Researchers from the Shenyang Institute of Automation (SIA) of the Chinese Academy of Sciences have developed an electrohydraulically actuated soft robotic fish that can swim at high speeds and perform agile three-dimensional (3D) maneuvers. The soft robotic fish addresses a longstanding design challenge by combining a rigid–flexible coupled propulsion system with dynamic buoyancy regulation. This allows for fast propulsion without sacrificing maneuverability.
The study was published in IEEE/ASME Transactions on Mechatronics on October 5.
Soft robotic fish show great potential for underwater environmental monitoring and resource exploration. However, conventional designs often sacrifice swimming speed for maneuverability, especially when performing complex 3D movements.
Inspired by the coordinated action of fish muscles and skeletons, as well as the buoyancy regulation provided by the swim bladder, the researchers incorporated these biological mechanisms into the robotic design. The system combines electrohydraulic propulsion with active buoyancy control to enable rapid propulsion and flexible 3D movement.
The researchers designed a rigid–flexible electrohydraulic actuator with two degrees of freedom. Local rigid constraints reduce undesired deformation during actuation. Alternating movements of the two driving units mimic antagonistic muscle contractions, generating high-frequency tail oscillations.
Experimental results demonstrated that the robotic fish can swim at a maximum speed of 2.13 body lengths per second (approximately 26 cm/s) with a minimum transport cost of 9.4 J/(kg·m). This sets a new speed record for soft robotic fish using body-caudal-fin (BCF) propulsion.
To enable active control of the robot's orientation, the researchers developed a biomimetic swim bladder that operates through a liquid-to-gas phase transition. By regulating the local buoyancy of the robotic fish, the system generates a pitching moment and enables posture adjustment from −20° to 58°.
By coordinating electrohydraulic propulsion with dynamic posture regulation, the robotic fish can perform various maneuvers, such as horizontal cruising, turning, S-shaped swimming, ascending, diving, and spiral ascent. This combination allows the robot to move beyond horizontal swimming and perform complex 3D maneuvers.
By combining rigid–flexible coupled electrohydraulic propulsion with dynamic buoyancy regulation, the design enables the robotic fish to retain structural compliance while achieving high-speed swimming and 3D maneuverability, offering a potential approach to the design of high-performance underwater robots.
The research team has long focused on bio-syncretic robotics, exploring the deep integration of biological mechanisms, materials, and structures with electromechanical systems, and advancing robotic systems from conventional electromechanical platforms toward integrated bio-electromechanical systems.
This work was supported by the National Natural Science Foundation of China, the New Cornerstone Science Foundation, the Chinese Academy of Sciences, and others.
IEEE/ASME Transactions on Mechatronics
Experimental study
Not applicable
Electrohydraulic Actuated High-Speed Biomimetic Soft Robotic Fish With Flexible 3D Maneuverability
5-Oct-2026