🚀 Launch & Config Files

In the LIMO Pro + MyCobot + YOLO system, launch files and configuration files are critical for ensuring every node starts in the correct order, with the right parameters, and without conflicts.
This guide explains how to write, structure, and manage them.

📝 Writing Custom Launch Files

We use Python-based ROS2 launch files to control startup.

Example minimal launch file:

from launch import LaunchDescription
from launch_ros.actions import Node

def generate_launch_description():
    return LaunchDescription([
        Node(
            package='my_package',
            executable='my_node',
            name='my_node',
            output='screen',
            parameters=[{'example_param': 'value'}]
        )
    ])

⏱ Startup Sequencing with TimerAction

Our full_system.launch.py uses TimerAction so nodes launch only after dependencies are ready:

from launch.actions import TimerAction

TimerAction(period=2.0, actions=[nav2_node]),  # Start Nav2 after 2s
TimerAction(period=3.0, actions=[pose_setter]), # Pose setter after Nav2
TimerAction(period=10.0, actions=[mission_manager]), # Mission Manager last

Why?

Nav2 must load the map before pose_setter runs.
mission_manager must wait until localization and YOLO detection are ready.

⚙️ Configuration File Formats

We use YAML for parameters like nav2_params.yaml:

amcl:
  ros__parameters:
    min_particles: 500
    max_particles: 2000
    update_min_a: 0.2
    update_min_d: 0.25

Tips:

Use ros__parameters root key for ROS2.
Keep one YAML per node for clarity.
Store in config/ inside the package.

🔄 Parameter Management

You can pass parameters in three ways:

Inline in Launch
From YAML
From CLI

Node(
    package="my_package",
    executable="my_node",
    parameters=[{'m5_ip': '192.168.137.75'}]
)

Node(
    package="nav2_bringup",
    executable="bringup_launch.py",
    parameters=["config/nav2_params.yaml"]
)

ros2 run my_package my_node --ros-args -p m5_ip:=192.168.137.75

💡 Launch File Best Practices

Do This

Use FindPackageShare so your launch files work from any workspace.
Keep launch files modular — one per subsystem (YOLO, navigation, arm).
Use SetLaunchConfiguration for values reused across nodes.
Log key events so the startup process is traceable.

Avoid

Hardcoding absolute paths — always resolve relative to the package share.
Starting all nodes at once — it causes race conditions.
Embedding too much logic in launch files — keep them orchestration-only.

✅ Checklist Before Committing

☐ Launch file runs without errors.
☐ Config YAML loads correctly (no tab characters — YAML only allows spaces).
☐ Dependencies start in the right order.
☐ Works both from ros2 launch and as part of full_system.launch.py.

Next: Parameter Tuning & Optimization

📝 Writing Custom Launch Files​

⏱ Startup Sequencing with TimerAction​

⚙️ Configuration File Formats​

🔄 Parameter Management​

💡 Launch File Best Practices​

✅ Checklist Before Committing​

📎 Related​