Animal and Robotic Locomotion on Wet Granular Media

Most of the terrestrial environments are covered with some type of flowing ground; however, inadequate understanding of moving bodies interacting with complex granular substrates has hindered the development of terrestrial/all-terrain robots. Although there has been recent performance of experimental and computational studies of dry granular media, wet granular media remain largely unexplored. In particular, this encompasses animal locomotion analysis, robotic system performance, and the physics of granular media at different saturation levels. Given that the presence of liquid in granular media alters its properties significantly, it is advantageous to evaluate the locomotion of animals inhabiting semi-aquatic and tropical environments to learn more about effective locomotion strategies on such terrains. Lizards are versatile and highly agile animals. Therefore, this study evaluated the brown basilisk, which is a lizard species from such habitats that are known for their performance on wet granular media. An extensive locomotion study was performed on this species. The animal experiments showed that on higher saturation levels, velocity of the animal was increased due to an increase in the stride length. A basilisk-inspired robot was then developed to further study the locomotion on wet granular media and it was observed that the robot can also achieve higher velocities at increased saturation levels. This work can pave the way for developing robotic systems which can explore complex environments for scientific discovery, planetary exploration, or search-and-rescue missions.