A Study of a Class of VibrationDriven Robots: Modeling, Analysis, Control and Design of the Brushbot In this paper we present a study of a specific class of vibrationdriven robots: the brushbots. In a bottomup fashion, we start by deriving dynamic models of the brushes and we discuss the conditions under which these models can be employed to describe the motion of brushbots. Then, we present two designs of brushbots: a fullyactuated platform and a differentialdrivelike one. The former is employed to experimentally validate both the developed theoretical models and the devised motion control algorithms. Finally, a coordinatedcontrol algorithm is implemented on a swarm of differentialdrivelike brushbots in order to demonstrate the design simplicity and robustness that can be achieved by employing a vibrationbased locomotion strategy.

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.