  The collective ability of organisms to move coherently in space and time is
ubiquitous in any group of autonomous agents that can move and sense each other
and the environment. Here we investigate the origin of collective motion and
its loss using macroscopic self-propelled Bristle-Bots, simple automata made
from a toothbrush and powered by an onboard cell phone vibrator-motor, that can
sense each other through shape-dependent local interactions, and can also sense
the environment non-locally via the effects of confinement and substrate
topography. We show that when Bristle-Bots are confined to a limited arena with
a soft boundary, increasing the density drives a transition from a disordered
and uncoordinated motion to organized collective motion either as a swirling
cluster or a collective dynamical stasis. This transition is regulated by a
single parameter, the relative magnitude of spinning and walking in a single
automaton. We explain this using quantitative experiments and simulations that
emphasize the role of the agent shape, environment, and confinement via
boundaries. Our study shows how the behavioral repertoire of these physically
interacting automatons controlled by one parameter translates into the
mechanical intelligence of swarms.
