ros_ethercat

Overview

This is a reimplementation of the main loop of pr2_ethercat without dependencies on PR2 software. It was mainly developed to be used by Shadow Robot Company. It may be useful to anyone people that has developed ROS software for their own robot and used etherCAT for communication. Most likely such software would be based on the software for Willow Garage’s PR2. ros_ethercat reuses existing etherCAT drivers (eml package) and instantiates a ros_control controller manager. Part of the software in this repository comes from repositories pr2_mechanism, pr2_robot, pr2_ethercat_drivers. The parts specific to the pr2 robot only have been removed. Therefore, the same license (BSD) has been used.

pr2 packages no longer required

1. ethercat_hardware
2. pr2_bringup
3. pr2_ethercat
4. pr2_mechanism
5. pr2_controller_interface
6. pr2_controller_manager
7. pr2_hardware_interface
8. pr2_mechanism_diagnostics
9. pr2_mechanism_model

You can find the architecture diagram below for a closer look at how this works.

Compatibility

In software with previous pr2 dependencies that is switched to this package, the following modifications are required.

Controllers

1. #include <controller_interface/controller.h>
   instead of
   #include <pr2_controller_interface/controller.h>
2. class MyController : public controller_interface::Controller<ros_ethercat_mechanism_model::RobotState>
   instead of
   class MyController : public pr2_controller_interface::Controller
3. Controller’s update function should be declared as
   virtual void update(const ros::Time&, const ros::Duration&)
   and starting function as
   virtual void starting(const ros::Time& time),br.
4. controller_manager and controller_interface should be used as dependencies in CMakeLists.txt and package.xml files instead of pr2_controller_manager and pr2_controller_interface respectively.
5. In package.xml file in export tag use <controller_interface plugin="${prefix}/controller_plugins.xml"/>
6. In controller_plugins.xml file use base_class_type="controller_interface::ControllerBase" />

launch files

1. Replace pr2_ethercat with ros_ethercat_loop in launch files
2. Since pr2_controller_manager is no longer used, joint_states or mechanism_statistics are no longer published by it. Joint states are now published with the join_state_controller from ros_controllers. To start this controller this line need to be added in the main launch file
   <include file="$(find ros_ethercat_model)/launch/joint_state_publisher.launch"/>
3. calibrate.py file from pr2_bringup is now included in ros_ethercat_model package and renamed to just calibrate according to ROS convention. Launch files that execute calibrate.py should be modified to find it there.

transmissions

Transmissions are still defined in urdf in the pr2 style and inherit from ros_ethercat_model::Transmission. This class will initialize the actuators associated with this transmission.

New features

1. ros_ethercat accepts a new argument --period which is the period of main ethercat loop in msec. If not given the default value is 1ms.
2. There is a helper bash script called ethercat_grant. This will grant to the ros_ethercat_loop executable the ability to be ran from a normal user without root privileges. E.g. of use
   rosrun ros_ethercat_loop ethercat_grant