Line follower is an autonomous robot which follows black line in white area as fast as possible. Robot must be able to detect particular line and keep following it, no matter what form this line is. Robot should sense the line with its sensors that installed under the robot. Sensors give the robot a signal where the line is located.
 
For robot sensors typically use phototransistors and infrared diodes or infrared sensors and infrared diodes. First variant are the simplest and cheapest. However, this sensor signal can be affected by ambient light. The version with an infrared sensor and an infrared diod is a little bit more expensive, but it's completely unaffected by the ambient light. This robot can move well along the line in complete darkness.
 
The engine provides a robot motion. It is important that the engines are strong, but they must be compact and lightweight. The robots speed and movement smoothness depends on the type of control regulator which use in a program algorithm. The most commonly used P, PI or PID controller, or combinations of them.