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From: fowler@uw-beaver (Rob Fowler)
Newsgroups: net.physics
Subject: Re: Gravity-based drive mechanism
Message-ID: <960@uw-beaver>
Date: Tue, 26-Mar-85 15:46:33 EST
Article-I.D.: uw-beave.960
Posted: Tue Mar 26 15:46:33 1985
Date-Received: Thu, 28-Mar-85 00:02:29 EST
References: <1182@ihuxi.UUCP>
Reply-To: fowler@uw-beaver.UUCP (Rob fowler)
Distribution: net
Organization: U of Washington Computer Science
Lines: 26
Summary: 

The U.S. Navy was investigating a drive mechanism of the sort described.
In particular, the problem is how to get a landing craft up a beach far
enough for men and vehicles to disembark rapidly with relatively dry
feet.  The other part of the problem is to get the boat back into the
water.

The drive mechanism is really simple:  A shaft that swings  a big weight
(actually a pair to cancel high order moments).  The axis of the shaft is
perpendicular to the long axis of the boat.  All you do is rotate this
sucker with a lot of enthusiasm.  When the weight is being swung downwards
the reaction partially lifts the boat from the shaft's bearings.  The
horizontal impulse of the following horizontal motion can move the
boat because it is working against the boat's inertia and REDUCED friction
between the beach and the boat's bottom.  When the weight is rising it
presses the bottom into the beach and the following horizontal impulse
works against increased friction so rearward motion is inhibited.  In 
short, this thing deliberately uses and enhances the "walking" tendancy
of any unbalanced rotating machinery.  The boat sort of hops out of the
water onto shore.  To back up all you need to do is reverse the direction
of rotation.

It has worked in prototypes.  The only problem (as you might guess) is that
it generates a hell of a lot of unpleasant vibration.  I don't know whether
anyone has ever used this mechanism for anything practical.

-- Rob Fowler (fowler@washington, uw-beaver!fowler)