Module 1 Assessment: ROS 2 Package Development Project

Overview

This project assesses your understanding of ROS 2 fundamentals by requiring you to build a complete ROS 2 package that demonstrates nodes, topics, services, actions, launch files, and URDF integration.

Duration: Weeks 3-5 Weight: 15% of final grade Submission: End of Week 5

Learning Objectives

By completing this project, you will demonstrate your ability to:

1. Create a properly structured ROS 2 package using colcon
2. Implement publisher and subscriber nodes
3. Design and implement custom service and action servers
4. Write launch files with parameters and node configuration
5. Create or modify a URDF model for a robot
6. Document your code and test functionality

Project Requirements

1. Package Structure (10 points)

Create a ROS 2 package named <yourname>_robot_controller with:

• Proper package.xml with all dependencies
• CMakeLists.txt or setup.py configured correctly
• Organized directory structure:

  <yourname>_robot_controller/
  ├── <yourname>_robot_controller/
  │   ├── __init__.py
  │   ├── sensor_publisher.py
  │   ├── control_node.py
  │   ├── emergency_stop_service.py
  │   └── navigation_action_server.py
  ├── launch/
  │   ├── robot_system.launch.py
  │   └── params.yaml
  ├── urdf/
  │   └── my_robot.urdf
  ├── config/
  │   └── controller_params.yaml
  ├── package.xml
  ├── setup.py
  └── README.md

2. Sensor Publisher Node (15 points)

File: sensor_publisher.py

Create a node that publishes simulated sensor data:

• Topic: /sensors/lidar (type: sensor_msgs/LaserScan)
• Topic: /sensors/camera (type: sensor_msgs/Image)
• Topic: /sensors/imu (type: sensor_msgs/Imu)
• Frequency: 10 Hz for all sensors
• Requirements:
  • Use a single node with multiple publishers
  • Simulate realistic sensor data (random noise, valid ranges)
  • Implement proper QoS settings for each sensor type

3. Control Subscriber Node (15 points)

File: control_node.py

Create a node that subscribes to sensor data and publishes control commands:

• Subscribes to: /sensors/lidar, /sensors/imu
• Publishes to: /cmd_vel (type: geometry_msgs/Twist)
• Logic:
  • If LIDAR detects obstacle < 1.0m ahead, stop (velocity = 0)
  • If obstacle is 1.0-2.0m ahead, slow down (velocity *= 0.5)
  • Otherwise, move forward at 0.5 m/s
  • Use IMU data to log orientation (roll, pitch, yaw)

4. Service Server (15 points)

File: emergency_stop_service.py

Create a service that provides emergency stop functionality:

• Service Name: /emergency_stop
• Service Type: std_srvs/SetBool
• Behavior:
  • When data=True, publish stop command to /cmd_vel and return success
  • When data=False, resume normal operation
  • Log all emergency stop requests with timestamps

Test Command:

ros2 service call /emergency_stop std_srvs/srv/SetBool "{data: true}"

5. Action Server (20 points)

File: navigation_action_server.py

Create an action server for goal-based navigation:

• Action Name: /navigate_to_goal
• Action Type: geometry_msgs/action/Navigate (you may use a standard action or create a custom one)
• Behavior:
  • Accept a goal position (x, y, theta)
  • Publish periodic feedback showing distance remaining
  • Simulate movement by publishing to /cmd_vel
  • Return success when "within 0.1m of goal"
  • Allow preemption (cancellation) of goals

Test Command:

ros2 action send_goal /navigate_to_goal geometry_msgs/action/Navigate "{goal: {x: 5.0, y: 3.0, theta: 1.57}}"

6. Launch File System (10 points)

File: robot_system.launch.py

Create a launch file that:

• Starts all nodes (sensor_publisher, control_node, emergency_stop_service, navigation_action_server)
• Loads parameters from params.yaml
• Launches RViz2 with a custom configuration
• Publishes the robot URDF to /robot_description
• Starts robot_state_publisher node

