ROS2 Mecabot: A Mecanum Robot Simulation

This is a ROS2 Jazzy based mecanum drive robot project simulated in Gazebo Harmonic with features such as rotary encoder based odometry, PID kinematics control, directed graph map based motion, and A* pathfinding.

Installation

Make sure you have installed ROS2 Jazzy Jalisco, Gazebo Harmonic, common C++ and Python toolchain and the dependencies listed in package.xml in your environment.

1. Clone the repository.
2. Change into the repository home directory, then source the environment.

source install/setup.bash

3. Build the package with colcon.

colcon build --symlink-install

Add this argument if you'd like to use clang for the workspace:

--cmake-args -DCMAKE_EXPORT_COMPILE_COMMANDS=ON

Usage

A few tips here, run the simulator at 0.01s step size otherwise the robot might rotate endlessly during autonomous mode, and set the odometry_worker node to a high priority during runtime to avoid latency in odometry calculations.

There are multiple ways to move/interact with the robot:

• Using /path_command topic to have the robot find the shortest path and move from one landmark/frame in the map to another.
• Using /trajectory_command topic to move the robot in a certain simple trajectory in either absolute or relative coordinate reference.
• Publishing directly to /cmd_vel to control the robot without in an open-loop fashion.
• To change speed, set speed_multiplier parameter of the kinematics_control node to a desired value. Default is 1.

/path_command

This topic uses std_msgs/String interface with my custom format: "start_frame end_frame"

• start_frame should be the robot's current or closest frame.
• end_frame is the goal frame.

Example:

ros2 topic pub /path_command std_msgs/msg/String "{data: 'start end'}" --once

/trajectory_command

This topic uses std_msgs/String interface with my custom format: "trajectory/string_arguments/numeric_arguments"

• trajectory type of trajectory or motion for the robot to execute. Available trajectory(s):
  • point moves robot to a certain coordinate with encoder feedback. Have one string argument with two options: Absolute abs and relative rel coordinate reference. When using abs the input coordinate will be calculated relative to the initial point of the world frame. When using rel the input coordinate will be calculated relative to the robot's current position which is relative to the world frame. It has three numeric arguments: x,y,theta, which are the input coordinates, theta uses radian.
• string_arguments string arguments that are trajectory specific, separated with comma , symbol.
• numeric_arguments numeric (float) arguments that are trajectory specific, separated with comma , symbol.

Example:

(Moves the robot to the input coordinate relative to the world frame.)

ros2 topic pub /trajectory_command std_msgs/msg/String "{data: 'point/abs/2,7,1.57'}"

/cmd_vel

Compatible with the teleop_twist_keyboard executable.

References

These are references and algorithm explanations used in the project.

• Rotary Encoder Based Odometry Youtube: Odometry 101 for FIRST Tech Challenge Robots by DrBatanga
  
• Locomotion Kinematics Youtube: How to Use Mecanum Wheels in 200 Seconds by Gavin Ford
  
• A* Pathfinding Algorithm Youtube: A* Pathfinding (E01: algorithm explanation)