We study the problem of achieving global behavior in
a group of distributed robots using only local sensing and minimal
communication, in the context of formations. The goal is to have
mobile robots establish and maintain some predetermined geo-
metric shape. We report results from extensive simulation exper-
iments, and 40+ experiments with four physical robots, showing
the viability of our approach. The key idea is that each robot keeps
a single friend at a desired angle , using some appropriate sensor.
By panning the sensor by degrees, the goal for all formations be-
comes simply to center the friend in the sensor's field of view. We
also present a general analytical measure for evaluating formations
and apply it to the position data from both simulation and physical
robot experiments. We used two lasers to track the physical robots
to obtain ground truth validation data.