Running your robot with Gazebo

GRIP features a simulation mode that allows you to quickly make sure that what you want to deploy works properly. We are going to explain in this page how to make sure you can use it with your robot. GRIP relies on Gazebo, which is natively installed with ROS.
Disclaimer: The purpose of the simulation mode is mainly to make sure all components work as expected, not to provide a high performance simulation environment to develop new methods!

Before starting

For now, the simulated controllers to actuate the joints of your robot must compatible with the ROS control framework. So if you want to integrate your own controller, please follow this tutorial.
Please note that you must have a MoveIt! configuration package for your robot to use GRIP’s simulation mode. If you don’t have one, you can find more details about how to create one here.
You also must have Gazebo description files (i.e. a .world file as well as a folder containing meshes and description of the objects to be spawned). If you need further information, see here.

Make your package Gazebo-compatible

In order to use ROS controllers with your robot, you need to add some elements to your urdf.xacro file. Gazebo uses a specific element that links actuators to joints, called <transmission>. Each of these elements must contain at least:

  • <joint name= >: which corresponds to the name of a defined joint in your urdf file that you want Gazebo to be able to actuate.

  • <type>transmission_interface/SimpleTransmission</type>: which specifies the type of transmission. More information here.

  • <hardwareInterface> that should be present in both <joint> and <actuator> tags. It makes the gazebo_ros_control plugin aware of which hardware interface to load (position, velocity or effort interfaces).

The last step is to add the gazebo_ros_control plugin to the URDF file. The plugin should look like this: .. code-block:: xml

<gazebo>
<plugin name=”gazebo_ros_control” filename=”libgazebo_ros_control.so”>

<!– Optional - Default being the value of robot name in the urdf/sdf file–> <robotNamespace>my_name_space</robotNamespace> <!– Optional - The period of the controller update (in seconds), default is Gazebo’s period –> <controlPeriod>my_value</controlPeriod> <!– Optional - The location of the robot_description (URDF) on the parameter server, default being ‘/robot_description’ –> <robotParam>my_param_value</robotParam> <!– Optional - The pluginlib name of a custom robot sim interface to be used (see below for more details), default being ‘gazebo_ros_control/DefaultRobotHWSim’ –> <robotSimType>my_value</robotSimType>

</plugin>

</gazebo>

You can find examples of URDF files containing these modifications here, here and here.

Set the simulation parameters

  1. Start GRIP: roslaunch grip_api start_framework.launch

  2. Leave simulation ticked

  3. Specify the Gazebo world file

  4. Specify the associated folder containing all the models to be spawned

  5. If you want your robot to start in a specific joint states, you can define it in the Starting pose edit line (optional). The input must respect this formatting: -J <joint_name1> <value> -J <joint_name2> <value>, as shown in the following image.

../_images/simulation_example.png

Now, if you follow this tutorial, you should be able to run your robot in simulation with Gazebo.