In total, there were over five designs that were proposed between us three. As discussed in the background research many designs were considered. There will be three designs discussed here, with the last being our final design. Every design was a build-up of previous design configurations, and that knowledge was used to cut out a lot of flaws in our initial designs. Our unofficial rules were to make the design based on previous designs that we knew worked well. This was because, for our time and budget, which we did not have much of, we had to design this effectively. Another rule was the ease of fabrication. It could be made in less than a day with less than twenty components. Lastly, we just kept with simplicity. And all of these unofficial rules paid off with our final design.
Our initial design was a quadcopter configuration. There has been limited research on a quadcopter-style submarine that can fly at the same time, but this concept is very difficult to complete in the budget and time allotted to this project. Our preliminary design was to come up with a quadcopter configuration. But as we started looking at it we saw all of the problems that would come along and it was quickly ruled out. To save us a headache we decided to go with more of an open frame or submarine-style since being able to fly in the air and land was not part of our requirements or constraints. The control systems would be a lot easier if it were just water too. Below is a picture of what it may have looked like if we decided to stick with this route, but we will name some of the many issues that occur with this design.
1. Vertical Thrusters. One of the biggest design challenges with this style of design was that there were no vertical thrusters. This means that simple tasks such as fighting the current or maneuvering meant that the quadcopter itself had to spin. So, the control system inside of the quadcopter would consistently be spinning around just to keep itself stable and if it stops being then it would drift along wherever needed to go, and this had multiple negative effects. One noticeable one is the fact that the camera would not be still it would be very shaky, thus hindering our overall objective of monitoring the seabed.
2. Time and budget. The sheer time and money it would take to develop this quadcopter are crazy to think about. As we've said it has been done before by the naval research laboratories with a couple of thousand dollars and a team of people. They also had the best knowledge and most resources. This would contradict our unofficial rule of making it as easy as possible for us in the long run. There is no doubt about it this paper would not have been written on our current design bragging about how it brings all of our best components together if we stuck with this quadcopter configuration. Now it is time to get onto more of our official designs
The first design and CAD model was the “Star Wars” style design. It was drawn up when we were first getting our feet wet with the design. We have a few rendered images, below showing how the design looked. This design consisted of a center PVC tube and an outer wall. The motors were connected to the outer walls, and the truss members were made of sheet metal. Initially, we liked how this design was implemented, and the protection and versatility it offered. But it was eventually dismissed due to some serious design flaws, the three most notable below.
1. The hydrodynamics. This was the biggest flaw with this design, and if it were to be perpendicular to the current, it would essentially be like putting a flat wall underwater. If it were parallel to the current, then the flat wall introduced plenty of friction, and that increases drag and mean more thrust with the motors and more power used. Lastly, diving and surfacing were not hydrodynamic at all. Using simple hand calculations, it was decided this design was not streamlined or adequate for our purposes.
2. The thruster placement. As one can tell from the figure above the thrusters are very close. The two thrusters facing in the back lose some efficiency since there is almost no water in front because the vertical thrusters are in front of it. And when the UUV moves backward then water is having nowhere to go.
3. The view. When showing this design to Dr. Matin, he mentioned a very good point that we forgot to look at, the scope of our mission is to view the sea floor so how would we do that with this design? This may be single-handedly the biggest reason we tossed this design because our entire mission is based on seeing the sea floor. As seen in the next proposed designs we solved this problem and was a very good observation by Dr. Matin
The second design was drastically different from the first but also had some serious design flaws so it was also dismissed. We had decided to look at the submarine style and see if that would fit our mission better, it was never drawn up in CAD, but we drew a quick 2D sketch of it and decided that it would not fit the scope of our mission and will not be finished in time. With this design, we tried to solve the two previous problems with the thrusters being too close in the hydrodynamics. The hydrodynamic difference is clearly visible between these two designs with one being shaped like a bullet and the other a brick. The thrusters being too closed was also solved since with this design there are only two Motors and they do not interfere with paths at all. But the reason this model did not make it to CAD was because of the major drawbacks it introduced.
1. The limited mobility. Having two thrusters on the back allowed the UUV to spin in the yard direction, but now since there is just one motor in the back and one to side shift, then spinning is no longer possible without velocity. This can be a major problem since we want to theoretically align with the current to be the most hydrodynamic, we can be, but this option is removed with this design. Also, the ballast tank may make our dive speed and surface speed very small.
2. The watertight seal. With this design, the blue is where water would be, which means the hull would not be watertight. The electronics as seen in the middle of the figure is the only seal-proof thing, this means we must effectively run wires and tubes out of this compartment without any leaks whatsoever, and it made us feel very uneasy about this design. If something were to go wrong, we would essentially short all our electronics and lose around one hundred to two hundred dollars’ worth of components.
3. The moving parts. Another thing we did not like about this design was the moving parts. The fewer moving parts a system has the less chance there is of something failing and the easier the diagnostic is. This design had tons of moving parts including the rudder and ballast tank. This means we would have electronics integrated with pneumatics integrated with servos and wires to move the rudders, and we determined that there was way too much going on for us to effectively make in the budget and time allotted.