ROS 2 Lyrical lab 07 · 2 hours

tf2, URDF and xacro

Describe a small arm, publish its state and verify every coordinate frame.

Before you start

Lab 06 complete
Radians and coordinate frames

Files you will touch

src/training_arm_description/urdf/training_arm.urdf.xacro
src/training_arm_description/launch/display.launch.py

Step 1

Set up

sudo apt install ros-lyrical-tf2-tools ros-lyrical-robot-state-publisher ros-lyrical-joint-state-publisher-gui ros-lyrical-rviz2

Step 2

Create the file

<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="training_arm">
  <link name="base_link"/>
  <link name="tool0"/>
  <joint name="tool_joint" type="fixed">
    <parent link="base_link"/><child link="tool0"/>
    <origin xyz="0 0 0.5" rpy="0 0 0"/>
  </joint>
</robot>

Step 3

Build, run and inspect

ros2 launch training_arm_description display.launch.py
ros2 run tf2_ros tf2_echo base_link tool0
ros2 run tf2_tools view_frames

Proof that it works

RViz shows the model without TF errors
tf2_echo reports the 0.5 m transform
view_frames creates a connected frame tree

Recovery notes

Every non-root link must have exactly one parent joint.
Use SI units: metres, kilograms, seconds and radians.

ROS 2 URDF tutorials