ROS2 Control Demos diffbot hardware interface publisher. Useful for micro-ROS hardware control.

diffbot_system.cpp

// Copyright 2021 ros2_control Development Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.


/*ROS2 Control Demos diffbot hardware interface publisher. My use-case is sending hardware commands from a Raspberry Pi 4 running a diffrential drive robot controller to a Teensy 4.1 microcontroller controlling the actual hardware. The Teensy is running micro-ROS and can subscribe and publish to topics over a USB connection to the Raspberry Pi. The important change between this gist and the official demos is the presence of a node class, and the addition of a shared pointer member for the node in DiffBotSystemHardware. The shared pointer gets assigned in the on_init() member function, at which point its publisher can be used.
*/

#include "ros2_control_demo_hardware/diffbot_system.hpp"

#include <chrono>
#include <cmath>
#include <limits>
#include <memory>
#include <vector>

#include "hardware_interface/types/hardware_interface_type_values.hpp"
#include "rclcpp/rclcpp.hpp"
#include "std_msgs/msg/string.hpp"
#include <rclcpp_components/register_node_macro.hpp>



namespace ros2_control_demo_hardware
{

HardwareCommandPub::HardwareCommandPub() : Node("hardware_command_publisher")
{
  publisher_ = this->create_publisher<std_msgs::msg::String>("test_topic", 10);
}

void HardwareCommandPub::publishData()
{
  auto message = std_msgs::msg::String();
  message.data = "Hello, world! ";
  publisher_->publish(message);
}


CallbackReturn DiffBotSystemHardware::on_init(const hardware_interface::HardwareInfo & info)
{
  base_x_ = 0.0;
  base_y_ = 0.0;
  base_theta_ = 0.0;

  hw_cmd_pub_ = std::make_shared<HardwareCommandPub>();  //fire up the publisher node

  if (hardware_interface::SystemInterface::on_init(info) != CallbackReturn::SUCCESS)
  {
    return CallbackReturn::ERROR;
  }

  // START: This part here is for exemplary purposes - Please do not copy to your production code
  hw_start_sec_ = stod(info_.hardware_parameters["example_param_hw_start_duration_sec"]);
  hw_stop_sec_ = stod(info_.hardware_parameters["example_param_hw_stop_duration_sec"]);
  // END: This part here is for exemplary purposes - Please do not copy to your production code
  hw_positions_.resize(info_.joints.size(), std::numeric_limits<double>::quiet_NaN());
  hw_velocities_.resize(info_.joints.size(), std::numeric_limits<double>::quiet_NaN());
  hw_commands_.resize(info_.joints.size(), std::numeric_limits<double>::quiet_NaN());

  for (const hardware_interface::ComponentInfo & joint : info_.joints)
  {
    // DiffBotSystem has exactly two states and one command interface on each joint
    if (joint.command_interfaces.size() != 1)
    {
      RCLCPP_FATAL(
        rclcpp::get_logger("DiffBotSystemHardware"),
        "Joint '%s' has %zu command interfaces found. 1 expected.", joint.name.c_str(),
        joint.command_interfaces.size());
      return CallbackReturn::ERROR;
    }

    if (joint.command_interfaces[0].name != hardware_interface::HW_IF_VELOCITY)
    {
      RCLCPP_FATAL(
        rclcpp::get_logger("DiffBotSystemHardware"),
        "Joint '%s' have %s command interfaces found. '%s' expected.", joint.name.c_str(),
        joint.command_interfaces[0].name.c_str(), hardware_interface::HW_IF_VELOCITY);
      return CallbackReturn::ERROR;
    }

    if (joint.state_interfaces.size() != 2)
    {
      RCLCPP_FATAL(
        rclcpp::get_logger("DiffBotSystemHardware"),
        "Joint '%s' has %zu state interface. 2 expected.", joint.name.c_str(),
        joint.state_interfaces.size());
      return CallbackReturn::ERROR;
    }

    if (joint.state_interfaces[0].name != hardware_interface::HW_IF_POSITION)
    {
      RCLCPP_FATAL(
        rclcpp::get_logger("DiffBotSystemHardware"),
        "Joint '%s' have '%s' as first state interface. '%s' expected.", joint.name.c_str(),
        joint.state_interfaces[0].name.c_str(), hardware_interface::HW_IF_POSITION);
      return CallbackReturn::ERROR;
    }

