Sensors provide the robot with information about itself (internal sensors) and the enviornment (external sensors). The sensor info is used to adjust the robot behavior. Some sensors, like foot contact sensors, help the robot to adjust its balance. Other sensors, like the directional or distance sensor help the robot move toward a target.
Sensors, when attached to the robot, are automatically updated every frame, which occur between 20 and 60 times per second. This depends on the speed of the computer simulating Xemo.
The contact sensor provides information when a body part of the robot collides with another part or an object in the environment. Floor contact sensors specifically look for contact with the floor or other objects that will support the robot (stairs, for example). The sensors also relay information regarding the amount of contact force.
The orientation sensor measures the upright direction of the robot. Think of a line from the center of the pelvis to the base of the neck. This line changes its orientation as the robot leans or falls. The line can be represented by a vector with (X,Y,Z, theta) components. The theta component is used to indicate the rotation of the robot along its long axis. If you are writing code, you can ask for the orientation as a set of angles or as a Quaternion. The quaternion is an advanced math concept - it is used to perform calculations using rotation that is more efficient than using angles (known as Euler angles).
The direction sensor measures the angle between the forward direction of the robot and some object in the environment. There are two angle measurements - one parallel to the floor plane, and another expressing the angle up from the floor. Since the forward direction of the robot affects the sensor, the direction sensor can be used to help line up the robot with an object in the room while walking or crawling.
The distance sensor measures distance from the robot (typically the pelvis) to some target object. These sensors in Xemo will only respond to a particular type of object, so you may need multiple sensors to locate multiple objects in the lab or on the challenge floor. The sensor calculates distance to the target in meters.