Design and implementation of a bioinspired robotic fish driven by undulating pectoral fins for surface water environmental monitoring

Abstract Bioinspired robotic fish have garnered significant interest in recent decades due to their agile maneuverability and diverse marine applications. However, accurate modeling and physical prototyping of flexible fan-shaped membranous pectoral fins remain challenging. This paper presents the mathematical framework, modular design, and fabrication of an underwater robotic fish propelled by a pair of single-degree-of-freedom (DOF) membranous fins. To capture the complex fluid-structure interactions, the Morison force model is applied to establish a dynamic formulation that couples the fin motion, the robot body, and the surrounding fluid. A crank-rocker mechanism is proposed to drive the fin rays, generating fan-shaped membrane undulations for backward fluid propulsion while allowing straightforward phase shift adjustments. Experimental results demonstrate that the fabricated prototype achieves a peak forward swimming speed of approximately 0.59 body lengths per second (BL/s) and a turning radius of 0.14–0.53 BL. Furthermore, the modular architecture accommodates a water-quality monitoring payload, thereby demonstrating its capability for in situ measurement of total dissolved solids (TDS) and turbidity. This work provides a validated computational and experimental framework for advanced control and environmental monitoring in aquatic applications.