Friction modulation in limbless, three-dimensional gaits and heterogeneous terrains

TL;DR

This paper presents a unified friction-based model explaining 3D limbless locomotion and terrain interactions, supported by simulations and experiments, revealing how environmental heterogeneity influences movement behaviors and enabling passive navigation design.

Contribution

It introduces an 'everything-is-friction' modeling approach that unifies biological observations of limbless locomotion with terrain heterogeneity effects, including optical analogies and passive navigation strategies.

Findings

Friction modulation explains diverse 3D gait behaviors.

Terrain heterogeneity modeled as high friction regions affects locomotion.

Passive snake navigation achieved through engineered friction patterns.

Abstract

Motivated by a possible convergence of terrestrial limbless locomotion strategies ultimately determined by interfacial effects, we show how both 3D gait alterations and locomotory adaptations to heterogeneous terrains can be understood through the lens of local friction modulation. Via an `everything-is-friction' modeling approach, compounded by 3D simulations, the emergence and disappearance of a range of locomotory behaviors observed in nature is systematically explained in relation to inhabited environments. Our approach also simplifies the treatment of terrain heterogeneity, whereby even solid obstacles may be seen as high friction regions, which we confirm against experiments of snakes `diffracting' while traversing rows of posts [1], similar to optical waves. We further this optic analogy by illustrating snake refraction, reflection and lens focusing. We use these insights to engineer surface friction patterns and demonstrate passive snake navigation in complex topographies. Overall, our study outlines a unified view that connects active and passive 3D mechanics with heterogeneous interfacial effects to explain a broad set of biological observations, and potentially inspire engineering design.