From: rat@erg.sri.com (Ray Trent)
Subject: Re: Flywheel batteries as EV power source
Reply-To: rat@erg.sri.com (Ray Trent)
Organization: SRI International, Menlo Park, CA
Date: Wed, 23 Dec 92 20:12:47 GMT

In the referenced article, stead@skadi.CSS.GOV (Richard Stead) writes:
>then you've only saved 25% of the energy.  So 400 MJ goes to 300 MJ,
>300MJ is still a huge explosion.
>
>> gasoline powered vehicles, nor are they intended to be used for
>> towing. We're talking commuter cars here.
>
>But the Company making the claims talked about a 600 mile range in
>Popoular Science.  That's not a short commute.

Someone's actually claiming to have *developed* a flywheel car?!?
Sounds like a stupid bit of vapor ware and false advertizing to me.
Did they specify the velocity at which the vehicle has a 600 mile
range? On a salt flat at 1 mph, for example, it takes almost no energy
to go 600 miles. Sigh. 

>> pipe in normal operation. This much energy, at least, would not
>> present in a flywheel.
>
>Q losses would be present however, as well as losses involved in maintaining
>vacuum and maintaining magnetic suspension.  These are energy losses that
>occur before the power ever gets to the motor.

True enough. I would hope that the system would be completely sealed,
though, requiring little or no energy to maintain vacuum.
Carbon-carbon is a pretty low Q material if I remember correctly, but
it is another factor to consider.  On the other hand, a gasoline
engine has much higher friction losses...who knows.  It might be a
wash. On the other hand, Gasoline engines are what, 30% efficient?
Transmission and accessory losses are what, about 20% of that? If I
remember correctly, the best electric motors are order of 95%
efficient. 

Comparing to a gasoline engine seems likely to be extremely difficult.
Let's make this much easier: how much energy is supposed to be stored
in the batteries of an electric vehicle? Use that as a benchmark, it
will be much easier (I don't know what the answer will be, BTW, I'm
just arguing from a devil's advocate position that there could well be
reasonable explanations as to why flywheel failure might not be
incredibly dangerous...though the arguments put forth so far don't
seem to fall into that catagory...I've seen the results of dropping a
simple physics lab gyro (with considerably less energy) off its
mounts...don't worry, it'll take a lot of convincing for me as well
before I step into one of these things). It just seems like a waste to
dismiss a technology that has so many potentially nice features
without at least exploring it fairly.

>equallly well to this vehicle.  The "big problem" with lead-acid storage
>is the weight.  All of the savings associated with vehicle design
>changes can be applied to the standard electric as well.  Then the battery
>problem becomes less and will remain more practical than flywheels
>for any vehicle design.

Actually, I thought the big problem with lead-acid storage was a bit
more obvious than that: fifty gallons of 10M sulphuric acid and a
few hundred pounds of lead released into the immediate environment
(which may well contain a burning gasoline powered vehicle as well). I
hate to think what mining and manufacturing all those toxics is going
to do...it's pretty bad already and they only use the damn things for
*starting* cars.

But in any case, all designs I've seen lately for electric cars
contain most if not all of these features. 

>Depends on what you consider loss.  The standard physics environment
>of no gravity, smooth frictionless plane, no air, etc., says the only
>energy that is real (not "loss") is that required to accelerate the car
>initially.  That is tiny indeed, but irrelevant.  The real world has

Actually, it doesn't even cost that, since you can theoretically
recoup the kinetic energy upon accelerating in the opposite direction
at the end of the trip. But I really wasn't thinking of that ideal a
situation.  Let's just talk about normal frictive losses: air
resistance and rolling resistance (for the moment, assume a 2 way
trip, so the potential energy change is 0). Last I heard, the HP
required to maintain a normal not particularly aerodynamic passenger
car at 60 MPH was something like 15 HP.  That's around 1100
Joules/second. A 600 mile range would require roughly 40 MJ. It's
still a lot of energy. But it's getting down to the range where it's
not totally unfeasible to contain. And that's for the rather
ridiculous claim of 600 miles range at 60 MPH, which I don't believe
for a minute.

Add far better (ugly, admittedly) aerodynamics that would be practical
if you didn't have to worry about an engine compartment and engine
cooling and subtract a fair amount of rolling resistance for the lower
mass, and I'd be willing to bet you could get it down another order of
magnitude. Again, same is true for an electric vehicle, though they
might still need all that frontal area to allow enough space for the
batteries...

Of course, charging time on a flywheel would be limited only by the
available electric power, so "recharging" in a minute or so is
perfectly *possible* (note: I'm not claiming it's *likely*). I just
don't understand the driving need :-) for a 600 mile range.

>efficient than the gas one.  Are there any gas vehicles that
>can go 600 miles on 2 gallons of gas?

Actually, yes, there are. Not that that's really relevant to the
discussion at hand (they're experimental, low speed, and *totally*
impractical). If I remember corectly (and no one's broken the record
again in the last year or so) the current record is something like
1200 MPG (not a typo, that's a 4 digit number).

>> Actually, though, the thing I'm curious about is: how do they manage
>> to find strong enough materials to make the mounts that connect the
>> counter-rotating flywheels? There's one hell of a lot of precessional
>> energy released in a change of orientation of even minor proportions,
>
>And if this energy is not recovered, it represents more losses.

Ah, I mis-spoke. I meant precessional force. It's not energy unless
the force is applied though a distance. If you manage to find a stiff
enough, strong enough, usable material for the housing to "connect" the
flywheels, very little energy will be lost.

Does anyone know how they are proposing to extract the energy from the
flywheels, BTW? Induction off of some kind of windings seems a
plausible method, which would be very nearly lossless (much better
than battery discharge efficiencies anyway), but it might be
unfeasible for some reason I can't think of. There are some
interesting electromagnetic tricks that might be effective at using
the precessional force from each flywheel to pump the other one and
solve this problem at the same time, though...interesting.

-- 
"When you're down, it's a long way up
 When you're up, it's a long way down
 It's all the same thing
 And it's no new tale to tell"                      ../ray\..