NetNews Usenet Archive 1992 #31/NN_1992_31.iso/spool/sci/electron/21662

Internet Message Format | 1992-12-29 | 2.5 KB

Xref: sparky sci.electronics:21662 sci.energy:6481 rec.autos.tech:17205
Path: sparky!uunet!gatech!darwin.sura.net!seismo!skadi!stead
From: [e-mail] (Richard Stead)
Newsgroups: sci.electronics,sci.energy,rec.autos.tech
Subject: Re: Flywheel batteries as EV power source
Message-ID: <[e-mail]>
Date: 29 Dec 92 01:04:51 GMT
References: <[e-mail]> <[e-mail]>
Sender: [e-mail]
Followup-To: sci.energy
Lines: 35
Nntp-Posting-Host: skadi.css.gov

In article <[e-mail]>, [e-mail] writes:
> Jim many people have brought this up with fantasies of cars failing to bank
> on corners and rolling wildly on hilly roads.  This rest on the ignored
> assumption that the housing is rigidly mounted on the car frame.  If the
> housing is mounted on flexible elastic mounts, the gyroscopic effects on
> the car could be brought lower than the effects of a heavy set friend
> bopping to heavy metal in the back seat.

Ok, let's just check that.  Angular momentum (L) of the rotor is the energy
stored divided by the angular velocity.  The energy stored is about 92000 kCal.
The angular velocity is anywhere from 2775 radians/s to 40,000, given the
various designs posted.  At 2775, this gives about 140,000 J-s.
Now, let's say you take 5 seconds to make a 90 degree turn.  Torque is
the change in angular momentum over time.  The vector direction of the
change in torque is tangential to the curve, and the torque is 1.414*L/5
or about 40,000 N-m.  How about the bopper?  Let's say he's 200 kg (big),
and is able to swing his body back and forth (180 degree) once a second
and is 2 meters tall (we'll assume he's standing, and all his weight is in his
head).  That's a heck of a bopper.  Ok, L=200*2*2*pi = 2500 J-s, and torque
would be 5000 N-m, 1/8th of the slow-rotating big flywheel in a turn
(the flywheel was 100 kg and 1 meter radius).  A smaller flywheel would
exert less torque due to its higher velocity (this seems counter-intuitive,
but it is true since energy is constant and energy goes as v^2, while
momentum goes as v).  Of course, no one can bop like the bopper I proposed,
and most turns succeed in much less than 5 seconds, so it would be a very
small flywheel that would actually store the 92000 kCal and still exert
less torque than your bopping buddy.  However, such flywheels are beyond the
strength limits of any material, so they are figments of the imagination.


--
Richard Stead
Center for Seismic Studies
Arlington, VA
[e-mail]