These are the commands to explore a new robotic system.
Returns a list of topics for both publishers and subscribers. Below is a list of topics available on a simple robot.
can@ubuntu:~$ ros2 topic list
/cmd_vel
/joint_states
/odom
/parameter_events
/robot_description
/rosout
/rosrider/diagnostics
/scan
/tf
/tf_static
Listen on the given topic name and prints its output to the terminal.
Below command prints /odom topic:
can@ubuntu:~$ ros2 topic echo /odom
header:
stamp:
sec: 1716665922
nanosec: 124206471
frame_id: odom
child_frame_id: base_footprint
pose:
pose:
position:
x: 0.0
y: 0.0
z: 0.0
orientation:
x: 0.0
y: 0.0
z: 0.0
w: 1.0
twist:
twist:
linear:
x: 0.0
y: 0.0
z: 0.0
angular:
x: 0.0
y: 0.0
z: 0.0
Below command prints wheel positions:
can@ubuntu:~$ ros2 topic echo /joint_states
header:
stamp:
sec: 1716666515
nanosec: 667963578
frame_id: ''
name:
- wheel_left_joint
- wheel_right_joint
position:
- 0.0
- 0.0
velocity: []
effort: []
Prints information about which node is publishing the topic, and which nodes are subscribed to this topic, as well as the message data type.
can@ubuntu:~$ ros2 topic info /odom
Type: nav_msgs/msg/Odometry
Publisher count: 1
Subscription count: 1
The -vvv flag will provide verbose output.
can@ubuntu:~$ ros2 topic info /odom -vvv
Type: nav_msgs/msg/Odometry
Publisher count: 1
Node name: rosrider_node
Node namespace: /
Topic type: nav_msgs/msg/Odometry
Endpoint type: PUBLISHER
GID: 01.0f.65.91.01.05.d8.7e.01.00.00.00.00.00.12.03.00.00.00.00.00.00.00.00
QoS profile:
Reliability: RELIABLE
History (Depth): UNKNOWN
Durability: VOLATILE
Lifespan: Infinite
Deadline: Infinite
Liveliness: AUTOMATIC
Liveliness lease duration: Infinite
Subscription count: 1
Node name: _ros2cli_1336
Node namespace: /
Topic type: nav_msgs/msg/Odometry
Endpoint type: SUBSCRIPTION
GID: 01.0f.65.91.38.05.f3.b9.01.00.00.00.00.00.05.04.00.00.00.00.00.00.00.00
QoS profile:
Reliability: RELIABLE
History (Depth): UNKNOWN
Durability: VOLATILE
Lifespan: Infinite
Deadline: Infinite
Liveliness: AUTOMATIC
Liveliness lease duration: Infinite
Will measure the publication speed of the topic and report in hertz. When there is a problem with a sensor, use this to verify it is publishing with the desired speed.
can@ubuntu:~$ ros2 topic hz /odom
average rate: 20.001
min: 0.048s max: 0.052s std dev: 0.00078s window: 22
average rate: 19.998
min: 0.048s max: 0.052s std dev: 0.00084s window: 42
average rate: 19.996
min: 0.048s max: 0.052s std dev: 0.00083s window: 62
average rate: 19.998
min: 0.048s max: 0.052s std dev: 0.00082s window: 83
The below command publishes to /cmd_vel and will make the robot move in a circular pattern. For the robot to continue moving, /cmd_vel must receive data not less than 10 hz.
can@ubuntu:~$ ros2 topic pub /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.1}, angular: {z: 0.1}}" -r 10
publisher: beginning loop
publishing #1: geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=0.1, y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=0.1))
publishing #2: geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=0.1, y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=0.1))
publishing #3: geometry_msgs.msg.Twist(linear=geometry_msgs.msg.Vector3(x=0.1, y=0.0, z=0.0), angular=geometry_msgs.msg.Vector3(x=0.0, y=0.0, z=0.1))
Publishes just once
ros2 topic pub --once /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.1}, angular: {z: 0.0}}"
Publishes at 20 hz
ros2 topic pub --rate 20 /cmd_vel geometry_msgs/msg/Twist "{linear: {x: 0.0}, angular: {z: 0.2}}"
Lists nodes running on the robot. Each node is a computer program handling specific aspects of the robot.
can@ubuntu:~$ ros2 node list
/ldlidar
/robot_state_publisher
/rosrider_node
Used to send static transforms
ros2 run tf2_ros static_transform_publisher "0" "0" "0" "0" "0" "0" "map" "odom"
Add a common joystick to generate velocity commands
ros2 launch teleop_twist_joy teleop-launch.py joy_config:='f710'
Activate the feedback motors on the joystick
ros2 topic pub -1 /joy/set_feedback sensor_msgs/JoyFeedback "{type: 1, id: 0, intensity: 1.0}"
Plot anything within the ROS system
ros2 run rqt_plot rqt_plot
Save Maps from mapping for use with later navigation
ros2 run nav2_map_server map_saver_cli -f ~/map
Next Chapter: Parameter System