I have started with cheap small magnets to see what happens.