NonUniform Robot Densities in Vibration Driven Swarms Using Phase Separation Theory In robot swarms operating under highly restrictive sensing and communication constraints, individuals may need to use direct physical proximity to facilitate information exchange. However, in certain taskrelated scenarios, this requirement might conflict with the need for robots to spread out in the environment, e.g., for distributed sensing or surveillance applications. This paper demonstrates how a swarm of minimallyequipped robots can form highdensity robot aggregates that coexist with lower robot densities in space. We envision a scenario where a swarm of vibrationdriven robotsxe2x80x94which sit atop bristles and achieve directed motion by vibrating themxe2x80x94move randomly in an environment while colliding with each other. Theoretical techniques from the study of farfromequilibrium collectives and statistical mechanics clarify the mechanisms underlying the formation of these high and low density regions. Specifically, we capitalize on a transformation that connects the collective properties of a system of selfpropelled particles with that of a wellstudied molecular fluid system, thereby inheriting the rich theory of equilibrium thermodynamics. Real robot experiments as well as simulations illustrate how interrobot collisions can precipitate the formation of nonuniform robot densities in a closed and bounded region.

Segregation and Flow of Modules in a Robot Swarm Utilising the Brazil Nut Effect A lot of research has been conducted on swarm and modular robots and their reconfiguration. For this kind of robot system, it is best to simplify each individual module in order to avoid making the swarm system too complex in the interest of reducing the computing power necessary for a task.This paper proposes a swarm robot system capable of selfsegregation by changing the size of each agent, utilising the Brazil Nut Effect. The selfsegregation allowed by this effect lead to the simplification of the control protocol necessary for the swarm.We simulated a swarm robot system consisting of circular modules capable of changing their radius and, with the aid of externally supplied vibrations, utilising the Brazil Nut Effect to achieve segregation of the swarm. The effect also allowed for the migration of individual modules through the swarm. Additionally, we harnessed this segregation effect in simulation to create a flow of modules within the swarm, whilst the swarm was confined within a vibrating container.Lastly, we took the first steps toward physical verification of the experimental results by designing and building a prototype for a circular robot module capable of changing its radius in a manner inspired by a spiral torsion spring.