Using a Servo Motor with Raspberry Pi

Introduction

A servo motor is a rotary actuator that provides precise control over angular position, speed, and acceleration. It consists of a small DC motor, a gear mechanism, and a control circuit. Servo motors are commonly used in robotics, automation systems, and remote-controlled vehicles. They can rotate to a specific angle within a range of 0 to 180 degrees and maintain their position based on input signals they receive. Servo motors use closed-loop control and feedback mechanisms to ensure accurate positioning. They maintain their position by using feedback from a built-in potentiometer or an encoder. They are controlled using pulse width modulation (PWM) signals, where the duration of the pulses determines the desired position. Servo motors offer reliable and efficient control over rotational movements, making them widely used in various applications.

Problem Statement

Controlling servo motor using a Raspberry Pi.

Requirements

To complete this project, you will need the following components:

1. Raspberry Pi
2. Servo motor
3. Jumper wires
4. Breadboard (optional)

Working

The control circuit interprets input signals, usually in the form of pulse width modulation (PWM), which specify the desired position or angle for the motor shaft. The position feedback mechanism, such as a potentiometer or an encoder, provides information about the motor's current position.

The control circuit compares the desired position with the actual position indicated by the feedback mechanism. If there is a deviation, the control circuit adjusts the motor's output to correct the difference and bring the motor to the desired position. This closed-loop control system ensures accurate and consistent positioning.

The DC motor, coupled with a gear mechanism, converts the electrical signals into rotational motion. The gear mechanism reduces speed and increases torque output, allowing for precise and controlled movement of the motor shaft.

PWM frequency is set to 50Hz, which is a common frequency used for servo motors. However, different servo motors may have different frequency requirements.

Circuit Diagram

Follow the circuit diagram below to connect the servo and Raspberry Pi:

• Connect the red wire from servo motor to the PIN2 for 5V.
• Connect the black wire to PIN6 for grounding.
• Connect the yellow wire to GPIO18 (PIN12) for control.
  

Code

Now let's write the Python code for obtaining ECG values. Follow the steps below:

1. Connect to your Raspberry Pi using VNC or Desktop environment.
2. Launch the Geany Python IDE or open a text editor to write the code.
3. Create a new file named servo.py and save the following code into it
4. You can copy and paste the following code from here into the file.

import RPi.GPIO as GPIO
import time

GPIO.setmode(GPIO.BCM)                    # Set up BCM GPIO numbering
GPIO.setwarnings(False)                   # disable warnings

SERVO_PIN = 18                            # GPIO18 as Servo pin
GPIO.setup(SERVO_PIN,GPIO.OUT)            # Set GPIO18 as an output
servo = GPIO.PWM(SERVO_PIN,50)            # Set PWM to 50Hz
servo.start(0)                            # Start PWM at 0% duty cycle

try:
    while(1):
        # Rotate Servo 0 to 180 degrees by changing duty cycle
        for i in range(0,180,1):
            servo.ChangeDutyCycle(2+(i/18))
            time.sleep(0.1)
            servo.ChangeDutyCycle(0)
            time.sleep(0.1)
        # Rotate Servo 180 to 0 degrees by changing duty cycle
        for i in range(180,0,-1):
            servo.ChangeDutyCycle(2+(i/18))
            time.sleep(0.1)
            servo.ChangeDutyCycle(0)
            time.sleep(0.1)

except KeyboardInterrupt:                  # If CTRL+C is pressed, exit cleanly:
    pass

servo.stop()  # Stop the PWM output
GPIO.cleanup()

5. After saving the file execute it by clicking on messenger like icon on geany editor or open terminal and navigate tothe folder you saved the file, execute it by typing python servo.py

Output

The servo motor performs a continuous rotation from 0 to 180 degrees and back to 0 degrees in small increments. The servo motor moves gradually, changing its position in steps of (i/18) where 'i' represents the angle. It holds each position briefly before transitioning to the next one. This action results in a smooth back-and-forth motion of the servo motor, allowing for controlled and precise angular positioning.

Conclusion

By following this guide and utilizing the provided code, you have acquired the knowledge to control a servo motor using a Raspberry Pi 3B+. The Raspberry Pi generates pulse width modulation (PWM) signals, enabling you to exert precise control over the servo motor's position by adjusting the pulse duration. By experimenting with various pulse durations and time intervals, you can achieve the desired angular position for your specific application requirements. Whether it's controlling robotic limbs, adjusting camera angles, or automating precise movements, the Raspberry Pi 3B+ and servo motor combination offers a versatile platform for achieving accurate and controlled motion. With the ability to fine-tune the pulse width, you can customize the servo motor's behavior to suit your project's needs.