  Networks of rigid bars connected by joints, termed linkages, provide a
minimal framework to design robotic arms and mechanical metamaterials built out
of folding components. Here, we investigate a chain-like linkage that,
according to linear elasticity, behaves like a topological mechanical insulator
whose zero-energy modes are localized at the edge. Simple experiments we
performed using prototypes of the chain vividly illustrate how the soft motion,
initially localized at the edge, can in fact propagate unobstructed all the way
to the opposite end. We demonstrate using real prototypes, simulations and
analytical models that the chain is a mechanical conductor, whose carriers are
nonlinear solitary waves, not captured within linear elasticity. Indeed, the
linkage prototype can be regarded as the simplest example of a topological
metamaterial whose protected mechanical excitations are solitons, moving domain
walls between distinct topological mechanical phases. More practically, we have
built a topologically protected mechanism that can perform basic tasks such as
transporting a mechanical state from one location to another. Our work paves
the way towards adopting the principle of topological robustness in the design
of robots assembled from activated linkages as well as in the fabrication of
complex molecular nanostructures.
