# Permanent Magnet Hoverboard and base?

1. Jan 14, 2009

### bodkin77

G'day. I was wondering about the possibilities of making a permanent magnet hoverboard that levitates above a permanent magnet floor. They say that these new neodymium magnets can attract hundreds of kilos/pounds. Since repulsion and attraction forces are the same magnitude from what I hear, why couldn't they also lift hundreds of kilograms/pounds. Maglev trains use permanent magnets in Halbach arrays (one side is attractive like a fridge magnet and the other side is repulsive like, like.. the opposite of a fridge magnet?). see here... http://www.fastransitinc.com/halbach.html# [Broken]. They are tilt stabilised by seperate electromagnetic compensating systems, but on a hoverboard, I guess you could might be able to tilt stabilise by leaning or hanging onto something.

What exact forces are involved here in the vertical direction (not horizontal/tilt)? Obviously the force down (F=mg) needs to be equated with the forces up to solve for the equilibrium radius/distance. But what is the equation for the repulsion between 2 permanent magnets in Halbach arrays that have an r in it to find the equilibrium position? I think that permanent magnetism is ferromagnetism and it is the strongest, but what effect will other forces like paramagnetism and diamagnetism have on the setup? Maybe there's something that will make it completely impractical? Magnetic Saturation? Hysteresis?

Also, can the powerful neodymium magnets be bought as the 2 different types of Halbach arrays. Or maybe they have 2 poles and require bolting together into Halbach arrays?

Thanks

Last edited by a moderator: May 3, 2017
2. Jan 15, 2009

Staff Emeritus
How do you keep your hoverboard from flipping over and then crashing to the ground?

3. Jan 15, 2009

### Andrew Buren

If you see the link you will find that you need two paralel magnetic repulsors to keep it level.

4. Jan 15, 2009

### bodkin77

quick replies. Great! I believe that just using your foot to touch the magnet bed and/or holding onto something up above might keep you balanced if it's just a wobble type of force. I'm not sure if there would be an actual force, like a strong force to pull the board over, hence overpowering your leg balance. About the flipping over and crashing thing. I don't think that would be a strong impact or any impact at all because Halbach arrays are like monopolar.

5. Jan 15, 2009

Staff Emeritus
Yes, but that requires two actual tracks - if you have a board on a single plane, it's not stable against the kind of flipping I describe. When I hear "hoverboard", I think hovering skateboard - free to move in any direction - which is unstable against flipping.

6. Jan 15, 2009

### bodkin77

I reckon it could move in any direction. maybe have halback arrays side by side and end on end to make like a 3 square meter rink (small for economy purposes). I see what you mean about being unstable. It could be a problem. At first I'd be happy for it to roll around a bit because I reckon it could be corrected by foot contact with the ground or by holding something above as you move. Maybe later could use some solenoids or something with some kind of a counterbalancing system. I think the counterbalancing of the Maglev trains is solely underneath the Halback array on the undercarraige. I'm pretty sure there's only the propulsion magnets on the side.

DOes anyone know any equations to figure out how much clearance I'd get? Need to balance the force of gravity with some equation to solve for height (of equilibrium)?

Does any have any propulsion/turning ideas other than by foot? :)

7. Jan 15, 2009

Staff Emeritus
You can't create a permanent magnet configuration that stably floats over a permanent magnet floor. Earnshaw's Theorem.

8. Jan 15, 2009

### bodkin77

true for the static case, but introduce dynamics (other forces) and I think it could be done practically. This website... http://www.hfml.kun.nl/levitation-possible.html [Broken] discusses five ways to overcome the Theorem and another one might be to redistribute body weight on the board or grab a support. Thanks, I didn't know about Earnshaw's Theorem, so keep em comin'.

