Design, modeling, and experiment of a bio-inspired dual-fin gliding robotic fish

This paper presents the development, dynamic modeling, and experimental validation of a novel dual-fin gliding robotic fish inspired by the multi-modal locomotion of the ocean sunfish. Conventional hybrid underwater gliders typically rely on mechanically separate systems for propulsion and buoyancy-driven gliding, which inherently increases structural complexity and parasitic drag. To address this gap, we propose an integrated dual-fin mechanism in which a pair of fins functions as both oscillating propulsors and stationary gliding hydrofoils. A modular mechatronic design is employed to facilitate this functional reuse. We establish a comprehensive dynamic framework for horizontal swimming and vertical gliding. Crucially, the hydrodynamic formulations are empirically validated against tank-based experimental data. Swimming trials demonstrate a maximum cruising speed of 0.315 m/s (1.06 body lengths per second) and exceptional maneuverability via zero-radius pivot turns. Furthermore, comparative gliding experiments confirm the energy-conservative capabilities of the unactuated biomimetic fins, achieving a steady-state lift-to-drag ratio of 1.38 and converging to predictable pitch angles. This research provides a validated, streamlined approach to integrating high-agility propulsion with unpowered gliding, offering a robust foundation for multi-modal, bio-inspired underwater vehicles deployed in complex maritime missions.