Nautilus Project Highlights
Duration: Spring 2023 – Fall 2024
Tools Used:
- SOLIDWORKS for CAD design
- Basic FEA for structural analysis
- 3D printing for prototyping
- Laser cutting for component fabrication
- Electronics design tools for power distribution board creation
- Underwater ROV-specific tools and software
Project Summary:
Project Nautilus is a submersible ROV designed to explore the depths of Lake Washington, where a PB4Y bomber rests at 175 feet under 5.3 atmospheres of pressure. The project focused on building a durable vessel capable of operating under extreme underwater conditions and capturing high-quality images and videos.
Highlights and Insights Gained:
- Enhanced understanding of pressure vessel design for underwater exploration.
- Gained practical experience in laser cutting and electronics design.
- Improved collaboration, time management, and budgeting skills.
- Applied engineering concepts to overcome real-world challenges.
The use of 3D printing
Cost-Effective PVC Framework: The entire external frame was constructed from PVC, using epoxy resin as a sealant to physically bond components together. The frame was designed as an open, non-pressure vessel to eliminate the need for watertight sealing of the structure itself.
Motor Mounting & Multi-Axis Motion: The frame provides dedicated mounting locations for all thrusters, enabling the vehicle to strafe on all three axes and rotate freely. Ballast and buoyancy tanks are also mounted to the frame to lock and maintain vehicle orientation.
Low-Cost Pressure Vessel Penetrations: Wiring was fed through the rear of the vehicle and sealed with epoxy resin, serving as a cost-saving alternative to commercial pressure vessel penetrators, which fell outside the project budget.
Minimized Part Count: To reduce complexity and cost, off-the-shelf Lego components were utilized where applicable, taking advantage of their tight tolerances and reliable material properties for example, as pins on the camera module assembly.
Modular Internal Section: The entire internal assembly, housing the battery, electronics, and camera module, was designed to be fully removable from the external frame for easy access, maintenance, and reconfiguration.
Simplified Programming Architecture: The drivetrain configuration was intentionally designed to support a simpler degree of freedom layout, making the control system more accessible while still enabling full translational and rotational maneuverability.
Multi-Phase Structural Testing: The external frame underwent a full testing sequence including pool testing to validate pressure vessel integrity, finite element analysis to evaluate structural performance under a 5-atmosphere load, and eventual saltwater environment testing.
Corrosion Mitigation Strategy: Steel components were avoided wherever possible throughout the design. In cases where steel was necessary, only stainless steel or surface-coated variants were used to prevent corrosion degradation in the marine environment.
Iterative Validation Process: Each phase of testing informed design refinements, ensuring the vehicle met structural and environmental requirements before progression to the next stage of evaluation.
Nautilus Project Summary
The objective of Project Nautilus was to develop a remotely operated vehicle (ROV) capable of exploring underwater at depths of up to 175 feet. The project was conceived in an Engineering Graphics class as a challenge to our team. Given the experience level of the team members, we used this opportunity to push the course's expectations and create something unique. The challenge focused on exploring a sunken YB-24 bomber at the bottom of Lake Washington. The bomber lies around 175 feet underwater, where the vehicle would experience over five atmospheres of pressure. As a team, we were responsible for funding the project, which imposed financial constraints that required unique solutions to the engineering problems we faced.
The ROV hull is designed in two sections: the inner hull and the outer hull. The inner hull is made from a 4-inch PVC pipe, designed to be pressurized and house all sensitive components like the battery, Raspberry Pi, and Pixhawk control module. It is sealed at both ends, with the rear seal using epoxy resin and the front seal utilizing an interface between a dome insert purchased from Blue Robotics and the PVC outer wall, supported by O-rings to prevent leakage. Currently, the resin seal does not provide adequate sealing at the test depth of 8 feet. New methods of sealing the rear end are being considered and are expected to be implemented soon. The inner hull is centered around an electronics package that holds all the electronic components of the submersible. This package is designed to be inserted and removed from the front of the submersible, allowing for easy maintenance of the ROV.
The outer hull is depressurized by drilling holes in sections of the external frame of the ROV, allowing the PVC pipes to flood. This reduces concerns about pressure differentials within the components. The external frame is designed to increase the overall mass of the ROV, making it less susceptible to underwater currents and improving stability. It also provides mounting points for the six brushless motors that provide three dimensions of strafe movement and one dimension of roll movement around the Z-axis. The primary external frame is depressurized, with the exception of the four ballast tanks. The two upper ballast tanks are sealed and filled with air, while the lower ones are allowed to flood with a filter and filled with sand. This buoyancy differential allows the ROV to maintain stability around the X and Y axes and retain its orientation.
Nautilus is currently in the testing stage of development. The primary frame and internal hull, including the electronics package and wiring, have been set up and configured properly. The primary objective is to properly seal the pressurized hull to prevent leaks and make any adjustments to prevent implosion at 5 atmospheres of pressure. The initial leak test was performed in a bathtub to check for any major leaks, and none were found. Following this, a secondary set of leak tests were performed at a depth of eight feet, which yielded suboptimal results, resulting in the flooding of the pressurized chamber. Further analysis indicated that the rear seal using epoxy resin was inadequate.
After this stage of testing, the empty hull of the Nautilus will be taken to a deeper location and tested for leaks at the expected operational depth. Following this, cyclic testing will be performed on the hull by repeatedly raising and lowering the submersible to and from the operating depth. This process will check for cracks or issues with sealing to prevent failure during operation.