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From: grege@gold.GVG.TEK.COM (Gregory Ebert)
Newsgroups: sci.physics,sci.electronics
Subject: Re: Homopolar generators/conservation of angular momentum -- how?
Message-ID: <911@gold.GVG.TEK.COM>
Date: 12 Apr 90 16:58:12 GMT
References: <1990Apr12.043832.6000@ns.network.com>
Organization: Grass Valley Group, Grass Valley, CA
Lines: 28

In article <1990Apr12.043832.6000@ns.network.com> logajan@ns.network.com (John Logajan) writes:
>Okay, so a homopolar generator stops in 1/3rd rotation.  Where did the
>angular momentum go?  Surely it didn't exit via the axle.  Surely it
>didn't exit (mechanically) via the (as I understand it) diametrically
>opposing brushes.
>
>Signed -- confused in Minnesota.
>
     Think of it as a flywheel driving a conventional generator. As electrical
     energy is consumed (by a projectile ?) the beast coasts to a stop.

     One point that needs to be clarified is the location of the brushes.
     One brush is the axle itself, and the other(s) are along the
     circumference of the drum. The induced voltage is zero across
     diametrically opposing brushes.

     The homopolar generator will produce a current through a closed circuit
     through the axle, outward to the circumference of the drum, and through
     the brush (and of course through the load). A MAGNETIC FIELD IS REQUIRED.

     To get mongo currents, you aid the initial magnetic field produced by a
     permanent magnet, with large coils driven by the generator itself. This
     is positive feedback at its height of glory!

     To get the thing to stop in 1/3 revolution (eek!) you need a lot of
     low inductance coils in parallel. The exact equation describing the
     time it takes to stop is a second-order differential equation. Perhaps
     I should work it out and post my findings.