Apparently working Hoverboard... with some constraints.

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HungryHobo
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Apparently working Hoverboard... with some constraints.

Postby HungryHobo » Tue Nov 04, 2014 6:36 pm UTC

So when I first heard this I was very dubious but apparently it's workable and just in time for the 2015 deadline.

https://www.kickstarter.com/projects/14 ... hoverboard

I could imagine some metal skate parks being quite interesting.

http://www.google.com/patents/US20140265690

Some discussion I came across on this:

OK, does someone actually fluent in electromagnetics (i.e., not me) want to read their patent and determine whether it’s B.S.?



Credentials: Bachelor’s degree in engineering physics (mechatronics specialization); Master’s thesis on motor design, currently do magnetomechanics as a career.

It is workable in principle. However, their claims that it will eventually run over non-conducting surfaces *is* absurd. This technology will likely only run on copper or aluminum surfaces.

Rather than suggesting that the hoverboard will run over non-conductive surfaces, Hendo’s patent suggests that a variety of surfaces may in the future be rendered electrically conductive by suitable additives, e.g. electrically conductive concrete. That’s… a plausible future technology, but comes across to me as wishful thinking.

They use a rotating disc of magnets, which is a pretty smart idea. The alternating N-S poles sweep across the copper surface, which induces currents that attempt to counter the field of permanent magnets. The copper plane behaver as a ‘mirror': the induced electric currents in the copper create the same magnetic field as would be created by a mirror-image of the spinning disc below the surface. That means the N poles on the hoverboard will be facing the N poles on the mirror image, and likewise with the S poles. Like poles repel, and the lift is provided this way.

If the copper were instead a superconductor, the magnets would not have to rotate at all. Even a stationary magnet lowered down onto a superconducting surface would induce a perfect mirror image current that would repel it. However, in a non-superconductor, the currents will decay with time due to the finite resistance of the metal, and the magnets would settle down to rest on the copper surface as the currents disappear. Spinning the magnets keeps the current going, and thereby sustains the lift, making up for the fact that copper is not a superconductor.

There are some practical concerns, so I’ll quickly run some numbers. The important ones are:
* Magnetic field needed to lift a practical load
* Power needed to sustain the lift

The hoverboard discs look about 20 cm in diameter, and there’s four of them, and they have magnets just along the perimeter. To support someone who weighs 80 kg, 800 N of thrust is needed. So the force per unit area is something like 20 kN per sq. metre.

The pressure between two repelling magnets can be approximated roughly as 400,000*(B^2) N/m^2. A reasonable magnetic field density obtained by neodymium magnets is between B=0.1 Tesla to 0.5 Tesla, depending on the ratio of the magnet thickness to hover height. It looks like about 0.2 T would be enough to develop the necesary lift, which is definitely practical. It will take a lot of magnet though, which makes it pricey.

The spacing of the N-S poles of the magnets should be not smaller than the hovering clearance, or else the magnetic field won’t be forced to go through the copper. It also shouldn’t be to much bigger or else it wastes a lot of magnet material. Assuming it hovers 1 cm off the ground, there could be about 20 north/south pole pairs.

It’s very hard to calculate the resistance for current flowing through a solid copper surface, but I’ll do a first-order approximation by assuming that it flows in a uniform rectangular pattern along the top side and back along the bottom side. If the copper is 6 mm thick, and the magnets are spaced at a pitch of 25 mm, then about 10,000 A of current flows in the copper and the equivalent resistance is about 0.8 micro-ohms.

So that amounts to 80 watts of power draw to keep the magnets spinning, or 320 watts for the whole hoverboard. (Again, this is a very rough calculation; I don’t know the size and specs of the actual Hendo design nor its surface, so I’m just choosing the numbers that I would use if I built one). 320 watts is quite high, but for a lithium-battery system it’s not too impractical, since the battery life doesn’t need to be that long. A 1.5 kg battery pack will keep it going for an hour.

