A coverage robot including a chassis, multiple drive wheel assemblies disposed on the chassis, and a cleaning assembly carried by the chassis. Each drive wheel assembly including a drive wheel assembly housing, a wheel rotatably coupled to the housing, and a wheel drive motor carried by the drive wheel assembly housing and operable to drive the wheel. The cleaning assembly including a cleaning assembly housing, a cleaning head rotatably coupled to the cleaning assembly housing, and a cleaning drive motor carried by cleaning assembly housing and operable to drive the cleaning head. The wheel assemblies and the cleaning assembly are each separately and independently removable from respective receptacles of the chassis as complete units.