LiDAR Operations

This guide covers LiDAR sensor operations, setup, and troubleshooting for the RCR Common Robotics Platform. The robot uses a 2-dimensional LiDAR sensor for obstacle detection, mapping, and navigation. The LiDAR provides 360-degree range measurements around the robot.

Launch ROS Node

⚠️ Important: Ensure a ROS discovery server is running (see Discovery Server Setup)

Launch LiDAR:

cd ~/repos/common_platform/common_platform_ws/
source install/setup.bash
ros2 launch sensors rplidar.launch.py

You will need to leave this window open for as long as you want the LiDAR running. If you want to verify that the LiDar data is streaming you can echo the topic, to do so open a new terminal window 📟

Verify LiDAR Data:

ros2 topic echo /${ROS_NAME}/scan

You should see a stream of data points here if your LiDAR is publishing data to ROS.

Monitor data rate

ros2 topic hz /${ROS_NAME}/scan

Once you have checked the data stream, you can close this window as this is just for testing and diagnosis. You want to get in the habit of looking for the ros topic to verify data is streaming. You can do this with:

View all ROS topics

ros2 topic list

LiDAR Data Analysis

Scan Message:

std_msgs/Header header
float32 angle_min
float32 angle_max
float32 angle_increment
float32 time_increment
float32 scan_time
float32 range_min
float32 range_max
float32[] ranges
float32[] intensities

Check for:

  • Consistent range values

  • No missing data points

  • Reasonable intensity values

Diagnostic Commands

# Check USB devices
lsusb | grep -i lidar

# Check serial devices
ls /dev/tty*

# Test serial communication
ros2 run rplidar_ros rplidar_node --ros-args -p serial_port:=/dev/ttyUSB0

# Monitor data quality
ros2 topic echo /${ROS_NAME}/scan
ros2 topic hz /${ROS_NAME}/scan

Troubleshooting

No LiDAR Data:

  • Check USB connection

  • Verify Teensy is powered and running

  • Ensure a discovery server is running

  • Connect Cursor to your Pi via SSH and ask for diagnosis help

Hardware Connection

  1. Physical Mounting

    • Mount LiDAR on designated mounting point

    • Ensure clear 360° rotation

    • Secure mounting to prevent vibration

  2. Power Connection

    • Connect power cable to robot power system

    • Verify voltage requirements (5V)

    • Check for proper grounding

  3. Data Connection

    • Connect USB cable to robot controller

    • Verify serial communication

    • Test connection stability

Calibration

Mounting Calibration

Check Mounting:

  • Verify LiDAR is level

  • Ensure no obstructions

  • Check for vibration

Test Rotation:

ros2 service call /${ROS_NAME}/stop_motor std_srvs/srv/Empty {}
ros2 service call /${ROS_NAME}/start_motor std_srvs/srv/Empty {}

Range Calibration

Test Range Accuracy:

  1. Place known objects at known distances

  2. Compare LiDAR readings with actual distances

  3. Adjust calibration if needed

Verify Range Limits:

  • Test minimum range (0.15m)

  • Test maximum range (12m)

  • Check for blind spots

LiDAR Specifications

  • Model: RPLidar A1M8

  • Range: 0.15m - 12m

  • Angular Resolution: 0.33°

  • Scan Rate: 5.5 Hz

  • Interface: Serial (USB)

Performance Optimization

Data Processing

Filtering:

  • Remove noise from data

  • Filter out invalid readings

  • Smooth data for better performance

Downsampling:

  • Reduce data rate if needed

  • Maintain sufficient resolution

  • Balance performance vs. accuracy

Parameter Tuning

Scan Parameters:

# In launch file
scan_time: 0.1
range_min: 0.15
range_max: 12.0

Update Rates:

  • Adjust scan frequency

  • Balance performance vs. accuracy

  • Consider computational load

For camera operations, see Camera Operations For IMU operations, see IMU Operations For troubleshooting, see Troubleshooting