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 nonlocally 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 behavioural repertoire of
these physically interacting automatons controlled
by one parameter translates into the mechanical
intelligence of swarms.