Feather Star-Inspired Soft Robot Reaches 3D Underwater Maneuverability With Two Actuators

Engineers at North Carolina State University and the University of California, Berkeley have developed a soft underwater robot inspired by marine feather stars that achieves full three-dimensional movement using only two actuators, according to a report from TechXplore and research published in Science Advances.

Conventional aquatic robots capable of moving vertically, horizontally, and rotationally typically require at least six separate actuators. The research team reduced this requirement by leveraging mechanical intelligence, an engineering approach in which a machine's dynamic behaviors are governed primarily by physical structure and environmental interactions rather than complex motor arrays or heavy computational control.

The swimmer features a central disk housing two internal actuators flanked by four elastic, monostable wings that snap back to their resting geometry after bending. When both actuators are powered on simultaneously, all four wings snap downward, returning upward when the power is removed.

The platform achieves 3D control by cycling through three primary operational modes. In 'jellyfish mode,' rapidly activating and deactivating both actuators drives the robot upward, cutting power allows it to descend, and slow flapping enables stationary hovering. In 'fish mode,' engaging a single actuator flutters one wing like a tail fin to push the unit forward or backward. In 'rotor mode,' alternating rapidly between the two actuators causes the robot to pivot around its central axis, allowing directional steering.

During laboratory tests, the team demonstrated the robot's utility by mounting a camera to inspect submerged spaces and showing that individual or coordinated units could lift underwater objects. The researchers noted that future iterations will focus on building a fully wireless version and collaborating across disciplines for field applications.