Contact sensors for a mobile robot

A robot comprising:

• a body movable relative to a surface;
• a bumper mounted on the body and movable relative to the body, the bumper comprising a backing movable relative to the body in response to a force applied to the bumper;
• a first sensor to output a first electrical signal that varies with an amount of movement of the bumper, at least part of the first sensor being mounted to the backing, and
• a second sensor to output a second electrical signal that varies with the amount of the movement of the bumper, at least part of the second sensor being mounted to the backing;
• and
• a controller to receive the first electrical signal and the second electrical signal, and to determine one or more attributes of the force applied to the bumper based on the first electrical signal and the second electrical signal.