Autonomous coverage robot

An autonomous coverage including a chassis, a drive system and a floor proximity sensor carried by the chassis and configured to detect a floor surface below the robot, wherein the floor proximity sensor includes a beam emitter and a beam receiver responsive to a reflection of the directed beam from the floor surface and mounted in a downwardly-directed receptacle of the chassis, and a main cleaning head carried by the chassis and driven to rotate about a horizontal axis to engage a floor surface while the robot is maneuvered across the floor, and a container to collect debris, wherein the main cleaning head includes at least one roller and a suction duct integrated with a brush chamber wherein a leading portion of the brush chamber comprises a curved surface that follows a circumference of the at least one roller at a substantially constant clearance.