Inverted and Inclined Climbing Using Capillary Adhesion in a Quadrupedal Insect-Scale Robot

Many insects demonstrate remarkable locomotive capabilities on inclined or even inverted surfaces. Achieving inverted locomotion is a challenge for legged insect-scale robots because repeated attachment and detachment to a surface usually requires the design of special climbing gaits, adhesion mechanisms, sensing, and feedback control. In this study, we propose a novel adhesion method that leverages capillary and lubrication effects to achieve simultaneous adhesion and sliding. We design a 47 mg adhesion pad and install it on a 1.4 g insect-scale quadrupedal robot to demonstrate locomotion on inverted and inclined surfaces. On an inverted acrylic surface, the robot's climbing and turning speeds are 0.3 cm/s and 23.6 °/s, respectively. Further, the robot can climb a 30° inclined acrylic surface at 0.04 cm/s. This light-weight, passively stable, and versatile adhesion design is suitable for insect-scale robots with limited sensing, actuation, and control capabilities.