Helical morphology-inspired bistable gripper for UAV upward perching and grasping in field environment

There is a growing interest in unmanned aerial vehicles (UAVs) being able to perch onto objects, which expands their scope of applications. Many perching strategies are inspired by natural organisms, including birds, insects, and helical morphologies such as tendrils and tails. Inspired by these helical structures, a bistable hybrid gripper is developed that enables a quadcopter to perch on branches and perform aerial grasping. The gripper integrates a bistable steel shell (BSS) as the stiff element, analogous to skeletal support, with a soft 3D-printed helical exoskeleton, analogous to muscular compliance, to achieve both structural strength and adaptability. This hybrid design not only enables conformal wrapping and high load capacity but also allows the UAV to grasp without continuous energy input due to its bistable mechanism. Static models are established to predict the pneumatic transition pressure between the two states, and the results are validated experimentally. Furthermore, the holding and grasping forces, along with robustness against tilt and rotation offsets, are systematically characterized, confirming adaptability to branches with varying diameters and orientations. Experimental demonstrations confirm that UAVs equipped with the gripper can reliably perch on tree branches and perform aerial grasping in realistic field environments.