Altas 的难点并不是后空翻这个动作,难点是在后空翻前的运动规划和接触地面后的控制(例如如何保持平衡,如何控制接触力等)。(One of the major difficulties in making a legged robot walk or run is keeping its balance: where should the robot place its feet, how should it move its body in order to move safely in a given direction, even in case of strong perturbations? This difficulty comes from the fact that contact forces with the environment are an absolute necessity to generate and control locomotion, but they are limited by the mechanical laws of unilateral contact)。