Enabling High-Speed Taxiing Motion in a Bionic Robotic Fish Using a Compliant Passive Joint

Abstract

Achieving cross-medium locomotion remains a longstanding challenge in the field of bionic robotic fish. Current locomotion strategies often fail to enable effective aerial motion after water exit, primarily due to limitations in propulsion performance. To address this, we propose a novel cross-medium approach inspired by the taxiing behavior of flying fish. To validate this strategy, we developed a lightweight, high-speed robotic fish that integrates an electromechanical coupling drive system and a compliant passive joint. Based on the Lagrangian method, we established a kinetic model for the taxiing motion to investigate how passive joint stiffness and driving frequency influence taxiing performance. Extensive simulation and experimental results demonstrate that surface propulsion performance can be effectively enhanced by tuning passive joint stiffness to match driving frequency and intrinsic frequency to enter a resonant state. This enables the robotic fish to achieve a successful transition to taxiing motion at the resonant frequency, with a stable speed of 1.74 m/s (equivalent to 6.78 body lengths per second) and a lower Cost of Transport. These findings provide valuable insights for the design and optimization of robotic fish with passive joints and offer a promising pathway to realizing efficient cross-medium locomotion.