NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/sci/electron/21013

Text File | 1992-12-18 | 6.8 KB | 139 lines

Newsgroups: sci.electronics
Path: sparky!uunet!seas.smu.edu!mustafa
From: [e-mail] (Mustafa Kocaturk)
Subject: EV Power Source versus Gyroscope - Newtonian Mechanics
Message-ID: <[e-mail]>
Summary: Precession will not cause significant friction
Sender: [e-mail] (USENET News System)
Nntp-Posting-Host: turbo_f.seas.smu.edu
Cc: mustafa
Organization: SMU - School of Engineering & Applied Science - Dallas
References: <Ligon-161292082905@3.1.100.11> <[e-mail]> <[e-mail]>
Date: Thu, 17 Dec 1992 20:46:54 GMT
Lines: 124

In article <[e-mail]> [e-mail] misinterprets
the effects of precession while quoting [e-mail] (Vance Morrison),
who wrote in article <[e-mail]>:
>> 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.

  I believe this is a joke.  The motion of the flywheel housing
  relative to the car will be limited, as will the energy lost in
  friction in the gimbal bearings.  The reasons are given below.

  I would prefer an overdamped gimbal-spring suspension
  to an undamped spring suspension used in the electromechanical
  battery model shown in the special report entitled
  "The great battery barrier" of the November issue of IEEE Spectrum.

  There will be precession as long as there is a torque
  applied to the the spinning flywheel with a component outside
  the axis of spin.  The precession is proportional
  to the external torque causing it.  Precession stops when
  the external torque is removed.

  Frictionless gimbal bearings are essential in gyroscopes
  because they are designed to keep an accurate
  attitude angle over a reasonable period of time,
  and any external torque would destroy the initial attitude
  angle information.  Not only are gimbal bearings necessary, but
  external effects such as air friction, cable stress, and
  electromagnetic forces must also be minimized by the same token.

  There is no such requirement in the case of a flywheel-powered
  electrical vehicle, since we are not worried about destroying the
  precision of the attitude angle of the flywheel axis.

>> 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 flywheel attempts to precess only when there is an external
  *torque* not parallel to its axis of rotation.  I used the word
  "parallel", because I am speaking about a torque as opposed to
  a force.  The torque is the vector product of a force and a distance
  vector.

  In a flywheel-powered vehicle, the torque will exist only when the car
  has an acceleration component not perpedicular to the flywheel axis
  and it will be negligible because the flywheel will have a negligible
  reaction due to the relatively small friction of the gimbal bearings.

  The motion will be limited because all that has to occur is that
  the flywheel should either retain its original attitude angle
  or assume the new attitude forced by the vehicle.  There will be
  a reaction torque from the flywheel proportional to the angular
  acceleration of the vehicle, the angular momentum of the flywheel
  and perpendicular to both.  Equilibrium will be reached
  as the vehicle absorbs the reaction torque,
  which was already described in other articles of this thread.

  A more critical design question is whether the magnetic suspension
  of the flywheel can handle the forces involved if springs are used.
  The springs act as shock absorbers and can be used to ensure that
  the maximum possible angular acceleration of the vehicle
  does not drive the flywheel out of its axis.

  For coupling energy, no brushes will be necessary:
  Flexible wiring can be used instead,
  as the flywheel axis will try to retain its vertical position,
  and all the motion will be fluctuations around this attitude angle
  equal in magnitude to the changes in the attitude angle of the vehicle.

  A small force times a small distance will produce a small amount
  of work.  Then the energy lost in the precession effects will
  be negligible compared to the loss in wiring, imperfect vacuum,
  hysteresis, eddy currents, etc, let alone that caused by
  the dynamics of the vehicle, tires and air turbulance, etc.

  [ ... discussion that I mainly agree deleted for brevity ... ]

>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.)

  I agree with these cost arguments.  I am not sure, however that the "rectenna"
  concept can be applied at lightwave frequencies.  The drawbacks are

   o Natural light is not coherent, i. e. it does not have a single
     frequency and phase.  By this token, the powers are added rather
     than multiplied.  The "rectenna" technology is suited to coherent
     radiation, to which the receptors can be tuned for maximum
     efficiency.

   o It may be considerably more difficult to build small, high precision
     antennas using microelectronics technology, not to mention
     the fast diodes required to rectify lightwave frequencies with
     available semiconductor materials, than to build higher efficiency
     photovoltaic cells.

>
>    --- Jamie Hanrahan, Kernel Mode Consulting, San Diego CA
>Internet:  [e-mail], [e-mail], or [e-mail]
>Uucp:  ...{crash,eisner,uunet}!cmkrnl!jeh

Yours respectfully,
Mustafa
--
Mustafa Kocaturk   [e-mail]  EE Dept., Room 305A, Caruth Bldg.
Home: 214-706-5954  Office: 214-768-1475  SMU Box 753190, Dallas, TX 75275