ROS2 YAML - Parameter Loading

🧠 Concept: ROS2 Parameters

Parameters let you configure a node's behaviour without changing code. Think of them like command-line arguments or config files for your node.

Two-step pattern — always declare before reading:

# Step 1: Declare with a default value
self.declare_parameter('speed', 1.0)

# Step 2: Read the value
speed = self.get_parameter('speed').value

Why this matters: In real robots, you don't recompile to change max_speed. You pass it as a parameter at launch time: ros2 run my_pkg my_node --ros-args -p max_speed:=2.5

Problem Statement

Learn how to load parameters from a YAML file into a ROS2 node. This is the standard way to configure robots without recompiling code — change the YAML, restart the node.

Requirements

• Create a node yaml_config_node
• Declare two parameters with defaults:
  • max_speed (float, default: 1.5)
  • robot_name (string, default: "my_robot")
• Read both parameters using get_parameter() and .value
• Log both values using get_logger().info()

Input/Output Format

Output (console logs):

[yaml_config_node]: Max speed: 1.5
[yaml_config_node]: Robot name: my_robot

How YAML loading works in ROS2

When launched with a YAML file, your declared parameters are automatically overridden by the file values:

/**:
  ros__parameters:
    max_speed: 3.0
    robot_name: "production_bot"

Your node doesn't need to read the file directly — ROS2 injects the values via the parameter system.

⚠️ Common Pitfalls

• YAML indentation errors (tabs vs spaces) will silently break parameter loading
• Forgetting .value when reading a parameter: get_parameter('max_speed').value
• Not calling declare_parameter() before get_parameter() (unless allow_undeclared_parameters=True)

📚 Helpful Resources

• ROS2 Parameters Tutorial