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YDLidar Knowhow - ROS2 Jazzy Setup Guide

This document captures all the lessons learned from setting up the YDLidar (X4 Pro / S2PRO) with ROS2 Jazzy.

📋 Hardware Information

Property Value
Marketed Model YDLidar X4 Pro
Detected Model (by SDK) S2PRO
Firmware Version 3.1
Hardware Version 3
Serial Port /dev/ttyUSB1 (may vary)
Baudrate 128000
Sample Rate 5.00 KHz
Scan Frequency 10.00 Hz
Points per Scan 720 (Fixed Size)

🔧 Key Configuration Parameters

Our lidar, although marketed as "X4 Pro", reports as S2PRO to the SDK, so it requires specific settings:

# Critical parameters for our lidar (S2PRO protocol)
baudrate: 128000          # NOT 115200!
isSingleChannel: true     # MUST be true for S2PRO
lidar_type: 1             # TYPE_TRIANGLE
sample_rate: 5            # 5 KHz
reversion: true           # Required for S2PRO
support_motor_dtr: false  # Does not support DTR

⚠️ Common Mistake: isSingleChannel

If you set isSingleChannel: false, you will get this error:

[error] Error, cannot retrieve Lidar health code -1
[error] Failed to start scan mode -1

Solution: Set isSingleChannel: true

🚨 Problem: RViz2 QoS Incompatibility

Symptom

[WARN] New subscription discovered on topic '/scan', requesting incompatible QoS. 
No messages will be sent to it. Last incompatible policy: RELIABILITY_QOS_POLICY

Cause

  • The lidar driver publishes with Best Effort reliability (standard for sensor data)
  • RViz2 subscribes with Reliable reliability by default
  • These are incompatible QoS policies

Solution

In RViz2 LaserScan display settings:

  1. Expand the Topic section
  2. Change Reliability Policy from Reliable to Best Effort
  3. Set Topic Value to /scan

🚀 Quick Start Commands

1. Build the Package

cd ~/robot_ws
colcon build --symlink-install --packages-select ydlidar_ros2_driver
source install/setup.bash

2. Launch the Driver (without RViz)

ros2 launch ydlidar_ros2_driver ydlidar_launch.py

3. Launch with RViz

ros2 launch ydlidar_ros2_driver ydlidar_launch_view.py

4. Check Topics

ros2 topic list
ros2 topic echo /scan --once
ros2 topic hz /scan

5. Check Serial Port

ls -la /dev/ttyUSB*

📁 Important Files

File Purpose
params/ydlidar.yaml Main configuration file
config/ydlidar.rviz RViz2 visualization config
launch/ydlidar_launch.py Launch driver only
launch/ydlidar_launch_view.py Launch driver + RViz
src/ydlidar_ros2_driver_node.cpp Driver source code

🔄 ROS2 Jazzy Compatibility Changes

The driver was updated from ROS2 Humble to Jazzy with these changes:

1. Parameter Declaration API

// OLD (Humble) - deprecated in Jazzy
node->declare_parameter("port");
node->get_parameter("port", value);

// NEW (Jazzy)
auto value = node->declare_parameter<std::string>("port", "/dev/ydlidar");

2. Service Callback Signature

// OLD (Humble)
[](const std::shared_ptr<rmw_request_id_t> request_header,
   const std::shared_ptr<Request> req,
   std::shared_ptr<Response> response) -> bool

// NEW (Jazzy) - removed rmw_request_id_t
[](const std::shared_ptr<Request> req,
   std::shared_ptr<Response> response)

3. Launch File API

# OLD (Humble)
node_executable='...'
node_name='...'
node_namespace='...'

# NEW (Jazzy)
executable='...'
name='...'
namespace='...'

4. C++ Standard

Changed from C++14 to C++17 in CMakeLists.txt

5. Static Transform Publisher

# OLD
arguments=['0', '0', '0.02', '0', '0', '0', '1', 'base_link', 'laser_frame']

# NEW (Jazzy)
arguments=['--x', '0', '--y', '0', '--z', '0.02',
           '--roll', '0', '--pitch', '0', '--yaw', '0',
           '--frame-id', 'base_link', '--child-frame-id', 'laser_frame']

🛠️ Troubleshooting

Problem: Lidar not found

[error] Lidar communication error

Solution: Check the port in ydlidar.yaml - run ls /dev/ttyUSB* to find correct port

Problem: Permission denied on serial port

sudo chmod 666 /dev/ttyUSB1
# Or add user to dialout group (permanent fix):
sudo usermod -a -G dialout $USER
# Then logout and login again

Problem: RViz won't start (no display)

qt.qpa.xcb: could not connect to display

Solution: Run RViz in a terminal with GUI access, or use X11 forwarding if using SSH

Problem: No laser scan visible in RViz

  1. Check Topic is set to /scan (not /laser_frame)
  2. Check Reliability Policy is set to Best Effort
  3. Check Fixed Frame is set to laser_frame

📊 TF Frames

base_link
    └── laser_frame (offset: z=0.02m)

The static transform publisher creates the link from base_link to laser_frame.

🔗 Dependencies

  • ROS2 Jazzy
  • YDLidar SDK (installed at /usr/local/lib/cmake/ydlidar_sdk)

Install YDLidar SDK (if not installed)

git clone https://github.com/YDLIDAR/YDLidar-SDK.git
cd YDLidar-SDK
mkdir build && cd build
cmake ..
make
sudo make install

📝 Version Info

  • Driver Version: 1.0.2-jazzy
  • SDK Version: 1.2.19
  • ROS2 Distribution: Jazzy
  • Last Updated: 2025-12-29

📚 References