  Despite advances in a diversity of environments, snake robots are still far
behind snakes in traversing complex 3-D terrain with large obstacles. This is
due to a lack of understanding of how to control 3-D body bending to push
against terrain features to generate and control propulsion. Biological studies
suggested that generalist snakes use contact force sensing to adjust body
bending in real time to do so. However, studying this sensory-modulated force
control in snakes is challenging, due to a lack of basic knowledge of how their
force sensing organs work. Here, we take a robophysics approach to make
progress, starting by developing a snake robot capable of 3-D body bending with
contact force sensing to enable systematic locomotion experiments and force
measurements. Through two development and testing iterations, we created a
12-segment robot with 36 piezo-resistive sheet sensors distributed on all
segments with compliant shells with a sampling frequency of 30 Hz. The robot
measured contact forces while traversing a large obstacle using vertical
bending with high repeatability, achieving the goal of providing a platform for
systematic experiments. Finally, we explored model-based calibration
considering the viscoelastic behavior of the piezo-resistive sensor, which will
for useful for future studies.