The power loss will appear as drag torque on the spinning magnet discs. The discs will need to be arranged in counter-rotating pairs to keep the whole hoverboard from spinning (just like the rotors on a Chinook helicopter).

Directional thrust could probably be achieved by tilting the plane of the rotating magnets, although I’m not going to work out the details of this.

My conclusion: It’s not a hoax. But it will only hover on metal surfaces for the forseeable future.

Hendo technology probably won’t make maglev trains cheaper; actually, it’s based on inductrack maglev train technology. The rotating permanent magnets are a smart way of saving energy, rather than a more traditional approach of using electromagnets in an alternating-current configuration. But in enormous vehicles like trains, it becomes cheap to have a liquid-nitrogen cryogenic system and use superconducting magnets (Japan’s approach, currently with a working prototype). Meanwhile inductrack uses the train’s forward motion to generate the lift, rather than needing the magnets to spin.
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stoppedcaring
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Re: Apparently working Hoverboard... with some constraints.

Postby stoppedcaring » Tue Nov 04, 2014 6:58 pm UTC

Trying to run this thing on anything other than pure copper/aluminum would be hella tricky. "Additives" seem like the handwaving of a MAJOR hurdle.

HungryHobo
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Re: Apparently working Hoverboard... with some constraints.

Postby HungryHobo » Tue Nov 04, 2014 7:08 pm UTC

stoppedcaring wrote:Trying to run this thing on anything other than pure copper/aluminum would be hella tricky. "Additives" seem like the handwaving of a MAJOR hurdle.


I agree, I could imagine it maybe working on some other conductive surfaces but marketing is marketing and nobody is going to rip up roads to make them hoverboard accessible.
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stoppedcaring
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Re: Apparently working Hoverboard... with some constraints.

Postby stoppedcaring » Tue Nov 04, 2014 8:07 pm UTC

HungryHobo wrote:
stoppedcaring wrote:Trying to run this thing on anything other than pure copper/aluminum would be hella tricky. "Additives" seem like the handwaving of a MAJOR hurdle.


I agree, I could imagine it maybe working on some other conductive surfaces but marketing is marketing and nobody is going to rip up roads to make them hoverboard accessible.

Copper is one of the most common super-low-resistance materials around; not going to do much better than that. Anything more resistive than Copper will require incredible power and produce massive amounts of heat.

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Re: Apparently working Hoverboard... with some constraints.

Postby p1t1o » Wed Nov 05, 2014 10:35 am UTC

Isn't it going to be impossible to turn on that thing? I don't see how the board would not have identical friction in any direction, even if you angled the board, would not the repulsive force still be perpendicular to the ground?

Wheels are a good solution for a reason...

stoppedcaring
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Re: Apparently working Hoverboard... with some constraints.

Postby stoppedcaring » Wed Nov 05, 2014 3:23 pm UTC

I could see a tech-heavy university spending some stagnating building grant funds to put a series of slightly-concave aluminum trailways all around its campus. My university wasted a bunch of money giving all the cops useless Segways.

Hypnosifl
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Re: Apparently working Hoverboard... with some constraints.

Postby Hypnosifl » Wed Nov 05, 2014 5:09 pm UTC

p1t1o wrote:Isn't it going to be impossible to turn on that thing? I don't see how the board would not have identical friction in any direction, even if you angled the board, would not the repulsive force still be perpendicular to the ground?

Wheels are a good solution for a reason...

This article indicates it'll have some system where pressing on different parts of the board can vary the relative strength of the field from each of the four rotating magnetic discs, producing a torque that can rotate the board:
Riding the contraption was a lot fun, but also quite the challenge: The Hendo hoverboard doesn't ride at all like McFly's flying skateboard. In fact, without a propulsion system, it tends to drift aimlessly. Arx Pax founder and Hendo inventor Greg Henderson says it's something the company is working on. "We can impart a bias," he tells me, pointing out pressure-sensitive pads on the hoverboard's deck that manipulate the engines. "We can turn on or off different axes of movement." Sure enough, leaning on one side of the board convinces it to rotate and drift in the desired direction.

