ROS 2 (Robot / AGV Middleware)

ROS 2 (Robot Operating System 2) is the standard middleware for mobile robots, AGVs, collaborative robots, and drones. It provides publish/subscribe, service, and action communication over DDS (Data Distribution Service, RTPS over UDP/TCP). The typical approach is to subscribe to topics (e.g., /odom, /imu, /battery_state) to monitor robot status.

The gateway's ROS2 driver is a real implementation driver that connects to the JSON over WebSocket endpoint of the standard ROS 2 bridge rosbridge_suite (rosbridge_server) to subscribe to topics. As it does not connect directly to DDS, you only need to run rosbridge_server on the ROS 2 side. It is read-only.

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Prerequisites — rosbridge_server

Install and run the standard package rosbridge_suite on the ROS 2 side (on the robot itself or a PC on the same network).

# 예: ROS 2 Humble
sudo apt install ros-humble-rosbridge-suite
ros2 launch rosbridge_server rosbridge_websocket_launch.xml   # 기본 ws 포트 9090

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Registration Form Input Values

Input Field	What to Enter	Example
IP Address	rosbridge_server host	192.168.0.30
Port	rosbridge WebSocket port	9090 (ws default) / 9443 (wss default)
Path (rosbridge)	WebSocket endpoint path — optional path	/ (default)
TLS	false = ws / true = wss — optional tls	false (default)

Write Not Supported

The ROS 2 driver is read-only. Topic publishing (e.g., /cmd_vel motion commands) is not supported because it requires rosbridge advertise. Use a separate route for sending robot commands.

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PLC Address Notation for Tags

The address uses <topic>:<field.dot.path> — the first : separates the topic from the field path (ROS topics include / but have no :).

Notation	Meaning
/temperature:data	The data field of std_msgs/Float64
/imu:orientation.z	Nested field of sensor_msgs/Imu (dot-path)
/scan:ranges.0	Array element — numeric segment is the index
/odom	Entire msg if : is omitted (JSON string)

• Leaf fields are returned as text values; objects/arrays are returned as JSON strings.
• Lazy subscribe — the topic is subscribed once on the first read, and rosbridge then pushes new samples. Therefore the first value arrives from the next collection cycle.

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Data Type Matching

msg field	Data Type
float fields (data, orientation.z …)	Float / Double
int / enum fields	Integer
bool fields	Boolean
string / entire msg (JSON)	String

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Frequently Used Topic Mappings (Reference)

Address	Meaning	Recommended Format
/battery_state:percentage	Battery level (sensor_msgs/BatteryState)	Float
/odom:pose.pose.position.x	Robot position x (nav_msgs/Odometry)	Float
/odom:twist.twist.linear.x	Forward velocity (nav_msgs/Odometry)	Float
/diagnostics	Full diagnostic message	String (JSON)

For large messages like /scan (raw LiDAR), avoid collecting the entire msg and register only the necessary elements (e.g., /scan:ranges.0).

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Common Issues

Symptom	Possible Cause	Solution
Empty value right after registration	Lazy subscribe — the first read only performs the subscription	Wait until the next collection cycle (one timecycle)
Connection failed (connect failed)	rosbridge_server not running / port mismatch	Run rosbridge_server on the ROS 2 side and verify the port (9090)
wss connection failure	TLS settings / certificates	If tls=true, rosbridge must also run with TLS (wss default port 9443)
Value updates then stops	WebSocket disconnection — the driver switches to disconnected immediately (does not keep returning stale cached values)	Check network / restart rosbridge
Topic name is correct but empty value	Field dot-path typo (path not present in msg)	Check the msg structure with ros2 topic echo <topic> and fix the path

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Other Integration Routes (Reference)

If rosbridge cannot be used, the following routes are also available.

Situation	Alternative
Multiple robots + cloud collection needed	MQTT bridge → Sparkplug B / MQTT Client
Industrial robot controllers (ABB / KUKA / UR)	OPC UA Robotics Companion → OPC-UA