Ubuntu Linux for Robotics · Lesson 58 of 96

joint_state_publisher

Using the GUI sliders to test joints before any simulation or hardware.

Estimated time · 30–45 min

Learning goals

What you will understand

Explain joint_state_publisher in your own words
Use it in a small workstation example
Verify the result instead of assuming it worked

Understand the idea first

The mental model

joint_state_publisher publishes /joint_states with default values; joint_state_publisher_gui adds sliders for each movable joint. Install with sudo apt install ros-lyrical-joint-state-publisher-gui. It reads the description from robot_description, so start robot_state_publisher first.

Use the sliders to check joint limits and directions. Stop the GUI when a simulator or real driver publishes /joint_states, because two publishers of the same topic fight each other.

Guided lesson

Work through these steps

1.
Open a terminal and record the current state before changing anything.
2.
Read the joint_state_publisher commands and predict what each one does.
3.
Run the commands one at a time and compare each output with your prediction.
4.
Write the commands that worked in a setup note you can repeat later.

Worked example

Read it before you run it

sudo apt install ros-lyrical-joint-state-publisher-gui
# Install the GUI.
ros2 run joint_state_publisher_gui joint_state_publisher_gui
# Open the sliders.
ros2 topic echo /joint_states --once
# See the values the sliders publish.
ros2 topic hz /joint_states
# Check the publishing rate.
rviz2
# Watch the robot move as you drag the sliders.

What the example is doing

1.Lines without sudo only inspect or change files you own; sudo authorizes a system-wide change.
2.Read command output before moving to the next line. Stop if names, versions, disks, or paths differ from the lesson.
3.Comments beginning with # explain safety checks and are not executed by the shell.

Watch it run · Robot arm

See what this code does

The terminal types this lesson's practice solution and runs it. The scene shows the kind of robot behaviour that code drives. It plays by itself and loops.

Practice code

Now type it yourself

Open a terminal, run the starter line by line (or save it as practice.sh and run bash practice.sh), and replace every TODO with your own command.

# TODO: start the joint_state_publisher_gui node

Expected output

The sliders window opens and /joint_states is published

Stuck? Show the full solution (try it yourself first)

ros2 run joint_state_publisher_gui joint_state_publisher_gui

Expected result

How you know it worked

Each command completes without an unexplained error.
Your notes contain the command, the important output, and what it proves.

Practical exercise

Apply the lesson

Open the sliders for a two-joint arm, move each joint to both limits, and record the values shown by ros2 topic echo. Confirm the robot in RViz2 respects the limits.

Before you continue

You recorded the starting state
Every command and output is understood
The change can be repeated from your notes

If something goes wrong

A command says permission denied.

Check ownership and permissions first. Do not add sudo unless the command changes a documented system location.

A command or package is not found.

Check spelling, Ubuntu version, enabled repositories, and whether the previous installation command succeeded.