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Help with permanent magnets configuration as a movement source.

  1. Jul 11, 2014 #1
    please delete this post

    Accidentally I have noticed a strange behaviour using two different magnets, which I would like to discuss.
    The picture shows a disc magnet (shown also in the right to see the magnetization) with it's N facing upwards.
    Onto the disc magnet N side, a cylinder magnet is placed. When the cylinder magnet is placed, as shown in the picture, an attraction force happens to it's S (as the arrow shows), because it is attracted by the disc magnet N. The cylinder magnet N is repelled as the arrow shows.
    All the above are the facts as noticed by experimentation.

    Now the question.
    If I force the cylinder magnet to this place shown and I do not alow it to move in any direction other than right or left, the magnet tends to slip from my hand and follow the direction of the red arrow.
    I think I can explain this fact, what I cannot explain is the next one:

    What if I continuously force the cylinder magnet to be in that angular position in respect to the center hole of the disc magnet? Will the cylinder try to move forwards indefinitely, and as a result spin around the center hole? Well, of course not! but why this would not work?

    I appreciate your explanations
    Last edited: Jul 11, 2014
  2. jcsd
  3. Jul 11, 2014 #2
    I remember when I was younger working with magnets and trying to get the correct configuration, every time it would never work, no matter how clever I thought I was. The magnets 'knew' and always stopped moving or getting to a sticky point.

    With this configuration (if I'm looking at it right), try to imagine the set up where the cylinder magnet can spin around the axis (where the hole is). Let's say we spin it around its axis and take a picture of it at every 36 degrees (10 pictures for a full rotation). You will see it will stop after a bit if spun (from the initial energy you put into rotating it). The reason is, nothing is really changing in this set up.

    If you look at the pictures of it spinning and line them up where the cylinder magnet is in the same position in each, you will notice the magnet that is spinning never really does anything. The cylinder magnet never increases its distance from the hole, and doesn't feel a net change if constricted to an axis.

    If the magnet is free to 'choose' where to go and not restricted to an axis, the cylinder magnet will reach a point where it will move and settle in a place. If you try to remove it from that place, it will require more energy, as it's at the bottom of the 'magnetic' well.

    I hope I see your description correctly, I'll try to draw a picture soon.
    Last edited: Jul 11, 2014
  4. Jul 11, 2014 #3
    Thanks a lot for your explanation,
    That was what I initially thought, that nothing really changes there, two permanent magnets can never yeld to a rotation.
    Thanks once again
  5. Jul 11, 2014 #4
    No problem! There are some interesting ideas floating around on the web, but as magnetic fields are conservative (like gravity), you can never get more out than in. Keep thinking about them, as this really helps in visualizing and thinking about unrelated things in life.
  6. Jul 11, 2014 #5
    It will be the ultimate challenge to achieve constant movement from stationary magnets and maybe some help components.
    I have a feeling that the answer lies in "instantly rerouting" the magnetic field of permanent magnets.
    In fact I have seen an experimental linear motor on the web doing so but I cannot find it now.
    Thanks for not discouraging new experimenters to experiment even with crazy ideas like this. Even if nothing comes out, we all learn from the mistakes and sometimes the mistakes lead to new ideas :)
  7. Jul 12, 2014 #6


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    What picture?
  8. Aug 2, 2014 #7
    That is weird,
    Today I tried this configuration without having to hold the magnets with my hands.
    I mounted the big disc magnet permanently on the desk using glue.
    Then I used a motor form an old computer hard disc (as a bearing only) and I mounted the cylinder magnet to it's moving part, using some metalic tie wraps.
    The other part of the motor was stationary glued into another structure above the disc magnet.
    The whole purpose was to have the cylinder magnet move freely in circular motion relative to the disc magnet, and always be at the same radius away from the disc magnet center.
    I tested this configuration and here are the results:

    As blainiac explained, the cylinder magnet did not spin around the disc magnet center! Well it did spin for half a turn and then stoped. But this was not due to this magnet idea, this was due to slight difference in the relative distance or radius of the two magnets (I could never build a perfectly balanced system using so simple materials).

    When I made the tie wraps a bit looser, so that the cylinder magnet could barely slip through them, but still be held tight, The magnet tended to slip to the direction shown by the red arrow. But it did not transfer this force to the bearing!

    It is really weird to me.
    There is always a net force present that tends to slip the cylinder magnet forwards no matter what is the angular position of the cylinder magnet onto the disc one. But no rotation of the magnet occurs!

    It seems that it does not work from experimenting, but I do not know why and how the explanation of blainiac applies here. Does it really not work because the relative position of the magnets does not change form one angular position to the other? but what about this force that always tends to slip the cylinder magnet?
    I would like to know your thoughts on this.

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    Last edited: Aug 2, 2014
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