    if (joint.state_interfaces[1].name != hardware_interface::HW_IF_VELOCITY)
    {
      RCLCPP_FATAL(
        rclcpp::get_logger("DiffBotSystemHardware"),
        "Joint '%s' have '%s' as second state interface. '%s' expected.", joint.name.c_str(),
        joint.state_interfaces[1].name.c_str(), hardware_interface::HW_IF_VELOCITY);
      return CallbackReturn::ERROR;
    }
  }
  
  return CallbackReturn::SUCCESS;
}

std::vector<hardware_interface::StateInterface> DiffBotSystemHardware::export_state_interfaces()
{
  std::vector<hardware_interface::StateInterface> state_interfaces;
  for (auto i = 0u; i < info_.joints.size(); i++)
  {
    state_interfaces.emplace_back(hardware_interface::StateInterface(
      info_.joints[i].name, hardware_interface::HW_IF_POSITION, &hw_positions_[i]));
    state_interfaces.emplace_back(hardware_interface::StateInterface(
      info_.joints[i].name, hardware_interface::HW_IF_VELOCITY, &hw_velocities_[i]));
  }

  return state_interfaces;
}

std::vector<hardware_interface::CommandInterface> DiffBotSystemHardware::export_command_interfaces()
{
  std::vector<hardware_interface::CommandInterface> command_interfaces;
  for (auto i = 0u; i < info_.joints.size(); i++)
  {
    command_interfaces.emplace_back(hardware_interface::CommandInterface(
      info_.joints[i].name, hardware_interface::HW_IF_VELOCITY, &hw_commands_[i]));
  }

  return command_interfaces;
}

CallbackReturn DiffBotSystemHardware::on_activate(
  const rclcpp_lifecycle::State & /*previous_state*/)
{
  // START: This part here is for exemplary purposes - Please do not copy to your production code
  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Activating ...please wait...");

  for (auto i = 0; i < hw_start_sec_; i++)
  {
    rclcpp::sleep_for(std::chrono::seconds(1));
    RCLCPP_INFO(
      rclcpp::get_logger("DiffBotSystemHardware"), "%.1f seconds left...", hw_start_sec_ - i);
  }
  // END: This part here is for exemplary purposes - Please do not copy to your production code

  // set some default values
  for (auto i = 0u; i < hw_positions_.size(); i++)
  {
    if (std::isnan(hw_positions_[i]))
    {
      hw_positions_[i] = 0;
      hw_velocities_[i] = 0;
      hw_commands_[i] = 0;
    }
  }

  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Successfully activated!");

  return CallbackReturn::SUCCESS;
}

CallbackReturn DiffBotSystemHardware::on_deactivate(
  const rclcpp_lifecycle::State & /*previous_state*/)
{
  // START: This part here is for exemplary purposes - Please do not copy to your production code
  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Deactivating ...please wait...");

  for (auto i = 0; i < hw_stop_sec_; i++)
  {
    rclcpp::sleep_for(std::chrono::seconds(1));
    RCLCPP_INFO(
      rclcpp::get_logger("DiffBotSystemHardware"), "%.1f seconds left...", hw_stop_sec_ - i);
  }
  // END: This part here is for exemplary purposes - Please do not copy to your production code

  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Successfully deactivated!");

  return CallbackReturn::SUCCESS;
}

hardware_interface::return_type DiffBotSystemHardware::read()
{
  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Reading...");

  double radius = 0.02;  // radius of the wheels
  double dist_w = 0.1;   // distance between the wheels
  double dt = 0.01;      // Control period
  for (uint i = 0; i < hw_commands_.size(); i++)
  {
    // Simulate DiffBot wheels's movement as a first-order system
    // Update the joint status: this is a revolute joint without any limit.
    // Simply integrates
    hw_positions_[i] = hw_positions_[1] + dt * hw_commands_[i];
    hw_velocities_[i] = hw_commands_[i];

    // START: This part here is for exemplary purposes - Please do not copy to your production code
    RCLCPP_INFO(
      rclcpp::get_logger("DiffBotSystemHardware"),
      "Got position state %.5f and velocity state %.5f for '%s'!", hw_positions_[i],
      hw_velocities_[i], info_.joints[i].name.c_str());
    // END: This part here is for exemplary purposes - Please do not copy to your production code
  }

  // Update the free-flyer, i.e. the base notation using the classical
  // wheel differentiable kinematics
  double base_dx = 0.5 * radius * (hw_commands_[0] + hw_commands_[1]) * cos(base_theta_);
  double base_dy = 0.5 * radius * (hw_commands_[0] + hw_commands_[1]) * sin(base_theta_);
  double base_dtheta = radius * (hw_commands_[0] - hw_commands_[1]) / dist_w;
  base_x_ += base_dx * dt;
  base_y_ += base_dy * dt;
  base_theta_ += base_dtheta * dt;

