Build a Line Follower Robot for Easy Indoor AGV and Package Transporting

In the era of smart automation, Automated Guided Vehicles (AGVs) have become the backbone of modern warehousing and internal logistics. While industrial-grade AGVs can cost thousands of dollars, the core technology—line following—is surprisingly accessible. By building a line follower robot designed for package transport, you can create a functional prototype for moving small items across a home, office, or workshop floor automatically.

This guide will walk you through the process of building a heavy-duty line follower robot capable of acting as a DIY AGV. We will focus on stability, load-bearing capacity, and precise navigation.

Why Use Line Following for Indoor Transport?

Line following is one of the most reliable and cost-effective ways to automate indoor movement. Unlike GPS, which doesn't work well indoors, or LiDAR, which requires complex processing power, line following relies on a simple visual track. This offers several advantages:

• Predictability: The robot always follows a fixed path, reducing the risk of collisions.
• Low Cost: High-quality IR sensors are inexpensive compared to cameras or laser scanners.
• Ease of Setup: Changing the robot’s route is as simple as moving the tape on the floor.

Hardware Components Needed

To build an AGV capable of carrying packages, you need slightly more robust components than a standard toy robot kit.

• Microcontroller: Arduino Uno or Mega (Mega is preferred if you plan to add weight sensors or LCDs later).
• Motor Driver: L298N or BTS7960 (The BTS7960 is better for high-torque motors used in package transport).
• Motors: 2x 12V High Torque DC Gear Motors.
• Sensors: 5-Channel IR Sensor Array (More sensors provide smoother movement).
• Chassis: A sturdy wood, acrylic, or aluminum plate large enough to hold a package.
• Power Supply: 11.1V or 14.8V Li-Po battery for long-lasting operation.
• Wheels: High-traction rubber wheels.

The Working Principle

The robot operates on the principle of infrared (IR) light reflection. IR sensors consist of an emitter and a receiver. When the sensor is over a light-colored surface (the floor), the IR light reflects back. When it is over a dark-colored surface (the black line), the light is absorbed. By interpreting these signals, the Arduino can determine if the robot is centered, drifting left, or drifting right, and adjust the motor speeds accordingly.

Wiring the AGV

Proper wiring is crucial for a robot that will carry weight. Ensure your motor driver shares a common ground with the Arduino.

• Connect the IR Sensor outputs to Digital Pins 2, 3, 4, 5, and 6 on the Arduino.
• Connect the Motor Driver (L298N) Input pins to Digital Pins 7, 8, 9, and 10.
• Connect the Enable pins (PWM) to pins 11 and 12 to control the speed.
• Wire the motors to the output terminals of the driver.

The Programming Logic

Below is a clean, optimized Arduino script for a 5-sensor line follower. This code uses basic proportional logic to ensure the robot doesn't "jitter" while transporting a package.

// Motor Pins
const int IN1 = 7;
const int IN2 = 8;
const int IN3 = 9;
const int IN4 = 10;
const int ENA = 5;
const int ENB = 6;

// Sensor Pins
int sensor[5];

// Speed Settings
int baseSpeed = 150; 

void setup() {
  pinMode(IN1, OUTPUT);
  pinMode(IN2, OUTPUT);
  pinMode(IN3, OUTPUT);
  pinMode(IN4, OUTPUT);
  pinMode(ENA, OUTPUT);
  pinMode(ENB, OUTPUT);
  
  for (int i = 0; i < 5; i++) {
    pinMode(2 + i, INPUT);
  }
}

void loop() {
  // Reading sensor values (1 = Line detected, 0 = Floor)
  for (int i = 0; i < 5; i++) {
    sensor[i] = digitalRead(2 + i);
  }

  // Logic for movement
  if (sensor[2] == 1) { // Center sensor on line
    moveForward();
  } else if (sensor[1] == 1) { // Slight left
    turnLeft(100);
  } else if (sensor[3] == 1) { // Slight right
    turnRight(100);
  } else if (sensor[0] == 1) { // Hard left
    turnLeft(150);
  } else if (sensor[4] == 1) { // Hard right
    turnRight(150);
  } else { // No line detected (Stop for safety)
    stopMotors();
  }
}

void moveForward() {
  analogWrite(ENA, baseSpeed);
  analogWrite(ENB, baseSpeed);
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, HIGH);
  digitalWrite(IN4, LOW);
}

void turnLeft(int speed) {
  analogWrite(ENA, speed);
  analogWrite(ENB, baseSpeed);
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, HIGH);
  digitalWrite(IN3, HIGH);
  digitalWrite(IN4, LOW);
}

void turnRight(int speed) {
  analogWrite(ENA, baseSpeed);
  analogWrite(ENB, speed);
  digitalWrite(IN1, HIGH);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW);
  digitalWrite(IN4, HIGH);
}

void stopMotors() {
  digitalWrite(IN1, LOW);
  digitalWrite(IN2, LOW);
  digitalWrite(IN3, LOW);
  digitalWrite(IN4, LOW);
}

Optimizing for Package Transport

Building a robot that moves is easy, but building one that transports cargo requires attention to detail. Here are three tips to optimize your AGV:

1. Center of Gravity

When carrying a package, the center of gravity shifts upward. To prevent the robot from tipping during turns, place the heaviest components (the battery and motors) as low as possible on the chassis. Ensure the cargo platform is centered over the drive wheels.

2. Slow Acceleration

Sudden starts and stops can cause cargo to slide off. Instead of jumping straight to baseSpeed, you can modify the code to gradually increase the PWM signal to the motors.

3. Use Traction Tape

Standard plastic wheels often slip on tiled or wooden floors, especially under load. Use rubber-treaded wheels or wrap your wheels in silicone tape to ensure the robot can move the added weight without spinning its wheels in place.

Conclusion

Creating a line follower AGV is a rewarding project that bridges the gap between hobbyist electronics and practical industrial applications. With a sturdy chassis and a well-tuned sensor array, you can automate the movement of tools in a workshop or mail in an office. As a next step, consider adding an Ultrasonic Sensor (HC-SR04) to provide obstacle detection, ensuring your transport robot stops automatically if someone walks in its path.