How to make a cylinder roll uphill

TL;DR

This paper demonstrates a novel method to induce rolling motion in elastomeric cylinders using asymmetric swelling and shrinking cycles caused by solvent evaporation, enabling movement uphill and carrying heavy loads.

Contribution

It introduces a new soft robotic locomotion mechanism based on differential swelling, allowing cylinders to roll uphill and carry loads, which was not previously demonstrated.

Findings

Cylinders can roll uphill on inclined planes.

Cylinders can carry weights 8-10 times their own.

A scaling law for optimizing velocity is derived.

Abstract

Slithering, crawling, slipping, gliding are various modes of limbless locomotion that have been mimicked for micro-manipulation of soft, slender and sessile objects. A lesser known mode is rolling which involves periodic, asymmetric and lateral muscular deformations. Here we enable an elastomeric cylinder of poly(dimethylsiloxane) to roll on a substrate by releasing small quantity of a solvent like chloroform, toluene, hexane, heptane and so on, which swells differentially a portion of the cylinder, but evaporates from portion of it which remains exposed to the atmosphere. In a dynamic situation, this asymmetric swelling-shrinking cycle generates a torque which drives the cylinder to roll. The driving torque is strong enough that the cylinder can roll up an inclined plane, within a range of inclination, its velocity even increases. The cylinder can even drag a dead weight significantly larger, ~8-10 times its own weight. A scaling law is derived for optimizing the rolling velocity.