  Sidewinding, a locomotion strategy characterized by the coordination of
lateral and vertical body undulations, is frequently observed in rattlesnakes
and has been successfully reconstructed by limbless robotic systems for
effective movement across diverse terrestrial terrains. However, the
integration of compliant mechanisms into sidewinding limbless robots remains
less explored, posing challenges for navigation in complex, rheologically
diverse environments. Inspired by a notable control simplification via
mechanical intelligence in lateral undulation, which offloads feedback control
to passive body mechanics and interactions with the environment, we present an
innovative design of a mechanically intelligent limbless robot for sidewinding.
This robot features a decentralized bilateral cable actuation system that
resembles organismal muscle actuation mechanisms. We develop a feedforward
controller that incorporates programmable body compliance into the sidewinding
gait template. Our experimental results highlight the emergence of mechanical
intelligence when the robot is equipped with an appropriate level of body
compliance. This allows the robot to 1) locomote more energetically
efficiently, as evidenced by a reduced cost of transport, and 2) navigate
through terrain heterogeneities, all achieved in an open-loop manner, without
the need for environmental awareness.
