When line following, the robot will try to align itself centered over the boundary between white and black (not centered over the black line), with black to the robot's left.  Here the brightness seen by the sensor is halfway between the black/min and white/max readings

When prompted to sample the "Min" or "Black" reading, position the sensor so that the red spot is centered over the line and then press the Enter button on the NXT. When prompted to sample the "Max" or "White" reading, position the sensor so that the red spot is completely over the surface away from the line and press the Enter button on the NXT.

This motor shaft will make 3 rotations, in the same time the output shaft makes 5 Gears used: 20 tooth on motor, 12 tooth on output Gear Ratio: 3:5 Power: 3/5x motor Speed: 5/3x motor (faster)

This motor shaft will make 1 rotations, in the same time the output shaft makes 3 Gears used: 24 tooth on motor, 8 tooth on output Gear Ratio: 1:3 Power: 1/3x motor Speed: 3x motor (faster)

10:30:40 = 1:4 9:27 = 1:3 10:20 = 1:2 10:13:20 = 1:2 Overall 1:48  

The Roomba Remote, Virtual Wall, and Home Base operate using an invisible infrared technology.

equipped with four infrared Cliff Sensors that prevent robots from falling off stairs or ledges. The Cliff Sensors are located along the inside of the bumper

. If the Sensors become obstructed by dust or debris, the infrared signal is weakened