[PSUBS-MAILIST] Re: Thank you Phil !

[Phil Nuytten <pnuytten@compuserve.com>]

Hi, Dan:
        Re water hydraulics: This is a closed cycle system that can run on
any fluid, including water.Essentially, you use a small, powerful PM motor
to move a rack or worm gear attached to a piston head and contained in a
cylinder. This is typically a low pressure system that uses large diameter
pistons on the manipulator end and smaller diameter (but longer strok)e
pistons on the motor end. If you've done your sums correctly, the long
stroke of the smaller piston will move the larger piston through its full,
short stroke. 
        
        The  circuit is a 'suck and blow' system. When you engergize the
motor, the motor piston will force the fluid through the  connecting lines
and cause the larger manip piston to move forward. When you reverse the
motor direction by switching the polarity, the motor piston will retract
and cause the manip piston to do the same - or any degree inbetween, Not as
'strong 'as a high pressure hydraulic system, but with a large (say, 21/2"
to 3" diameter) set of pistons in the manip, you can approach signficant
load and force levels. The arm itself acts as the 'cylinder' for the manip
piston - Rigid PVC or Delrin is a good material for the whole arm - use a
plastic that's not hygroscopic (doesn't absorb water).
        
        You need a separate motor for each function - best are high
performance, small size, RC model vehicle PM motors which are readily
available at hobby shops that cater to model car/boat/aeroplane
enthusiasts. 
        The obvious advantage is no hydraulic pump and no expensive
solenoid valve pack. 

The system that we use on 'Deep Rover' can pick about 70 lbs at full, 6
foot, reach.

Something to think about - and while you are thinking - think about a
submersible water pump of the type used in wells. Cheap, rugged, available
in 12 VDC, and pressure proof to at least 300 psi  - use it in place of a
hydraulic pump and just pump ambient water to a double acting piston that
vents back to ambient water.   
Phil




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