Mechanical Subsystem
Mechanical Design
Hull
McGill Robotics’ main design goals this year was to make a small, compact and agile robot, improving the accessibility of the electronics in the hull and adjusting the center of mass to have a well balanced AUV. The hull is rectangular, with a large opening on the top, allowing easy access to the internal electrical systems. This is a change from this AUV’s predecessor, Clarke, which had a cylindrical hull with tightly-layered electronics shelves that were difficult to access. The hull has windows on the front and bottom for cameras, and a window on the top to view an electronic board that displays the AUV’s system status.
Mechanical Design
Design Verification
Our testing process focused on ensuring the hull's durability and seal integrity under simulated pressure conditions.
Finite element analysis verified that the hull could withstand 30m depth with a safety factor of two. The weight and buoyancy were consistently monitored to maintain the AUV’s center of mass near the hull's center. Dry ice was used to simulate two atmospheres of water pressure with carbon dioxide gas to test the hull's seal quality. The ideal gas law calculated the required dry ice, and pressure was monitored to detect leaks. The test showed that the early version of the hull was not completely sealed under two atmospheres of pressure.
Mechanical Design
Internals
The electronics were secured within the hull using a combination of acrylic and 3D-printed mounts. Each mount underwent multiple design iterations to achieve optimal security, accessibility, and thermal management. The bottom mounting plates and the electronic stack were precision laser-cut from clear acrylic, enhancing visibility for both electronic monitoring and leak inspection. The batteries were encased in a custom 3D-printed mount and secured with rubber bands, allowing for necessary ventilation. Final positioning of electronic components was strategically planned alongside the electrical team, prioritizing accessibility and optimal weight distribution.
Mechanical Design
Thruster positioning
The thruster positioning configuration was selected by comparing various potential setups involving different distances, angles, and placements. To determine the optimal configuration, an algorithm and simulations were used to compare the thrust required for various maneuvers. As a result, the most energy efficient configuration was implemented in the robot as shown in the image on the left.
To secure the thrusters in their optimal positions, custom mounts were designed and machined. After multiple design iterations, prototyping, and calculations, the final version of the thruster mounts were CNC milled to achieve the desirable strength and precision.
Mechanical Design
Chassis
The team designed a minimalistic yet functional chassis for effective task actuator support.
The chosen material, Aluminum 6061, offers suitable structural and chemical properties for marine applications, allowing for slender designs and improved hydrodynamics. The chassis is attached with screws for easy transportation and future modifications. Structural integrity is validated through finite element analysis of inertial forces. Task mechanisms are placed below the hull to stay within the camera's view, avoid thruster wash, and lower the center of mass below the center of buoyancy. Buoyancy is adjusted to +5% using a custom hydrodynamic polyurethane foam topper, with fine-tuning done through additional components. The center of mass is balanced with small weights on guide rails, allowing quick, tool-free adjustments. This fine-tuning reduces thruster workload, enhancing maneuverability.
Mechanical Design
Grabber
To address the dropper and sample collection tasks the AUV is equipped with a mechanical claw attached to the bottom of its chassis, positioned within the view of the downward-facing camera. The claw features interlacing fingers to enhance current sensing capabilities. Additionally, an extra layer of rubber has been added to the claw to improve grip.