From 2D to 3D Maneuverable Robotic Fish: A Systems Perspective

Robotic fish, as an emerging member of marine robots, have received lots of attention in recent years. Because of its unique propulsion mechanism, a large amount of research work today focuses on robotic fish design. Due to the complex hydrodynamics, the modeling of the robotic fish has become a challenging topic, and the research on control and application is still in its beginning. This study systematically introduces the development and application of a robotic fish from the perspective of design, modeling, and control. A three-joint robotic fish propelled by a Double-Slider-Crank (DSC) mechanism, which uses one DC motor to achieve oscillating foil propulsion, is designed. From the design aspect, DSC helps the robotic fish in mimicking a real fish's two-dimensional free-swimming. The robotic fish's top speed is 0.35 m/s at 3 Hz, equivalent to 0.98 body length (BL) per second. DSC also benefits the control of the robotic fish by independently adjusting its steering and swimming speed. This characteristic is studied in a hydrodynamic model that derives the thrust within a DSC frame. A semi-physics-based and data-driven linear model is established to connect the bias angle to the robotic fish's steering. A linear model is used to design a controller, called event-trigger-control, to overcome the adverse effects of communication drop-off. Furthermore, the work is extended to a robotic fish application study that uses robotic fish to estimate the flow field. Besides, the three-dimensional maneuverability is also addressed by developing a buoyancy control device to change depth. Overall, the proposed robotic fish has an excellent performance in free-swimming and shows great application value in environmental surveys.