Design, Modeling and Direction Control of a Wire-Driven Robotic Fish Based on a 2-DoF Crank�Slider Mechanism
Yita Wang, Chen Chen, Yicheng Chen, Jinjie Li, Yuichi Motegi, Kenji Ohkuma, Toshihiro Maki, Moju Zhao
AI summary
Problem
Existing wire-driven robotic fish struggle to balance high swimming speeds with precise maneuverability, as single-motor designs restrict turning agility while multi-servo systems limit oscillation frequency and speed.
Approach
The authors design a wire-driven robotic fish with a 2-degree-of-freedom Crank–Slider mechanism that independently controls tail oscillation frequency and mean angle, paired with a combined feedforward and feedback yaw control strategy.
Key results
- Novel 2-DoF Crank–Slider actuation mechanism that decouples propulsion from steering
- Dynamic model of the elastic body and actuation system to estimate motor loads for hardware selection
- Combined feedforward and feedback yaw control strategy for independent speed and direction regulation
- Experimental validation on a physical prototype demonstrating successful swimming, turning, and precise directional control
Why it matters
Overcomes the traditional speed-manoeuvrability trade-off in biomimetic underwater robots, enabling quieter, more agile platforms for close-range marine observation and ecological surveys.
Abstract
Robotic fish have attracted growing attention in recent years owing to their biomimetic design and potential applications in environmental monitoring and biological surveys. Among robotic fish employing the Body–Caudal Fin (BCF) locomotion pattern, motor-driven actuation is widely adopted. Some approaches utilize multiple servo motors to achieve precise body curvature control, while others employ a brushless motor to drive the tail via wire or rod, enabling higher oscillation and swimming speeds. However, the former approaches typically result in limited swimming speed, whereas the latter suffer from poor maneuverability, with few capable of smooth turning. To address this trade-off, we develop a wire-driven robotic fish equipped with a 2-degree-of-freedom (DoF) Crank–Slider mechanism that decouples propulsion from steering, enabling both high swimming speed and agile maneuvering. In this paper, we first present the design of the robotic fish, including the elastic skeleton, waterproof structure, and the actuation mechanism that realizes the decoupling. We then establish the actuation modeling and body dynamics to analyze the locomotion behavior. Furthermore, we propose a combined feedforward–feedback control strategy to achieve independent regulation of propulsion and steering. Finally, we validate the feasibility of the design, modeling, and control through a series of prototype experiments, demonstrating swimming, turning, and directional control.