Efficient walking gait with different speed and step length: Gait strategies discovered by dynamic optimization of a biped model

The selection of walking gait for biped robots depends on the requirement of walking environment. Walking with different situations of walking speeds and step lengths, the gait strategies are different. In this paper, we study the energetically optimal walking gait strategies under the different walking situations using a simple biped walking model with dynamic optimization method. The walking model with mass legs and three actuations, which is designed upon Srinivasan’s model, is built for the purpose of the paper. Dynamic optimization is used for a free search with minimal constraints. The analysis of the COT of the optimal gaits and its two components COTswing and COTpush-off show that the COT is increasing with the increase of the walking speed. For a certain walking speed, the minimal value of COT can be found with a corresponding step length. According to the joint torques output strategies, we discover four gait patterns including two typical walking gaits patterns that the hip torque impulse is only at the beginning or at the end of the swing phase, respectively, and two other new transitional gait patterns.