ROS Skill

Controls and monitors ROS/ROS2 robots via rosbridge WebSocket.

Architecture: Agent → ros_cli.py → rosbridge (WebSocket :9090) → ROS/ROS2 Robot

All commands output JSON. Errors contain {"error": "..."}.

For full command reference with arguments, options, and output examples, see references/COMMANDS.md.

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Setup

1. Install dependency

pip install websocket-client

2. Launch rosbridge on the robot

ROS 1:

sudo apt install ros-${ROS_DISTRO}-rosbridge-server
roslaunch rosbridge_server rosbridge_websocket.launch

ROS 2:

sudo apt install ros-${ROS_DISTRO}-rosbridge-server
ros2 launch rosbridge_server rosbridge_websocket_launch.xml

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Important: Always Connect First

Before any operation, test connectivity:

python {baseDir}/scripts/ros_cli.py connect
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> connect

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Global Options

Flag	Default	Description
--ip IP	127.0.0.1	Rosbridge IP address
--port PORT	9090	Rosbridge port number
--timeout SECONDS	5.0	Connection and request timeout

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Command Quick Reference

Category	Command	Description
Connection	connect	Test rosbridge connectivity (ping, port, WebSocket)
Connection	version	Detect ROS version and distro
Topics	topics list	List all active topics with types
Topics	topics type <topic>	Get message type of a topic
Topics	topics details <topic>	Get topic publishers/subscribers
Topics	topics message <msg_type>	Get message field structure
Topics	topics subscribe <topic> <msg_type>	Subscribe and receive messages
Topics	topics publish <topic> <msg_type> <json>	Publish a message to a topic
Topics	topics publish-sequence <topic> <msg_type> <msgs> <durs>	Publish message sequence
Services	services list	List all available services
Services	services type <service>	Get service type
Services	services details <service>	Get service request/response fields
Services	services call <service> <type> <json>	Call a service
Nodes	nodes list	List all active nodes
Nodes	nodes details <node>	Get node topics/services
Params	params list <node>	List node parameters (ROS 2)
Params	params get <node:param>	Get parameter value (ROS 2)
Params	params set <node:param> <value>	Set parameter value (ROS 2)
Actions	actions list	List action servers (ROS 2)
Actions	actions details <action>	Get action goal/result/feedback fields (ROS 2)
Actions	actions send <action> <type> <json>	Send action goal (ROS 2)

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Key Commands

connect

python {baseDir}/scripts/ros_cli.py connect
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> connect

version

python {baseDir}/scripts/ros_cli.py version

topics list / type / details / message

python {baseDir}/scripts/ros_cli.py topics list
python {baseDir}/scripts/ros_cli.py topics type /turtle1/cmd_vel
python {baseDir}/scripts/ros_cli.py topics details /turtle1/cmd_vel
python {baseDir}/scripts/ros_cli.py topics message geometry_msgs/Twist

topics subscribe

Without --duration: returns first message. With --duration: collects multiple messages.

python {baseDir}/scripts/ros_cli.py topics subscribe /turtle1/pose turtlesim/Pose
python {baseDir}/scripts/ros_cli.py topics subscribe /odom nav_msgs/Odometry --duration 10 --max-messages 50
python {baseDir}/scripts/ros_cli.py topics subscribe /scan sensor_msgs/LaserScan --timeout 10

topics publish

Without --duration: single-shot. With --duration: publishes repeatedly at --rate Hz. Use --duration for velocity commands — most robot controllers stop if they don't receive continuous cmd_vel messages.

# Single-shot
python {baseDir}/scripts/ros_cli.py topics publish /trigger std_msgs/Empty '{}'

# Move forward 3 seconds (velocity — use --duration)
python {baseDir}/scripts/ros_cli.py topics publish /cmd_vel geometry_msgs/Twist 
  '{"linear":{"x":1.0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}}' --duration 3

# Rotate left 2 seconds
python {baseDir}/scripts/ros_cli.py topics publish /cmd_vel geometry_msgs/Twist 
  '{"linear":{"x":0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0.5}}' --duration 2

# Stop
python {baseDir}/scripts/ros_cli.py topics publish /cmd_vel geometry_msgs/Twist 
  '{"linear":{"x":0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}}'

Options: --duration SECONDS, --rate HZ (default 10)

topics publish-sequence

Publish a sequence of messages, each repeated at --rate Hz for its corresponding duration. Arrays must have the same length.

# Forward 3s then stop
python {baseDir}/scripts/ros_cli.py topics publish-sequence /cmd_vel geometry_msgs/Twist 
  '[{"linear":{"x":1.0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}},{"linear":{"x":0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}}]' 
  '[3.0, 0.5]'

# Draw a square (turtlesim)
python {baseDir}/scripts/ros_cli.py topics publish-sequence /turtle1/cmd_vel geometry_msgs/Twist 
  '[{"linear":{"x":2},"angular":{"z":0}},{"linear":{"x":0},"angular":{"z":1.5708}},{"linear":{"x":2},"angular":{"z":0}},{"linear":{"x":0},"angular":{"z":1.5708}},{"linear":{"x":2},"angular":{"z":0}},{"linear":{"x":0},"angular":{"z":1.5708}},{"linear":{"x":2},"angular":{"z":0}},{"linear":{"x":0},"angular":{"z":1.5708}},{"linear":{"x":0},"angular":{"z":0}}]' 
  '[1,1,1,1,1,1,1,1,0.5]'

