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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

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.

Design, Modeling and Direction Control of a Wire-Driven Robotic Fish Based on a 2-DoF Crank-Slider Mechanism

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.
Paper Structure (23 sections, 25 equations, 14 figures)

This paper contains 23 sections, 25 equations, 14 figures.

Table of Contents

  1. Introduction
  2. Hardware Design
  3. Body Skeleton Design
  4. Actuation Mechanism Design
  5. Waterproof Design
  6. Modeling and Analysis
  7. Kinematic Model of the Actuation Mechanism
  8. Dynamic Model of the Elastic Body
  9. Control system
  10. Feedforward Control
  11. Feedback Direction Control
  12. Experiment
  13. Prototype and Equipment Specification
  14. Oscillation in Air
  15. Swimming Performance
  16. ...and 8 more sections

Figures (14)

  • Figure 1: The biomimetic fish robot based on a 2-DoF crank-slider mechanism
  • Figure 2: Hardware design of the robotic fish: (a) rigid head shell; (b) segmented body sections; (c) passive caudal fin; (d) 2-DoF crank–slider actuation mechanism; (e) elastic spine; (f) driving wire; (g) pectoral fins.
  • Figure 3: The 2-DoF crank-slider based actuation mechanism.
  • Figure 4: Waterproof design of the fish: (a) O-ring based primary waterproof structure for the rigid head; (b) the skin composed of two sections that enclose the entire body of the robotic fish.
  • Figure 5: Operating modes of the 2-DoF crank–slider actuation mechanism for directional control. (a) Principle of the symmetric mode; (b) reel output in symmetric mode; (c) principle of the asymmetric mode; (d) reel output in asymmetric mode.
  • ...and 9 more figures