  We study the spontaneous motion, binary collisions, and collective dynamics
of "polar disks", i.e. purpose-built particles which, when vibrated between two
horizontal plates, move coherently along a direction strongly correlated to
their intrinsic polarity. The motion of our particles, although nominally
three-dimensional and complicated, is well accounted for by a two-dimensional
persistent random walk. Their binary collisions are spatiotemporally extended
events during which multiple actual collisions happen, yielding a weak average
effective alignment. We show that this well-controlled, "dry active matter"
system can display collective motion with orientationally-ordered regions of
the order of the system size. We provide evidence of strong number density in
the most ordered regimes observed. These results are discussed in the light of
the limitations of our system, notably those due to the inevitable presence of
walls.
