Performance of different foot designs for a water running robot

The water runner robot is designed to run on the surface of water in a manner similar to the basilisk lizard. To do so, it must generate a lift force greater than its weight by slapping and stroking its foot through the water, creating an air cavity in the process. In addition, it must remove its foot before this cavity collapses. Basilisk lizards deal with this problem by folding their feet during retraction from the air cavity to avoid prematurely collapsing the cavity and generating excess drag. Several different passive foot designs for the water runner were analyzed to determine which had the largest lift and created the least amount of drag. Feet with folding sections which collapse during retraction and spring back into place once the foot has exited the water were found to work best. Those feet which allowed air to pass through during retraction provided the least net lift. Elliptic feet with their major axis in line with the direction of running performed better than simple circular feet. Consequences of these results are discussed.