A Wire-driven Flexible Vector-propelled Robotic Fish with Omnidirectional Adaptive Caudal Fin

Current robotic fish often require initial velocity or center of gravity and buoyancy adjustment modules to accomplish movement in three dimensions in the water. This paper primarily proposes a compliant tail-based vector propulsion system, where the tail fin can vary its orientation with flapping direction, enabling the generation of propulsive force in any direction in space, not limited to the horizontal or vertical plane. The propulsion system consists of two sets of wire-driven mechanisms driving the active body, and the rear part is made of compliant tail made of silicone gel. The robotic fish is equipped with communication modules, IMU, and depth sensors, with its motion control independently achieved by two CPG controllers receiving high-level control commands. Finally, we conducted experiments in a pool to demonstrate that the robotic fish proposed in this paper can not only perform basic fish-like movements but also the vector propulsion system can generate thrust in any direction in space. This allows for a series of movements, including vertical ascent and descent, to be performed without any initial velocity.