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1.7 Servo

Introduction

In this project, we will learn how to control a servo motor using a Raspberry Pi. Servo motors are commonly used in robotics and automation for precise control of angular motion.

What You’ll Need

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

COMPONENT	PURCHASE LINK
Servo	BUY
Fusion HAT+	-
Raspberry Pi	-

Circuit Diagram

The circuit diagram below shows the connections required for controlling the servo motor.

Wiring Diagram

Running the Example

All example code used in this tutorial is available in the ai-lab-kit directory. Follow these steps to run the example:

cd ~/ai-lab-kit/python/
sudo python3 1.7_Servo.py

After running the script, the servo connected to PWM 0 smoothly sweeps from −90° to 90° in 10-degree steps, pausing briefly at each position. It then moves back from 90° to −90° in the same way. This back-and-forth motion repeats continuously.

Code

The following Python code demonstrates how to control the servo motor by moving it between various angles:

#!/usr/bin/env python3
from fusion_hat.servo import Servo   # Import Servo class
from time import sleep               # Import sleep for delays

# Initialize servo on channel 0
servo = Servo(0)

try:
   while True:
      # Sweep from -90° to +90° in steps of 10°
      for angle in range(-90, 91, 10):
            servo.angle(angle)
            sleep(0.1)   # Smooth movement delay

      # Sweep back from +90° to -90° in steps of 10°
      for angle in range(90, -91, -10):
            servo.angle(angle)
            sleep(0.1)

except KeyboardInterrupt:
   # Stop the program safely when Ctrl+C is pressed
   servo.angle(0)        # Return servo to center position
   sleep(0.1)

This Python script controls a servo motor connected to PWM 0. When executed:

The servo moves from -90 degrees to 90 degrees in 10-degree increments.
It pauses for 0.1 seconds between each movement.
It then reverses the direction and moves from 90 degrees to -90 degrees in 10-degree increments.
The process repeats indefinitely.

Understanding the Code

Library Import

The fusion_hat library simplifies GPIO interactions, while the time library provides delay functions.

from fusion_hat.servo import Servo   # Import the Servo class for controlling servos
from time import sleep               # Import sleep for timing delays

Servo Initialization

The Servo object is initialized with PWM 0.
```
servo = Servo(0)
```

Servo Movement

The servo is moved to different angles in a loop. The angle method sets the servo’s position, and sleep pauses the loop for a specified duration.

while True:
   # Sweep from -90° to +90° in steps of 10°
   for angle in range(-90, 91, 10):
         servo.angle(angle)
         sleep(0.1)   # Smooth movement delay

   # Sweep back from +90° to -90° in steps of 10°
   for angle in range(90, -91, -10):
         servo.angle(angle)
         sleep(0.1)

Troubleshooting

Servo Does Not Move
- Cause: Incorrect GPIO pin connection or power supply issues.
- Solution: Ensure the servo is connected to PWM 0 and verify the power supply.
Servo Movement is Erratic or Unresponsive
- Cause: Insufficient power supply to the servo.
- Solution: Use an external power source for the servo if the Fusion HAT+ does not provide enough power.

Extendable Ideas

User-Controlled Servo

Allow users to control the servo position interactively through keyboard input:

while True:
   position = float(input("Enter position (-90 to 90): "))
   servo.angle(position)

Servo Position Tracking

Record the servo position over time and plot the trajectory:

positions = []
for i in range(-90, 91, 10):
   servo.angle(i)
   sleep(0.1)
   positions.append(servo.angle())
plt.plot(positions)
plt.show()

Conclusion

This project demonstrates how to control a servo motor. Understanding servo control opens the door to building robots, mechanical arms, and other motion-based projects.