Re: [PSUBS-MAILIST] Manipulator actuation / design

[Phil Nuytten <pnuytten@compuserve.com>]

HI, Frank:
        We do use regular deep-cycle batteries with gelled cells (not the
tradename 'gelcell') The Deep Workers carry 20 X 12 VDC to give a nominal
240 VDC. The reason we use 'old fashioned' lead-acids is simple; no other
battery currently available gives as much bang for the buck. We toss the
old batteries every season - even tho' they are still working OK - (there's
always some cell deterioration and when a cell goes . . . bye bye dive!)
Since we have at least three subs in service fulltime -and sometines four
or five, that's at least 60 batteries per year! We pile 'em up in the lane
at the back of the shop with a sign that says "FREE - with money-back
guarantee" The neighboring businesses love it!  If we had to double the
capacity in the same size pod, we'd go to nickel-metal hydride or
lithium-ion but the cost would not double but be many times the cost of the
lead acids. At Nuytco, we've looked thoroughly into each new 'miracle'
battery - and there are a surprising number of them that are not public
knowlege. Because our subs are obvious battery users that make for good
press, we are often approached by new battery inventors/manufacturers. So
far, no-one has come close to the lead-acid cost per hour of bottom time,
the ability to tolerate high current draws, availability, and so on. Even
with hi-def cameras grinding, HMI lights blazing, manipulators twitching
and thrusters whirring - we still get an honest 6 hours bottom time at 2000
feet - and if we're just driftin' along with the breeze, that can extend up
to 8 hours . . .and it only takes about 15-20 minutes to swap battery trays
and be ready to go again. 
        Summary: the exotics are interesting and useful for specific
missions where recharging/swapping is not an option (tunnel,
aquaduct,surveys, etc.) and prce is not an object - but lead-acids still
hold a strong majority for the reasons stated.
Phil



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