Dynamic Modeling and Performance Analysis for a Wire-Driven Elastic Robotic Fish

The complex and continuous undulation of fishtail facilitates extraordinary underwater motion performance for natural fish. For the widely used Multi-Joint robotic fish, a lot of joints are used to simulate continuum fishtail, resulting in some challenges, e.g., the mechanism complexity, friction losses of adjacent joints, load disequilibrium and unsmooth servomotor output power. To overcome these intractable hurdles, motivated by natural fish, this letter proposes a wire-driven elastic robotic fish, which simulates fish muscle through multi-wire drive and adopts a fishlike spine design based on elastic component. Compared with the existing wire-driven robotic fish with discrete multiple-joints-spine and single-wire drive, our robotic fish not only has continuum fishtail, but also can swing with C-Shape and S-Shape owing to multi-wire coupling drive, and simulate the energy storage behavior of fish by elastic component. Further, a Lagrangian dynamic model that models a robotic fish with continuum fishtail and passive flexible joint is developed to explore the propulsive performance and validated by extensive experiments and simulations, and our robotic fish reaches the maximum swimming speed of 0.58 m/s, i.e., 1.04 BL/s. Finally, the superiority of the proposed drive mechanism in disposing of load disequilibrium and smoothing output power of servomotor, is analyzed and validated by the comparisons between a Multi-Joint robotic fish and our robotic fish.