Figure 1

(A) Passive dynamic walking model where φ is the angle of the swing leg, θ is the angle of the stance leg, m is the point mass at the respective foot, M is the mass at the hip, γ is the angle of inclination of the supporting surface, and g is gravity. Both legs are of length ℓ. (B) Cascade of bifurcations in the step time interval of the passive dynamic walking model with no toe-off impulse applied (e.g., J = 0). A period-1 gait means the model selects the same step-time interval for gait pattern, a period-2 means that the model alternates between two different step-time intervals, and a period-4 means that the model uses four different step-time intervals. Nonlinear gait patterns that are chaotic are found when the ramp angle is between 0.01839 radians and 0.0189 radians when J = 0. No stable gaits are present if the ramp angle is greater than 0.019 radians [19].