Designing falling motions for a humanoid soccer goalie

Most of the research related to the topic of falling strategies considers falling to be an unavoidable part of bipedal walking and is focused on developing strategies to avoid falls and to minimize mechanical damage. We take an alternative point of view and regard falling as a means to an end. We present our falling strategy for the specific case of a robot soccer goalie that deliberately jumps in front of a moving ball to prevent it from rolling into the goal. The jump decision is based on observed ball position, speed and direction of movement. We show how we implement a targeted falling into the appropriate direction, minimize the time from the jump decision to ground impact, and what solutions we developed to prevent mechanical damage. The presented falling technique was used in RoboCup Humanoid KidSize and TeenSize competitions and proved to be essential for winning.