Compliant Bistable Grippers Enable Passive Perching for Micro Aerial Vehicles

Micro aerial vehicles (MAVs) with multiple rotors, or multicopters, have many promising applications ranging from environmental monitoring, agricultural inspection, to package delivery. These applications, however, usually face a critical problem: the flight time of MAVs is limited due to the low aerodynamic efficiency and high energy consumption. One promising solution is to make them rest on desired objects using perching, an important capability in biological flyers (e.g., birds). In this article, we present the design and experimentation of a novel perching mechanism: a low cost, 3-D-printed gripper with bistability (i.e., two stable states). The gripper has two unique characteristics. First, using bistability, it can passively switch from open to closed state using the impact between the gripper and the perching object, alleviating the requirement for precise motion control. Second, the gripper has two perching methods for different objects. For objects with a small height, it can form a closed diamond shape to encircle the objects (encircling method). For objects with a large height, the gripper's two fingers can clip on each side of the objects to utilize the friction forces for perching (clipping method). We analyze the proposed gripper design to predict the required force for opening and closing the gripper. We also predict the size of objects that will allow for successful perching for the clipping method. All the theoretical analyses are experimentally verified. Finally, we integrate the gripper onto a palm-size quadcopter to enable a mechatronic system for perching, and demonstrate successful perching with both clipping and encircling methods as well as aerial grasping. Although our bistable gripper is used with a palm-size quadcopter, the design strategy can also be applied to large-size MAVs for both energy efficient perching and aerial grasping.