BabyROS Publisher/Subscriber Tutorial

Goal: Create and run a Publisher and Subscriber node using Python.

Level: Beginner

Time: ~2 minutes

Contents

1. Background
2. Prerequisites
3. Tasks
   1. Create a Publisher Node
   2. Create a Subscriber Node
   3. Run the Nodes
4. Summary
5. Next Steps

Background

In this tutorial, you will create two nodes that exchange information over a topic. One node publishes data (called a Publisher), and the other subscribes to that topic to receive messages (called a Subscriber).

We will use BabyROS to send simple dictionary messages representing sensor data, such as IMU readings.

1. Create a Python Script for the Publisher

Create a file name publisher_example.py:

import time
import babyros

if __name__ == "__main__":
    # Create a publisher node for the "imu" topic
    imu_pub = babyros.node.Publisher(topic="imu")

    print("Starting IMU data stream... (Press Ctrl+C to stop)")
    count = 0
    try:
        while True:
            data = {
                "acceleration": [0.1, 0.0, 9.8],
                "gyro": [0.0, 0.01, 0.0],
                "seq": count
            }
            imu_pub.publish(data=data)
            print(f"Sent seq: {count}")
            count += 1
            time.sleep(0.1)  # 10 Hz
    except KeyboardInterrupt:
        print("\n[Publisher] Interrupted by user.")
    finally:
        imu_pub.delete()
        print("[Publisher] Cleanup complete.")

2. Create a Python Script for the Subscriber

Create a file named subscriber_example.py:

import time
import babyros

def log_imu(msg: dict):
    """
    Callback to print received IMU messages.
    """
    print(f"Received IMU data: Seq {msg['seq']} | Accel: {msg['acceleration']}")

if __name__ == "__main__":
    # Create a subscriber node for the "imu" topic
    sub = babyros.node.Subscriber(topic="imu", callback=log_imu)
    print("Subscriber created successfully!")

    try:
        while True:
            time.sleep(1)  # Keep script alive
    except KeyboardInterrupt:
        print("\n[Subscriber] Interrupted by user.")
    finally:
        sub.delete()  # Clean up resources
        print("Subscriber cleanup complete.")

3. Run the Nodes

1. Open one terminal and run the publisher:

python publisher_example.py

You should see messages being published every 0.1 seconds.

2. Open a second terminal and run the subscriber:

python subscriber_example.py

The subscriber will print each IMU message as it receives it.

INFO

Press Ctrl+C in both terminals to stop the nodes.

Summary

You have:

• Created a publisher node that sends dictionary messages over a topic.
• Created a subscriber node that receives and processes those messages.
• Observed real-time messaging using BabyROS with minimal setup.

Next Steps

• Experiment with different data types in your messages.
• Add multiple subscribers to the same topic.
• Integrate with real sensors or simulation data for robotics applications.