LiDAR Setup (RPLIDAR A1M8)

RPLIDAR USB Adapter
├── USB Type-A  ──→  Raspberry Pi USB Port
└── 5V Power (from motor)

# Install RPLIDAR ROS2 driver
sudo apt install ros-jazzy-rplidar-ros

# Find LiDAR device
ls -l /dev/ttyUSB*
# Example output: /dev/ttyUSB0

# Add udev rule (one-time setup)
echo 'KERNEL=="ttyUSB*", ATTRS{idVendor}=="10c4", ATTRS{idProduct}=="ea60", MODE="0666"' | \
  sudo tee /etc/udev/rules.d/99-rplidar.rules

# Reload udev rules
sudo udevadm control --reload-rules
sudo udevadm trigger

# Add user to dialout group
sudo usermod -a -G dialout $USER

# Logout and login for changes to take effect

from launch import LaunchDescription
from launch_ros.actions import Node
from launch.actions import DeclareLaunchArgument
from launch.substitutions import LaunchConfiguration

def generate_launch_description():
    # Arguments
    serial_port = LaunchConfiguration('serial_port')
    frame_id = LaunchConfiguration('frame_id')

    declare_serial_port_cmd = DeclareLaunchArgument(
        'serial_port',
        default_value='/dev/ttyUSB0',
        description='Serial port for RPLIDAR')

    declare_frame_id_cmd = DeclareLaunchArgument(
        'frame_id',
        default_value='lidar_link',
        description='Frame ID for laser scan')

    # RPLIDAR node
    rplidar_node = Node(
        package='rplidar_ros',
        executable='rplidar_node',
        name='rplidar_node',
        parameters=[{
            'serial_port': serial_port,
            'serial_baudrate': 115200,
            'frame_id': frame_id,
            'inverted': False,
            'angle_compensate': True,
            'scan_mode': 'Standard'
        }],
        output='screen'
    )

    return LaunchDescription([
        declare_serial_port_cmd,
        declare_frame_id_cmd,
        rplidar_node,
    ])

ros2 launch mecanum_description lidar.launch.py

rplidar_node:
  ros__parameters:
    # Serial port
    serial_port: /dev/ttyUSB0
    serial_baudrate: 115200

    # Frame ID (must match URDF)
    frame_id: lidar_link

    # Scan settings
    inverted: false              # Flip scan direction
    angle_compensate: true       # Compensate for motor speed variation

    # Scan mode
    scan_mode: Standard          # Standard, Express, Boost

    # Quality filtering
    scan_frequency: 10.0         # Target scan rate (Hz)

# List USB devices
lsusb
# Look for: "Silicon Labs CP210x UART Bridge"

# Check device appears
ls /dev/ttyUSB*
# Should show: /dev/ttyUSB0 (or ttyUSB1, etc.)

ros2 launch mecanum_description lidar.launch.py

rviz2

ros2 topic echo /scan

header:
  stamp:
    sec: 1234567890
    nanosec: 123456789
  frame_id: lidar_link
angle_min: -3.14159
angle_max: 3.14159
angle_increment: 0.0174533  # ~1 degree
time_increment: 0.0
scan_time: 0.18  # ~5.5 Hz
range_min: 0.15
range_max: 12.0
ranges: [1.234, 1.567, 2.345, ... ]  # 360 distance measurements
intensities: []  # A1M8 doesn't provide intensity

# Monitor scan rate
ros2 topic hz /scan
# Expected: ~5.5 Hz

# Check data size
ros2 topic bw /scan
# Expected: ~30-50 KB/s

# In RViz, observe scan
# Point object directly in front of robot
# Check if object appears at 0° (straight ahead)

<!-- In URDF lidar joint -->
<origin xyz="0 0 0.20" rpy="0 0 1.57"/>
<!--                       Yaw offset (90° if needed) -->

local_costmap:
  local_costmap:
    ros__parameters:
      # ... other params ...

      obstacle_layer:
        plugin: "nav2_costmap_2d::ObstacleLayer"
        enabled: True
        observation_sources: scan

        scan:
          topic: /scan
          data_type: "LaserScan"
          marking: True        # Mark obstacles
          clearing: True       # Clear when no obstacle

          # Range limits
          obstacle_max_range: 11.5  # Slightly less than max (12m)
          obstacle_min_range: 0.2   # Ignore very close readings
          raytrace_max_range: 12.0  # Clear up to max range
          raytrace_min_range: 0.0

          # Obstacle size
          max_obstacle_height: 2.0  # meters
          min_obstacle_height: 0.0

slam_toolbox:
  ros__parameters:
    scan_topic: /scan
    max_laser_range: 12.0    # RPLIDAR A1M8 max
    minimum_travel_distance: 0.2
    minimum_travel_heading: 0.2

# Install laser filters
sudo apt install ros-jazzy-laser-filters

# In launch file
from launch_ros.actions import Node

scan_filter_node = Node(
    package='laser_filters',
    executable='scan_to_scan_filter_chain',
    parameters=[{
        'cloud_threshold': 0.05,
        'filter_chain': [
            {
                'name': 'range',
                'type': 'laser_filters/LaserScanRangeFilter',
                'params': {
                    'use_message_range_limits': False,
                    'lower_threshold': 0.15,
                    'upper_threshold': 11.5
                }
            },
            {
                'name': 'shadows',
                'type': 'laser_filters/ScanShadowsFilter',
                'params': {
                    'min_angle': -3.14,
                    'max_angle': 3.14,
                    'neighbors': 10,
                    'window': 1
                }
            }
        ]
    }],
    remappings=[
        ('scan', 'scan_raw'),
        ('scan_filtered', 'scan')
    ]
)

# Launch node, check logs
ros2 launch mecanum_description lidar.launch.py

# Look for: "Firmware version: X.XX"