  // START: This part here is for exemplary purposes - Please do not copy to your production code
  RCLCPP_INFO(
    rclcpp::get_logger("DiffBotSystemHardware"), "Joints successfully read! (%.5f,%.5f,%.5f)",
    base_x_, base_y_, base_theta_);
  // END: This part here is for exemplary purposes - Please do not copy to your production code

  return hardware_interface::return_type::OK;
}

hardware_interface::return_type ros2_control_demo_hardware::DiffBotSystemHardware::write()
{
  // START: This part here is for exemplary purposes - Please do not copy to your production code
  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Writing...");


  for (auto i = 0u; i < hw_commands_.size(); i++)
  {
    // Simulate sending commands to the hardware
    RCLCPP_INFO(
      rclcpp::get_logger("DiffBotSystemHardware"), "Got command %.5f for '%s'!", hw_commands_[i],
      info_.joints[i].name.c_str());
  }
  RCLCPP_INFO(rclcpp::get_logger("DiffBotSystemHardware"), "Joints successfully written!");
  // END: This part here is for exemplary purposes - Please do not copy to your production code
  
  hw_cmd_pub_->publishData();  //publish to topic
  return hardware_interface::return_type::OK;
}
}  // namespace ros2_control_demo_hardware

#include "pluginlib/class_list_macros.hpp"
PLUGINLIB_EXPORT_CLASS(
  ros2_control_demo_hardware::DiffBotSystemHardware, hardware_interface::SystemInterface)

diffbot_system.hpp

// Copyright 2021 ros2_control Development Team
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

#ifndef ROS2_CONTROL_DEMO_HARDWARE__DIFFBOT_SYSTEM_HPP_
#define ROS2_CONTROL_DEMO_HARDWARE__DIFFBOT_SYSTEM_HPP_

#include <memory>
#include <string>
#include <vector>

#include "hardware_interface/handle.hpp"
#include "hardware_interface/hardware_info.hpp"
#include "hardware_interface/system_interface.hpp"
#include "hardware_interface/types/hardware_interface_return_values.hpp"
#include "rclcpp/rclcpp.hpp"
#include "rclcpp/macros.hpp"
#include "rclcpp_lifecycle/node_interfaces/lifecycle_node_interface.hpp"
#include "rclcpp_lifecycle/state.hpp"
#include "ros2_control_demo_hardware/visibility_control.h"
#include "std_msgs/msg/string.hpp"


#include <geometry_msgs/msg/twist.hpp>

namespace ros2_control_demo_hardware
{

class HardwareCommandPub : public rclcpp::Node  //the node definition for the publisher to talk to micro-ROS agent
{
  public:
    HardwareCommandPub();
    void publishData();

  private:
    rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;

};

class DiffBotSystemHardware : public hardware_interface::SystemInterface
{
public:
  RCLCPP_SHARED_PTR_DEFINITIONS(DiffBotSystemHardware);

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  CallbackReturn on_init(const hardware_interface::HardwareInfo & info) override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  std::vector<hardware_interface::StateInterface> export_state_interfaces() override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  std::vector<hardware_interface::CommandInterface> export_command_interfaces() override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  CallbackReturn on_activate(const rclcpp_lifecycle::State & previous_state) override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  CallbackReturn on_deactivate(const rclcpp_lifecycle::State & previous_state) override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  hardware_interface::return_type read() override;

  ROS2_CONTROL_DEMO_HARDWARE_PUBLIC
  hardware_interface::return_type write() override;

  std::shared_ptr<HardwareCommandPub> hw_cmd_pub_;    //make the publisher node a member

private:
  // Parameters for the DiffBot simulation
  double hw_start_sec_;
  double hw_stop_sec_;

  // Store the command for the simulated robot
  std::vector<double> hw_commands_;
  std::vector<double> hw_positions_;
  std::vector<double> hw_velocities_;

  // Store the wheeled robot position
  double base_x_, base_y_, base_theta_;
};

}  // namespace ros2_control_demo_hardware

#endif  // ROS2_CONTROL_DEMO_HARDWARE__DIFFBOT_SYSTEM_HPP_

Thanks for sharing this! This example got me unstuck.

Hi I get errors related to method overriiding with on_init(), read() and write() functions