In this research the role of thick flexible soles in energy-efficient humanoid walking is analyzed. It is
hypothesized that, the addition of underactuated degrees of freedom under the foot gives the robot
the potential to execute a pseudo-passive walking motion 1, which yields a decrease in ankle torque
and energy expenditure. Furthermore it is hypothesized that, if these principles are applied to toed
gait walking patterns, instead of flat foot walking patterns the decreases will be larger in magnitude.
To isolate the effects of adding a sole, a toe joint and both at the same time, four walking types are
compared in simulation; flat foot and toed gait walking, both with and without sole. To asses the cases
without sole, energy-optimized walking pattern generation is used. For walking on soles, the optimized
walking patterns are used as input for a deformation estimator that calculates the sole compression.
Simulation results show that the rolling motion of the sole reduces the ankle torque and the energy
consumption. The results prove that the reduction effects are especially large for toed gait walking,
thereby validating both the hypotheses.