A method of foot clearance achievement and frontal plane stability of 3D bipeds is mathematically analyzed. The independency of the robot's body vibration amplitude from the foot clearance is also proven. The analyzed method takes advantage of the sideways vibration of the body generated by periodically shortening each leg to obtain the required foot clearance. A mathematical model of the biped in the frontal plane is suggested and analyzed in two separate phases, resulted in the calculation of the steady state working point. It is demonstrated that in steady state, the amplitude of the body vibration becomes independent from the leg length vibration amplitude. A direct advantage of the proof is the possibility of achieving of high foot-to-ground distances by increasing the leg length vibration amplitude as the robot reaches its steady state. The results have been verified using both simulations and real robot experiments. To guarantee the stability of the robot in the transient phases a method is suggested based on an energy criterion.
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