  Legged robots have demonstrated high efficiency and effectiveness in
unstructured and dynamic environments. However, it is still challenging for
legged robots to achieve rapid and efficient locomotion on deformable, yielding
substrates, such as granular terrains. We present an enhanced resistive force
model for bipedal walkers on soft granular terrains by introducing effective
intrusion depth correction. The enhanced force model captures fundamental
kinetic results considering the robot foot shape, walking gait speed variation,
and energy expense. The model is validated by extensive foot intrusion
experiments with a bipedal robot. The results confirm the model accuracy on the
given type of granular terrains. The model can be further integrated with the
motion control of bipedal robotic walkers.
