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Design of a Double-joint Robotic Fish Using a Composite Linkage

Ruijia Zhang, Wenke Zhou, Min Li, Miao Li

TL;DR

Addresses propulsion efficiency and control complexity in biomimetic robotic fish by introducing a single-motor, double-joint design based on a composite linkage. Develops a BCF-consistent kinematic framework and derives analytic expressions for tail swing $\theta$ and lateral tail displacement $S_{CY}$, then validates the concept with a modular, 3D-printed prototype. Experimental results reveal how swing angle amplitude and swing frequency affect steady-state swimming speed, identifying optimal ranges and practical limits (e.g., $0.09$ m/s at $75^{\circ}$ and $0.065$ m/s at $1.5$ Hz). The work demonstrates a compact, robust propulsion approach for underwater robots and provides groundwork for optimizing fish-like propulsion in real-world applications.

Abstract

Robotic fish is one of the most promising directions of the new generation of underwater vehicles. Traditional biomimetic fish often mimic fish joints using tandem components like servos, which leads to increased volume, weight and control complexity. In this paper, a new double-joint robotic fish using a composite linkage was designed, where the propulsion mechanism transforms the single-degree-of-freedom rotation of the motor into a double-degree-of-freedom coupled motion, namely caudal peduncle translation and caudal fin rotation. Motion analysis of the propulsion mechanism demonstrates its ability to closely emulate the undulating movement observed in carangiform fish. Experimental results further validate the feasibility of the proposed propulsion mechanism. To improve propulsion efficiency, an analysis is conducted to explore the influence of swing angle amplitude and swing frequency on the swimming speed of the robotic fish. This examination establishes a practical foundation for future research on such robotic fish systems.

Design of a Double-joint Robotic Fish Using a Composite Linkage

TL;DR

Addresses propulsion efficiency and control complexity in biomimetic robotic fish by introducing a single-motor, double-joint design based on a composite linkage. Develops a BCF-consistent kinematic framework and derives analytic expressions for tail swing and lateral tail displacement , then validates the concept with a modular, 3D-printed prototype. Experimental results reveal how swing angle amplitude and swing frequency affect steady-state swimming speed, identifying optimal ranges and practical limits (e.g., m/s at and m/s at Hz). The work demonstrates a compact, robust propulsion approach for underwater robots and provides groundwork for optimizing fish-like propulsion in real-world applications.

Abstract

Robotic fish is one of the most promising directions of the new generation of underwater vehicles. Traditional biomimetic fish often mimic fish joints using tandem components like servos, which leads to increased volume, weight and control complexity. In this paper, a new double-joint robotic fish using a composite linkage was designed, where the propulsion mechanism transforms the single-degree-of-freedom rotation of the motor into a double-degree-of-freedom coupled motion, namely caudal peduncle translation and caudal fin rotation. Motion analysis of the propulsion mechanism demonstrates its ability to closely emulate the undulating movement observed in carangiform fish. Experimental results further validate the feasibility of the proposed propulsion mechanism. To improve propulsion efficiency, an analysis is conducted to explore the influence of swing angle amplitude and swing frequency on the swimming speed of the robotic fish. This examination establishes a practical foundation for future research on such robotic fish systems.
Paper Structure (12 sections, 11 equations, 8 figures, 2 tables)

This paper contains 12 sections, 11 equations, 8 figures, 2 tables.

Table of Contents

  1. Introduction
  2. Principle and Design of Propulsion Mechanism
  3. BCF Mode in Fish Locomotion
  4. Propulsion Mechanism Principle
  5. Motion Analysis
  6. Prototype Experiments and Analysis
  7. Overall Structural Design and Prototyping
  8. Experimental Methods
  9. Experimental Results and Analysis
  10. Effect of Swing Angle Amplitude on Velocity
  11. Effect of Swing Frequency on Velocity
  12. Conclusion

Figures (8)

  • Figure 1: Schematic diagram of the fish body wave during one motion period. The red curve represents the midline of the fish body.
  • Figure 2: Fish body wave curve at various time points along with its amplitude envelope curve.
  • Figure 3: (a) Schematic diagram of the propulsion mechanism, including the composite linkage mechanism and the fishtail. (b) Transmission diagram of the propulsion mechanism.
  • Figure 4: (a) Motion pattern of lateral displacement with time. (b) Motion pattern of swing angle with time.
  • Figure 5: 3D model of the modular-designed robotic fish, including head shell, driving module, fishtail skeleton, flutter mechanism, pitching mechanism, and control module.
  • ...and 3 more figures