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ROS2 Publisher/Subscriber Assignment

Overview

In this assignment, you will create a ROS2 package with a publisher node that publishes your student ID and a random number. Then you'll verify it works by subscribing to the topic.

Your Unique Student ID: STUD_[last 4 digits of your student number] Example: If your student number is 12345678, use STUD_5678

Part 1: Create Your ROS2 Package

1.1 Navigate to your workspace and create a package

TODO - create workspace

cd ~/ros2_ws/src
ros2 pkg create --build-type ament_python student_publisher --dependencies rclpy std_msgs

1.2 Navigate to your package directory

cd student_publisher/student_publisher

Part 2: Create the Publisher Node

2.1 Create a new Python file

nano student_id_publisher.py

2.2 Write your publisher code

Create a publisher that: - Publishes to a topic called /student_data - Uses std_msgs/String message type - Publishes a message containing your student ID and a random integer (1-1000) - Message format: "STUD_XXXX:random_number" (e.g., "STUD_5678:742") - Publishes every 1 second - Generates a NEW random number each time it publishes

Hints: - Use import random for random numbers - Use random.randint(1, 1000) to generate random integers - Follow the structure from the ROS2 Foxy tutorials on creating publishers - Remember to import: rclpy, Node from rclpy.node, and String from std_msgs.msg

Submission Item 1: Your complete student_id_publisher.py code file

Part 3: Configure the Package

3.1 Edit setup.py

Add your node to the entry_points so ROS2 can run it:

cd ~/ros2_ws/src/student_publisher
nano setup.py

In the entry_points section, add: 

entry_points={
    'console_scripts': [
        'student_publisher = student_publisher.student_id_publisher:main',
    ],
},

3.2 Make your script executable

chmod +x ~/ros2_ws/src/student_publisher/student_publisher/student_id_publisher.py

Part 4: Build and Source

4.1 Build your package

cd ~/ros2_ws
colcon build --packages-select student_publisher

**Submission Item 2:** Screenshot of successful build output (showing "Finished <<< student_publisher")

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## Part 5: Run and Test Your Publisher

### 5.1 Run your publisher node
```bash
ros2 run student_publisher student_publisher

You should see log messages showing your node is running.

Submission Item 3: Screenshot showing your publisher running with any logger messages

5.2 In a NEW terminal, list the active topics

source ~/ros2_ws/install/setup.bash
ros2 topic list

You should see /student_data in the list.

Submission Item 4: Screenshot of ros2 topic list output showing /student_data

5.3 Echo your topic to see the published messages

ros2 topic echo /student_data

Let it display at least 5 messages to show the random numbers are changing.

Submission Item 5: Screenshot of ros2 topic echo showing at least 5 messages with your student ID and DIFFERENT random numbers

5.4 Check the publishing rate

ros2 topic hz /student_data

Submission Item 6: Screenshot showing the average publishing rate (should be approximately 1 Hz)

Part 6: Create a Subscriber

Create a subscriber node called student_id_subscriber.py in the same package that: - Subscribes to /student_data - Prints out each message it receives - Keeps a count of total messages received - Calculates and prints the average of all random numbers received

Submission Item 7: - Your student_id_subscriber.py code - Updated setup.py with the subscriber entry point - Screenshot showing both publisher and subscriber running in separate terminals - Screenshot showing the subscriber's message count and average calculation

Submission Checklist

Submit a single PDF containing:

  1. Your student_id_publisher.py code (formatted and readable)
  2. Screenshot of successful colcon build
  3. Screenshot of publisher running
  4. Screenshot of ros2 topic list
  5. Screenshot of ros2 topic echo with 5+ messages showing different random numbers
  6. Screenshot of ros2 topic hz output
  7. Subscriber code, setup.py, and screenshots

Important: Your student ID must be visible in ALL screenshots showing message data. Each student will have different random numbers, ensuring unique submissions.

Troubleshooting Tips

  • Build errors? Check your setup.py entry_points syntax
  • Can't find node? Make sure you sourced: source ~/ros2_ws/install/setup.bash
  • No messages appearing? Check if your publisher is actually running
  • Topic not listed? Verify your publisher created the topic with the exact name /student_data

Resources