
Electromagnetic Levitation Quadcopter [video] - zhirzh
https://www.youtube.com/watch?v=pCON4zfMzjU
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Gravityloss
[https://www.youtube.com/watch?v=OI_HFnNTfyU](https://www.youtube.com/watch?v=OI_HFnNTfyU)

They could do it with stationary electromagnets. :)

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ricardobeat
I think that's the idea for the boosters that would appear at even intervals
in the Hyperloop track. It would be infeasible to build the whole track as one
huge linear motor, which is why Musk's paper suggests an air cushion instead.

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Gravityloss
In the video I linked the other part of the system is just a flat disk of
aluminum.

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Animats
This works better linearly than as a rotary system. See Inductrack.[1]

[1]
[https://en.wikipedia.org/wiki/Inductrack](https://en.wikipedia.org/wiki/Inductrack)

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falcolas
I'm naively surprised at the amount of torque and power required to spin the
magnet heads. Those are huge motors.

It would require some serious refinement to have benefits over air cushions,
but I can certainly see a practical use for moving heavy loads slowly.

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adrianN
One benefit over air cushions is that it also works in evacuated tunnels where
you don't have enough air to blast it around.

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falcolas
I would be a touch concerned in such an environment due to the need to cool
the "floor". Lacking air, you would only be able to dissipate heat via
radiation.

But yeah, no air? No problem.

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mcphage
You can wrap the tunnel's copper sheath with cooling on the outside; only the
inside of the tunnel is evacuated.

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stcredzero
Where Halbach arrays would excel is in levitating fast moving vehicles. Such
levitation is passively self regulating, and uses tracks which can be simply
manufactured out of bulk materials. (Basically, make a track out of conductive
aluminum loops in the cheapest way you can think of.) Contrast this with
maglev technologies that require fast reacting active regulation and
supercooled magnets.

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grondilu
BTW are Halbach arrays more efficient than the magnets built by polymagnet?

[http://www.polymagnet.com/](http://www.polymagnet.com/)

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moftz
I think the point of polymagnets aren't to maximize the magnetic attraction in
one specific direction but to allow for custom magnetic field designs. From
what their site says, it appears as if they are just controlling in fine
detail which parts of a face of a magnet point north and which point south.
Pointing sideways inside the magnet might not be possible for their equipment.
Its probably easier and cheaper to just assemble arrays of regular neodymium
to create the Halbach array than using something like polymagnets.

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grondilu
> I think the point of polymagnets aren't to maximize the magnetic attraction
> in one specific direction but to allow for custom magnetic field designs.

Getting strong magnets in one specific direction is one of their applications.
See the "attach" example of their /polymagnets page[1]:

"Polymagnets are the world’s strongest magnets because their magnetic energy
has been concentrated near the surface. Polymagnets are up to 5x stronger than
conventional magnets."

1\.
[http://www.polymagnet.com/polymagnets/](http://www.polymagnet.com/polymagnets/)

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neom
Pardon ignorance - why doesn't SpaceX and co use electromagnets to stick the
landing of a rocket (in either polarity it seems interesting)?

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vkou
Magnetic forces follow the inverse cube law. So, a magnet is 8 times weaker at
2 times the distance.

This means that over long distances (Of more then a few centimeters),
magnetism is incredibly weak. So, you can build a maglev train that hovers a
few centimeters above the track, but you can't pull a rocket that's a few
meters over the landing pad into place.

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sandworm101
Unless the rocket is moving upwards along a tallish launch tower. There you
could impart a large force for a few seconds (linear magnets in vertical
strip). Nasa studied it but i think the concept produced too many
complications. Strapping on another SRB kerbal-style is much easier.

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rtkwe
You also have to carry the weight of the corresponding track to at least a
couple thousand feet to jettison it safely I bet. It's also at the point where
the rocket is at it3 heaviest so the assistance it could give would be really
limited.

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msandford
I think you'd have much better luck turning the rocket into some kind of a
sabot round and spending a week compressing a bunch of air into huge tanks and
launching it that way. That's how subs launch ICBMs.

The reason that's not done is that rockets aren't reliable enough yet and
nobody wants to bet their billion dollar cargo on the engines starting the
first time, every time. If you lose every 100th ICBM it's a bummer, but it
doesn't make MAD not happen.

[https://www.youtube.com/watch?v=1aPvGGvnAGQ](https://www.youtube.com/watch?v=1aPvGGvnAGQ)

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sandworm101
For non-human spaceflight, a 1% loss is an option. Insurance ussually assumes
a 5ish percent chance that the payload wont survive and another 5ish that it
wont be delivered into the ideal orbit.

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throwayguestman
never mind the actual sums involved, 1% on top of 10% is a 10% increase in
coverage. Is coverage inclusive of the time lost in labor as well?

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exabrial
It seems like an air compressor might do the same thing but more
efficiently... But then I remembered they're trying to do this in a vaccuum

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candiodari
Not in a vacuum, difficult in near-vacuum (relevant for Musk's Hyperloop).

Also hovercraft are not known for efficiency. Ground-effect airplanes on the
other hand can be nearly as efficient as cars.

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dnautics
I wonder why this hasn't been "invented" yet. Halbach arrays have been around
for a long time. My best guess is that the control circuitry to make sure the
rotors are spinning in "just the right amount" is not so simple.

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chris_va
This is basically how an EDS maglev train works, though with linear motion
instead.

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seltzered_
Reminds me of the hendo Hoverboard startup, which from looking at some of
their prototypes i think used the same principle:
[http://hendohover.com/](http://hendohover.com/)

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Animats
Hendo has a great technology. Their first human-rideable version was
frictionless in all directions. This was un-steerable, and even Tony Hawk
couldn't do much with the thing. By 2015, they had a version that was a little
more controllable. But not much.[1] No new news in over a year.

If Hendo ever gets something that works and is available in volume, it's time
to get the a real place equipped for it. The plaza in front of the San Mateo
County Historical Society building in Redwood City looks like Courthouse
Square from Back to the Future. Skateboarders use that plaza now, and it's
used for ice skating some winters, so why not?

[1]
[https://www.youtube.com/watch?v=RCmQnM_iFhQ](https://www.youtube.com/watch?v=RCmQnM_iFhQ)
[2] [http://peninsulapress.com/wp-
content/uploads/2015/10/1_histo...](http://peninsulapress.com/wp-
content/uploads/2015/10/1_historic_center.jpg) [3]
[https://upload.wikimedia.org/wikipedia/commons/6/67/Hill_Val...](https://upload.wikimedia.org/wikipedia/commons/6/67/Hill_Valley_Court_House.jpg)

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jacquesm
This technology (Halbach Arrays) has also been used to create passive
electromagnetic bearings (a couple of windings of wire sent any field
imbalance to the opposite side of the array).

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mrfusion
Would this work over salt water

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DigitalJack
Time for an experiment!

I think this wouldn't work for the same reason you can't walk on water.

