Stigmergic formation of soft matter structures in a robophysical collective

Biological collectives like ants and termites manipulate environmental soft materials (soil, twigs, leaf litter) to create 3D structures that can be redesigned to suit the swarm's needs, despite no individual having knowledge of the global design. To discover principles by which groups perform such tasks, we develop a robophysical system where robotic agents manipulate soft material to create simple structures in response to environmental cues. We use a geometrically cohesive material composed of U-shaped particles which can form 3D structures such as walls, slopes, and arches. Further, we develop a scalable mudskipper-inspired robophysical model (length = 24 cm, width and height = 16 cm) to traverse the complex terrain formed during material manipulation. The robots move at 12 cm/s and negotiate 5 cm tall obstacles via a combination of limb, wheel, and tail actuation. These agents operate within a dark arena (length = 1.8 m, width = 1.2 m) in which light cues dictate different behaviors based on color intensity. A single agent transports ~10% of the initial staple mound over 4 hours. We aim to assign these robots with low level tasks such as material transport coordinated by the environment (i.e., "stigmergy") and posit that the resulting structures will facilitate higher level tasks. Behaviors discovered during structure formations will provide insight on the methods of collective construction in soft matter environments and develop hypotheses for how complex habitats emerge in biological collectives.