Abstract: Discoveries in geckos locomotion have advanced the bio-inspired robotics. However, the gecko-inspired robots still lag behind animals in attachments and maneuvers due to our failure to understand and implement gecko bionics thoroughly. Here, we studied the toe deployments that facilitate the upside-down motion of geckos by focusing on the directions and contact area of toes to offer inspirations for the design and control of feet of legged robots that must operate on inverted surfaces. Instead of clustering toes, geckos align toes in varying directions. They distribute adhesion to toes by controlling the magnitude of contact area, with one square millimeter setae generating ~153.8 mN shear force and ~39.5 mN attractive force on ceilings. Front feet deploy toes in a ~190? span that centers on ~16? from the motion direction. Toes distribute uniformly and contribute similarly. Whereas, hind feet deploy toes in a ~220? span centering around ~90? relative to the fore-aft direction. The last two toes point toward the rear and contribute most in hind feet while the first two toes adhere barely. Such deployments involving distributed control among toes not only provide insight into biological adhesion but will also deliver useful information to the next generation of climbing robotics.

Key words: gecko-inspiration, ceiling-walking, hierarchical feet, deployments of toes, distributed control