As said previously most people use PVC pipe for the hull construction, Looking round the internet for ideas I have come across Ian Leverington’s site ROV Robot Submariner, that sells a how to guide for building an Remotely Operated Vehicle, complete with on-board video camera for under £200 for £6.50; I have bought a copy of the guide. soI can use it as a starting point for my design;
Also on the internet I found a kit called the SRV-1 by Dry Dock Products, sold via Mike’s Subworks, it looks like a simple design; and suggests that it is also possible to use the motor pods for fully functional vector control instead of requiring the use of the dive planes, or rudder for steering.
The rotating thrusters allow you to power the sub nearly straight down, or up to the surface, with the dual motor control option, the sub will be able to spin round on its axis.
Most model submarine hulls are made of fibreglass. but more RC submarine kits are being made out of ABS or Styrene plastic because of the reduced cost and ease of construction; however I don’t think these materials are as strong as PVC pipe, due to the nominal wall thickness being much thiner, and not designed for the external pressure being as high (Most model submarines have an operational depth of between 2 and 8 feet).
There is a hole in my water tight box…
While making a completely sealed water tight box that is resistant to pressure would be relatively easy; it leads its self to some problems;
- Just how do you get all your wires in and out?
- How do you make things move outside the water tight box?
- how do you keep it watertight?
The holes where wires pass through your pressure vessel are the easiest to deal with; as they can be made secure using potting compound, like Epoxy.
There is a good How-To on this very subject at http://www.homebuiltrovs.com/howtosealingwireexits.html, Home Built ROVs show all the cables having there insulation stripped out in the epoxy bung; so that ingress outside the pressure vessel, will not propagate along the conductor, or bundle into the hull;
As this makes total sense to me; its the method I shall go with at the moment; unless I can think of something better. although I am sort of a fan of having two sets of water proof bulkheads with a monitored interspace between them (working at CCFE has left some impression ).
Push and Pull Rods
These tend to be delft with by tight bushes, or ruber bellows; neither of which I am convinced are as impervious to ingress as I would like; I guess that using the two in combination, and filling the bellows as much as possible with hydrophobic grease would help.
Another option would be to use magnetic sliders; meaning that there would be no penetration of the pressure vessel.
Propeller and rotary shafts
Prop shafts for RC boats are generally not designed for large pressure differentials, however there are some prop shafts that are designed to be ‘waterproof’, one example consist of a brass tube and inner bearing housing with a stainless steel shaft. The outer bearing is made from Delrin and the inner bearing from sintered Bronze with a lipped G ring seal that make these tubes water tight.
I don’t know how these would cope at larger pressure differentials.
Water ingress detectors
The easiest way I can think of for ingress detection is the use of Printed circuit boars with a large number of parallel tracks so that any moisture will complete the circuit;
A similar pattern can also be laid directly onto the inside of the pressure vessle with copper tape.
The voltage signal from these sensors can then be passed to the control circuit.