Collective behavior of BOBbots, a robotic active matter system

We introduce BOBbots (Behaving, Organizing, Buzzing Robots, named to honor the late Bob Behringer), a custom low-cost active matter system composed of disk-shaped “granular” robots. The robots are equipped with controllable vibration that can react to light and stress. The vibration couples to two bristles on the base of the robot which generates translation and rotation. The robots can attract each other via loosely constrained magnets in cavities on a robot’s circumference. We first investigate the clustering of the collective which results from a competition between the attraction and driving. In experiments and discrete element method simulations, increasing magnet strength leads to a rapid increase in steady-state cluster size which saturates for sufficient attraction. The dynamics of this nonequilibrium system resemble those in an equilibrium lattice model. An algorithm by which robots decrease drive upon increased stress increases clustering rate at fixed magnet strength. Formation of clusters enables the collective to perform a task no individual can: transport of a free obstacle.