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Magnetic anti torque reaction device

  1. Jun 7, 2012 #1
    Hi Have got a device that is puzzling to say the least. The device is suspended by a thread i.e. no interaction with the ground. I am rotating four tubes each containing magnets which are being rotated into the repelling magnetic field of a magnet that is fixed to the body The following reactions occur :-
    1 100 rpm and above torque reaction present.

    2 slow to around 60 rpm no torque reaction, body remains stationary while rotors rotate?

    3 slow to around 40 rpm or lower and body begins to move in same direction as rotors?????????.

    Concept is to create an asymmetrical magnetic collision. In collision F + { F + -F } = F but what happens after collision a bit of a mystery.
    Any ideas, comments would be gratefully appreciated
     
  2. jcsd
  3. Jun 7, 2012 #2

    mfb

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    At least for me, it is hard to understand your setup with the description you gave.
    And what do you mean by "torque reaction present"?
    What are the timescales of the systems in you setup and which reactions do you expect where?
     
  4. Jun 7, 2012 #3
    Hi appologies for any misunderstanding in the description. I am rotating four tubes by means of a 12v motor which is attatched to the body. The whole system is suspended from a single point. I do have a short video of the device in operation .
    "torque reaction present" means as the rotors rotate clockwise the body will rotate anti clockwise.
    Not certain what you mean by timescales, as for reactions expected it would be assumed that after the collision torqe reaction would take place which does not happen.
    That the body moves in the same direction as the body????????
     
  5. Jun 7, 2012 #4

    mfb

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    To be more specific, some open questions:

    - how does your body look like? Does it contain anything else than the magnet and the motor?
    - how is this magnet oriented?
    - how is the direction of rotation oriented?
    - how are the 4 tubes oriented relative to the direction of rotation? How are the magnets oriented inside?
    - which "collision" in your second post?
    - is there any significant friction involved?
    - how long did you operate the system before you observed it?
    - can the whole device rotate without twisting the thread?

    A hint where I can fine a short video or some sketch would help.

    Based on your two post, my guess:
    - With high rpm, torque from the thread is negligible, at least when you observed it
    - With medium rpm, torque from the thread is sufficient to slow down the body, the tubes can rotate
    - With low rpm, some magnetic force between tubes and body becomes important. However, I have no idea how that looks like, based on the issues mentioned above.
     
  6. Jun 7, 2012 #5
    The body is L shaped and made of wood it does not contain anything else other than the motor and body magnet
    Body magnet is rectangular in shape with north facing rotors
    Direction of rotation can be either way
    Tubes rotate so ends facing body magnet, tube magnets are north facing so are propelled up the tube when travelling across body magnet to negate a push backwards
    As the rotors rotate, the body will attempt to rotate in the opposite direction colliding the body magnet with the rotating magnet so locking the body as the motor begins to literally push against itself
    The only significant friction is the rotors overcoming the repelling magnet forces
    The device works every time the main problem is getting the rotational speed right to observe the reactions described
    The device if suspended by the thread cannot rotate without twisting the thread, however since the thread applies a restoring force when twisted it gives the reaction more credibility
    Video on you tube but will need email address as can only send to invited person, if this is unacceptable please advise as to alternate way.
    In response to your comments all reactions are from close to rest position so no winding up thread like a child winding up a swing and letting go so giving a false observation. Medium rpm does not slow body it stops body completely. I agree that it is due to the magnetic interaction but am, at the present time baffled to say the least
     
  7. Jun 8, 2012 #6
    I have as yet not asked any specific questions for anyone to answer so
    1 Assuming that the repelling magnetic fields cancel the torque reaction in the magnetic collision, torque reaction should still occur after the collision so the body should rotate in the opposite direction to the rotors. Is this right?
    2 Assuming that as the rotor slows in the collision and there is a transfer of momentum, after the collision torque reaction will occur so that the body would simply oscillate around a fixed point?
    3 Since in the collision we now have compressive forces, do the magnets weigh more and if so does the whole device in a horizontal sense weigh more as well. Would this gain / loss in weight with each interaction produce an imbalance in force?
    4 As the rotor moves closer to the body magnet, the repelling magnet forces increase the torque forces of the magnets themselves. As the repelling forces suddenly collapse would this snapping back of these magnetic torque forces create an imbalance in force?
     
  8. Jun 8, 2012 #7

    mfb

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    The axis of the rotation is more important - vertical? horizontal?

    Sorry, I don't think I can fully understand your system without a sketch or something else graphical. Maybe you can make the video available for everyone with the link, without restricting it to specific youtube accounts?

    ..., you have no net torque left and therefore no angular acceleration of the rotating part. However, the thread may accelerate the body. And I think that this point is not stable.

    You cannot determine the angular velocity based on the acceleration at a single position only.

    The system body/rotor might do this. However, if one driving force is the motor (active, but forced to ~0 rotation), I would expect significant damping there.

    ??

    Where? Why?
     
  9. Jun 8, 2012 #8
    http://youtu.be/U5s0t_6fb3I
    Hi
    The link to the video is above, the video is unlisted so you do not need an account, any problems please contact. The effect seems a little dramatic but remember that the motor is being slowed so torque reaction is decreasing. The loose thread is to show that the device is winding up the thread, not down. I have moved the body magnet away from the rotating magnets to allow for more control if you wish I can send you a video of the device with no torque reaction at all.
    Thank you for replying to the questions. The first two were just highlighting what should happen as, like a helicopter , if the rotor blades go one way the body will attempt to go the other.
    As for question 3, to reconcile the observations with current theoretical thinking is not going to be easy so going “off piste” so to speak may be necessary. Anyhow by the look of your response you appear unimpressed by it , so we will give that a definite thumbs down for the moment
    The video should go some way to explain question 4 as the magnets are propelled along the tubes.
    Thanks again and I await your comments on the video, I know the device is of basic construction but am trying to keep any magnetic material to a minimum.
     
  10. Jun 8, 2012 #9

    mfb

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    I do not think this is the intended way to get 10 posts ;).

    Ok, let's see: You begin with the rotating rotor, the L object does not rotate and the thread does not apply significant angular momentum. You have a total angular momentum in your system. The power for the motor just accounts for friction, mainly in the motor itself and a part from the moving magnets. Now you switch the motor off. The rotor still rotates and now drives the motor. The friction there slows down the rotor and accelerates the L-object. As soon as their relative velocity is small, the forces between the magnets become important, and the rotor will prefer to have no arm in the direction of the magnet at the L.
     
  11. Jun 9, 2012 #10
    The purpose of the experiment was to show that momentum is transferred from the rotor to the body by the magnetic collision. On just this point alone I am sure that you will agree that from an attitude control application it would have certain advantages over a reaction wheel.
     
  12. Jun 9, 2012 #11

    mfb

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    In order to do so, you would have to decouple the rotor from the motor.

    No. It has more moving parts without good control over them.
     
  13. Nov 16, 2012 #12
    Hi have been busy, in response to your reply on the video of the device i am lowering the power to it, not switching the power off. So there is always forward emf when the arms are rotating.
     
  14. Nov 25, 2012 #13
    Hi
    If anyone other than mfb would like to comment or ask a question, please feel free
     
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