There is provided a mobile robot including a chassis, a drive system, and a collision detection system. The collision detection system includes first and second parts of the mobile robot, the first and second body parts being disconnected and moveable relative to the chassis in response to a collision with an object, and first and second sensors configured to sense relative movement between the chassis and the first and second body parts respectively and, in a collision event, to send a control signal causing the drive system to take corrective action. The mass of the second body part is substantially lower than the mass of the first body part.