Initialization

The ros2_ex package is a ROS 2 metapackage. It uses the Python3 package pyquaterion. To install this package run:

  $ pip3 install pyquaternion

Update the environment variables and after that, compile the project. Run on a terminal:

  $ source <your_ros2_workspace>/install/setup.bash

  $ colcon build --packages-select ros2_ex

With the package compiled, initialize the simulation:

  $ ros2 launch robot_controller robot_simulation_launch.py

Initialize the controllers, running on another terminal:

  $ ros2 launch robot_controller controllers.launch.py 

Using the Package

This package has the implementation of a semi-autonomous differential robot. The robot has 2 modes: teleop_mode and semi_autonomous mode. On the teleop_mode you can control the vehicle using the teleop_twist_keyboard package to send velocities commands to it. On the semi-autonomous mode you can send the command to move the vehicle directly to a specific Pose. On this mode you also has the functionality to move back, in a semi-autonomous way, to a defined start position. Once initialized, the robot starts on the teleop_mode.

As the robot is initialized on the teleop_mode, to control the vehicle, open a terminal and run:

  $ ros2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args --remap cmd_vel:=/teleop/cmd_vel

The --remap argument is important in order to send the command through the correct topic. If the command was not sent through this topic, the vehicle will not move on the teleop_mode.

To switch between the modes, there is a service available with the name /set_semi_autonomous. To enable the semi-autonomous mode, you should call the service sending the resquest.data as True. To send this command you can open another terminal and run:

  $ ros2 service call /set_semi_autonomous example_interfaces/srv/SetBool data: true 

Another possibility is using the rqt gui. On the terminal, run:

  $ rqt

Once the rqt window is opened, add the Service Caller plugin through, Plugins -> Service -> Service Caller. With the Service Caller plugin added, select the /set_semi_autonomous service, change the data area to True and press the Call button.

To change from semi_autonomous mode to teleop_mode the process is the same. Although, the request.data should be sent as False.

The robot also has the functionality of record a path and drive back through this path to the initial position. First, it is necessary to record the path. To start the recording, there is another service called /start_tracking. To enable the recording, call the service running on a terminal:

  $ ros2 service call /start_tracking example_interfaces/srv/SetBool data: true 

As explained on the /set_semi_autonomous service, this service can, also, be called using rqt. To disable the path tracking, just call the /start_tracking service passing the request.data as False.

Now that you have your path recorded you MUST set the mode to semi_autonomous mode and call the /go_home service running this command on the terminal:

  $ ros2 action send_goal /go_home robot_controller/action/GoHome start: true  

The robot should start moving back on the recorded path to the position where you started the /start_tracking.