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Help with Magnetic Clutch design

  1. Jan 29, 2014 #1
    I'm just designing a simple magnetic clutch that i can can alter the Break-away force by changing the air gap between the two diametric magnets.

    I guess I'm having a hard time understanding the practical difference between flux density, field strength and Force at a given distance of magnets… and how i apply the figures to my design.

    As far as i understand, the flux density is measured from the cross sectional area through the magnet, and so an N52 will have a higher flux density than an N28 for neodymium magnets… but this is just relevant inside if the magnet.

    However, when i look at data sheets for these magnets, the N28 appears to generate a greater force Fr for a given distance S than an Equivalent N52 magnet.

    So if i want the strongest magnetic coupling and so the highest Break-away toque, am i right in saying that i should use N28 magnets?


  2. jcsd
  3. Feb 1, 2014 #2


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    Science Advisor

    Using N28 magnets, if you can still get them, will not give the strongest break-away torque.

    The best way to improve torque will be to complete the magnetic circuit by placing two iron segments outside each magnet. That magnetic path will prevent saturation of the contacting surface, increase the radius and so the torque.

    It is also important that the magnet mount be non-magnetic. That way the flux will flow through the coupling and not through the mount.

    Rather than an air gap between the magnets you might consider a spacer such as paper or card. That will give better control of the gap. When not broken, the magnetic clutch will have a significant rotational phase difference for small loads. The friction component of paper may also be an advantage there as it will reduce slip of the magnet faces under low varying loads.
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