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Re: Apparently working Hoverboard... with some constraints.

Postby p1t1o » Thu Nov 06, 2014 11:01 am UTC

Hypnosifl wrote:
p1t1o wrote:Isn't it going to be impossible to turn on that thing? I don't see how the board would not have identical friction in any direction, even if you angled the board, would not the repulsive force still be perpendicular to the ground?

Wheels are a good solution for a reason...

This article indicates it'll have some system where pressing on different parts of the board can vary the relative strength of the field from each of the four rotating magnetic discs, producing a torque that can rotate the board:
Riding the contraption was a lot fun, but also quite the challenge: The Hendo hoverboard doesn't ride at all like McFly's flying skateboard. In fact, without a propulsion system, it tends to drift aimlessly. Arx Pax founder and Hendo inventor Greg Henderson says it's something the company is working on. "We can impart a bias," he tells me, pointing out pressure-sensitive pads on the hoverboard's deck that manipulate the engines. "We can turn on or off different axes of movement." Sure enough, leaning on one side of the board convinces it to rotate and drift in the desired direction.


Sounds like pretty weak sauce, damn thing needs a rudder. Maybe if acquiring speed is easy enough, then aerodynamic steering might be feasible, like wearing a mini-wingsuit?

Also cant resist this:

"Roads? Where we're going, we'll definitely need roads. Like copper or aluminium roads."

MoffKalast
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Re: Apparently working Hoverboard... with some constraints.

Postby MoffKalast » Sat Nov 15, 2014 9:58 am UTC

Although what effort (except paying for the copper) would it take to mix grinded copper powder into asphalt? Roads need replacing every now and then as they obviously wear out. My guess is that the particles would wear out rubber tires faster and the concentration of copper wouldn't be enough for the magnets to reflect from... right? Just imagine everyone crusing around in hovercars though :O

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Re: Apparently working Hoverboard... with some constraints.

Postby Copper Bezel » Sat Nov 15, 2014 10:48 am UTC

Doping isn't enough - you need a continuous conductive surface, apparently.
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Hypnosifl
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Re: Apparently working Hoverboard... with some constraints.

Postby Hypnosifl » Sat Nov 15, 2014 6:06 pm UTC

I think the issue is that for it to work, the oscillating magnetic field from the rotating magnets in the hoverboard need to create eddy currents in the conductor below (I wrote up a post here on what I understand of the physics principles at work in the Hendo hoverboard, if anyone's interested, though most of it is already covered in the long quote in the opening post of this thread). If you just had a bunch of particles of conductive material embedded in asphalt, I think you wouldn't get the type of large-scale loops of currents needed.

According to the table here, there are some materials with conductivity almost as good as copper and aluminum, don't know if any would be cheaper than aluminum. One I noticed is calcium, which is apparently has a conductivity of 76% that of aluminum--maybe we could just make our hover-roads from the bones of the dead? (edit: sadly no, this page mentions that "Calcium actually has an electrical conductivity about forty percent that of copper; however, its conductivity under normal atmospheric conditions is usually limited by its chemical reactivity with air.")

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Re: Apparently working Hoverboard... with some constraints.

Postby Frenetic Pony » Sun Nov 16, 2014 12:58 am UTC

The question of what it would be able to be used over is indeed fascinating. I'm trying to find a place to put this into my next book as a kind of ice-rink. Except its a hover rink, yeah? That would seem more practical than trying to build paths everywhere just for magnetic hoverboards, that are going to be fantastically unstable anyway. I'm imagining you might be a bit jealous of stability and friction afforded to ice skaters, all considered

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Re: Apparently working Hoverboard... with some constraints.

