

The Mechanical Battery - ph0rque
http://www.damninteresting.com/?p=909#more-909

======
ivank
Don't miss Radiatidon's comments, especially #7

~~~
Flemlord
For convenience:

Christopher S. Putnam said ”unique to flywheel designs is the gyroscopic
effect, which causes spinning objects to resist changes to their orientation.

As stated a flywheel resists change in its angular location. In playing with
various test apparatuses during the 1970,s & 1980’s, we strove to design and
build a “floating” cradle to contain the flywheel. This cradle would in theory
keep the flywheel facing in the same direction no matter how the vehicle moved
and/or turned. Theory does not always pan out in the real world.

Christopher S. Putnam said ”all of which must be released very quickly if the
flywheel breaks apart or falls off its axle.”

We did sufferer various breakdowns, as the flywheel’s mounts would shatter
under the extreme forces that such a device operates under. Also we had a
casualty when one test apparatus had a minor flaw in structure of that
flywheel.

We had powered-up the flywheel and was preparing to test yet another
combination of bearings, magnets, and high tensile frame structure. It was
giving off a most pleasant thrum and there was hardly any deviation in the
floating axis. Suddenly there was a weird sounding pop, and the warning
systems came on-line. This shut down the power to the flywheel and engaged the
slow-brake to power down the spin. Unfortunately this was too little and too
late. The floating axis shifted and sent harmonic vibrations throughout the
support structure. With an ear-piercing squeal the highly spinning metal gave
off its death cry. The device literally came apart sending shrapnel in a
vector perpendicular to the common axis of the flywheel. The safety shield
that incased the device did not live up to its design as the debris tore
through it like so much tissue paper. Unfortunately there was a fellow
standing in front of it when this happened. Like a scene out of some sick
horror flick, he was instantly split from crotch to forehead. Considering the
amount of damage, it was amazing that we suffered only the one death.

The project was canceled shortly after that.

…as interesting as this article is, I wish that I had not read the damn thing.
It brought back bad memories. Memories that are just as vivid as if it just
happened. I was standing next to him, and as he fell I tried to catch him…

------
timtrueman
I'm surprised nobody's mentioned Formula 1 yet. Next season will see the
introduction of the Kinetic Energy Recovery System (KERS). Basically it's 40kg
flywheel capable of storing 60kW of energy recovered from braking that will
allow for 6.5 seconds of additional acceleration. This is an attempt to make
overtaking a more frequent and exciting proposition. Regulations allow for
electrical or mechanical implementations. BMW chose electrical and has already
seen how dangerous it can be: <http://www.youtube.com/watch?v=fzaQ-t1ojPU>

<http://www.formula1.com/news/headlines/2008/7/8086.html>

------
mdasen

      A flywheel-based battery, on the other hand, can reach energy densities 3-4 times higher, at around 100-130 watt-hours per kilogram.
    

The problem is that the author compares fly-wheels to lead-acid batteries.
Lithium-ion batteries can easily achieve 150-200Wh/kg beating flywheels. Plus,
there are huge advances being made in chemical batteries such as those made by
A123 Systems.

~~~
DabAsteroid
(Energy per weight is not energy _density_. It is _specific_ energy. Energy
_density_ is energy per volume.)

A123 batteries are not notably high in specific-energy capacity. They are
notably low in internal resistance. Big difference.

------
mixmax
Flywheels are actually used in some state of the arts yachts to keep the yacht
level no matter how the weather is. It is mounted midship in the hull below
the waterline and keeps the yacht from rolling. Ferretti uses this system.

Since storing electricity is a problem at sea, and most yachts carry a
truckload of batteries maybe there is a business opportunity for some
flywheel-hacker...

~~~
ph0rque
I just found my stabilization system + battery storage for my super secret
artificial island plan :~)

~~~
mixmax
<http://thebuilderblog.wordpress.com/2008/03/25/az-island/>

~~~
ph0rque
Actually, I was thinking more along the lines of:
[http://ecoble.com/2007/11/18/250000-bottles-amazing-
recycled...](http://ecoble.com/2007/11/18/250000-bottles-amazing-recycled-
mexican-island-paradise/)

------
JoelSutherland
I wonder what it is like to steer a bus with a 3 ton spinning disc inside:

<http://en.wikipedia.org/wiki/Precession#Torque-induced>

~~~
eru
Just take two and spin them in opposite directions.

~~~
eru
While I think about it: You could even install the two disks spinning
horizontally, and the bus would be even more stable against tilting.

