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Neat! https://youtu.be/pCON4zfMzjU seems to use the same principle for levitation.

⬐ None

None

⬐ Animats

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

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

⬐ 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.

⬐ 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.

⬐ 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.

⬐ mcphage

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

⬐ jacquesm

The currents induced in that 1/4" copper plate will be substantial. Enough to warm up the plate!

⬐ OscarCunningham

I would guess that the motors are harder to turn than they would be if they were just in the air. There must be some current in the baseplate which creates a magnetic repulsion opposing their motion.

⬐ 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.

⬐ dnautics

this is already part of the "inductrack" design (that is being proposed for hyperloop). It's been around for decades but was stalled in real development until recently, I'm guessing because of patents. As for how "fast" you need to make it - the answer, surprisingly, is "not very". IIRC, 10 kph is sufficient to levitate a vehicle.

It is a bit of a pain to make all those loops. A flat sheet of metal would be much simpler, manufacturing-wise

⬐ stcredzero

The loops don't have to be pretty, just able to carry the current and the physical forces. You could punch the material out of sheet and use rollers to crudely form. I have no idea if that's worth any efficiency gain, or if just using sheet material is better, however.

⬐ dnautics

yeah that's a good point!

⬐ grondilu

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

http://www.polymagnet.com/

⬐ 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.

⬐ 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/

⬐ F2

Halbach arrays are just a pattern or orientation of magnets that biases the total magnetic field to one direction.[1]

Polymagnets are just magnets with a pattern of multiple north-south poles on one face. [2]

At best you could have a Halbach array on a single polymagnet and have it be just as effective as individual magnets in the same pattern.

Though for large scale applications there wouldn't be much point as you could just use cheaper off the shelf magnets.

[1] https://www.kjmagnetics.com/images/blog/halbachvsalt.png [2] https://i.imgur.com/Nz9QJTV.png

⬐ neom

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

⬐ M_Grey

Electromagnets are big and heavy, and then you have to power them, which is usually more "big and heavy". "Big and Heavy" are the enemies of modern rocketry.

⬐ neom

I thought about that, but I wondered If the landing pad was the magnet and the rocket itself wasn't? (I literally have no idea wtf I'm talking about to be clear)

⬐ grzm

I suspect your parent is suggesting on the platform rather than the rocket. I'm not arguing whether or not it's a good idea, but that should shift a large part of the "big and heavy" issue off of the rocket.

⬐ M_Grey

That's a good point, and lets assumes that you can rig the rocket's legs for that without adding any weight. The issues I can imagine would be that you wouldn't get much help very far from the pad, given how quickly the EM force drops off with distance. Even worse, in those last crucial instants, instead of only having to calculate in relation to gravity, now you have to consider the rapidly increasing electromagnetic force. I'm wondering if you'd just rip any realistic feet off the lander?

Either way, it seems more like adding complexity, than a safety net. The really hard part isn't the last foot, it's getting it into that position.

⬐ mulmen

They have pulled it off several times now without the additional complication so I assume it is just not worth the effort. Also what does an electromagnet capable of holding up a rocket require in power?

Would the barge still be agile enough to function? Would the benefits outweigh the additional complication? The absence of such a system on the SpaceX barges suggests the answer to those questions is no.

⬐ soperj

Couldn't do that on another planet without installing them first. They want their system to be usable everywhere.

⬐ neom

lol, this is the actual right answer. Cleaver, thank you.

⬐ 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.

⬐ neom

Makes sense. Thanks! :)

⬐ 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.

⬐ 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.

⬐ 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

⬐ 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.

⬐ 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?

⬐ 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

⬐ 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.

⬐ 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.

⬐ chris_va

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

⬐ 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/

⬐ amelius

Can we use them only on conducting sidewalks then? Might become pretty expensive, especially if copper is used.

⬐ 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 [2] http://peninsulapress.com/wp-content/uploads/2015/10/1_histo... [3] https://upload.wikimedia.org/wikipedia/commons/6/67/Hill_Val...

⬐ 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).

⬐ mrfusion

Would this work over salt water

⬐ DigitalJack

Time for an experiment!

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

⬐ None

None

⬐ Gravityloss

https://www.youtube.com/watch?v=OI_HFnNTfyU

They could do it with stationary electromagnets. :)

⬐ Meegul

What an excellent presentation. I don't have much of a physics background, but this was immediately understandable.

⬐ 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.

⬐ Gravityloss

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

⬐ andysinclair

Thanks for posting that, I found it intriguing and ended up watching the entire video. Amazing to think this was back in 1975!