Performance‐Oriented Understanding and Design of a Robotic Tadpole: Lower Energy Cost, Higher Speed

ABSTRACT A compliant plate driven by an active joint is frequently employed as a fin to improve swimming efficiency due to its continuous and compliant kinematics. However, very few studies have focused on the performance‐oriented design of multijoint mechanisms enhanced with flexible fins, particularly regarding critical design factors such as the active‐joint ratio and dimension‐related stiffness distribution of the fin. To this aim, we developed a robotic tadpole by integrating a multijoint mechanism with a flexible fin and conduct a comprehensive investigation of its swimming performance with different tail configurations. A dynamic model with identified hydrodynamic parameters was established to predict propulsive performance. Numerous simulations and experiments were conducted to explore the impact of the active‐joint ratio and the dimension‐related stiffness distribution of the fin. The results reveal that (a) tails with different active‐joint ratios achieve their best performance at a small phase difference, while tails with a larger active‐joint ratio tend to perform worse than those with a smaller active‐joint ratio when a larger phase difference is used; (b) the optimal active‐joint ratio enables the robot to achieve superior performance in terms of swimming velocity and energy efficiency; and (c) with the same surface area, a longer fin with a wide leading edge and a narrow trailing edge can achieve higher swimming speeds with lower energy consumption. This work presents novel and in‐depth insights into the design of bio‐inspired underwater robots with compliant propulsion mechanisms.