  We have developed an experimental setup of very simple self-propelled robots
to observe collective motion emerging as a result of inelastic collisions only.
A circular pool and commercial RC boats were the basis of our first setup,
where we demonstrated that jamming, clustering, disordered and ordered motion
are all present in such a simple experiment and showed that the noise level has
a fundamental role in the generation of collective dynamics. Critical noise
ranges and the transition characteristics between the different collective
patterns were also examined. In our second experiment we used a real-time
tracking system and a few steerable model boats to introduce intelligent
leaders into the flock. We demonstrated that even a very small portion of
guiding members can determine group direction and enhance ordering through
inelastic collisions. We also showed that noise can facilitate and speed up
ordering with leaders. Our work was extended with an agent-based simulation
model, too, and high similarity between real and simulation results were
observed. The simulation results show clear statistical evidence of three
states and negative correlation between density and ordered motion due to the
onset of jamming. Our experiments confirm the different theoretical studies and
simulation results in the literature about collision-based, noise-dependent and
leader-driven self-propelled particle systems.
