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Passive dynamic walking has been developed as a possible explanation for the efficiency of the human gait. In this paper, we investigate the effects of foot shape on energetic efficiency and dynamic stability of passivity-based bipeds with upper body. Three walking models with point feet, round feet and flat feet were presented. Each model has an upper body constrained to keep midway between legs. We use computer simulations to find which foot shapes are indeed optimal in view of energetic efficiency and dynamic stability for a passive dynamic biped with upper body. Simulation results indicate that feet improve both the energetic efficiency and dynamic stability of passive dynamic bipeds.

This paper presents a passive dynamic walking model with segmented feet. The model extends the Simplest Walking Model with the addition of flat feet and torsional springs based compliance on ankle joints and toe joints, to achieve stable walking on a slope driven by gravity. The push-off phase includes foot rotations around toe joint and around toe tip, which shows a great resemblance to human normal walking. Experimental results show the effects of adding segmented feet to passive dynamic walkers on energetic efficiency.

The energetic effects of knee locking and addition of linear elastic members to different joints of a seven-link fully actuated planner bipedal robot were studied. The focus was on the reduction of energy consumption during walking. An impactless walking gait was studied and the energetic cost of walking was determined without joint stiffness and knee locking as a baseline for comparison. The gait trajectory was then optimized by adding spring to different joints, energetic cost of walk was then calculated at different walking speeds. Support knee was then mechanically locked and gait was optimized to find the walking cost. The energetic cost of walking determined for the above two cases was then compared to the baseline cost. It was observed that addition of torsional springs at both hips can reduce the walking cost up to 38%, support hip up to 40% with spring stiffness as an optimization parameter for both cases while mechanically locking the support knee can reduce the cost of walking up to 92% at slow walking speeds with gait and knee locking angle optimized.

In order to create efficient legged robots it is needed to care about energy consumption. During motion, energy is used in two different ways: positive energy to generate movement, and negative energy to brake movement. The use of passive components to dissipate the energy by friction could be a possible solution to avoid braking with active elements. This paper deals with the problem of determining experimentally the benefits of damping the knee by absorbing negative energy in MRF dampers, against actively braking using the actuators.