Build a Line-Following Robot from Scratch

A line-following robot is the classic "Hello World" of autonomous robotics. While simple to build, making one run quickly and smoothly requires understanding control theory.

The Hardware

You will need a chassis, two DC gear motors, an L298N or TB6612FNG motor driver, a microcontroller (see our recommendations), and an IR sensor array (e.g., QTR-8RC). The sensor array is critical; using 8 sensors provides much better resolution than a basic 2-sensor setup.

The Problem with Bang-Bang Control

The simplest code logic is: "If the left sensor sees the line, turn left. If the right sensor sees the line, turn right." This is called bang-bang control, and it results in a robot that violently zig-zags down the line.

Implementing PID Control

To achieve smooth, high-speed tracking, we use a Proportional-Integral-Derivative (PID) controller. The PID algorithm calculates an error value (how far off the center of the line we are) and adjusts the motor speeds proportionally.

• Proportional (P): Steers harder the further away from the center you are.
• Derivative (D): Looks at how fast the error is changing, applying a dampening effect to prevent overshoot and oscillation.
• Integral (I): Corrects for small, persistent errors over time (rarely needed for line followers).

Start tuning by setting I and D to zero. Increase P until the robot tracks the line but oscillates. Then, slowly increase D until the oscillation stops.