Line-Following Robot

A line-following robot built as the second project for the school showcase. Adapted from a coursework project I had built for my own Robotics class — scaled down in scope and complexity to work with the LEGO SPIKE Prime kit and sensors available.

Programs

Line_Following.llsp3 — “Benito” (84 blocks)

Original version built with flippermotor blocks (speed-based motor control). Movement on ports EF, color sensor on port B, distance sensor on port D.

Line_Following_mid1.llsp3 — “DD” (95 blocks)

Tuned version with flippermoremotor (power-based individual motor control). Movement on ports CD, color sensor on port A, distance sensor on port F. Non-zero PID variables (Error=-22.5, Correction=-13.5) confirm it was field-tested and tuned.

Program Flow

Both versions follow the same structure:

flowchart TD
    Start["🏁 Program Starts"] --> Init["▶ Variables & Constants<br/>Set color_midpoint, clear variables"]
    Init --> Find["▶ Find Line<br/>Drive forward until line detected"]
    Find --> Acquire["▶ Acquire the Line<br/>Position robot on the line"]
    Acquire --> Follow["▶ Follow the Line<br/>PID tracking loop"]
    Follow --> Follow

PID Loop Detail

flowchart LR
    Sense["Read reflectivity<br/>from color sensor"] --> Compare{"Error = midpoint - value"}
    Compare --> Compute["Correction = Error × Kp"]
    Compute --> Adjust["Adjust motor powers<br/>Left = base + Correction<br/>Right = base - Correction"]
    Adjust --> Sense

Procedure Breakdown

Variables and Constants — Sets color_midpoint=58.5, initializes motor_left, motor_right, Error, Correction, sensor_color, sensor_distance

Find Line — Sets movement ports, starts moving forward, waits until line is detected under the sensor, then stops

Acquire the Line — Resets timer, repeats until the robot is properly positioned on the line, then stops

Follow the Line / Follow the Line 1 — Forever loop containing the PID control logic:

• Reads reflectivity from the color sensor
• Compares against the midpoint to calculate Error
• Computes Correction using PID math (proportional term)
• Adjusts left and right motor power independently to steer back to the line

PID Control

I used this project to introduce the scholars to PID controllers — a fundamental engineering concept. Rather than a bang-bang approach (hard left/hard right), the robot uses proportional correction to follow the line smoothly. The scholars didn’t need to master the math, but they learned that there’s a difference between something that works and something that’s tuned.

Track

We built the track ourselves — black tape on white paper with red markers at the start and end. The scholars laid out the course and tested the robot under real showcase conditions.

Video

Line-following robot demo — tracking black line, red markers signal start/end.

Line-following robot tracking the course