How To Move Turtlebot3 Without Diff_drive_controller

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Introduction

In this article, we will explore the process of moving a Turtlebot3 without using the diff_drive_controller. This is a common requirement in robotics and autonomous systems, where the standard diff_drive_controller may not be suitable for certain applications. We will use ROS2 Humble, Gazebo, and the Turtlebot3 Burger model to demonstrate this process.

Understanding the Problem

The diff_drive_controller is a widely used controller in ROS2 for differential drive robots like the Turtlebot3. However, in certain situations, we may need to move the robot without using this controller. This could be due to various reasons such as:

  • Customized motion planning: We may need to implement a customized motion planning algorithm that doesn't rely on the diff_drive_controller.
  • Alternative control methods: We may want to use alternative control methods such as PID control, model predictive control, or other advanced control techniques.
  • Simulation and testing: We may need to simulate and test the robot's motion in a virtual environment without using the diff_drive_controller.

Preparing the Environment

To move the Turtlebot3 without using the diff_drive_controller, we need to prepare the environment first. We will use ROS2 Humble, Gazebo, and the Turtlebot3 Burger model for this demonstration.

Step 1: Install ROS2 Humble

First, we need to install ROS2 Humble on our system. We can do this by following the official installation instructions for ROS2 Humble.

Step 2: Install Gazebo

Next, we need to install Gazebo, a popular robotics simulator. We can do this by following the official installation instructions for Gazebo.

Step 3: Create a New Workspace

After installing ROS2 Humble and Gazebo, we need to create a new workspace. We can do this by running the following command:

mkdir -p ~/turtlebot3_ws/src
cd ~/turtlebot3_ws/src

Step 4: Clone the Turtlebot3 Package

Next, we need to clone the Turtlebot3 package from the official repository. We can do this by running the following command:

git clone https://github.com/ros2/turtlebot3.git

Step 5: Build the Turtlebot3 Package

After cloning the Turtlebot3 package, we need to build it. We can do this by running the following command:

cd ~/turtlebot3_ws
colcon build --symlink-install

Modifying the SDF File

To move the Turtlebot3 without using the diff_drive_controller, we need to modify the SDF file. The SDF file is used to define the robot's model and its components.

Step 1: Locate the SDF File

First, we need to locate the SDF file. We can do this by navigating to the turtlebot3_burger package and looking for the model.sdf file.

Step 2: Delete the Diff Drive Plugin

Next, we need to delete the diff drive plugin from the SDF file. We can do this by commenting out the following lines:

<plugin name="diff_drive_controller" filename="libdiff_drive_controller.so">
    <rosparam param="~type">diff_drive</rosparam>
    <rosparam param="~left_wheel_joint">left_wheel</rosparam>
    <rosparam param="~right_wheel_joint">right_wheel</rosparam>
    <rosparam param="~left_wheel_radius">0.035</rosparam>
    <rosparam param="~right_wheel_radius">0.035</rosparam>
    <rosparam param="~wheel_separation">0.35</rosparam>
    <rosparam param="~wheel_circumference">0.111</rosparam>
    <rosparam param="~max_translational_velocity">0.5</rosparam>
    <rosparam param="~max_rotational_velocity">1.0</rosparam>
    <rosparam param="~publish_rate">20</rosparam>
    <rosparam param="~odom_topic">odom</rosparam>
    <rosparam param="~base_frame_id">base_footprint</rosparam>
    <rosparam param="~child_frame_id">odom</rosparam>
</plugin>

Creating a Custom Controller

To move the Turtlebot3 without using the diff_drive_controller, we need to create a custom controller. We can do this by creating a new C++ node that publishes the robot's velocity commands.

