Emergent swarm robot behaviors induced by confinement and contact interactions*

Building on our study of phase changes in contact-mediated robot collectives [Li et al, Science Advances 2021], we study the dynamics and task capabilities of a confined programmable swarm of twelve disk-shaped (8 cm diameter) wheel-driven robots that make decisions based on local collisions. Each robot differentiates contact between other agents and environmental features (e.g., rigid walls, obstacles) via a force-sensitive resistor pad on its surface. The robots’ light sensors enable individual phototaxis via run-and-tumble dynamics. To enhance robot interactions and generate swarms of different collective mechanical properties, we place the swarm within a movable, flexible membrane which can actively change perimeter length. When the perimeter is small, the robots cluster and form a solid-like state; when expanded, the swarm functions like an active gas. The robots can control the perimeter and shape of the membrane via collisions and contact; the membrane can actively respond to the collisions to dynamically induce phase changes in the swarm. We posit that we can utilize the multiphase swarm dynamics in conjunction with membrane induced rigidity to perform tasks like object engulfment and transport.