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Passive magnetic bearing

  1. Sep 29, 2014 #1
    Hi, I am hoping to get some feedback on the following question please: Can permanent magnets, such as neo magnets be set up in a polar array configuration so as to act as a magnetic bearing? I have seen various examples of actively-controlled magnetic bearings that use finely-tuned computer software and electromagnets, but have never seen any example of the above. I have attached a sketch of what I have in mind. I hope that everything is legible. If this is an improper place to post this thread, I apologies in advance, but would still please ask for advice on where to place it then!

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  2. jcsd
  3. Oct 4, 2014 #2
    Thanks for the post! Sorry you aren't generating responses at the moment. Do you have any further information, come to any new conclusions or is it possible to reword the post?
  4. Oct 4, 2014 #3


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    One may wish to read - Permanent magnet bearings for horizontal- and vertical-shaft machines: A comparative study


  5. Oct 6, 2014 #4
    Thanks Astronuc, your assistance is much appreciated! I'll have a look and see if this will help.
    Seems to be a very shrouded subject though, since people understand so little about magnetic forces?
  6. Oct 6, 2014 #5
    Actually, what I was really trying to check was whether the arrangement in the attached drawing makes any sense.
    The 'axial magnetic bearing' illustrated in one of your links seems to me like a strange combination of magnetic flux, but maybe this is the only way to configure such a bearing. Imagine if you will 2 identical soup bowls, one with an array of several small flat block magnets around the under outer rim equally spaced (magnetised through the thickness) placed inside the other bowl which has the same magnetic array around the top outer rim, thereby (hopefully!) suspending the bowl inside it. The bowls have 45 degree sides, such that when one is place inside the other it should rest at an equilibrium air gap, which is small enough to allow very little 'rocking' due to unstable forces. If this configuration is still unstable, it could be mirrored along the horizontal axis. This is the concept I've tried illustrate on the attachment.
  7. Oct 6, 2014 #6
    oh, and of course the question is...can it work?
  8. Oct 8, 2014 #7


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    The problem is that ANY configuration you can create with permanent magnets is unstable, this is known as Earnshaw's law.
    The only way to get around this is to use diamagnetic materials, which is why superconducting materials work well for this application.
  9. Oct 8, 2014 #8
    Thanks f95. I'll check up on Earnshaw's, but I have heard of it...so even if one were to place magnets around a conical rotor which basically centres the weight of the whole thing to a middle axis (since none of the magnets in the array can touch each other?), it still cannot work? Dunno if I need a sketch here...
  10. Oct 8, 2014 #9


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    It might work, you would have to analyse it carefully...Earnshaw's theorem is strictly speaking only applicable to static systems, meaning if you have e..g a rotating field it might still work. However, it is impossible to tell if something would work by just looking at the static situation which partly explains why magnetic bearings are difficult to make.
    I guess it a bit like analyzing a spinning top. It is unstable in that you can't balance it unless it is spinning.
  11. Oct 9, 2014 #10
    Thanks for the feedback...at least there's hope!? Spinning is exactly what it should be doing, all the time (gyroscopic effect applicable here?)
    Must confess, I don't fully understand the DYNAMICS of what Earnshaw's is all about. What I certainly understand is that you cannot just repel one magnet on top of another and levitate it perfectly there because unstable flux makes it impossible. What I've tried on my attached sketch (which is purely a basic CONCEPT to show the various parts of the apparatus) is to mirror the principle I stated above, thereby not just levitating the rotor on a magnetic array, but also pushing it down with an identical one from the top, hopefully keeping it in place. If there is any chance of this working, obviously the magnet size, shape and number would have to be optimised. The resulting magnetic force vector (45 degrees or so) must then keep it levitated and centralised towards the axis.
  12. Oct 25, 2014 #11
    any luck?, i have a thing for magnets i think they are the way of the future in propulsion
  13. Oct 27, 2014 #12
    Hi, thank you for your concern. I'm still working on the concept, but there seems to be too many unknowns. I think that if I can eliminate the unknowns one by one I can see if this thing is even workable! There are 3 parts to this design: the generator, magnetic bearing (if it can work!) and the winding coil (which will need to handle up to 25 amps). I have changed the basic design in the meantime. I previously wanted it to work as a stack system: design a standard 5kW unit and simply stack 5kW units on top of each other to deliver the required output. In my country we use 220V. Thing is, one may need to split the power among several circuits in a house, so having it centralised makes no sense!

    You may have seen all the clips on the internet concerning magnet motors. I am not looking into 'free energy', because everyone should know this does not exist - there's a great deal of 'production energy' that goes into making rare-earth magnets and I'm not even sure that these magnets with their high coercivity can retain their potential energy indefinitely when made to do work continuously. What I am aiming for is a plug-and-play, standalone portable unit that can deliver power anywhere it is needed. I am passionate about green technologies, but this unit will use a combination of rare-earth magnets (bearing) and high-grade ferrite magnets (generator). There are sensitive issues between the US and China over rare-earths. The viability of such a design depends on replacement frequency of these magnets. If the magnets don't last this idea cannot work, because the maintenance costs will outstrip the cost savings in a utility bill.

    If you can offer some insight into magnet dynamics, I would much appreciate any assistance you could offer. I am going to try update my concept today and upload it here and any comments would be most welcome. Like I say, I'm a novice at this stuff, I first need to learn a lot more.
  14. Oct 29, 2014 #13
    Took longer to update my concept, but this is what I had in mind, more or less. A PDF is attached for your amusement!
    The internal diameter is roughly 4"/100mm and the entire device is about 515mm long, without stand 'feet'. It consists of a revolving magnetic array in an a high-strength aluminium casing with a valve on top for removing all air from the vessel once operational. The stopper (purple) would lock into place under air pressure. No air means no drag (or corrosion of the magnets, so they may not even need coating!) It is supposed to 'float' on a permanent magnet magnetic bearing (I forgot to wedge the magnet shapes of the bottom magnets so that they don't dislodge). Neo magnets are used for the bottom bearing system, orange secured into casing, green into revolving rotor (yellow bits). They repel at 45 degrees to keep the rotor centralised at the bottom end. A top bearing system keeps the rotor centralised and the magnets are swivelled at an angle to hopefully provide rotational thrust (this remains the tricky part!) The rotor consists of 28 high-strength aluminium wedge-shaped vanes that hold the (white) ferrite/ceramic generator magnets in place (28-off per ring x 48 rings). Two stiffener rings at third intervals should limit deflection. Each generator magnet is only 9x10x8mm (I only showed the begin and end range). I've given roughly a 1mm air gap from magnet to coil face. Coil (brown) is 1.8x1.8mm insulated square section (custom-made?) I've tried to allow for deflection of the vanes due to centripetal forces as it spins. The targeted 220 volts depends on 2 basic unknowns: rotational velocity and true measured magnet strength. The total magnetic area required could be adjusted accordingly. The coil is a single layer winding up and down, going around the cylinder and imbedded about 1mm into the casing. Hopefully any heat generated could be dispersed by the encasing. I once looked at a shorter, larger diameter vessel, but I think centripetal forces limit rotational velocity in such a case. Any constructive or destructive criticism or comments welcome!

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