From: jeh@cmkrnl.com
Newsgroups: sci.electronics
Subject: Re: Flywheel batteries as EV power source
Date: 16 Dec 92 16:05:33 PST
Organization: Kernel Mode Consulting, San Diego, CA

In article <BzD4As.Cup@cs.uiuc.edu>, morrison@cs.uiuc.edu (Vance Morrison) writes:
> Ligon@macgw1.ge.com (Woody Ligon) writes:
> 
>>If such effects are significant they could be, I suppose, an additional
>>selling point both in terms of ride quality and safety. 
> 
>>I am assuming of course that the flywheel axle is vertical and the plane of
>>rotation is horizontal. 
> 
>>Also wouldn't it seem that the gyroscopic effects would put terrific
>>strains on the flywheel bearing systems whenever the car hit a bump in the
>>road?  And how do you make a bearing strong enough to take that beating and
>>still be extremely low friction?
> 
> Actually, the rotational inertia is not really the big problem with flywheels.
> First of all, if you do it right, the inertia can help, not hurt (mounting
> the flywheel horizontally will keep the car from tipping left to right
> or up and down, which is desirable (just the wheels move up and down)).

I'm not sure what you mean by "mounting the flywheel horizontally".  If you
mean with a vertical axis of rotation, and horizontal plane of rotation, 
it will precess when the car enters a banked turn (and again when the car
leaves the banked turn) or when the car's pitch (in airplane terminology) 
changes,  as when you enter a sharp incline.  

If the flywheel is mounted with its axis of r. either parallel to the wheel
axles or parallel to the car's centerline, it will precess during turns.  

> If you REALLY don't want the angular inertia, you can get rid of it one
> of two ways.  First, you could mount the flywheel in a gyroscope.  Thus
> the flywheel simply moves without effecting the car.  This also removes
> flywheel axial loads.  

I think what you mean here is "mount the flywheel in a gimbal mounting".  Fine,
but now you have to come up with a really creative way of coupling large
amounts of mechanical or electrical energy to the part of the car that's
outside the gimbal mount.  This coupling, plus the gimbal bearings on which the
flywheel assembly pivots, needs to be just as frictionless as the ones the
flywheel spins on -- any heat produced here is energy drained from the
"battery".  This ain't gonna be cheap!  Nor is it likely to survive long under
the "maintenance habits" of the typical American car owner. 

> The other possibilty is to have to counter-rotating
> flywheels.  In this case the angular inertia cancels out (there is high
> axial load between the two flywheels, however).  

The real problem I see with all such ideas is that the flywheel's attempts to
precess are going to increase the friction in its bearings -- which need to be
VERY low friction. 

> The REAL problem with flywheels is safety and weight.   Remember that a
> flywheel has the energy equivalent of gallons of gasoline.  If you were
> in a accident, this energy could all be released suddenly.   Thus there
> MUST be some sort of containment system to insure that even in the worst
> case the flywheel does not turn into a very large hand grenade.  

Yup.  You need this anyway, since the flywheel has to be spun in a vacuum, or
you lose too much energy to air resistance.  Someone else mentioned that carbon
fibers would do the job, and would just "disintegrate" upon hitting the
container.  I'm not so sure that this would be sufficient, given the large
amounts of energy involved.  You're right to compare it to a tank of gas --
imagine the energy stored in, say, ten gallons of gasoline, released in *one*
explosion!  

It reminds me of the idea of finding asteroids on collision course with earth
and blowing them up with nuclear warheads -- unless you turn the asteroid to
dust, all you do is make a bunch of smaller asteroids, and their total kinetic
energy is the same as what you started with.  (The dust has the same total k.e.
too, but the particles are small  enough that they'll burn up on hitting
atmosphere.) 

There are many stories from early computer days of the platters in early disk
drives (which were several feet in diameter) getting loose and doing lots of
damage before finally coming to a halt in the middle of a pile of wreckage. 

I have no doubt that a flywheel "battery" could be made that would be safe in
a collision.  I do have doubts about whether the units actually installed in
mass-market vehicles would be safe.  Remember the Pinto?  We have known how to
build explosion-proof gas tanks since at least WW II, but Ford wanted to build
inexpensive cars...

> It seems to me that flywheels DO have good potential in small, stationary
> applications (for example storing PV solar electricity during the day
> for use at night, here weight is not a problem, and the flywheel's
> VERY long life is a major advantage).  

The real trouble with this is that PV electricity is just too damned expensive
in the first place.  The cost of the money to build the system, plus the cost
of the land, plus the cost of the PV cells (which is an ongoing cost -- they
don't last forever!), is so high that having free energy doesn't make much
difference.  (there may be a breakthrough here soon with "rectennas" that work
directly at lightwave frequencies.) 

	--- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA
Internet:  jeh@cmkrnl.com, hanrahan@eisner.decus.org, or jeh@crash.cts.com
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