Dawson Virtual Lab

# DC Motor Robot Control

# Introduction to DC Motors

Meet our DC motor robot. This robot uses standard DC motors controlled by an H-bridge (L298N motor driver). DC motors are the most common type of motor used in robotics and provide continuous rotation with speed and direction control.

# Wiring Configuration

Our robot uses the following pin configuration (standard L298N setup):

# Left Motor

  • IN1 (Direction) → Pin 4
  • IN2 (Direction) → Pin 5
  • ENA (Enable/Speed) → Pin 6 (PWM)

# Right Motor

  • IN3 (Direction) → Pin 7
  • IN4 (Direction) → Pin 8
  • ENB (Enable/Speed) → Pin 9 (PWM)

# Ultrasonic Sensor (optional)

  • Trigger → Pin 2
  • Echo → Pin 3

# Basic Control

# Speed Control (PWM)

Speed is controlled using analogWrite() with values from 0 to 255:

  • 0 = stopped
  • 128 = half speed
  • 255 = full speed

# Direction Control

Direction is set using two pins (IN1/IN2 for left, IN3/IN4 for right):

  • IN1=HIGH, IN2=LOW → Forward
  • IN1=LOW, IN2=HIGH → Backward
  • Both LOW → Stop

# Forward Movement

Let's start with the simplest possible motor control - using digitalWrite() and analogWrite() directly.

Exercise

Can you get all the coins??

# Using Helper Functions

As you can see, controlling motors directly takes a lot of code. Let's use helper functions as methods to make our code cleaner, easier to understand and more versatile.

Exercise

Can you get all the coins in the environment?

# Movement Patterns

# Basic Movements

// Forward
drive(180, 180);

// Backward
drive(-180, -180);

// Turn left (spin in place - left backward, right forward)
drive(-180, 180);

// Turn right (spin in place - left forward, right backward)  
drive(180, -180);

// Curve left (slow down left wheel)
drive(90, 180);

// Curve right (slow down right wheel)
drive(180, 90);

// Stop
drive(0, 0);

# Key Concepts

# PWM (Pulse Width Modulation)

  • Controls motor speed by rapidly switching power on/off
  • Value 0-255 represents duty cycle (0% to 100%)
  • Arduino's analogWrite() generates PWM automatically

# H-Bridge

  • Electronic circuit that allows bidirectional motor control
  • The L298N chip contains two H-bridges (one per motor)
  • Handles high currents that Arduino pins cannot provide

# Differential Drive

  • Two independently controlled wheels
  • Turn by running wheels at different speeds
  • Most common configuration for small robots

# Tips

  1. Start with low speeds (~100-150) to test your code
  2. Motors may not be perfectly matched - you might need different speeds for straight movement
  3. Use delays carefully - timing is critical for distance traveled
  4. The drive() function makes code much more readable
  5. Negative speeds reverse direction - very intuitive! Make sure you wire up your physical robots correctly.

# Try these challenges

  • Make the robot drive in a square
  • Create a function to turn exactly 90 degrees
  • Make the robot drive in a figure-8 pattern

Next we will learn about the ultrasonic sensor for detecting obstacles and use the feedback we get as logic for navigation.

Ultrasonic Sensor →