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B How to Design and set up a strong electromagnet?

  1. May 31, 2016 #1
    Hello guys. I am new member of this forum and I am looking for some guidance on a certain project.
    Now, the reason I am posting is that I need your help with a project I am currently just starting and of which unfortunately I have little details figured out as well, so please bear with me if you will and I will try to provide as many information as best as I can on request.

    So here we go: I am looking to design and create a source of magnetic field of which I want to be able to control its strength, hence I suppose I am looking for an electromagnet.
    Its intended use will be to be able to make flexible rods (material of rods yet undicided) to bend towards it. Now these rods are expected to be a few inches thick (lets say between 1.5" to 3" thick), one end made immobile on the ground and I would guess a length of say close to one (1) meter or so.
    What I would also like would be to be able to affect, using a single electromagnetic setup, more than one such rods, the closest of which would be, say, 3 meters away from the electromagnet and the farthest about, let's say 8-10 meters away.

    Regarding the power, I am already guessing I will be needing some shorts of heavy duty power generator (contrary to the typical capacitor relays used in DIY home experimental projects).

    With regards to temperature, let's just suppose I may be able to choose from the absolute minimum options out there (yet unknown/undecided but I'd say water(?))

    So, bearing in mind that I have only a vague idea of this project (note: it is not in nature an industrial or of great precision project), could you guys provide me with your thoughts and a few directions for me to consider and explore?
     
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  3. May 31, 2016 #2

    berkeman

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    Welcome to the PF.

    Your distances to the rods you want to bend with magnetic power are too large. It's not practical to try to build an electromagnet with that high of a field. Maybe you can just attach ropes and use winches to bend the rods instead?
     
  4. May 31, 2016 #3
    Thank you very much for your response berkeman.
    I am afraid that motion through mechanical means is not an option for this project. However, I need to ask, do you find it impractical or impossible? As I mentioned in my first post, it is not an industrial type of project, so the only limitation would be the required budget and, ehm, physics. Do you suppose I could achieve the desired effect for the close range rods? If so, maybe I could consider moving the electromagnet around (but keeping a minimum distance of, hopefully, 1-2 meters) close to the rods myself (meaning mechanical means of moving it).
     
  5. May 31, 2016 #4

    berkeman

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    If the rods are not too thick, and you use a distance of 1m, then the large electromagnets that are used to pick up cars at wrecking yards may be able to do it (but I'm not sure):



    https://i.ytimg.com/vi/lSmuqLtmuwg/hqdefault.jpg
    hqdefault.jpg
     
  6. May 31, 2016 #5
    Well, it will depend on how much do you want to bend these rods. A few angstroms at the tip would be quite different than a few centimeters.
     
  7. May 31, 2016 #6
    Thank you for your reply. Of course you are right. I would ideally like a displacement of ~20-30cm from resting axis for the tip of the rods. Please allow me to add once more that I am still looking for the material to be used for this rod and I am, of course, looking for materials with a greater Young modulus than steel.
     
  8. May 31, 2016 #7

    berkeman

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    Well, to be attracted toward the electromagnet, the rods will have to be made of some ferrous material. Also, you will get more force and displacement if there can be a ferrous ball at the top of each rod. Is that a possibility? Like a ball about 10cm in radius...
     
  9. May 31, 2016 #8
    That is a great idea! I was so far considering the rods being made of the ferrous material. I could definately profit from an elastic material for the bending and ferrous tips (such as the suggested balls) for the magnetic force. Thank you very much for this idea, greatly appreciated!
     
  10. May 31, 2016 #9

    russ_watters

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    What is the budget?
     
  11. May 31, 2016 #10
    As funny as this might sound, it is not yet decided. To be frank, currently this is me trying to get the general picture of the limitations of electromagnets for such a project, so as to scale it up or down for an art project of mine. And by art, I kinda mean that the budget is to be dictated after I am able to present a model version of the project. So, yeah.... I am in the very first baby steps..
     
  12. May 31, 2016 #11

    russ_watters

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    Surely you must have an idea of the order of magnitude? A hundred dollars? Ten billion dollars?
     
  13. May 31, 2016 #12
    Having a vague idea, I'd say a few thousand dollars, but this would have to be distributed to the entire scale of the project as well. Being in such an early stage, the building limitations and the cost of such electromagnets seem to me to be the main factors that will dictate scale and budget of the projects.
     
  14. May 31, 2016 #13

    anorlunda

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    Can you also narrow how stiff these rods are? From what you said so far, anything in the range from wet spaghetti to rigid building jacks fit the description.

    The quality of the advice you get from this forum is proportional to how specific you are in sharing the details of your ambitions.
     
  15. May 31, 2016 #14

    berkeman

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    Keep in mind that you will need to keep observers a fair distance away from your art exhibit. It wouldn't sit too well with them if their credit cards stopped working after visiting your exhibit.

    You might find out the cost of buying a used one of those junkyard electromagnets, and find out the cost of the power source that is needed to energize them.
     
  16. May 31, 2016 #15
    As berkeman hinted at above, the pulling strength of a magnet decreases very quickly with distance. The video of the scrap yard magnet shows the magnet physically touching the metal parts before the metal is visibly attracted to it. This poses a problem, because there's a very fine line between not enough attraction to bend the rod, and too much attraction, which tears the rod from the base and launches it into the magnet at high speed. There's a positive feedback in attractive force as the rod is pulled toward the magnet.

    Strong magnets can be dangerous. You can smash things between the magnet and some hunks of iron. Also, you'll want to make sure you keep anyone with a pacemaker away from your apparatus.

    I'm not sure if you expect the rods to support their own weight. If you make a very flexible joint on the bottom (a cable, perhaps), then the whole thing will just slump over. It might be easier to make the rod hanging from above. (It needs to be very flexible if you expect a magnet to exert enough force at 3m to show a deflection. It also needs to be strong because of the positive feedback effect noted above.)

    You should take a look at this video of someone destroying things with neodymium magnets.

    These medium-sized neodymium magnets can overcome the static friction of the wood at about 0.5m distance. They quickly traverse from almost unnoticeable force to bone-crushing force as distance is decreased a little bit. You can make a stronger electromagnet than these Nd magnets, but don't expect effects at huge distances. If you hang the rod instead of sticking them in the ground, you can measure small deflections. I suppose 3m might be possible. But 8-10m might be impossible and/or extremely dangerous.
     
  17. May 31, 2016 #16

    russ_watters

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    Based on that budget, the updated answer to post #3 is "impossible".
     
  18. Jun 1, 2016 #17
    Guys thank you all very much for your input, despite the little information I was able to provide, as correctly observed. I will need some time to study through your comments and will get back to you for an update for anyone interested.

    Once again, thank you all for the contribution. It's really exciting to interact with you.
     
  19. Jun 1, 2016 #18
    This is a physics forum. Why not show the questioner a little physics?
    For example, I vaguely recall that the magnetic field of a bar magnet (dipole) decreases roughly as 1/d^3 from the end (pole).
    Is that right? Corrections?
     
  20. Jun 1, 2016 #19
  21. Jun 1, 2016 #20
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