Machined PartsAt first we struggled with the type of seal we were going to use for the compartment. Although we knew we wanted to use an o-ring seal, we wanted something that would give us the largest opening into the watertight compartment and keep it within the 5"x5" size of our sub. Our first thought was to use an axial o-ring seal. While this seal is effective, it takes up too much room for a number of reasons. First off this type of seal needs constant pressure around its circumference which means we would have need 8+ bolts to create a good seal. Secondly, we want to use a double seal to ensure our compartment doesn't leak – with two axial o-rings the access opening would go under 3.5", which is too small to be useful. While talking with one of our mentors, Jon Amory, he mentioned the idea of using a radial o-ring seal. This design would follow the form of our sub better (it is longer not wider) and therefore would allow us to have both a larger access hole and a double seal while still fitting inside of our 5"x5" constraint.
|Radial Seal (Apple Rubber)|
|Axial Seal (Apple Rubber)|
To design the aluminum fittings we used Apple Rubber, an rubber engineering company. They have a great introduction to o-ring design (static o-ring seal descriptions found here).
On one end of the compartment, the access end, we designed a plug and a plug housing. The plug is made out of a 4.75"x4.75"x2.5" piece of aluminum. The plug itself acts like a cork to keep the air in and water out of our compartment. The inside of the plug is hollowed out and has holes for running wires through. One side is square to match the interior of our sub body. An image of the plug is below. If you look close enough you'll also see a radial hole in the pocket -- this is for a bolt we will use to pull out the plug, a necessary feature because it will take a large amount of force.
And the two fitting together (with a transparent plug housing):
The third, and final, piece is the back plug. This part covers the end of the watertight compartment that will never be opened. It is made out of a 4.75"x4.75"x2.5" piece of aluminum. It has a large square pocket 2.25" deep and 3.25"x3.75". The plug housing has such a large pocket to give us more room inside of the watertight compartment for our electronics. Similar to the plug housing, the back end of the compartment has four bolt holes (two on each side) to connect sections together. Below is a picture of the part:
We will be welding the parts to our 5"x5" sub body to finish the watertight compartment. The aluminum parts slide into the compartment about .5", more than enough room to hold it in place while being welded from the outside. A picture of the finished compartment is below:
|Plug Assembly w/ Connectors|