Launch Command:

ros2 launch <yourname>_robot_controller robot_system.launch.py

7. URDF Robot Model (10 points)

File: my_robot.urdf

Create or modify a simple robot URDF with:

• Base link (chassis)
• At least 2 wheels (left and right)
• A sensor link (LIDAR or camera)
• Proper joint definitions (continuous for wheels)
• Visual and collision geometries
• Inertial properties

Validation:

check_urdf my_robot.urdf
ros2 run robot_state_publisher robot_state_publisher --ros-args -p robot_description:="$(cat my_robot.urdf)"

8. Documentation (5 points)

File: README.md

Provide clear documentation including:

• Package overview and purpose
• Installation instructions
• How to build and run the package
• Description of each node and its functionality
• Example commands for testing
• Known issues or limitations

Deliverables

Submit the following via the course portal:

1. Source Code: Complete ROS 2 package directory (zip file)
2. README.md: Comprehensive documentation
3. Demo Video: 2-3 minute screen recording showing:
   • Launch file starting all nodes
   • ros2 topic list and ros2 node list output
   • RViz2 displaying the robot model
   • Service call demonstration
   • Action goal execution
4. Written Report: 2-page PDF including:
   • Architecture diagram of your system
   • Challenges faced and how you solved them
   • Lessons learned

Grading Rubric

Component	Points	Criteria
Package Structure	10	Proper organization, dependencies, build system configuration
Sensor Publisher	15	Multiple publishers, realistic data, proper QoS
Control Node	15	Correct subscription logic, obstacle avoidance behavior
Service Server	15	Functional service, correct request/response handling
Action Server	20	Goal handling, feedback, preemption support
Launch File	10	All nodes launch correctly, parameters loaded
URDF Model	10	Valid robot description, visualizes in RViz2
Documentation	5	Clear README, demo video, written report
Total	100

Grade Breakdown

• 90-100: Exceptional - All requirements met, code is clean and well-documented, advanced features implemented
• 80-89: Proficient - All core requirements met, minor issues in documentation or edge cases
• 70-79: Developing - Most requirements met, some functionality incomplete or buggy
• 60-69: Beginning - Basic structure present, significant functionality missing
• Below 60: Incomplete - Major requirements not met

Testing Checklist

Before submission, verify:

• Package builds without errors: colcon build --packages-select <yourname>_robot_controller
• All nodes start successfully via launch file
• ros2 topic list shows all expected topics
• ros2 topic echo /sensors/lidar displays sensor data
• ros2 topic echo /cmd_vel shows control commands
• Emergency stop service responds correctly
• Navigation action accepts goals and provides feedback
• Robot URDF displays properly in RViz2
• No errors or warnings in terminal output
• README accurately describes the system

Tips for Success

1. Start Early: Begin in Week 3, don't wait until Week 5
2. Test Incrementally: Build one node at a time and test before moving on
3. Use ROS 2 Tools: Familiarize yourself with ros2 node, ros2 topic, ros2 service, ros2 action commands
4. Check Examples: Review ROS 2 tutorials and example packages
5. Ask for Help: Use office hours or discussion forums if stuck
6. Version Control: Use Git to track your progress

Common Pitfalls to Avoid

• Forgetting to source your workspace: source install/setup.bash
• Incorrect QoS settings causing message drops
• Not handling node shutdown gracefully (use rclpy.spin() correctly)
• URDF syntax errors (use check_urdf tool)
• Hardcoding values instead of using parameters
• Not testing on a clean build before submission

Resources

• ROS 2 Humble Documentation
• Creating a ROS 2 Package
• Writing a Publisher and Subscriber
• URDF Tutorials
• Launch File Documentation

Submission

Due Date: End of Week 5 (see course schedule for exact date) Submit to: Course portal (link provided in Canvas/LMS) Late Policy: 10% deduction per day, maximum 3 days late

Academic Integrity

This is an individual project. You may discuss high-level concepts with classmates, but all code must be your own. Copying code from online sources or classmates will result in a zero and academic misconduct report.

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Questions? Contact the instructor or TA during office hours or via the course forum.