I1: State Machines in ROS 2
Status: Content in development. See Intermediate Exercises for hands-on practice with this topic.
Learning Objectives
By the end of this lesson, you will be able to:
- Implement finite state machines in ROS 2 Python nodes
- Publish state information for monitoring
- Handle state transitions based on events and timers
- Integrate state machines with ROS 2 communication patterns
- Debug and test state machine implementations
Introduction
In the beginner tier, you learned about state machines conceptually. Now, you'll implement them in ROS 2 nodes, making them practical tools for managing robot behaviors. This lesson covers the patterns and best practices for building robust state machines that integrate seamlessly with ROS 2's communication infrastructure.
Coming Soon
This lesson is currently under development. In the meantime:
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Review the Beginner Content: Ensure you understand state machine concepts from Beginner Lesson 02
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Practice with Exercises: Complete Exercise 01: Delivery Robot State Machine which provides detailed implementation guidance
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Explore AI Prompts: Use Intermediate AI Prompts for implementation help
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Study Example Code: The exercises include starter code and complete solutions
Planned Topics
This lesson will cover:
1. Basic State Machine Implementation
- Creating state enums in Python
- Managing state in ROS 2 node classes
- State transition logic
- Publishing state for monitoring
2. Event-Driven Transitions
- Subscriber-based state transitions
- Timer-based state transitions
- Service-based state changes
- Action-based state management
3. State Machine Patterns
- Simple FSM pattern
- State with entry/exit actions
- Hierarchical state machines
- State persistence and recovery
4. Integration with ROS 2
- Publishing state on topics
- Logging state changes
- Parameter-based configuration
- Lifecycle node integration
5. Testing and Debugging
- Unit testing state machines
- Integration testing with other nodes
- Debugging state transition issues
- Visualization tools
Resources
While this lesson is in development, use these resources:
- ROS 2 Node Tutorial: https://docs.ros.org/en/humble/Tutorials/Beginner-Client-Libraries/Writing-A-Simple-Py-Publisher-And-Subscriber.html
- Python Enum Documentation: https://docs.python.org/3/library/enum.html
- State Machine Libraries: https://github.com/amaury-d/smach (for reference)
Next Steps
Continue to I2: Multi-Node Pipelines or practice with Intermediate Exercises