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 / action semantics on top of DDS (Data Distribution Service, RTPS over UDP/TCP). Monitoring robot status by subscribing to topics (for example /odom, /imu, /battery_state) is the common approach.

The gateway's ROS2 driver is a fully implemented driver that connects to the JSON over WebSocket endpoint of rosbridge_suite (rosbridge_server), the standard ROS 2 bridge, and subscribes to topics. It does not attach to DDS directly, so all you need on the ROS 2 side is a running rosbridge_server. It is read-only.

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Prerequisite — rosbridge_server

Install and run the standard rosbridge_suite package on the ROS 2 side (on the robot itself or on 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 entries

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 — option path	/ (default)
Use TLS	false = ws / true = wss — option tls	false (default)

Write not supported

The ROS 2 driver is read-only. Publishing to topics (for example /cmd_vel motion commands) requires rosbridge advertise and is not supported. Use a separate path for sending robot commands.

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PLC address notation for tags

The address format is <topic>:<field.dot.path> — the first : separates the topic from the field path (ROS topics contain / but no :).

Notation	Meaning
/temperature:data	The data field of std_msgs/Float64
/imu:orientation.z	A nested field of sensor_msgs/Imu (dot-path)
/scan:ranges.0	Array element — the numeric segment is the index
/odom	Without :, the entire msg (JSON string)

• Leaf fields are returned as text values; objects and arrays are returned as JSON strings.
• lazy subscribe — a topic is subscribed once on the first read, after which rosbridge pushes new samples. The first value therefore arrives from the next collection cycle onward.

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Data format matching

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

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Common 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	Entire diagnostics message	String (JSON)

For large messages such as /scan (LiDAR raw), avoid collecting the entire msg and register only the elements you need (for example /scan:ranges.0).

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Common problems

Symptom	Possible cause	Resolution
Value is empty right after registration	lazy subscribe — the first read only performs the subscription	Wait until the next collection cycle (one timecycle)
Connection failure (connect failed)	rosbridge_server not running / port mismatch	Verify that rosbridge_server is running on the ROS 2 side and check the port (9090)
wss connection failure	TLS settings / certificate	If tls=true, rosbridge must also run with TLS (wss default port 9443)
Values update, then stop	WebSocket dropped — the driver immediately switches to disconnected (it does not keep returning stale cached values)	Check the network / restart rosbridge
Topic name is correct but the value is empty	Typo in the field dot-path (path does not exist in the msg)	Check the msg structure with ros2 topic echo <topic> and correct the path

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Alternative integration paths (reference)

Where rosbridge cannot be used, the following paths are also possible.

Situation	Alternative
Many robots plus cloud collection required	MQTT bridge → Sparkplug B / MQTT client
Industrial robot controllers (ABB / KUKA / UR)	OPC UA Robotics Companion → OPC-UA