Re: [ATM] water drive

[GARY FUCHS <gary@rcn.com>]

Thanks Don - I appreciate your comments and explanations.

Gary Fuchs



---- Original message ----
>Date: Wed, 14 Jun 2006 14:42:34 +0000
>From: donald.good@comcast.net 
>Subject: Re: [ATM] water drive  
>To: Vladimir.Galogaza@zq.htnet.hr, atm@ATMList.net
>
>Sorry, there is no simple way for this type of drive to work 
smoothly.  Think of the ball floating on the water.  Now add a 
little wind gust to the side of the scope.  This will cause the ball 
to go up or down (depending on the direction of the wind).  Go 
ahead an give the ball a little push down and let go.  The ball 
goes up and down around its equilibrium level.  It causes little 
waves too.  This will not result in smooth motion.  Even a very 
small wind will cause unacceptable motion.
>
>Also as Jerry brought up, as the mount rotates, the imbalance, 
and therefore the load on the ball, increases and the ball begins 
to sink lower in the water, wherever that level happens to be.  
If the ball becomes completely submerged, it will then drop fast 
and the mount will rotate quickly to the end of its travel, where 
the sudden stop will have dire consequences.
>
>The tube in a container will not work, either.  The pressure at 
the drain does not depend on the water level in the container, 
but it does depend on the difference of the water level in the 
tube and the level of the drain.
>
>Gary, Siphoning off the surface can maintain a constant flow, 
but only if the control is at the surface end, not at the end 
outside the container.  This could be achieved by floating the 
valve a little below the surface connected to a flexible tube that 
goes through the bottom of the container (gravity flow from the 
valve, no lifting over the side).  As the water level drops, the 
valve drops too, maintaining a constant pressure at the valve.  
But this does not overcome the basic problem of the floating 
ball described in the first paragraph of this message.
>
>Only a closed hydraulic (incompressible liquid, no air or gas) 
system (e.g. nearly frictionless hydraulic piston) with some sort 
of constant flow valve (not pressure dependent) has any chance 
to work without being excessively complex.  Even so, 
temperature changes will have an effect on the liquid's viscosity 
and flow characteristics.  This will affect the repeatability of the 
tracking rate.  Tracking would likely have to be calibrated 
frequently.
>
>Don
>
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