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In a message dated 10/20/2009 11:53:29 P.M. Pacific Daylight Time,
empiricus@telus.net writes:
Hi Rick. First off, let me say that I'm a big fan of ambient subs provided
the builder/operator understands their limitations. As I've said before, a
recreational sub that only goes 50 feet deep will be able to see just as much as
a sub at 150 feet.
A thorough understanding of dive/depth duration and limits is required and
some means of assuring the sub can never exceed those limits is essential.
The basic systems in an ambient versus a 1 atm. are quite similar.
Depending on what the builder wants to accomplish in his sub, the design will
reflect those goals.
My own sub design was developed with specific goals in mind and although it
has limitations my hope is it can exceed the depths that I expect to dive to
with a large safety factor.
Obviously cost is an issue as well. I'd love to add a 48 inch dome window
but it's just out of my cost parameters.
On the actuators.....They are very smooth. The control system is as simple
as it can get. Again, I need to keep this boat as simple as possible so
maintenance and repair is both quick and inexpensive.
I'm using electric linear actuators to control dive plane angle, rudder
position,( exterior ) and the sliding weight mechanism. ( inside the
sub.)
Think of these actuators as the type that raise a convertible top on a '59
Cadillac.
The controls are very basic. A 12 volt "momentary" rocker switch controls
the actuator. Push the switch up and the dive plane goes up. Let go of the
button and the dive plane stops and stays there. Push the button down and the
dive plane goes down, and stays there.
Very simple wiring......wires go from the main electrical distribution
panel to the switch to the thru-hull to the actuator. That's it.
If the switch blows out, simply un plug it and plug in a new one. They cost
about $5 each. Naturally there are fuses and circuit breakers throughout the
system.
The actuators have a built-in limiter so when you reach the end of the
"throw" it stops.
We are using oil compensation to protect our Minnkotas. I'll be using the
same method for the actuators. Oil filled with a bladder to maintain ambient
pressure within the actuator. The actuators aren't made to be submerged at all,
so I'm putting them in a thick fiberglass housing and a rubber bellows is
attached to the housing and the extending shaft. The displacement doesn't really
change much as the rod extends, the oil just moves within the "envelope" and the
oil filled bladder will make up any minor change in volume.
The same thru-hull that holds the motor wiring also holds the actuator
wiring. Basically just 4 brass threaded rods sealed in epoxy with spade
connectors on each end. If for some reason the thru-hull were to start leaking,
I can pull the wires out and close the ball valve. The epoxy "plug" is larger
than the actual hole passing through the sub's hull so it can't "blow through"
creating a massive leak. My thru-hulls are 1 inch diameter X 4 inch long
nipples and the epoxy plug is located in a 1-1/4 inch X 1 inch reducer coupling
threaded to the outside of the welded-in nipple. The 1 inch ball valve is
threaded directly onto the inside of the nipple section and the 4 wires pass
through the valve going to the switch.
The biggest drawback to this system is the speed of operation. The actuator
speed is determined by the gear ratio of the internal actuator. The quickest
I've found is 2 inches of linear travel per second at 150 pounds of force. These
are made by "Firgelli" for automotive use like raising a convertible top or
truck bed lid.
The housing is machined from aluminum and the rod is stainless. Cost is
just over $100 each.
There are MANY types available with options for wet environments ( splash
) and several different sensing options with feedback for position etc.
There are even some double acting ones so once you reach the end of the first
stroke, you activate another switch and a second rod extends.
I'm going with the basic ones for reliability.
My expertise is welding and metal working. I've got three drawers of
hammers! When it comes to controls----I gotta keep it simple.
My designs are based on off-the-shelf parts that can be replaced in minutes
and usually purchased almost anywhere. That way if I'm down in Mexico diving the
Sea of Cortez or out past the Florida Keys I can get replacement parts.
The actuators have basic swivel mounts so replacing one is simply peeling
back the Vulchem coating, disconnect the hose fittings, pull out the wires, and
pull the two swivel pins. Mount a new one, plug in the wires, replace the hose
and Vulchem coating......and GO! ( gotta wait for the Vulchem to set up.)
I always refer to something Jay told me way back when I was designing my
sub....." Frank, keep it simple!"
Fortunately that also helps keep it cheap. An absolute minimum number of
high quality components, connected in such a way as to be simple to install and
maintain, with replacement/maintenance as a driving design factor.
Frank D.
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