Humans have liquid in their inner ears which allow them to balance. Many other animals have identical or similar systems that allow them to stabilize themselves. This robot must have the ability to sense its own orientation if it is to be able to walk or scan properly.

The reason why the robot requires orientation data to be able to scan properly requires some explanation:

The only difference between the two images to the right is that the upper one is rotated 20° clockwise. Through the robot's eyes the two situations look exactly the same: The ground in front slopes downward relative to the ground that the robot is presently standing on.

If the robot had no sensor resembling an inner ear it would be unable to differentiate between the two situations. If the robot simply assumes that it is always standing on level ground, the second situation would always appear to be the first, and the robot would be under the misimpression that there was a large slope infront of it.

The Nintendo64 is an obsolete (but still very fun) video game system. To the right you see a picture of the system's input device. There is a miniature joystick in the center. At one point in time the joystick's design was revolutionary.

The joystick contains two potentiometers, one turned by the sticks yaw, and one turned by the sticks pitch. The joystick is turned upside down, and a weight is attached to the stick. Gravity always pulls the joystick strait down. By monitoring the amount of electricity passing through the potentiometers the robot can determine which way is down.

There is a problem facing the orientation sensor. Inertia as well as the force of gravity effects its movements. When the robot accelerates the inertia of the weight resists the change in momentum and causes the stick to swing back and forth like a pendulum. The robot's body rocks slightly as it walks. As a result accurate information can only be gathered from the orientation sensor after the robot has stopped moving and waited long enough for the weight to be at rest (about 0.7 seconds). The computer program tells if the weight has stopped moving by taking two readings one tenth of a second apart. If the two readings are equal the sensor has not moved during the interval between readings, so it must be at rest.