  Multimodal UAVs (Unmanned Aerial Vehicles) are rarely capable of more than
two modalities, i.e., flying and walking or flying and perching. However, being
able to fly, perch, and walk could further improve their usefulness by
expanding their operating envelope. For instance, an aerial robot could fly a
long distance, perch in a high place to survey the surroundings, then walk to
avoid obstacles that could potentially inhibit flight. Birds are capable of
these three tasks, and so offer a practical example of how a robot might be
developed to do the same. In this paper, we present a specialized
avian-inspired claw design to enable UAVs to perch passively or walk. The key
innovation is the combination of a Hoberman linkage leg with Fin Ray claw that
uses the weight of the UAV to wrap the claw around a perch, or hyperextend it
in the opposite direction to form a curved-up shape for stable terrestrial
locomotion. Because the design uses the weight of the vehicle, the
underactuated design is lightweight and low power. With the inclusion of
talons, the 45g claws are capable of holding a 700g UAV to an almost 20-degree
angle on a perch. In scenarios where cluttered environments impede flight and
long mission times are required, such a combination of flying, perching, and
walking is critical.
