Undulatory motion of sailfish-like robot via a new single-degree-of-freedom modularized spatial mechanism

Bionic robotic fish remains a challenging yet intriguing topic in the field of robotics. Although various mechanical structures and materials have been employed in many fish-inspired robots, addressing the complexity and reliability of controlling multiple motors simultaneously in series joints of these robots remains an issue. This study introduces a new solution that utilizes mechanical coupling motion to replicate the undulatory motion of a swimming sailfish. To realize this, we propose a novel single-degree-of-freedom modularized spatial mechanism and develop a theoretical method to ensure the fish-inspired robot's body movement aligns with the undulatory locomotion of an actual sailfish. As all electronic components, including motors, can be installed in the head, waterproofing the undulatory part becomes unnecessary. This enhances the reliability of the sailfish-inspired robot. Two independently controlled pectoral fins are positioned on the head for steering purposes. An experimental prototype, measuring 1250 mm in length, is tested to assess its swimming performance. The results indicate that the proposed mechanism can effectively transmit torque and motion, and the sailfish-inspired robot is capable of mimicking the locomotion of a swimming sailfish.