AccScience Publishing / IJOCTA / Online First / DOI: 10.36922/IJOCTA026300185
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RESEARCH ARTICLE

Energy-storing analysis and fishtail stiffness optimization for a wire-driven elastic robotic fish

Xiaocun Liao1* ,  Chao Zhou1* ,  Junfeng Fan1 ,  Zhuoliang Zhang1 ,  Zhaoran Yin1 ,  Liangwei Deng1
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1 The Laboratory of Cognition and Decision Intelligence for Complex Systems, Institute of Automation, Chinese Academy of Sciences, Beijing , China
IJOCTA, 026300185 https://doi.org/10.36922/IJOCTA026300185
Received: 26 July 2026 | Revised: 31 August 2026 | Accepted: 11 September 2026 | Published online: 18 September 2026
© 2026 by the Author(s). This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution -Noncommercial 4.0 International License (CC-by the license) ( https://creativecommons.org/licenses/by-nc/4.0/ )
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Abstract

The robotic fish with high propulsion efficiency and good maneuverability achieves underwater fishlike propulsion by commonly adopting a motor to drive the fishtail, causing significant fluctuations within motor power due to the uneven swing speed of the fishtail in one swing cycle. Hence, we propose a wire-driven robotic fish with a controlled flexible unit that is a spring-steel-based fishlike tail. This unit can produce elastic deformation to store energy under the action of the wire driving and motor to respond to fluctuations in motor power. Further{more}, we analyze the effects of the energy-storing of the controlled flexible unit on the smoothness of motor power. Based on the developed Lagrangian dynamic model and the cantilever beam model, the power-variance-based nonlinear optimization model for the stiffness of the controlled flexible unit is established to respond to sharp fluctuations in motor power during each fishtail swing cycle. The results validate that the energy-storing of the controlled flexible unit plays a vital role in improving the power fluctuations and maximum frequency of the motor by adjusting its stiffness reasonably, which is beneficial for achieving high propulsion and high speed for robotic fish. Compared with the rigid counterpart that is incapable of storing energy, the energy-storing of the controlled flexible unit is beneficial to increase the maximum frequency of the motor and the average thrust of the fishtail by 0.41 Hz and 0.06 N, respectively.

Graphical abstract
Keywords
Wire-driven robotic fish
Stiffness optimization
Power fluctuations
Energy-storing
Controlled flexible unit
Funding
This work was supported in part by the National Natural Science Foundation of China (Grant No. 62503470), and in part by the Postdoctoral Fellowship Program of China Postdoctoral Science Foundation under Grant Number GZC20251177.
Conflict of interest
The authors declare they have no competing interests.
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An International Journal of Optimization and Control: Theories & Applications, Electronic ISSN: 2146-5703 Print ISSN: 2146-0957, Published by AccScience Publishing
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