Magnetic-Propulsion ROV

As part of my work in the SAIL Lab, I investigated magnetic torque coupling as a compact alternative to a conventional sealed driveshaft for millimeter-scale underwater vehicles. An internal motor rotates a drive magnet inside the protected electronics enclosure, while magnetic forces transmit torque through a stationary hull barrier to a separate external rotor. This allows mechanical power to reach the surrounding water without requiring a continuous rotating shaft to penetrate the enclosure.

I developed the system through repeated design, fabrication, and testing cycles. The iterations focused on magnetic orientation, coupling distance, rotor alignment, motor selection, structural packaging, electronics integration, power delivery, and control. Because the available space was extremely limited, changes to one subsystem frequently affected several others. Reducing the housing thickness could strengthen the magnetic coupling, for example, but also affected structural rigidity, component clearance, and manufacturability.

The electrical architecture progressed from basic benchtop motor tests to a self-contained battery-powered system with onboard motor control and Bluetooth communication. Each subsystem was tested independently before being integrated into the complete vehicle prototype.

Magnetic transmission through a stationary barrier. Separating the enclosed motor from the external rotating assembly removed the need for a direct shaft penetration and reduced the number of dynamic sealing interfaces.

Millimeter-scale component integration. The motor, battery, motor driver, microcontroller, wiring, magnetic drivetrain, and structural enclosure had to function within a tightly constrained vehicle volume. Component placement was therefore treated as part of the mechanical design rather than as a later electronics task.

Modular subsystem testing. I evaluated motor operation, magnetic coupling, power delivery, wireless communication, and external rotation separately before combining them. This helped distinguish mechanical failures from electrical and software issues.

Wireless prototype control. The system evolved from direct wired testing to Bluetooth Low Energy communication between an onboard microcontroller and a computer-based game-controller interface, allowing forward and reverse motor commands without a physical control tether.

The largest lesson was that miniaturization changes the relationship between every subsystem. At the millimeter scale, a small change in wall thickness, wire routing, magnet spacing, battery position, or component orientation can alter the mechanical, electrical, and hydrodynamic behavior of the entire vehicle.

I also learned that successful subsystem tests do not automatically produce a successful integrated system. A motor may operate correctly on a bench, magnets may couple reliably in air, and the control software may send accurate commands, but the complete assembly behaves differently once structural tolerances, water resistance, battery limitations, and packaging constraints interact.

Separating the project into testable subsystems made failures easier to diagnose. Designs that appeared feasible in CAD often revealed new constraints after fabrication, so physical testing became the primary basis for each subsequent iteration.

Future work will focus on converting the integrated proof of concept into a controlled swimming platform. Planned improvements include reducing propulsion-module volume, decreasing the separation between the internal and external magnets, improving rotor alignment, developing a more compact waterproof electronics enclosure, and refining the internal mass distribution for stable flotation.

The next testing phase will measure vehicle speed, thrust response, directional control, power consumption, magnetic synchronization, and operating duration under repeatable underwater conditions. Additional control development may include differential thrust steering, onboard sensing, closed-loop motor control, and a dedicated desktop application for game-controller operation.

Working within the SAIL Lab, I developed and integrated the magnetic propulsion concept for a millimeter-scale underwater robotic platform. I modeled the vehicle and drivetrain components in CAD, fabricated and assembled the prototypes, selected and integrated the motor-control electronics, programmed the embedded and computer-side control systems, and conducted iterative mechanical, electrical, and wireless-control testing.

I used the results from each prototype to revise the magnetic arrangement, housing geometry, component packaging, power system, and control architecture. Propeller geometry and hydrodynamic optimization were developed as a related research effort and are documented separately in the Propeller R&D project.