Skin deep: a novel biomimetic control strategy for rectilinear locomotion in snake robots

Snakes are masters of movement through cluttered, confined, and complex habitats, leading to attempts to replicate this mastery in snake robots to improve our access to these challenging environments. While snakes use a variety of locomotor modes, rectilinear allows snakes to move through even the narrowest of spaces. However, while other modes are driven by axial bending, rectilinear relies on motion of the muscular skin, making it challenging to replicate in robots. Prior robotic rectilinear was achieved using secondary actuator systems (e.g. prismatic joints), anteriorly propagating waves, and/or standing waves, which require additional mechanical complexity, high vertical clearance, or dedicated parts for symmetry-breaking (e.g. electromagnets, deployable frictional pads), respectively. Here, I present a new algorithm which closely matches the robot to the motion of the snake's ventral skin (rather than the whole body) during rectilinear locomotion. Robot segments are assigned roles of either rigid ventral scales or flexible inter-scale skin. As in biological snakes, 'scale segments' are lifted clear of the substrate and moved forward via contraction and expansion of the adjacent 'skin motors'. This 'cutaneous rectilinear algorithm' allows rectilinear locomotion without the need for additional actuators or other specialized modifications, and achieves similar displacement per cycle and current consumption to propagating vertical wave methods at a lower vertical height, improving access to highly confined spaces.