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XACRO

Xacro (XML Macros) Xacro is an XML macro language. With xacro, you can construct shorter and more readable XML files by using macros that expand to larger XML expressions. more

Install ROS support

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sudo apt install ros-humble-xacro

Usage

cli

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xacro hello.urdf.xacro > hello.urdf

launch file

  • Load and procee xacro file
  • Run robot_state_publisher to publish robot_description topic
  • Run joint_state_publisher_gui to publish TF's
  • Run rviz to view the robot
load xacro and view in rviz
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import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch.substitutions import PathJoinSubstitution
from launch_ros.actions import Node
import xacro

PKG_BRINGUP = "self_balancing_bringup"
PKG_DESCRIPTION = "self_balancing_description"
ROBOT = "robot.urdf"

URDF = "urdf"
CONFIG = "config"


def generate_launch_description():
    ld = LaunchDescription()

    pkg_path = os.path.join(get_package_share_directory(PKG_DESCRIPTION))
    xacro_file = os.path.join(pkg_path, URDF, ROBOT)
    robot_description_config = xacro.process_file(xacro_file).toxml()
    params = {"robot_description": robot_description_config, "use_sim_time": True}

    node_robot_state_publisher = Node(
        package="robot_state_publisher",
        executable="robot_state_publisher",
        output="screen",
        parameters=[params],
    )

    node_state_publisher_gui = Node(
        package="joint_state_publisher_gui",
        executable="joint_state_publisher_gui",
        output="screen",
    )

    rviz_node = Node(
        package="rviz2",
        executable="rviz2",
        name="rviz2",
        output="screen",
        arguments=[
            "-d",
            PathJoinSubstitution(
                [get_package_share_directory(PKG_BRINGUP), CONFIG, "display.rviz"]
            ),
        ],
    )

    ld.add_action(node_robot_state_publisher)
    ld.add_action(node_state_publisher_gui)
    ld.add_action(rviz_node)
    return ld

XACRO terms

Recommend xacro layout

  • robot.urdf.xacro: main xacro file
  • gazebo.xacro: all gazebo stuff
  • control.xacro: ros2 control
  • materials.xacro
  • macros.xacro
  • inertial.xacro
robot.urdf.xacro
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<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="my_robot">
  <xacro:include filename="gazebo.xacro"/>
  <xacro:include filename="control.xacro"/>

  <xacro:property name="a" value="0.1" />
</robot>
gazebo.xacro
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<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
  <gazebo reference="imu_link">
        <sensor name="link2_imu" type="imu">
            <always_on>1</always_on>
            <update_rate>50</update_rate>
            <visualize>true</visualize>
            <topic>imu-control</topic>
            <enable_metrics>true</enable_metrics>
        </sensor>
    </gazebo>


</robot>

tag

materials.xacro
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<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
  <material name="white">
        <color rgba="1 1 1 1"/>
    </material>

    <material name="orange">
        <color rgba="1 0.3 0.1 1"/>
    </material>

    <material name="blue">
        <color rgba="0.2 0.2 1 1"/>
    </material>

</robot>
inertial.xacro
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<robot xmlns:xacro="http://www.ros.org/wiki/xacro">
  <xacro:macro name="inertial_sphere" params="mass radius *origin">
        <inertial>
            <xacro:insert_block name="origin"/>
            <mass value="${mass}" />
            <inertia ixx="${(2/5) * mass * (radius*radius)}" ixy="0.0" ixz="0.0"
                    iyy="${(2/5) * mass * (radius*radius)}" iyz="0.0"
                    izz="${(2/5) * mass * (radius*radius)}" />
        </inertial>
    </xacro:macro>  


    <xacro:macro name="inertial_box" params="mass x y z *origin">
        <inertial>
            <xacro:insert_block name="origin"/>
            <mass value="${mass}" />
            <inertia ixx="${(1/12) * mass * (y*y+z*z)}" ixy="0.0" ixz="0.0"
                    iyy="${(1/12) * mass * (x*x+z*z)}" iyz="0.0"
                    izz="${(1/12) * mass * (x*x+y*y)}" />
        </inertial>
    </xacro:macro>


    <xacro:macro name="inertial_cylinder" params="mass length radius *origin">
        <inertial>
            <xacro:insert_block name="origin"/>
            <mass value="${mass}" />
            <inertia ixx="${(1/12) * mass * (3*radius*radius + length*length)}" ixy="0.0" ixz="0.0"
                    iyy="${(1/12) * mass * (3*radius*radius + length*length)}" iyz="0.0"
                    izz="${(1/2) * mass * (radius*radius)}" />
        </inertial>
    </xacro:macro>
</robot>

Reference