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Elasticity and mechanical metamaterials

How can a heat-driven rubbery ribbon steer itself out of a maze?

Zhao Y, Hong Y, Li Y, et al. · Science advances · 2023

Open access · cc by · source: Europe PMC

A heat-powered rolling ribbon with one twisted end and one helical end kept turning on its own and escaped mazes, while ribbons that were symmetric stopped turning and got trapped.

Study at a glance

Design
Other — Lab experiments tracking twisted, helical and hybrid liquid crystal elastomer ribbons self-rolling on a hot plate (mostly 120°C), in open space, between parallel walls and in mazes, supported by Abaqus FEA and an analytical turning model.
N
No single N; three ribbon geometries compared, each maze trial repeated from random start positions at least three times.
Population
Liquid crystal elastomer ribbons (twisted, helical and hybrid twisted-helical) on hot rigid and sand surfaces
Outcome
Turning angle and turning radius during free rolling; whether and how fast each ribbon escaped confined channels and mazes

Structured fields used in claim comparison tables when every cited study has a complete layer.

Key findings

Twisted and helical ribbons turned only briefly while they untwisted during heating, then rolled straight and became trapped bouncing between walls. The hybrid ribbon turned continuously because its helical end is slightly wider, giving a turning radius of 19 cm versus 170 cm for the twisted ribbon, and it escaped the parallel-wall channel after 12 snaps within 1000 s. It escaped every maze tested, including on sand and through gaps about a third narrower than its length, though complex mazes took over an hour.

Methodology

The researchers made ribbons of a liquid crystal elastomer that rolls by itself on a hot surface, in three shapes: fully twisted, fully helical, and a hybrid with a helical half and a twisted half. They tracked the ribbons' paths on an open hot plate, between two parallel walls, and in simple, complex, narrow-gap, sand-covered and time-changing mazes. Finite-element simulations and an analytical model were used to explain why each shape turns.

Limitations

The mazes were still much simpler than real labyrinths, and the authors say larger hot plates or new designs would be needed to go further; circular or irregular mazes were not tried. The ribbons need a hot surface as their power source, so the result does not show operation in ordinary environments. Escape relies on trial and error rather than any memory or planning, and the analytical model of asymmetric turning is simplified, with large error bars attributed to uneven hot-plate temperature.

How this study connects

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