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Author Topic: Magnetic Attraction Bearing  (Read 1126 times)
Hero Member

Posts: 1341
Here is a Magnetic Attraction Bearing I invented a couple years ago, I decided to disclose it to the public forum ... open source for everyone to use. I also posted it at OU.com under the Electronic Levitron thread as well as a few pics of some other devices I have built. I copied some of the discussion there which can be found below.

Take two magnets in attraction and slip a 1mm plastic shim between them, mine are N42 150 lb pull strength ring magnets. Now try to pull them apart, we cannot it's too hard so we must slide them apart pushing on one and pulling on the other. I was doing this when I thought Hmm...shear force?, why not have four magnets with a shaft in between the two inner magnets and a frame holding the two outer magnets attracted to the two inner magnets apart.

Frame--NS   NS--shaft--NS   NS--Frame

Now imagine the left hand side magnets pull 150 lb to the left and the right hand magnets pull 150 lb to the right thus the shaft in the middle is in perfect magnetic balance pulling neither left nor right when perfectly centered with equal gaps on both sides. The frame must be strong and rigid because the frame magnets are pulling with a force of 300 lb+ inward just as the shaft magnets are also pulling with a proportional force outward. The adjustment bolts are to set the 1mm gaps between the end magnets in attraction and to adjust for the fact the boards keep warping under the strain, lol.

The neat part is that the attractive magnetic forces are axial however the load acts radially downward, the load is carried by the magnetic shear force on the magnetic field between the magnet pairs on each end . I use a 5mm ball bearing on one end to stabilize the gaps and the axial load on the 5mm bearing is measured in grams while the radial load peaks at around 40 Kg on the bearing shown. Which raised a question in my mind, the pull force between the two magnet pairs can have literally any value (tons)while the magnetic shear force carries the load however if both attractive forces sum perfectly to zero then the axial load would still be in grams thus it is easy to see why the system is 99% passive.

In a perfect world the magnet gaps on each end of the load bearing shaft would be perfectly equal and the axial forces would sum perfectly to zero thus the axial load on the stabilizing bearing(s) would be near zero and the magnetic shear forces would carry 100% of the load.

I believe the idea really clicked while reading A.D. Moore's book on electrostatics at the time. That is a cube of aluminum the size of a sugar cube in which all the charges have been separated by a distance of 1 m will have an attractive force of 32 million million million pounds... and yet all of these forces somehow sum to zero in this little cube of aluminum. If that does not boggle the mind then I submit nothing will, lol.

Quote from TK
I still think your mag-bearing design is going to turn out to be a variation of the ones I mentioned, I don't quite get the image you drew. It would seem to me that the shaft would snap to one side or the other and stick there, and I don't quite see how it doesn't droop down from gravity and rest on the "pins" sticking out axially from the shaft. I'd like to see some good photos of the apparatus if you have them, or even better a video showing the parts and their orientations. Certainly I could describe the operation of the Mendocino Motor system in the same words you used in the first description. If not... maybe you've found a counterexample to Earnshaw's Theorem, and that would be a big deal indeed!

Earnshaw's theorem holds so far as I know, believe me I have tested it in every way possible, lol. However it is an observation of a phenomena without any specific details as to how it may be applied practically. My magnetic bearing capitalizes on the effects of Earnshaw's theorem as follows. Earnshaw basically said a system of magnets will always be unstable because there is no point of balance in the system and the magnets will always move towards one another. However what he did not say was that "the closer the magnets are to a point of equilibrium the smaller the force to hold them in equilibrium" which is my premise. Thus any load be it 1 Kg, 100 Kg or 1000 Kg may be applied to the shaft however the force to hold the load in equilibrium between the magnet pairs will not change because it is perpendicular to the load. I should note that I have since found a way to hold the equilibrium position without any pins or mechanical devices... a work in progress.

It should be noted this is a magnetic attraction bearing based on the premise that -- "the closer the magnetic forces are to a point of equilibrium the smaller the force to hold them in equilibrium". As such as the two magnet pairs force approaches equilibrium the stabilizing force required approaches zero.

It's yours use it.


I don't like morning people... or mornings or people

Be careful when you blindly follow the Masses... sometimes the "M" is silent.
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