Multi-directional control of a bio-inspired robot with a single undulating fin propulsion

Control of agile and highly maneuverable underwater vessels is fundamental to explore complex maritime environments including survey closed to ocean structures and shallow waters. Currently, traditional autonomous underwater vehicles (AUVs) and remote operated vehicles (ROVs) can encounter challenges navigating through these tight spaces. In this work, we explore the use of a flexible undulating membrane as a propulsive and force control mechanism for an underwater vehicle. We present a control scheme where modulations in the amplitude of two counter-propagating waves can provide a wide range of motion control including station keeping, heading, turning and speed control. We first present it through a user-operated control and then in closed-loop feedback to modulate the fin actuation to control the motion of the vessel. Free-swimming is executed with an elongated membrane positioned ventrally along the vehicle. The membrane fin was actuated through independently controlled flexible rays. The vehicle was tested in a flume at different flow speeds and pool where real-time tracking was used to obtain the position and orientation of the vessel. Using time-varying and spatial modulations of sinusoidal traveling waves, controlled trajectory of the vessel in addition to station-keeping in the presence of external perturbations can be achieved. Finally, we present the vessel swimming in the wake of an object where the fin has to overcome flow fluctuations from the shed vortices. We found that relatively simple controllers for flexible fin kinematics are sufficient to perform path following and station keeping and a variety of swimming maneuvers, providing a versatile alternative to conventional propulsion mechanisms in complex environments. Although control was implemented with sinusoidal traveling waves, it is envisioned that further exploration of a wider range of kinematics for optimal swimming will allow engineered vessels to the perform the graceful maneuvers that aquatic animals can.