
Magnetic Bearings Might Keep Motor Spinning for Millennia - oedmarap
https://hackaday.com/2019/03/25/magnetic-bearings-might-keep-this-motor-spinning-for-millennia/
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ip26
Arguing about how many millions of years it will run for seems to be missing
the forest for the trees. IMO the real message here is, holy crap magnetic
bearings are amazing, now how do we get them into everything else? _

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akiselev
By making significant improvements in the material science and manufacturing
of paramagnetic and diamagnetic materials. Magnetic bearings are limited by
Earnshaw's theorem [1] which states (roughly) that you can't stabilize some
regular magnets using only their charge - they have to dynamically respond ti
each other or they'll all just fly off. Usually this is done with
electromagnets and a control system like in jet engines but its expensive and
difficult. The alternative is passive para/diamagnetic materials whose
magnetic fields change based on the other fields around them but those are
usually rather exotic and have to be precisely engineered. Without that
stabilization, the bearings would be worse that useless since they would never
be able to prevent the rotor from touching the stator.

[1]
[https://en.wikipedia.org/wiki/Earnshaw%27s_theorem](https://en.wikipedia.org/wiki/Earnshaw%27s_theorem)

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ajuc
There're so many loopholes:

> Spinning ferromagnets (such as the Levitron) can—while spinning—magnetically
> levitate using only permanent ferromagnets

> Pseudo-levitation constrains the movement of the magnets usually using some
> form of a tether or wall. This works because the theorem shows only that
> there is some direction in which there will be an instability. Limiting
> movement in that direction allows levitation with fewer than the full 3
> dimensions available for movement (note that the theorem is proven for 3
> dimensions, not 1D or 2D).

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JoeAltmaier
When talking times like that, lots of 2nd-, 3rd- and 4th-order effects become
important. Like flexing of the mechanism due to Coriolis forces, or coupling
between the magnet and the earth's magnetic field. Heat losses that will stop
the motor in years, not millennia.

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sathackr
he's measuring the actual current draw of the running system with a meter.

Are you saying that Coriolis forces and the earth's magnetic field will have a
greater effect on the system in a few years as opposed to now?

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JoeAltmaier
The idea was, it could run forever in an evacuated chamber? Else the idea is
meaningless; the battery would decay to dust.

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JumpCrisscross
> _it could run forever in an evacuated chamber?_

Space?

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spenczar5
It's a cool project, but (as many other commenters noticed) most of the
battery's energy is being dissipated through the resistors, so it's not going
to last for millennia as built.

Still very cool, though.

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szczys
Actually, I think it could last for millennia as built. Just not the full
89,000,000 years as mentioned. Even if you ditch the theory, there's a good
chance this will keep running as built for several decades and that's pretty
crazy. Makes me want to build one and let it run.

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rootusrootus
They are only claiming 89,000 years, not 89 million. But yeah, probably a few
decades is plausible, the battery isn't going to last thousands of years.

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caf
I do wonder how long you could engineer a capacitor to last, though - given
you have little constraint on its physical size.

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blueadept111
This motor needs to put into a vacuum chamber pronto!

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sevensor
Funny you should mention that. Hi-vac turbo-molecular pumps often use maglev
bearings. This is the pump that takes a chamber from low vacuum (like 1 torr)
to high vacuum (like 1e-6 torr). It's a turbine that resembles a small jet
engine.

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hu3
Another long-lasting cool experiment:
[https://en.m.wikipedia.org/wiki/Pitch_drop_experiment](https://en.m.wikipedia.org/wiki/Pitch_drop_experiment)

"The pitch drop experiment is a long-term experiment which measures the flow
of a piece of pitch over many years. 'Pitch' is the name for any of a number
of highly viscous liquids which appear solid; most commonly bitumen. At room
temperature, tar pitch flows at a very low rate, taking several years to form
a single drop."

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tener
After pumping out the air and adding a small solar panel I guess it could spin
basically forever?

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MrEldritch
Solar panels wear out pretty quickly, actually - within decades. UV light's
nasty stuff.

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FreeFull
How quickly would a protective coating on the glass wear out? Or the
green/brown colouring that gets added to beer bottle glass.

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Pharmakon
How much would such a coating reduce the efficiency of the panel though? I’m
seriously asking btw, I don’t know the answer or very much about PV panels.

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14
That seems to be the fantastic part of this motor. Even if you traded off
almost all efficiency in order for protectiveness of the material instead,
this machine runs on such a low power you could make those trade offs. What
you could use this motor for I am unsure.

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Pharmakon
Too cool. Hey, could these bearings be used in something like a water wheel or
windmill? I realize the technology isn’t there yet, but if it could then
really you’d could have lowered maintenance costs, slightly increased
efficiency, and probably a lot less noise.

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MrEldritch
>technology isn't there yet

In what sense?

