Differential Drive Robot Gazebo Simulation

A ROS 2 package for simulating and controlling a differential drive robot. This repository includes everything needed to get started with differential drive robots in ROS 2, from URDF modeling and Gazebo simulation to navigation and control.

• Differential Drive Kinematics
• Installation & Launch
• Mapping with Nav2
• A* Path Planner
• Pure Pursuit Path Tracking
• Dependencies
• References

Differential Drive Kinematics

The main concept of differential drive is to rotate around the ICC (Instantaneous Center of Curvature) point with the left and right wheel speed.

• ICC: Instantaneous Center of Curvature.
• ω: Rotation about the ICC.
• L: Distance between the centers of the two wheels.
• Vr: Right wheel velocity along the ground.
• Vl: Left wheel velocity along the ground.
• R: Distance from ICC to the midpoint between the wheels.

$$ \omega (R + L/2) = Vr \\ $$

$$ \omega (R - L/2) = Vl \\ $$

$$ R = \frac{L}{2} \frac{Vl + Vr}{Vr + Vl} \quad \\ \text{and} \\ \quad \omega = \frac{Vr - Vl}{L} $$

• If Vl=Vr, robot move forward linear motion in a straght line. (R=∞)
• If Vl=-Vr, robot rotate its around. (R=0)
• If Vl>Vr, robot rotates right otherwise rotates left.

Installation & Launch

cd ~/ros2_ws/src/
git clone https://github.com/gurselturkeri/ros2_diff_drive_robot.git
mv ros2_diff_drive_robot diff_robot

colcon build

ros2 launch diff_robot robot.launch.py

cd ~/ros2_ws/src/diff_robot
chmod +x start.sh
./start.sh

Mapping with Nav2

Used Nav2 package to generate .pgm format map.

Add “use_sim_time:=True” to use the Gazebo time. If using the real robot, skip this argument.

ros2 launch nav2_bringup navigation_launch.py use_sim_time:=True

Same as previous code.

ros2 launch slam_toolbox online_async_launch.py use_sim_time:=True

So we need move our robot to discover map.

python3 ~/ros2_ws/src/diff_robot/control/keyboard_control.py

Once you get a good enough looking map, you can save it.

ros2 run nav2_map_server map_saver_cli -f my_map

A* Path Planner

Pure Pursuit Path Tracking

Dependencies

sudo apt install ros-humble-gazebo-ros-pkgs ros-humble-gazebo-ros2-control ros-humble-ros2-control ros-humble-ros2-controllers ros-humble-diff-drive-controller ros-humble-joint-state-broadcaster ros-humble-effort-controllers ros-humble-velocity-controllers ros-humble-position-controllers ros-humble-teleop-twist-keyboard ros-humble-rviz2 ros-humble-robot-state-publisher

sudo apt install ros-humble-nav2-bringup ros-humble-nav2-core ros-humble-nav2-common ros-humble-nav2-amcl ros-humble-nav2-behavior-tree ros-humble-nav2-bt-navigator ros-humble-nav2-costmap-2d ros-humble-nav2-dwb-controller ros-humble-nav2-map-server ros-humble-nav2-planner ros-humble-nav2-simple-commander ros-humble-nav2-smac-planner ros-humble-nav2-util ros-humble-nav2-waypoint-follower ros-humble-slam-toolbox ros-humble-nav2-msgs

References

Dudek, G., & Jenkin, M. (2010). Computational Principles of Mobile Robotics (2nd ed.). Cambridge: Cambridge University Press.

https://roboticsbackend.com/