After the RoboSub 2014 competition, there were some flaws that arose in the mechanical system in AquaUrsa during the competition. Many improvements were made to solve these problems as well as adding extra features AquaUrsa never had in the previous years.
The hull was not changed from the previous year. It is a cylindrical shaped hull to distribute the pressure uniformly and reduce stress concentrations at a single point. The mechanical team chose 1/4" thick acrylic plastic due to its' substantial strength and elegant transparency. There are two aluminum end caps with o-rings to create a vacuum seal inside the hull. The hull also incases a slide out electronics tray held up with carbon fiber rods that spans through the interior length of the hull. The hull will have an inner diameter of 11.2" which provides more than enough room for the electrical components.
The end caps are made of 1-1/4" thick aluminum with one end cap permanently sealed onto the hull. This end has all the subconn connectors between the electronic boards inside the hull to the components outside the hull. The other end has 2 parts: an outer frame section permanently connected to the hull and a removable lid that seals the hull. All 3 parts have o-rings and 1" diameter carbon fiber rods along the longitudinal side of the hull for sealing. The removable lid is kept in place by two tabs that are screwed in. Aluminum was chosen because it is non-magnetic and will not cause a magnetic interference with any of the electrical components.
We did not have a frame previously but multiple tubes attached to the main structure to mount peripherals, be a gripping point for ground transportation, and legs to stand on out of the water. The main reason for a new frame was for convenience and increased modularity. The new frame provided ease of transportation with 2 handles on each side. This frame is also equipped with thruster protection mounts to keep collision damage towards the thruster shrouds to a minimum. Horizontal aluminium bars are bolted onto the frame to support other mechanical components such as the marker dropper and claw. The bars can easily be re-arranged and relocated to a different position to accommodate for space and additional components. L-shaped tabs connected, on each side of the frame, to a semi-circle shaped mount holds up the hull itself.
Previously, we had two cameras, one facing forward and one facing down, in an isolated camera case that was screwed on to a mounting tray outside the hull. This isolated case had o-rings and screws for a good seal that eventually failed and leaked during Roboub 2014.
This year, we got rid of the isolated camera case and instead, placed the cameras inside the already perfectly sealed hull. The permanent end cap was modified to add a visible screen for the forward facing camera and the already transparent hull was used for downward facing camera.
For the forward facing camera, it was built into a 3 part assembly. The base of the camera lid houses an o-ring to maintain a seal around the front lid protrusion. This also houses a polycarbonate lens which gives the opening for the forward facing camera to see through. The polycarbonate lens is easily interchangable by removing the top piece of the camera lid assembly.
The electronics tray was redesigned to focus on electrical access. The electronics tray houses boards on both the topside and underside of the tray, with the most used boards closer to back for easy access. The front of the electronics tray contains a cutout which allows the forward facing camera to be attached to the tray. The tray is able to slide in and out of the hull with the assistance of 1" carbon fibre rods.
The IMU case was kept as the same from last year. The IMU is situated on a sleeve that slides easily into the IMU case. The sleeve itself has a slot that a plastic plate tightly slides into acting as a standoff for the actual IMU. To seal the whole case, a thick fine threaded screw cap topped off with an O-ring compression is used to compress the case tight. On the other end of the case a narrower cylinder extrusion was made to tightly seal it against the end of a carbon fiber rod.