Options: --rate HZ (default 10)

services list / type / details

python {baseDir}/scripts/ros_cli.py services list
python {baseDir}/scripts/ros_cli.py services type /spawn
python {baseDir}/scripts/ros_cli.py services details /spawn

services call

python {baseDir}/scripts/ros_cli.py services call /reset std_srvs/Empty '{}'
python {baseDir}/scripts/ros_cli.py services call /spawn turtlesim/Spawn 
  '{"x":3.0,"y":3.0,"theta":0.0,"name":"turtle2"}'
python {baseDir}/scripts/ros_cli.py services call /turtle1/set_pen turtlesim/srv/SetPen 
  '{"r":255,"g":0,"b":0,"width":3,"off":0}'

nodes list / details

python {baseDir}/scripts/ros_cli.py nodes list
python {baseDir}/scripts/ros_cli.py nodes details /turtlesim

params list / get / set (ROS 2 only)

Uses node:param_name format from params list output.

python {baseDir}/scripts/ros_cli.py params list /turtlesim
python {baseDir}/scripts/ros_cli.py params get /turtlesim:background_r
python {baseDir}/scripts/ros_cli.py params set /turtlesim:background_r 255

actions list / details / send (ROS 2 only)

python {baseDir}/scripts/ros_cli.py actions list
python {baseDir}/scripts/ros_cli.py actions details /turtle1/rotate_absolute
python {baseDir}/scripts/ros_cli.py actions send /turtle1/rotate_absolute 
  turtlesim/action/RotateAbsolute '{"theta":3.14}'

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Workflow Examples

1. Explore a Robot System

python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> connect
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> version
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> topics list
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> nodes list
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> services list
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> topics type /cmd_vel
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> topics message geometry_msgs/Twist
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> actions list
python {baseDir}/scripts/ros_cli.py --ip <ROBOT_IP> params list /robot_node

2. Move a Robot

Always check the message structure first, then publish movement, and always stop after.

python {baseDir}/scripts/ros_cli.py topics message geometry_msgs/Twist
python {baseDir}/scripts/ros_cli.py topics publish-sequence /cmd_vel geometry_msgs/Twist 
  '[{"linear":{"x":1.0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}},{"linear":{"x":0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}}]' 
  '[2.0, 0.5]'

3. Read Sensor Data

python {baseDir}/scripts/ros_cli.py topics type /scan
python {baseDir}/scripts/ros_cli.py topics message sensor_msgs/LaserScan
python {baseDir}/scripts/ros_cli.py topics subscribe /scan sensor_msgs/LaserScan --timeout 3
python {baseDir}/scripts/ros_cli.py topics subscribe /odom nav_msgs/Odometry --duration 10 --max-messages 50

4. Use Services

python {baseDir}/scripts/ros_cli.py services list
python {baseDir}/scripts/ros_cli.py services details /spawn
python {baseDir}/scripts/ros_cli.py services call /spawn turtlesim/Spawn 
  '{"x":3.0,"y":3.0,"theta":0.0,"name":"turtle2"}'

5. ROS 2 Actions

python {baseDir}/scripts/ros_cli.py actions list
python {baseDir}/scripts/ros_cli.py actions details /turtle1/rotate_absolute
python {baseDir}/scripts/ros_cli.py actions send /turtle1/rotate_absolute 
  turtlesim/action/RotateAbsolute '{"theta":1.57}'

6. Change Parameters (ROS 2)

python {baseDir}/scripts/ros_cli.py params list /turtlesim
python {baseDir}/scripts/ros_cli.py params get /turtlesim:background_r
python {baseDir}/scripts/ros_cli.py params set /turtlesim:background_r 255
python {baseDir}/scripts/ros_cli.py params set /turtlesim:background_g 0
python {baseDir}/scripts/ros_cli.py params set /turtlesim:background_b 0

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Safety Notes

Destructive commands (can move the robot or change state): - topics publish / topics publish-sequence — sends movement or control commands - services call — can reset, spawn, kill, or change robot state - params set — modifies runtime parameters - actions send — triggers robot actions (rotation, navigation, etc.)

Always stop the robot after movement. The last message in any publish-sequence should be all zeros:

{"linear":{"x":0,"y":0,"z":0},"angular":{"x":0,"y":0,"z":0}}

Always check JSON output for errors before proceeding.

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Troubleshooting

Problem	Cause	Solution
Connection refused	rosbridge not running	Start rosbridge: ros2 launch rosbridge_server rosbridge_websocket_launch.xml
Timeout errors	Slow network or large data	Increase timeout: --timeout 10 or --timeout 30
No topics found	ROS nodes not running	Ensure nodes are launched and workspace is sourced
Empty topic list	rosapi not available	Verify rosbridge includes rosapi (default in standard install)
Parameter commands fail	Using ROS 1	params commands only work with ROS 2
Action commands fail	Using ROS 1	actions commands only work with ROS 2
Invalid JSON error	Malformed message	Validate JSON before passing (watch for single vs double quotes)
Subscribe timeout	No publisher on topic	Check topics details to verify publishers exist
publish-sequence length error	Array mismatch	messages and durations arrays must have the same length