Accessing the ronex data directly from a controller

This tutorial shows how you can access RoNex data directly from a controller.

As input, we use here a potentiometer (a three-terminal resistor with a sliding contact that forms an adjustable voltage divider). And it is connected to the first analogue sampling channel (i.e., index 0) on the General I/O module with alias "test_ronex".

Files belonging to this tutorial can be found in the sr_ronex_examples package.

• model/simple_robot.urdf: a description of the robot.
• launch/sr_ronex_simple_controller.launch: a launch file to start the drivers, the controllers, and a few utils.
• config/data_access_controller.yaml: the parameter settings.
• controller_plugins.xml: the plugin settings.

For a detailed desription of how these files are use, please read this tutorial: Control a Joint Based Robot with RoNeX.

The code

Change directories to your sr_ronex_examples package.

$ roscd sr_ronex_examples/
$ cd src
$ pwd

C++ header file sr_ronex_simple_controller.hpp is located inside the include/sr_ronex_examples directory.

/*
 * Copyright (c) 2013, Shadow Robot Company, All rights reserved.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3.0 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library.
 */

/**
 * @file   sr_ronex_simple_controller.hpp
 * @author Yi Li <[email protected]>
 * @brief  Access RoNeX data directly from the controller.
 **/

#ifndef _SR_RONEX_SIMPLE_CONTROLLER_HPP_
#define _SR_RONEX_SIMPLE_CONTROLLER_HPP_

#include <ros/node_handle.h>

#include <pr2_controller_interface/controller.h>
#include <sr_ronex_hardware_interface/mk2_gio_hardware_interface.hpp>
#include <realtime_tools/realtime_publisher.h>
#include <sr_ronex_utilities/sr_ronex_utilities.hpp>

#include <std_msgs/Bool.h>
#include <sr_ronex_msgs/PWM.h>

namespace ronex
{
  class SrRoNeXSimpleController 
    : public pr2_controller_interface::Controller
  {
  public:
    SrRoNeXSimpleController();
    virtual ~SrRoNeXSimpleController();

    virtual bool init(pr2_mechanism_model::RobotState* robot, ros::NodeHandle &n);

    virtual void starting();

    virtual void update();

    virtual void stopping();

  private:
    int loop_count_;

    ronex::GeneralIO* general_io_;
  };
}

#endif /* _SR_RONEX_SIMPLE_CONTROLLER_HPP_ */

C++ source file sr_ronex_simple_controller.cpp is located inside the src directory.

/*
 * Copyright (c) 2013, Shadow Robot Company, All rights reserved.
 * 
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 3.0 of the License, or (at your option) any later version.
 * 
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
 * Lesser General Public License for more details.
 * 
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library.
 */

/**
 * @file   sr_ronex_simple_controller.cpp
 * @author Yi Li <[email protected]>
 * @brief  Access RoNeX data directly from the controller.
 **/

#include "sr_ronex_examples/sr_ronex_simple_controller.hpp"
#include "pluginlib/class_list_macros.h"

PLUGINLIB_EXPORT_CLASS( ronex::SrRoNeXSimpleController, pr2_controller_interface::Controller)

namespace ronex
{
SrRoNeXSimpleController::SrRoNeXSimpleController()
  : loop_count_(0)
{
}

SrRoNeXSimpleController::~SrRoNeXSimpleController()
{
}

bool SrRoNeXSimpleController::init(pr2_mechanism_model::RobotState* robot, ros::NodeHandle &n)
{
  assert (robot);
  
  std::string path("/ronex/general_io/test_ronex");
  general_io_ = static_cast<ronex::GeneralIO*>( robot->model_->hw_->getCustomHW(path) );
  if( general_io_ == NULL)
  {
    ROS_ERROR_STREAM("Could not find RoNeX module (i.e., test_ronex). The controller is not loaded.");
    return false;
  }
  
  return true;
}

void SrRoNeXSimpleController::starting()
{
  // Do nothing.
}

void SrRoNeXSimpleController::update()
{
  double position = general_io_->state_.analogue_[0];
  if (loop_count_++ % 100 == 0)
  {
    ROS_INFO_STREAM( "Position = " << position );
    loop_count_ = 0;
  }
}

void SrRoNeXSimpleController::stopping() 
{
  // Do nothing.
} 

}

The Code Explained

First we look for General I/O module "test_ronex".

bool SrRoNeXSimpleController::init(pr2_mechanism_model::RobotState* robot, ros::NodeHandle &n)
{
  assert (robot);
  
  std::string path("/ronex/general_io/test_ronex");
  general_io_ = static_cast<ronex::GeneralIO*>( robot->model_->hw_->getCustomHW(path) );
  if( general_io_ == NULL)
  {
    ROS_ERROR_STREAM("Could not find RoNeX module (i.e., test_ronex). The controller is not loaded.");
    return false;
  }
  
  return true;
}

If the module is found, we repeatedly read the data from the first analogue sampling channel and output it to the console.

void SrRoNeXSimpleController::update()
{
  double position = general_io_->state_.analogue_[0];
  if (loop_count_++ % 100 == 0)
  {
    ROS_INFO_STREAM( "Position = " << position );
    loop_count_ = 0;
  }
}