Postby gmalivuk » Mon Nov 17, 2014 3:57 am UTC

Yeah, there's a reason ice skates are constructed differently from baking sheets.
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ForOhForError
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Re: Apparently working Hoverboard... with some constraints.

Postby ForOhForError » Thu Nov 20, 2014 2:51 pm UTC

Solution: Traditional Skateboard with a surface of copper positioned beneath the hoverboard. :wink:

MarvinM
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Re: Apparently working Hoverboard... with some constraints.

Postby MarvinM » Sun Nov 23, 2014 9:45 pm UTC

Seems to me that if the engine is travelling, the force on the poles against the direction of travel should be greater than that the force with. So the hover engine produces a force that acts against the direction of travel. That's not the frictionless one push and it goes for miles I was hoping for. It's a lifting device and a magnetic brake.

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Re: Apparently working Hoverboard... with some constraints.

Postby Hypnosifl » Sun Nov 23, 2014 11:37 pm UTC

MarvinM wrote:Seems to me that if the engine is travelling, the force on the poles against the direction of travel should be greater than that the force with. So the hover engine produces a force that acts against the direction of travel. That's not the frictionless one push and it goes for miles I was hoping for. It's a lifting device and a magnetic brake.

Are you basing that on Lenz's law, or some other type of analysis? Also, this paper suggests it is possible to get a net thrust on a particular arrangement of magnets rotating over a conductor. The configuration analyzed in the paper is different than the one in the Hendo board, but this suggests at least that there must be a flaw in any general argument that gives the conclusion that the magnetic field from a conductor always opposes motion of a spinning collection of magnets above it (it would presumably oppose the rotation itself even if it doesn't oppose motion of the center of mass, but that's part of why you have to use powerful motors to keep the rotation rate constant).

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Re: Apparently working Hoverboard... with some constraints.

Postby partschmants » Mon Nov 24, 2014 1:42 pm UTC

Everyone seems to be looking for solutions to the issues the hoverboard faces, but few seem to wonder whether THIS IS EVEN WORTH IT.

HungryHobo
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Re: Apparently working Hoverboard... with some constraints.

Postby HungryHobo » Mon Nov 24, 2014 1:56 pm UTC

partschmants wrote:Everyone seems to be looking for solutions to the issues the hoverboard faces, but few seem to wonder whether THIS IS EVEN WORTH IT.


Humanity would still be huddled round campfires for warmth trying to kill lions for that skin if we took that approach so fast for everything.

Why would I want a cell phone? they're massive, heavy, expensive ,have terrible range and there's hardly any commercial network coverage. Few seem to wonder whether THIS IS EVEN WORTH IT!

Why would anyone want a car, they're noisy, dirty and you have to have someone to walk ahead of it with a flag. Few seem to wonder whether THIS IS EVEN WORTH IT!

the first iterations of a technology are rarely much use for seeing what people will end up using it for. Perhaps it will turn out to be dull to use, no fun and of no utility but until people have actually tried you don't know.
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Re: Apparently working Hoverboard... with some constraints.

Postby gmalivuk » Mon Nov 24, 2014 2:32 pm UTC

Why would we be huddled around fires? I know you say all your friends have fires but that's not true because the Johnsons down the street still eat their meat raw and we've been friends with them for years. Fires are hot, smelly, smokey, and extremely dangerous if they get even a little bit too big. Everyone's busy looking for solutions to those problems but few seem to wonder whether THIS IS EVEN WORTH IT.
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Re: Apparently working Hoverboard... with some constraints.

Postby Tyndmyr » Tue Nov 25, 2014 9:18 pm UTC

partschmants wrote:Everyone seems to be looking for solutions to the issues the hoverboard faces, but few seem to wonder whether THIS IS EVEN WORTH IT.


Oh god, you're right. Everyone IS trying to solve problems instead of not caring. How tragic. Obviously, the end is nigh.


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