Caffeine Robot Description File Structure

Written by: KJ

Familiarity with URDF, xacro and Gazebo plugins is assumed. See the following resources if necessary:

• On URDF + xacro
• On Gazebo plugins

Make sure you clone the necessary repository, and then source your work space before proceeding.

1. Terminal line commands relevant to this package

• Use the following command to launch caffeine in Gazebo:

roslaunch caffeine_description caffeine_gazebo.launch

• Use the following command to launch caffeine in rviz (this should be done after launching in Gazebo usually):

roslaunch caffeine_description caffeine_rviz.launch

These are the two main commands that you will use.

2. File structure

• /launch contains all the launch files necessary for running caffeine

• /urdf contains all the urdf and mesh files for caffeine

• /rviz contains the rviz configuration file used in caffeine_rviz.launch

3. Describing the files within the urdf folder

• The meshes folder contains .stl or .dae mesh files that are used in the robot. These are simply just CAD files of links (i.e. the houkyo laser).

• The constants.xacro file simply contains definitions for all the constants used.

• The inertias.xacro contain xacro macros defining methods to calculate moment of inertia tensors.

• The caffeine.urdf.xacro file contains the description of the robot

• The caffeine.urdf.gazebo file contains configurations necessary for Gazebo (e.g. giving laser scan, cmd_vel, etc)

4. More details on caffeine.urdf.xacro

Within this file, the base link is called base_link. This can be seen as the main reference frame of our robot. Afterwards, links and joints are defined.

Note: For the hokuyo sensor, it should be noted it's rotated in such a way so that the blind spot of the hokuyo sensor is facing the stand of the robot.

Note 2: Currently, the transmissions for the wheels use effort controllers. This shouldn't matter too much, but should be noted if it comes up.

5. More details on caffeine.gazebo.xacro

This file contains 3 main plugins.

The first one is ros_control. This is necessary to include to interface between ros and gazebo.

The second one is the differential drive plugin. This is used to create an the /odom topic, as well as an odom frame. Furthermore, this plugin gives us access to the /cmd_vel topic. Fundamentally, this plugin is used to move the robot.

The final plugin is the laser scan plugin. This is used to give us the /scan topic. This plugin basically allows our hokuyo sensor link to act as an actual sensor, and scan for things.