~~~
DaniFong
This actually messes up the steering geometry. you need the steering system to
be only barely in the region of stability, otherwise it takes too much effort
and energy to turn. And during turns, four wheeled vehicles bank slightly,
which is very important to maximize the normal force on the outside wheels to
increase frictional contact with the road.

In general, the dual-mass oppositely rotating flywheels work best: there's a
miniature system like this in every car to even out engine vibrations.

~~~
ph0rque
Question for you Danielle: are the dual-mass oppositely rotating flywheels
usually side-by-side, or wheel-in-wheel? Is there any advantage to one or the
other?

~~~
DaniFong
They're typically side by side. Generally in-wheel systems are expensive,
because they're harder to manufacture and of course the flywheel system should
be suspended, so you have to fit a suspension system in there as well.

Space isn't at a premium in cars, and on motorscooters and motorcycles they
just use a high rpm engine (10000 rpm in typical operation) to have smoother
torque output.

------
TrevorJ
Very interesting, although I take some issue with the thought that gasoline is
more dangerous than a fly wheel. Different dangers perhaps. In spite of what
the movies say, the energy in a gas tank can't be expended instantly in the
explosive way a disc can come apart.

~~~
eru
I had a CD come apart in a very cheap drive once.

I remember calculating that the outer regions of a CD spin at almost the speed
of sound in a modern CD drive. (But do not take my word for it - until I do
the calculation again, it's been some time.)

------
ph0rque
Just finished reading a 2000 Wired article about the state of the art of
flywheels at that point:
<http://www.wired.com/wired/archive/8.05/flywheel_pr.html>.

This makes me wonder: with all the excitement about graphene, what rpms would
a flywheel made from shells of graphene be able to achieve?

------
twopoint718
This reminds me of a little sidebar in "Fundamentals of Physics" (Halliday et
al. 6th ed.) that talks about how dangerous a rapidly spinning object can be.
They listed a case study from Test Devices Inc. where a solid steel disk
exploded from a test rig while spinning at 14 krpm. There were lead bricks
thrown into the hallway, a door was now in the parking lot, etc. Amazing.

(This was a solved exercise, ans: about 20 MJ)

------
rsheridan6
This seems like an ideal way to store energy from home solar or wind power.
The safety problems would not be an issue at home, where you could either bury
it or put a really heavy shield around it. Maybe this is irrelevant since you
can get paid for giving electricity to the grid - unless, of course, you're
not on the grid.

~~~
DaniFong
It's not quite ideal, since flywheels will still spin down, and the duty
factor on wind and solar ranges near 11%. Compressed air is actual a decent
contender in this area.

------
huherto
"to flywheel designs is the gyroscopic effect, which causes spinning objects
to resist changes to their orientation."

Is this why you do not fall from a bike when it is moving forward?

~~~
shimon
Yes.

~~~
DaniFong
Actually, the gyroscopic action contributes but it isn't dominant. The
dominant effect is the steering geometry, notably the caster angle -- the
amount the wheel is ahead of the forks.

This article is worth reading; it's an investigation into bicycle stability.

[http://ist-socrates.berkeley.edu/~fajans/Teaching/MoreBikeFi...](http://ist-
socrates.berkeley.edu/~fajans/Teaching/MoreBikeFiles/JonesBikeBW.pdf)

~~~
eru
Classic article. In order to find out what makes a bicycle stay upright, the
author tries to build an unridable bicycle. And that's harder than it sounds.
Quote:

"It seems a lot of tortuous effort to produce in the end a machine of
absolutely no utility whatsoever, but that sets me firmly in the mainstream of
modern technology."

------
maxklein
When you have an accident, what happens to the giant spinning wheel in your
car? Does it roll out and down the road?

~~~
eru
It's more likely to break apart violently.

