Analysing and solving body misplacement problems in walking robots with round rigid feet

Round rigid feet for multi-legged robots offer a number of advantages over flat feet, and even over flat feet with articulated ankles. The main benefits are low cost, low complexity and robustness. A round rigid foot of small radius works well on hard terrain; however, it is prone to sink into soft terrain. Sinking can be avoided by increasing the radius of the foot, but in that case a round foot will roll during the leg-support phase, causing the hip to become misplaced and the robot to assume an incorrect attitude. This paper analyses this problem and provides a hip-control algorithm for restoring leg coordination. The algorithm is implemented in a real leg with a large-radius ball foot in order to evaluate how the algorithm would perform if applied to a real robot.