Last edited by a moderator: May 3, 2017
9. Jan 15, 2009

### mgb_phys

You could use frogs ;-)

10. Jan 15, 2009

### nuby

11. Jan 15, 2009

### mgb_phys

It's not a question of the force.
There isn't a stable solution for fixed levitating magnet in a constant field - it would slip out of the field or flip over.
You can either have tracks , spin the levitating magnet or add field coils and actively move the field on the ground plane to steer the object (that's how levitating globes work)

12. Jan 15, 2009

Staff Emeritus
You should re-read that article. It doesn't say anything whatever about super-cooled magnets.

13. Jan 15, 2009

### f95toli

Yes, it would sort of work work, although if I am not mistaken you would only be able to move in one direction, I can't think of a field configuration that would allow both x and y motion (note also that it is not the MAGNET that is cooled, it is the superconductor the magnet is levitating over).
In fact, levitating people using a superconductor this is a common "party trick" at low-temperature conferences (I attended one a few months ago where people who tried it even got a badge: "I have been levitated" :tongue:).

14. Jan 16, 2009

### bodkin77

@ Nuby

From looking into supercooling a little bit (and I mean a little bit), I think I get the impression that it will only induce diamagnetism (in the presence of electromagnets), which is very weak in comparison to permanent magnetism. Also, since supercooling leads to the Meissner effect, which prevents the magnetic lines of a material from passing through the material, it may also prevent OTHER magnetic lines from passing through the medium, which may remove or reduce the permanent magnetism. Though I'm guessing here. Maybe if it gets set up it could just be tried, since it wouldn't be difficult to throw down some liquid nitrogen onto either the board or base or both.

@ mgb_phys

You said "There isn't a stable solution for fixed levitating magnet in a constant field - it would slip out of the field or flip over". Yes, but over a bed of magnets, could this be corrected for by shifting of body weight or holding onto something like an overhead bar? And if you didn't know, then I'm proposing Halbach array magnets for both base and board (single sided repulsion, so won't flip over through attraction from the topside of the magnets on the board). you also said "You can either have tracks , spin the levitating magnet or add field coils and actively move the field on the ground plane to steer the object (that's how levitating globes work)". I don't want to have tracks (only). What is the effect of spinning the magnets under the board? I heard something about this but I don't know the added force or the effect name. About the field coils, yes, maybe electromagnets/solenoids or whatever might be powerful enough for tilt-steering and auto-balance if used in conjunction with shifting of body weight on the board? To atively move the field on the ground plane. Tilt magnets on the side of the board and on the ground plane to face each other by some proximity control electronics to turn the board to the opposite side! Maybe just tilt your front foot to tilt the board magnets???!

@ f95toli

I've already guessed that the superconducting would not help, but what does it have to do with x-y motion? If you know something about what would happen if Halbach arrays were placed side by side then let me know!! We know that end to end Halbach arrays work because of the Maglev Tracks. How does that party trick work? Was it a combination of permanent magnets and superconductors or what?

choice bras

15. Jan 17, 2009

### Andrew Buren

It would be amost immpossible to keep the Board cooled at the right temp.

16. Jan 22, 2009

### bodkin77

How would you super cool the base magnet and why would it work? I bought 100 of 125 mm^3 N50 cubes for \$28AU. Hopefully it will lift my Yoda figurine.

17. Jan 22, 2009

Staff Emeritus
That's why I suggested nuby re-read the article. This relies on superconductivity, not cold magnets.

18. Jan 22, 2009

### LURCH

Also note; a Halbach array only works when the board is in motion. Kinetic energy supplied by the rider generates power for the levitating magnets. So, the board would still need wheels so that the rider could get it moving. It would only levitate after he reaches the critical minimum speed.

19. Jan 25, 2009

### bodkin77

That's very interesting. Maybe the equation F=q(E+vB) applies? If E=0 (electric field) and v=0 (velocity) then F=q(0 +0)=0. I still don't know for sure how to work out the height though. I know that the Maglev trains sit on their wheels until the train reaches 5mph. I'm ordering some 5mm^3 N50's to attempt a scaled-down setup.

Does anyone know if larger magnets are stronger or weaker than smaller magnets (apart from the obvious difference with proportion to their size)?