We describe a new class of decentralised control algorithms that link local wireless connectivity to low-level robot motion control in order to maintain both swarm aggregation and connectivity, which we term “coherence”, in unbounded space. We investigate the potential of first-order and second-order connectivity information to maintain swarm coherence. For the second-order algorithm we show that a single β parameter—the number of shared neighbours that each robot tries to maintain—acts as an “adhesion” parameter. Control of β alone affects the global area coverage of the swarm. We then add a simple beacon sensor to each robot and show that, by creating a β differential between illuminated and occluded robots, the swarm displays emergent global taxis towards the beacon; it also displays interesting global obstacle avoidance properties. The chapter then extends the idea of β heterogeneity within the swarm to demonstrate variants of the algorithm that exhibit emergent concentric or linear segregation of subgroups within the swarm, or—in the presence of an external beacon—the formation of horizontal or vertical axial configurations. This emergent swarm morphology control is remarkable because apparently simple variations generate very different global properties. These emergent properties are interesting both because they appear to have parallels in biology, and because they could have value to a wide range of future applications in swarm robotics.
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