A line-following robot is a small mobile robot that uses sensors to detect a dark line and adjust its motors to stay on track. This project connects physics, electronics, coding, and engineering design in one hands-on build. It is useful because the same ideas appear in factory robots, delivery vehicles, and automated machines that follow paths or detect edges.
For grades 7 to 12, it is a manageable project that still shows real feedback control.
Key Facts
- Two IR sensors can detect line position by comparing left and right reflected light values.
- If left sensor sees black and right sensor sees white, turn left by slowing or reversing the left motor.
- If right sensor sees black and left sensor sees white, turn right by slowing or reversing the right motor.
- Bang-bang control uses simple on or off decisions, such as error < 0 turn left and error > 0 turn right.
- PID control can be written as correction = Kp e + Ki ∫e dt + Kd de/dt.
- Motor speed depends on PWM duty cycle, with duty cycle = on time / total period.
Vocabulary
- IR sensor
- An infrared sensor shines infrared light and measures how much light reflects back from a surface.
- Motor driver
- A motor driver is a circuit that lets a low-power controller safely control higher-current motors.
- Calibration
- Calibration is the process of measuring sensor readings on known surfaces so the robot can make accurate decisions.
- Control loop
- A control loop repeatedly senses, decides, acts, and checks again to reduce an error.
- PWM
- Pulse width modulation controls average motor power by rapidly switching voltage on and off.
Common Mistakes to Avoid
- Placing the sensors too far apart makes the robot lose the line because neither sensor may detect the edge during a turn.
- Skipping calibration is wrong because black tape, white paper, room lighting, and sensor height can all change the readings.
- Connecting motors directly to a microcontroller pin is unsafe because motors need more current than most controller pins can supply.
- Using full speed before testing control logic causes overshooting because the robot moves farther before each sensor update can correct it.
Practice Questions
- 1 A robot reads 820 on white paper and 230 on black tape from one IR sensor. Choose a threshold halfway between them and state whether a reading of 500 should be treated as black or white.
- 2 A PWM signal has a period of 20 ms and is on for 6 ms. Calculate the duty cycle as a percentage and explain whether this is closer to low, medium, or high motor power.
- 3 A robot wiggles rapidly left and right while following the line. Explain how changing sensor spacing, speed, or control logic could reduce this motion.