RE: Technology Prediction

From: Bob Seidensticker (
Date: Tue May 02 2006 - 15:29:41 MDT

Charles: Good points about the flywheel. Sounds like it would be a bit
more complex than I thought...

-----Original Message-----
From: [] On Behalf Of Charles D
Sent: Tuesday, May 02, 2006 2:00 PM
Subject: Re: Technology Prediction

Bob Seidensticker wrote:
> Dani: And fuel cell technology was invented in 1839. Our proposed
> Hydrogen Economy has been a long time coming.
> Your comment about hybrids got me thinking.
> The benefits of a hybrid car are regenerative braking, having extra
> acceleration on startups (engine + motor), and being able to turn off
> the engine when idling or coasting, knowing that you have your motor
> available for instant power if necessary. But couldn't we replace the
> expensive and heavy motors and batteries with a flywheel? The energy
> stored in a flywheel probably wouldn't be as much as that stored in
> the batteries, but the car would be much cheaper and lighter. Seems
> like a nice approach to a poor man's hybrid.
> I read an article about flywheel cars in the 70s, I recall (Scientific
> American?). Apparently, a flywheel can in theory hold roughly as much
> energy as a tank of gas.
> (Sorry for the tangent.)
> ...
Flywheels depend on being heavy AND on fast rotation to store energy.
Also, they are merely a store, not a primary source. (Well, primary source
is a bit vague...but gas is rather easy to add and fairly energy dense given
an oxygen atmosphere.) So you can't use flywheels + electric unless you can
recharge the things fairly often. I've heard of some electric buses that
made effective use of them...but they could frequently connect to overhead
wires, and only used the flywheels when stepping from area to area.
Improved batteries may have made them obsolete.

I can accept that a flywheel can hold as much energy as a tank of gas...tell
me it's weight (and mass distribution) and the amount of energy it needs to
hold and I'll tell you how fast it needs to spin.
For anything very large you'll need to manage frictionless rotation. (I
suggest magnetic levitation in a vacuum as the easiest method to achieve
this.) Then you'll need to devise some way to transfer momentum from the
flywheel to the powertrain. A magnetic link is probably the only feasible
way, though perhaps something based on static electricity could be made to
work...unless that were better used for the levitation. At some point the
flywheel will need to be spun-up to's that magnetic coupling
again (think electric motor). If you spin faster than a certain amount, the
flywheel will disintegrate. This whole thing sounds like a bear to design
for durability, remember that roads tend to have bumps in them. Now
consider what will happen if the road tips...OK. Gyroscopic bearings are
needed, so that it can stay in alignment (a flywheel IS a gyroscope), and
the case needs room to turn (well, to stay stable while the vehicle turns).

To me flywheels sound like a "best choice" only for certain specialized
circumstances. I'm no mechanical engineer, so I could easily be wrong, but
I haven't been surprised by the limited success such vehicles have had.

This archive was generated by hypermail 2.1.5 : Wed Jul 17 2013 - 04:00:56 MDT