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Version: ROS 2 Jazzy

Extras

Despite all current customization options, we still would like our users to be able to add-in their existing custom URDF to the robot platform URDF and pass in and overwrite parameters to all platform nodes. Extras have the following entries:

  • urdf:
    • path: relative path within the package or absolute path to robot extras URDF
    • package: name of the ROS 2 package that contains the extras URDF (optional)
  • launch: a list of objects containing
    • path: relative path within the package or absolute path to robot extras launch file
    • package: name of the ROS 2 package that contains the extras launch file (optional)
    • args: launch arguments to pass to the launch file when it is started (optional)
  • ros_parameters: in YAML to pass in parameters to platform nodes. This is useful to change parameters such as the robot's velocity and acceleration.
extras:
  urdf:
    package: package_name
    path: relative/path/to/urdf/in/package.urdf.xacro # or can contain /absolute/path/to/urdf.urdf.xacro
  launch:
    - package: package_name
      path: relative/path/to/launch/in/package.launch.py
  ros_parameters: {} # node parameters, see below
note

Remember, absolute paths start with / and relative paths do not.

note

If your extras file is in a ROS package built from source in a workspace, make sure to add the workspace to robot.yaml by adding it to system.ros2.workspaces.

URDF Extras​

If an extras.urdf is specified, it is included as part of the robot_description. The specified URDF file can either be an absolute path on the robot's filesystem or a relative path within a ROS package:

Absolute path

platform:
  extras:
    urdf:
      path: /home/robot/my_urdf_extras.urdf.xacro

Relative path within a ROS package

platform:
  extras:
    urdf:
      package: my_robot_extras
      path: urdf/my_urdf_extras.urdf.xacro

URDF Extras Example​

note

This example assumes you are modifying robot.yaml on a physical robot. The same process will also work if you are using a simulation.

1. Create your URDF file

First, create a URDF file and save it on the robot. This example adds a simple cylindrical antenna:

<?xml version="1.0" ?>
<robot xmlns:xacro="http://wiki.ros.org/xacro">
  <link name="my_antenna">
    <visual>
      <geometry>
        <cylinder radius="0.01" length="0.4" />
      </geometry>
      <material name="grey">
        <color rgba="0.6 0.6 0.6 1.0" />
      </material>
      <origin xyz="0.0 0.0 0.2" rpy="0.0 0.0 0.0" />
    </visual>
    <collision>
      <geometry>
        <cylinder radius="0.01" length="0.4" />
      </geometry>
      <origin xyz="0.0 0.0 0.2" rpy="0.0 0.0 0.0" />
    </collision>
  </link>
  <joint name="my_antenna_joint" type="fixed">
    <parent link="default_mount" />
    <child link="my_antenna" />
    <origin xyz="-0.2 0.1 0.0" rpy="0.0 0.0 0.0" />
  </joint>
</robot>

Save this file as /home/robot/my_antenna.urdf.xacro on the robot.

2. Modify robot.yaml

Add the following to robot.yaml:

platform:
  extras:
    urdf:
      path: /home/robot/my_antenna.urdf.xacro

The robot's URDF will now include the antenna, as shown in the image below:

Husky A300 modified with the my_antenna custom URDF

Extras Launch​

The launch files specified in this section are started as part of the clearpath-platform-extras.service job. Each launch file can be specified either as an absolute path or as a relative path within a package. Additionally, launch arguments may be specified with the args field:

platform:
  extras:
    launch:
      - path: /absolute/path/to/some/file.launch.py
      - path: launch/my_launch_file.launch.py
        package: my_package
      - path: launch/my_launch_with_args.launch.py
        package: my_other_package
        args:
          spam: eggs
          foo: bar

The three launches above are equivalent to the following command-line invocations:

ros2 launch /absolute/path/to/some/file.launch.py

ros2 launch my_package launch/my_launch_file.launch.py

ros2 launch my_other_package launch/my_launch_with_args.launch.py spam:=eggs foo:=bar
note

In 2.7.x and earlier extras.launch only supported a single launch file:

platform:
  extras:
    path: launch/my_launch_file.launch.py
    package: my_package

If your robot.yaml file contains the old format you will see a deprecation notice. We recommend updating your robot.yaml to the new format by converting extras.launch to a list.

To check the status of the extras launch, run

systemctl status clearpath-platform-extras.service

To view the raw output from the extras launch, run

sudo journalctl -fu clearpath-platform-extras.service

ROS Parameters​

A common use case is to set and update the parameters to the platform_velocity_controller node. These can be used to modify the linear and angular velocity and acceleratation.

These can be passed in as follows:

A200 Husky Controller Defaults:

platform:
  extras:
    ros_parameters:
      platform_velocity_controller:
        wheel_radius: 0.1651
        linear.x.max_velocity: 1.0
        linear.x.min_velocity: -1.0
        linear.x.max_acceleration: 3.0
        linear.x.min_acceleration: -3.0
        angular.z.max_velocity: 2.0
        angular.z.min_velocity: -2.0
        angular.z.max_acceleration: 6.0
        angular.z.min_acceleration: -6.0
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