Helical locomotion in granular media

TL;DR

This paper investigates how a rotating helix propels itself in granular media, combining experiments and a theoretical model to optimize helix design for potential sand-robot applications.

Contribution

It introduces a theoretical model based on anisotropic friction to predict helix propulsion in granular media, validated by experimental data.

Findings

Good agreement between model and experiments

Helix design can be optimized for efficient propulsion

Granular pressure and external load influence propulsion

Abstract

The physical mechanisms that bring about the propulsion of a rotating helix in a granular medium are considered. A propulsive motion along the axis of the rotating helix is induced by both symmetry breaking due to the helical shape, and the anisotropic frictional forces undergone by all segments of the helix in the medium. Helix dynamics is studied as a function of helix rotation speed and its geometrical parameters. The effect of the granular pressure and the applied external load were also investigated. A theoretical model is developed based on the anisotropic frictional force experienced by a slender body moving in a granular material, to account for the translation speed of the helix. A good agreement with experimental data is obtained, which allows for predicting the helix design to propel optimally within granular media. These results pave the way for the development of an efficient sand-robot operating according to this mode of locomotion.