Step 1: Create a New C++ Node

First, we need to create a new C++ node. We can do this by running the following command:

ros2 pkg create turtlebot3_custom_controller

Step 2: Define the Controller

Next, we need to define the controller. We can do this by creating a new C++ file called controller.cpp and adding the following code:

#include <ros2_control/controller_interface.hpp>
#include <ros2_control/effort_controllers/effort_controllers.hpp>
#include <ros2_control/joint_trajectory_controller/joint_trajectory_controller.hpp>

class CustomController : public controller_interface::ControllerInterface 
public
CustomController() : joint_(0.0) {


void update(const rclcpp::Time &amp;time, const rclcpp::Duration &amp;period) override {
    // Publish the robot&#39;s velocity commands
    joint_.set_velocity(0.5);
}



private:
double joint_;
};

Step 3: Register the Controller

Next, we need to register the controller. We can do this by adding the following code to the controller.cpp file:

RCLCPP_COMPONENTS_REGISTER_CONTROLLER(CustomController, custom_controller);

Running the Simulation

To run the simulation, we need to launch the Gazebo simulator and the Turtlebot3 node. We can do this by running the following command:

ros2 launch turtlebot3_burger launch/turtlebot3.launch.py

Conclusion

In this article, we demonstrated how to move a Turtlebot3 without using the diff_drive_controller. We modified the SDF file to delete the diff drive plugin and created a custom controller to publish the robot's velocity commands. We also ran the simulation using Gazebo and the Turtlebot3 node. This is a common requirement in robotics and autonomous systems, where the standard diff_drive_controller may not be suitable for certain applications.

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Q: What is the diff_drive_controller and why is it used?

A: The diff_drive_controller is a widely used controller in ROS2 for differential drive robots like the Turtlebot3. It is used to control the robot's movement by publishing velocity commands to the left and right wheels.

Q: Why would I want to move the Turtlebot3 without using the diff_drive_controller?

A: There are several reasons why you may want to move the Turtlebot3 without using the diff_drive_controller. Some of these reasons include:

  • Customized motion planning: You may need to implement a customized motion planning algorithm that doesn't rely on the diff_drive_controller.
  • Alternative control methods: You may want to use alternative control methods such as PID control, model predictive control, or other advanced control techniques.
  • Simulation and testing: You may need to simulate and test the robot's motion in a virtual environment without using the diff_drive_controller.

Q: How do I modify the SDF file to delete the diff drive plugin?

A: To modify the SDF file, you need to locate the model.sdf file in the turtlebot3_burger package and comment out the lines that define the diff drive plugin.

Q: What is a custom controller and how do I create one?

A: A custom controller is a C++ node that publishes the robot's velocity commands. To create a custom controller, you need to create a new C++ node and define the controller's behavior.

Q: How do I register the custom controller?

A: To register the custom controller, you need to add the following code to the controller.cpp file:

RCLCPP_COMPONENTS_REGISTER_CONTROLLER(CustomController, custom_controller);

Q: How do I run the simulation?

A: To run the simulation, you need to launch the Gazebo simulator and the Turtlebot3 node using the following command:

ros2 launch turtlebot3_burger launch/turtlebot3.launch.py

Q: What are some common issues that I may encounter when moving the Turtlebot3 without using the diff_drive_controller?

A: Some common issues that you may encounter when moving the Turtlebot3 without using the diff_drive_controller include:

  • Velocity commands not being published: Make sure that the custom controller is publishing the velocity commands correctly.
  • Robot not moving: Make sure that the custom controller is publishing the correct velocity commands and that the robot's joints are properly configured.
  • Simulation not running: Make sure that the Gazebo simulator is running correctly and that the Turtlebot3 node is launched properly.

Q: How do I troubleshoot issues with the custom controller?

A: To troubleshoot issues with the custom controller, you can use the following steps:

  • Check the velocity commands: Make sure that the custom controller is publishing the correct velocity commands.
  • Check the robot's joints: Make sure that the robot's joints are properly configured and that the custom controller is publishing the correct velocity commands.
  • Check the simulation: Make sure that the Gazebo simulator is running correctly and that the Turtlebot3 node is launched properly.

Q: Can I use the custom controller with other robots?

A: Yes, you can use the custom controller with other robots. However, you may need to modify the controller's behavior to suit the specific robot's requirements.

Q: How do I contribute to the ROS2 community?

A: To contribute to the ROS2 community, you can:

  • Submit bug reports: Report any bugs or issues that you encounter while using the custom controller.
  • Submit pull requests: Submit pull requests to the ROS2 repository to contribute to the development of the custom controller.
  • Participate in discussions: Participate in discussions on the ROS2 forums and mailing lists to share your knowledge and experience with the custom controller.