Re: [PSUBS-MAILIST] "NewtSuit" type PSub

[Phil Nuytten <72020.572@compuserve.com>]

Hi, Anthony!
        >> I'm sure it can be done<< Well, that's the sort of optimism you
need to do a project like the Newtsuit. The NS torso is one size only, with
arm and leg length variable by use of extension (blank) rings between the
spacers and the rotary seals/bearings. I think the joints are all pretty
neccesary . . .if you had to eliminate some, the one between the upper knee
and the hip would be one and between the shoulder and upper elbow would be
another. That would eliminate 4 seals/bearings out of 20. A 130 psi model
would have much less total load in the bearings - on the same 6 inch wrist
I used as the previous example, it would be 25 square inches X 130 psi =
3,650 lbs X 2 ( to account for the centre conduit - the bearing ring sees
twice the load of ambient, since it is half the area) = 7,300 lbs . . .a
little over three and a half tons. In the wrist, you have very little
leverage to turn the rotary - from the centre of the wrist to the inside of
conduit - say 2 1/2 inches. This compares with 20 plus inches for the
shouder 'scythe' joint. All that says is that you can afford to have nearly
ten times the total friction (torque) on the shoulder than that of the
wrist.
        As I've said repeatedly with all this stuff - there's not much
magic . . .some cleverness, but not much magic. If you can figure out some
joints that will work, I'd consider building the suit/sub out of mild
steel. Easy to work with and low cost. Propusion is not a big deal, but
precise control is a very big deal. The bang-bang system commonly used with
trolling motors wont cut it. You need a fast ramp-up and shut down and some
sort of proportional controller in between - stepping is OK as long as the
steps are in small enough increments to give a kind of a 'virtual linear'
feel. The NS uses variable pitch props - the props crank away at 3000 RPM
and you cut the pitch in and out - very fast response! Anyhow, I wont bore
you to death . . let me know how you make out!
Phil Nuytten