>lowered maintenance costs

Not really, actually - hydrodynamic bearings _already_ work on the "zero wear
due to zero surface contact" principle. The reason this is using magnetic
bearings is just because it needs super-super low friction, under super-tiny
loads, in order to work.

>Probably a lot less noise

Bearings aren't generally noisy. If they were, they wouldn't be very good
bearings!

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Pharmakon
I stand massively corrected on all fronts, thanks!

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teekert
What about those devices that harvest radio (wifi a.o.?) waves? What do they
generate?

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carapace
Reminds me of the Long Now project 10,000 Year Clock[1].

If you just wanted a simple stable multi-millennia clock you could make a
large water clock[2] with pitch[3].

[1] [http://longnow.org/clock/](http://longnow.org/clock/)

[2]
[https://en.wikipedia.org/wiki/Water_Clock](https://en.wikipedia.org/wiki/Water_Clock)

[3]
[https://en.wikipedia.org/wiki/Pitch_drop_experiment](https://en.wikipedia.org/wiki/Pitch_drop_experiment)

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baybal2
No, diamagnetics will be receiving rotational momentum from the spinning
magnet, microscopic, but still non-zero.

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MertsA
It's a shame when comments like these are downvoted. You're spot on, magnetic
bearings certainly have a very small drag, but it's not zero. Going over that
reed switch will also produce a tiny amount of drag, it's miniscule by any
measure, but it's still additional drag. Even just the fact that it's a
spinning magnet passing by that conductive copper is going to induce a tiny
drag force.

What would be cool is a version of this but instead of permanent magnets in
the rotor make it an induction motor or an electrostatic motor.

~~~
MrEldritch
He's being downvoted because that's _completely irrelevant_ \- the thing isn't
relying on just _coasting_ for millennia. That figure's based on the _actual,
measured power draw_ of the motor, which includes the bearing friction and
other drag, and dividing by the energy stored in the battery.

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zizee
Are there super capacitors with expected lifetimes measured in centuries /
millennia?

Making a device that could keep running long enough for civilization to fall
into the dark ages, and then grow again from scratch does something funny to
my brain.

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hwillis
> Are there super capacitors with expected lifetimes measured in centuries /
> millennia?

No, certainly not. Supercapacitors self-discharge significantly faster than
batteries do. Capacitance is proportional to the surface area of the
electrodes and inversely proportional to the distance between them. Resistance
is the opposite, so roughly speaking higher capacitance means higher self-
discharge.

The current go-to for long lasting batteries is lithium thionyl chloried, used
in remote areas, embedded electronics and things like portable defibrillators.
Those are some of the most energy-dense batteries available (though not
rechargeable) and can hold most of their charge for over a half century.

The Oxford Electric Bell[1] was linked in the comments under the post, and it
has been ringing since 1840. It's not known what kind of battery it has, but
its some kind of dry pile. Dry piles generate voltage via corrosion of metal
(eg zinc) and have extremely high resistances between plates since there is no
liquid electrolyte. As long as they are kept relatively dry they have
incredibly long lifespans, although their power output is miniscule- orders of
magnitude smaller than even this motor.

It might make more sense to tap into an extremely long-lived source of power,
such as geothermal. Over millennia tectonic shift is only a problem across a
fault. As long as you can set up a thermal gradient (eg by pushing a stainless
steel wire deep into a hole), you can run a Peltier (Seebeck) generator. Some
semiconductors have meaningfully limited lifespans and eventually fail under
normal use, but many are effectively inert and last as near to forever as we
can figure. I'm pretty sure most thermoelectric junctions are the latter, with
exceptions for radiation. They have a standard MTBF of just under 23 years
with frequent thermal cycling, which is the most damaging thing you can do. It
wouldn't be hard to imagine it lasting millennia in a sufficiently stable
environment.

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

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acomjean
might be useful for those "flywheel" based energy storage devices.

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

(My favorite part of the article where it talks about trying to use in
vehicles...)

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hossbeast
Page needs a Buy Now button

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beambot
Cool project -- sort of like an electromagnetic radiometer.

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stevespang
multimeters of this sort cannot accurately measure such low voltages and amps
since they by design inject low amounts of their own battery power into the
system and measure what comes back.

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PhantomGremlin
_multimeters of this sort cannot accurately measure such low voltages and
amps_

That's an interesting point. I've used similar multimeters for many years and
was not aware of that limitation.

But for this particular design it would be trivial to determine both the
voltage and the current to within about 1% accuracy.

V = I * R

Most of the voltage drop is across the 24 megohm resistor string. Measure the
voltage across that, and you get the current flow, since you know the
resistance is nominally 24,000,000 ohms. Most voltmeters have an impedance in
the 1000+ megohm range, so measuring across the resistors won't introduce much
inaccuracy.

The resistors themselves appear to be 5% tolerance. But by measuring the
resistance of the string (open circuit) with the multimeter you should be able
to determine their actual value to better than 1%.

