Understanding pr2_mechanism packages

The pr2_mechanism stack contain packages for writing ROS real-time controllers. The first package that we are going to discuss is the pr2_controller_interface package.

pr2_controller_interface package

A basic ROS real-time controller must inherit a base class called pr2_controller_interface::Controller from this package. This base class contains four important functions: init() , start(), update(), and stop(). The basic structure of the Controller class is given as follows:

namespace pr2_controller_interface
{
  class Controller
  {
  public:
    virtual bool init(pr2_mechanism_model::RobotState *robot,
                     ros::NodeHandle &n);
    virtual void starting();
    virtual void update();
    virtual void stopping();
  };
}

The workflow of the controller class is shown as follows.

Figure 1: Workflow of the controller

Initialization of the controller

The first function executing when a controller is loaded is init(). The init() function will...