Trajectory tracking controller for an underwater hexapod vehicle

Aqua is an underwater biomimetic vehicle designed and built at McGill University that uses six paddles to produce control and propulsion forces. It has the particularity of having time-periodic thrust due to its oscillating paddles. Using an existing dynamics model of the vehicle and a numerical simulation, three types of controllers were developed to provide trajectory tracking capabilities to the vehicle. The controllers were a PD/PID, a model-based linearizing controller and a model-based nonlinear controller. The performance of the controllers was first assessed on the dynamics simulation using different trajectories. The same controllers were then tested experimentally in the Caribbean Sea. We found that the vehicle was able to follow the prescribed trajectory using any of the three controllers, but that the model-based controllers gave better performance. Finally, the experimental results were compared to those obtained in simulation. The results were found to be fairly similar thus giving us more confidence in our dynamics simulation.