Underwater Capsule
NOV 2022
In our senior design class, a classmate and I were tasked with creating a device that could submerge in water and record pressure/depth data.
After going through the design process with the constraints and goals given, my teammate Adam Kramer and I favored a cylindrical body that would hold the electronics. A lid that would connect to the body would have flanges to attach fishing line to the capsule. This fishing line would be used in conjunction with a simple pulley system, enabling us to raise and lower the capsule in the water as needed. The whole assembly was generated in Fusion 360.
To measure pressure, we decided to utilize the Bar 02 10m sensor from Blue Robotics. The sensor had a built-in watertight seal, in addition to the fact that it was compatible with an Arduino when used jointly with a level converter. It also was said to yield more accurate data than other sensors available.
To provide a seal between the capsule and the lid, we opted for the AS568-229S o-ring. M5 machine screws would tighten the lid to the capsule.
We used a solid ABS cylinder as the main body of the capsule. The necessary cavities in our model were created with a CNC Tormach. Machining the body enabled us to control the exact dimensions of every part of the capsule, which would be important when creating a seal with the o-ring. A gland for the o-ring was machined with high precision using the Tormach, where we calculated the necessary dimensions based on the desired stretch of the o-ring for the best seal possible. We also could better create our desired aesthetic for the capsule using this method.
We first generated a 3D print of the lid such that we could then sand cast it for the final capsule. The casted lid would provide a dense weight for the capsule to overcome the buoyancy force of the water. We also found that casting the lid would provide the best waterproofing, where it would enable the lid to have the best contact with the o-ring and the capsule for a good seal.
For the electronics, we soldered an assembly together containing a battery, an Arduino nano, a 5V-3.3V level converter, a MicroSD card reader, and the Bar 02 Pressure sensor. We edited code provided online by Blue Robotics so that all of the components worked within our assembly.
Our final prototype is shown below. The electronics fit snugly into the main cavity, and our tests consistently showed that our o-ring and lid provided a watertight seal. We screwed in a block at the bottom of the assembly to provide more weight such that the capsule could sink more quickly.
We generated the following data from our assembly. While the general shape of the experimental results matched the target profile, they trajectories certainly aren't identical. If we were to redo the project, we would focus on simplifying the design to prioritize iterating many solutions and testing those models. This would enable us to create a prototype that could yield a more accurate data set for the final test.
