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Robophysical study of jumping dynamics on granular media

Nature Physics volume 12, pages 278283 (2016) | Download Citation

Abstract

Characterizing forces on deformable objects intruding into sand and soil requires understanding the solid- and fluid-like responses of such substrates and their effect on the state of the object. The most detailed studies of intrusion in dry granular media have revealed that interactions of fixed-shape objects during free impact (for example, cannonballs) and forced slow penetration can be described by hydrostatic- and hydrodynamic-like forces. Here we investigate a new class of granular interactions: rapid intrusions by objects that change shape (self-deform) through passive and active means. Systematic studies of a simple spring-mass robot jumping on dry granular media reveal that jumping performance is explained by an interplay of nonlinear frictional and hydrodynamic drag as well as induced added mass (unaccounted by traditional intrusion models) characterized by a rapidly solidified region of grains accelerated by the foot. A model incorporating these dynamics reveals that added mass degrades the performance of certain self-deformations owing to a shift in optimal timing during push-off. Our systematic robophysical experiment reveals both new soft-matter physics and principles for robotic self-deformation and control, which together provide principles of movement in deformable terrestrial environments.

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Acknowledgements

This work was supported by NSF Physics of Living Systems, Burroughs Wellcome Fund, and the Army Research Office. We thank A. Karsai for assistance in simulation work and P. Umbanhowar and L. London for insightful comments and discussion.

Author information

Affiliations

  1. School of Mechanical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    • Jeffrey Aguilar
  2. School of Physics, Georgia Institute of Technology, Atlanta, Georgia 30332, USA

    • Daniel I. Goldman

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Contributions

J.A. and D.I.G. conceived the study and wrote the paper. J.A. performed the experimental work, designed and ran the simulation models, and analysed the results.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to Jeffrey Aguilar or Daniel I. Goldman.

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DOI

https://doi.org/10.1038/nphys3568

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