Re: [ATM] water drive

[donald.good@comcast.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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