Koh, J.-s. | Search bioRxiv

bioRxiv2026

Springtail-inspired compliant hinge enables terrain-adaptable takeoff in insect-scale robots

Springtails execute millisecond-scale escape jumps with a single appendage, the furca, on soil, snow, leaf litter, and water. Across 15 taxonomic families (n=552 individuals), relative furca length is bimodal. High-speed video and confocal imaging show that in some long-furca springtails, the resilin-rich manubrium-dens joint behaves as a compliant hinge. It bends during push-off to prolong contact, suppress pitch, and bias takeoff forward, whereas rigid joints drive backward launches with rapid body rotation. We translate this mechanism to a 20-mm, 84-mg jumping robot with an elastic robo-furca hinge. This flexible hinge reduces body rotation by [~] 90% on flat ground compared to rigid-hinge designs, while maintaining takeoff speed on gravel, springboards, leaves, and pine needles, enabling passive, terrain-adaptable launches for power-limited insect-scale robots without onboard sensing or active control.

animal behavior and cognition↗

bioRxiv2024

Ultrafast elastocapillary fans control agile maneuvering in ripple bugs and robots

Millimeter-sized ripple bugs in the genus Rhagovelia exhibit exceptional agility and rapid maneuvers in fast, unsteady streams, comparable to animal fliers. Their remarkable interfacial transit and turning skills stem from a specialized fan structure on their middle legs. While researchers have suggested active fan actuation, the role of capillary forces and unique microstructure in self-spreading remains unclear. We reveal that Rhagovelias fans possess a flat-ribbon architecture with directional stiffness, enabling ultrafast elastocapillary morphing for passive actuation in under 10 ms, independent of muscle control, while producing high-thrust momentum through unsteady vortical wakes. These self-morphing fans allow Rhagovelia to execute [~]90 {degrees} turns at a rate of [~]4200 {degrees}/s, in [~]50 ms, with speeds reaching [~]120 BL/s - on par with the fastest recorded turns in animal fliers like fruit flies. Inspired by these, we develop an ultralight, ultrafast elastocapillary robotic fan ([~]1 mg, [~]100 ms opening/closing time) and integrate it into an insect-scaled robot (Rhagobot, [~]0.2 g). The engineered fans passively balance surface tension and water drag through stiffness anisotropy, enabling the robot to achieve high agility with speeds up to [~]2 BL/s and turning rates of 206 {degrees}/sec. Experiments with both insects and robots, with and without fans, show that a self-spreading passive fan significantly improves thrust, braking, and turning - key factors for controlled, high-speed maneuvers. This elastocapillary innovation enables ripple bugs to survive and thrive in turbulent streams and offers new insights for agile aquatic robotics.

biophysics↗