Raspberry Pi Servo

README.md

Raspberry Pi Servo

How to control a 9G servo motor with a Rasp Pi and a simple Python script

Resources

The use of the servo including the wiring and script is based on this YouTube tutorial - Raspberry Pi Servo Motor Control. There are also plenty of similar videos out there.

For Arduino, see Using Servo Motors with Arduino

Learn more about Rasp Pi under my Dev Resources.

Steps

1. Set up the Wiring as below.
2. Copy the demo script or this gist to your Pi.
3. Run the script.

   $ python3 pi_servo.py

Wiring

See GPIO set up at 5:25.

Servo wire	GPIO number	Purpose
yellow	11	IO
red	4	Power (5V)
brown	GND	Ground

Specifically for IO, we use PWD (pulse-width modulation) here.

Using the GPIO Python module

Start PWM running, but with value of 0 (pulse off). This seems to be needed to allow the rest to work but the initial value does not seem to matter.

servo1.start(0)

Positions

• 0 degrees (min)

  servo1.ChangeDutyCycle(2)

• 180 degrees (max)

  servo1.ChangeDutyCycle(12)

Even though the method generates help that allows 0.0 to 100.0, in practice the cycle must be a positive integer and any value below 2 or above 12 does nothing. You may get jittering at a certain position - choosing a value outside of the bounds seems to stops this.

Degrees	Cycle
0	2
?	3
?	4
?	5
?	6
?	7
?	9
?	10
?	11
180	12

pi_servo.py

"""
Pi Servo module.
"""
import time 

import RPi.GPIO as GPIO 

 
OUT_PIN = 11
PULSE_FREQ = 50

GPIO.setmode(GPIO.BOARD)
GPIO.setup(OUT_PIN, GPIO.OUT) 


def main():
    print("Starting")
    servo1 = GPIO.PWM(OUT_PIN, PULSE_FREQ) 

    servo1.start(0) 

    print("Spinning")
    
    # Test the full range of movement. Note only integers are allowed.
    for x in range(2, 12):
        servo1.ChangeDutyCycle(x)
        time.sleep(0.5)
    
    # Start over and move in bigger, slower movements.
    servo1.ChangeDutyCycle(2)
    time.sleep(1)
    servo1.ChangeDutyCycle(7)
    time.sleep(1)
    servo1.ChangeDutyCycle(12)
    time.sleep(4)
    
    # Jump between the opposite positions.
    servo1.ChangeDutyCycle(2)
    time.sleep(1)
    servo1.ChangeDutyCycle(12)
    time.sleep(1)
    servo1.ChangeDutyCycle(2)
    time.sleep(1)
    servo1.ChangeDutyCycle(12)
    time.sleep(4)
    
    # Test the fastest movement possible - no sleeping.
    servo1.ChangeDutyCycle(2)
    servo1.ChangeDutyCycle(12)
    servo1.ChangeDutyCycle(2)
    servo1.ChangeDutyCycle(12)
    servo1.ChangeDutyCycle(2)
    servo1.ChangeDutyCycle(12)
    servo1.ChangeDutyCycle(2)
    servo1.ChangeDutyCycle(12)
    
    servo1.stop() 
    GPIO.cleanup()


if __name__ == "__main__":
    main()