Researchers at Shanghai Jiao Tong University have developed a soft, amphibious robot powered by electrohydraulic flippers that can seamlessly transition between crawling on land, moving underwater, and swimming—all while functioning in temperatures ranging from -20 °C to 70 °C.
Study: A Multimodal Amphibious Robot Driven by Soft Electrohydraulic Flippers. Image Credit: boulham/Shutterstock.com
Published in Cyborg and Bionic Systems, the study highlights a versatile design that combines soft materials with high-performance actuation, opening up new possibilities for robotic applications in unpredictable environments. The robot reaches swimming speeds of up to 5.9 centimeters per second (cm/second), making it one of the most agile soft amphibious systems to date. Its performance and adaptability make it well-suited for use in search-and-rescue operations, environmental monitoring, and infrastructure inspection.
Background
Unlike rigid machines, soft robots can flex, twist, and conform to uneven or sensitive surfaces, making them ideal for unpredictable settings. A key enabler of this flexibility is electrohydraulic actuation, which uses electrical energy to generate hydraulic pressure, producing controlled, silent motion.
In this project, the Shanghai team used that principle to design a robot with three symmetrically placed soft flippers. Each flipper contains a silicone-oil pouch and carbon electrodes that bend under high voltage. A fin-like internal skeleton translates this deformation into directional flipper movements, allowing the robot to transition fluidly between land, underwater, and swimming modes, without mechanical reconfiguration.
This seamless switching is a major advance, addressing one of robotics' core challenges: building machines that can operate reliably across diverse and dynamic terrains.
Efficient, Adaptive Locomotion
The robot’s movement hinges on its electrohydraulic actuators, which deliver high energy efficiency with minimal noise. When voltage is applied, the carbon electrodes compress the silicone oil inside each flipper, causing it to bend. The embedded skeleton then guides this motion into coordinated propulsion across different environments:
- On land, it crawls at 2.9 cm/second by generating traction through asymmetric friction at the flipper tips.
- Underwater, where drag is reduced, it crawls at 3.2 cm/second, leveraging fluid interaction for movement.
- While swimming, the flippers oscillate in synchrony to create vortex rings, enhancing propulsion and pushing the robot to 5.9 cm/second.
Fluid dynamics simulations confirmed that these vortex rings play a key role in improving thrust and overall swimming performance.
Equally notable is the robot’s ability to operate across a wide temperature range. It maintained full functionality from -20 °C to 70 °C, with silicone oil viscosity being the only performance constraint in extreme cold. Even in near-freezing water, it achieved a swimming speed of 2.7 cm/second. This thermal resilience, paired with durable materials and efficient energy conversion, makes it well-suited for field deployment in harsh conditions.
Built for Real-World Tasks
What sets this robot apart is not just its mobility, but its versatility. It can traverse a flooded area by swimming, then crawl through debris to complete a mission—no hardware change required. This kind of adaptability significantly reduces operational complexity and expands its range of potential applications.
Looking ahead, the researchers plan to refine the robot’s materials to boost speed and payload capacity. They also aim to integrate autonomous navigation features and task-specific tools, such as onboard sensors, cameras, or water sampling devices. Scaling the robot for larger loads or shrinking it for confined environments are additional goals under active exploration.
The project is backed by the National Natural Science Foundation of China, reflecting strong national interest in advancing soft robotics for use in disaster response, field science, and other demanding domains.
Conclusion
This amphibious robot showcases the practical power of electrohydraulic actuation, blending efficiency, resilience, and terrain flexibility into a compact design. With further development, it could offer a reliable, all-terrain solution for complex missions in challenging environments, bridging the gap between experimental soft robotics and real-world deployment.
Journal Reference
Fang, F., Zhou, J., Zhang, Y., Yi, Y., Huang, Z., Feng, Y., Tao, K., Li, W., & Zhang, W. (2025). A Multimodal Amphibious Robot Driven by Soft Electrohydraulic Flippers. Cyborg and Bionic Systems, 6. DOI:10.34133/cbsystems.0253. https://spj.science.org/doi/10.34133/cbsystems.0253
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