Creating a URDF File

A URDF (Unified Robot Description Format) file is essential for operating a robot in the ROS ecosystem. It provides information on the robot’s kinematics, dynamics and other parameters in a standardized format.

Note

Due to the modular nature of RobCo robots, a large number of different robot configurations can be assembled from RobCo modules and a pre-configured URDF file cannot be provided. Instead, we provide xacro macros for each of the modules in our catalog. This way, given a robot configuration (list of module type IDs), a URDF file can be easily generated.

Finding Module Type IDs

Each type of RobCo module is assigned a unique numeric module type identifier. To find the module type identifiers that make up the connected robot, the /robco_robot_composition topic can be used:

ros2 topic echo /robco_robot_composition

A list of module type identifiers is returned. This can be used to assemble a URDF file for the connected robot.

Assembling the URDF File

A URDF file of the following form can be created for the above robot configuration as follows:

<?xml version="1.0" ?>

<robot name="robco" xmlns:xacro="http://www.ros.org/wiki/xacro">
   <xacro:include filename="$(find robco_description)/urdf/robco_modules.xacro" />
   <xacro:include filename="$(find robco_description)/urdf/robco.ros2_control.xacro" />

   <!-- Module type IDs: 304, 301, 318, 300, 300, 8, 300, 300, 800 -->
   <xacro:robco_module_0304 name="joint0" next="joint1" />
   <xacro:robco_module_0301 name="joint1" next="link0" />
   <xacro:robco_module_0318 name="link0" next="joint2" />
   <xacro:robco_module_0300 name="joint2" next="joint3" />
   <xacro:robco_module_0300 name="joint3" next="link1" />
   <xacro:robco_module_0008 name="link1" next="joint4" />
   <xacro:robco_module_0300 name="joint4" next="joint5" />
   <xacro:robco_module_0300 name="joint5" next="tool" />
   <xacro:robco_module_0800 name="tool" />

   <!-- ros2_control setup for joints defined above -->
   <ros2_control name="RobcoRobot" type="system">
      <hardware>
         <plugin>robco_hardware/RobcoHardware</plugin>
      </hardware>
      <xacro:robco_ros2_control_joint joint_name="joint0" />
      <xacro:robco_ros2_control_joint joint_name="joint1" />
      <xacro:robco_ros2_control_joint joint_name="joint2" />
      <xacro:robco_ros2_control_joint joint_name="joint3" />
      <xacro:robco_ros2_control_joint joint_name="joint4" />
      <xacro:robco_ros2_control_joint joint_name="joint5" />
   </ros2_control>
   </robot>

Running this through xacro will expand the macros provided by the robco_description package, with kinematics, inertia parameters and 3D models for visuals and collisions.

For more details on the provided macros and files, please see robco_description.