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I Electromagnetic levitation

  1. Mar 14, 2017 #1
    Hi, My name is Kendall. After seeing the Back to the Future again, I have been once again fascinated by the hoverboards, as I'm sure many others are also guilty of. A couple hours of research into magnetism later, and I'm still stuck.

    I have little to no experience with magnetism, but I figure that the best solution to creating a hoverboard, while not the most efficient, is as follows.
    A path (such as a sidewalk) is either paved over or coated with a magnetic plate, and a skateboard is fitted with an array of electromagnets and a servo to keep it levitating a couple of inches off the ground.

    First and foremost, is this at all feasible? regardless of the cost of such pathways, could something the size of a skateboard be fit with enough magnetism to hold up a person? If so, how would you go about stabilizing the rig for balance or even to allow for magnetic "braking"?

    I know that MagLev trains work similarly to what I'm describing, but they are much more grounded. Feel free to let me know if I am just way off the ball on this, or better yet offer up a different solution.

    Thanks,
    Kendall
     
  2. jcsd
  3. Mar 14, 2017 #2

    mfb

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    Permanent magnets plus electromagnets don't work well. If your ground doesn't have magnets on its own, you cannot let the board have a repulsive force. If the ground has magnets on its own, you either can't keep your height (if all magnets point in the same direction) or you have to switch the field orientation way too often (if they point in different directions). That is not practical. It is not an issue for maglev trains that are limited to one dimension.

    Superconducting levitation has been done. Humans can stand on it and use it as hoverboard. A quick google search should find videos and descriptions. The downside: You have to fill your hoverboard with liquid nitrogen.

    There is a loophole: You can use magnets that rotate very fast above a conducting (not magnetic) surface. That requires a lot of power, however. Here is a video.
     
  4. Mar 14, 2017 #3
    Some of the articles I read talked about spinning magnets, citing levitating tops, but it seemed like it would require a large setup and a lot of power as you said. As for the superconductor, it is another very interesting solution.

    Thanks a lot for your input, right now this is just another thought experiment for me but I may very well soon see hat I can create DIY style on amazon.
    As a quick follow up question, would the magnetic field created be more powerful using fewer, larger magnets like in the video, or an array of more smaller magnets?
     
  5. Mar 14, 2017 #4

    mfb

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    For the rotating magnet array? Big magnets are easier. You can get many small magnets and force them into the same shape, but that is just additional work.

    It might be possible to provide a significant fraction of the lifting force via permanent magnets, and just the remaining fraction via the rotating magnets. Not sure if that would work.
     
  6. Mar 14, 2017 #5
    It seems to me that the best way to go about this kind of thing, would be a "track" made out of copper sheeting, and a board with high-frequency electromagnets underneath - alternating magnetic fields induce a magnetic repulsion in conductive metals. This would solve a couple of key problems: 1.) you'd be able to electronically control the board by using pressure plates, allowing you to tilt the board to control your direction, slow down, speed up, etc., and 2.) it would provide for a smooth suspension as you moved - you wouldn't have to deal with the irregularities involved when you have an array of permanent magnets in opposition (though you could probably diffuse these irregularities with a thin iron sheet as a surface for the track).

    The problem is a portable power supply with enough wattage to drive the AC electromagnets long enough and strongly enough to suspend the board over the conductive plate material - we humans haven't gotten very far in the realm of batteries / power storage yet. Lithium ion batteries are about as good as we've got right now, and even those store a pitiful amount of power.

    But there is a possible alternative to that: evanescent field power transfer. That technology allows you to fill a room with oscillating electromagnetic fields that only couple to a specific antenna - that way you wouldn't need any batteries, you could absorb power wirelessly from the fields in the room. But they seem to be focusing on small levels of power transfer right now, to maintain a wireless trickle charge for laptops and cellphones. I don't see any reason why it couldn't be scaled up, although I'd first want to be darn sure that field wasn't coupling to the human body before I'd be comfortable spending hours in a room saturated with high-amplitude fields.
     
  7. Mar 14, 2017 #6
    That's an excellent experiment. It looks much more energy efficient than an AC current through electromagnetic inductors. They both work on the same principle, the Lenz law, but with the rotating magnets in that Halbach array configuration (https://en.wikipedia.org/wiki/Halbach_array), you only need enough energy to get them up to speed + overcome the mechanical friction of rotation (which can be minimized in a number of ways) + overcome the drag force described in the video. Perhaps you could surround the magnets with a ring of mass so the inertia would help keep the magnets spinning at the desired speed. And you could still use pressure sensors on the footpad to change the rotation speed of the spinning magnet arrays to induce a little banking in the board. I bet you could even use some gyros to rotate the board, by making them spin at nonuniform speed via pressure plate controls or a tilt control system.

    It looks like something that could be scaled down fairly easily, compared to that big heavy device in the video. There are lots of low-profile motors available today, and neodymium magnets are pretty cheap now. And you could get a stronger effect (and reduce the energy wasted on heating) if you had a thin silver plating on the track surface (silver's the best room-temperature electrical conductor, but pricey). I don't know how long you could stay afloat using a bunch of lithium ion batteries all over the bottom surface of the board, but it sounds like fun to find out!

    Here's neat video showing some of the hoverboards and hoverbikes that people have been working on lately - a couple of them employ the same kinds of ideas we've been talking about here:
     
  8. Mar 15, 2017 #7

    NascentOxygen

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    I think you could swap things around: have nothing but permanent magnets on the hoverboard and set the electromagnets embedded throughout the floor of the skatepark. Sensors could detect which electromagnets are at any one time under the board and cause just those electromagnets in the board's vicinity to be powered. As the board moves, the floor's electromagnetism would be moved along with it. The strength of the drive could be optimised to each individual rider's weight. Each board could be cheap aluminium or fibreglass, and with nothing on the board needing power, there would be no expensive battery pack required. Mains electricity would power the small active area of the floor.
     
  9. Mar 15, 2017 #8
    Why not skip electromagnetics altogether and use ultrasonic levitation... now you can go over any objects be it metallic or organic?
     
  10. Mar 15, 2017 #9

    mfb

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    With the weight of a human body? I doubt that is a safe approach.

    @NascentOxygen: That would make the track very complex and expensive.
     
  11. Mar 15, 2017 #10

    NascentOxygen

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    Initially, yes. But in the long term much cheaper, assuming a commercial park catering to dozens of users. No fancy hover boards, no lithium power packs, no recharging, no board breakages—no costly repairs.

    The floor—it would be modular.
     
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