Wi-Fi Controlled 6DOF Robotic Arm using PCA9685 and Arduino ESP Series

📌 Project Overview

This project demonstrates how to build and control a 6 Degree of Freedom (6DOF) robotic arm using:

ESP8266/ESP32 microcontroller (for Wi-Fi connectivity).
PCA9685 16-channel PWM driver (to control multiple servo motors).
Servo motors (6 total) to provide motion for the robotic arm.

The robotic arm is controlled wirelessly using a web interface, which allows the user to change servo angles from any device connected to the same Wi-Fi network.

🎯 Learning Objectives

Understand how to control multiple servo motors with PCA9685.
Learn how to create a web server using ESP8266/ESP32.
Explore Wi-Fi based control of robotic systems.
Implement basic Human-Machine Interaction (HMI) using a browser.

🔧 Hardware Requirements

ESP8266 (NodeMCU / Wemos D1 Mini) or ESP32 board
PCA9685 16-channel Servo Driver Module
6 × Servo Motors (SG90/MG996R or similar)
5V External Power Supply for servos (⚠️ Do NOT power servos directly from ESP8266/ESP32 5V pin)
Breadboard, jumper wires, and robotic arm frame

Degrees of Freedom (DOF)

A robotic arm with 6DOF can perform movements similar to a human arm:
1. Base rotation
2. Shoulder movement
3. Elbow movement
4. Wrist pitch
5. Wrist roll
6. Gripper control

🔌 Circuit Connections

ESP8266/ESP32 to PCA9685
- SDA → D2 (GPIO4 on ESP8266, or GPIO21 on ESP32)
- SCL → D1 (GPIO5 on ESP8266, or GPIO22 on ESP32)
- VCC → 3.3V / 5V (depending on board)
- GND → GND
PCA9685 to Servo Motors
- Connect each servo motor’s signal pin to PCA9685 channels 0–5.
- Provide external 5V and GND to servo power pins.

📜 Arduino Code

#include <Wire.h>
#include <Adafruit_PWMServoDriver.h>
#include <ESP8266WiFi.h>

// ====== Wi-Fi Credentials ======
const char* ssid = "YOUR_WIFI_SSID";
const char* password = "YOUR_WIFI_PASSWORD";

// ====== Web Server ======
WiFiServer server(80);

// ====== PCA9685 Setup ======
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver(0x40);

#define SERVOMIN  150
#define SERVOMAX  600

int servoAngles[6] = {90, 90, 90, 90, 90, 90};

int angleToPulse(int ang) {
  return map(ang, 0, 180, SERVOMIN, SERVOMAX);
}

void setup() {
  Serial.begin(115200);

  WiFi.begin(ssid, password);
  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("\nConnected! IP: " + WiFi.localIP().toString());
  server.begin();

  pwm.begin();
  pwm.setPWMFreq(60);

  for (int i = 0; i < 6; i++) {
    pwm.setPWM(i, 0, angleToPulse(servoAngles[i]));
  }
}

void loop() {
  WiFiClient client = server.available();
  if (!client) return;

  String request = client.readStringUntil('\r');
  client.flush();

  if (request.indexOf("/servo") != -1) {
    int chIndex = request.indexOf("ch=");
    int angIndex = request.indexOf("ang=");
    if (chIndex != -1 && angIndex != -1) {
      int ch = request.substring(chIndex + 3, request.indexOf("&", chIndex)).toInt();
      int ang = request.substring(angIndex + 4).toInt();
      if (ch >= 0 && ch < 6 && ang >= 0 && ang <= 180) {
        servoAngles[ch] = ang;
        pwm.setPWM(ch, 0, angleToPulse(ang));
      }
    }
  }

  String html = "<!DOCTYPE html><html><head><title>6DOF Arm</title></head><body>";
  html += "<h2>WiFi Controlled 6DOF Robotic Arm</h2>";
  for (int i = 0; i < 6; i++) {
    html += "Servo " + String(i) + ": ";
    html += "<a href='/servo?ch=" + String(i) + "&ang=" + String(servoAngles[i] - 10) + "'>-</a> ";
    html += String(servoAngles[i]);
    html += " <a href='/servo?ch=" + String(i) + "&ang=" + String(servoAngles[i] + 10) + "'>+</a><br>";
  }
  html += "</body></html>";

  client.print("HTTP/1.1 200 OK\r\nContent-Type: text/html\r\n\r\n");
  client.print(html);
}

🌐 Working Principle

Power Supply and Initialization
- When the system is powered ON, the ESP8266/ESP32 initializes and establishes a connection to the configured Wi-Fi network.
- The PCA9685 module is initialized via the I²C protocol, and all servos are moved to their neutral position (90°).
Web Server Operation
- The ESP8266/ESP32 runs a lightweight web server on port 80.
- The assigned IP address (shown in the Serial Monitor) acts as the access point for the robotic arm’s control page.
- Any device (laptop, smartphone, or tablet) connected to the same Wi-Fi can access the interface using a browser.
User Interaction
- The web page provides + / – buttons for each of the six servo motors.
- When a button is pressed, the browser sends an HTTP request (e.g., /servo?ch=2&ang=120) to the ESP8266/ESP32.
Command Processing
- The ESP8266/ESP32 extracts the channel number (ch) and target angle (ang) from the HTTP request.
- The angle is converted into a corresponding PWM pulse width using the function angleToPulse().
- The PCA9685 generates precise PWM signals, and the specified servo motor rotates to the commanded position.
Robotic Arm Movement
- Each servo corresponds to one joint of the robotic arm (base, shoulder, elbow, wrist, and gripper).
- Coordinated control of all six servos allows the arm to perform complex movements such as lifting, rotating, and gripping objects.

🏁 Conclusion

This project demonstrates a practical integration of IoT and robotics by using an ESP8266/ESP32 microcontroller with a PCA9685 servo driver to control a 6DOF robotic arm wirelessly.

The working principle shows how user commands given through a web browser interface are translated into servo motor movements via PWM signals. This enables real-time control of the robotic arm without the need for wired connections.

The project highlights key engineering concepts:

Embedded system programming
Wi-Fi based IoT communication
PWM signal generation and servo control
Human-Machine Interaction through a browser

Overall, the system provides a cost-effective and flexible platform for robotics education and experimentation. With further improvements such as sliders, inverse kinematics, or AI-based automation, this design can evolve into a powerful tool for research and industrial applications.