This paper discusses the importance of a nontumbling gait, a gait that allows preventing complete tumbling of the robot.
Nontumbling gait ismade possible by the effect of the swing leg whichmay contact the ground even when the robot is affected by an
external disturbance. Such an effect is present in both static walking and dynamic walking. Stability criterion required to maintain
the nontumbling gait is then considered and proposed through generalized directional normalized energy stability margin. The
validity of the introduced criterion is evaluated by a tumbling experiment with a simplified walking robot model.The concept is
also applied to the gait control of the newly developed walking robot TITAN-XIII.