A Novel Untethered Robotic Fish with an Actively Deformable Caudal Fin

Based on the observation that live fish caudal fins exhibit softness, flexibility, and active deformation, which are essential for generating thrust, stability, and maneuverability, herein, a comprehensive study on a novel type of bionic robotic fish with an actively deformable caudal fin is presented. The article first presents the design of the robot. Next, the quasisteady model theory is used to establish the hydrodynamic force for modeling the deformable caudal fin. Furthermore, three deformation modes are studied and compared: the conventional nondeformable mode, the sine‐based mode, and the instantaneous mode. Finally, a series of extensive experiments are conducted to evaluate various performance metrics of this innovative untethered biomimetic robotic fish, including thrust, swimming speed, yaw stability, turning radius, and turning rate. The results demonstrate that the introduction of active deformation of the caudal fin significantly enhances the swimming performance in the aforementioned indices when compared to the conventional nondeformable mode. Notably, the instantaneous mode exhibits best performance in terms of thrust, swimming speed, turning radius, and turning rate, while the sine‐based mode demonstrates the best yaw stability. Consequently, this research contributes to the advancement of robotic fish design and the development of underwater biomimetic robots.