Material for the ros2 crash course

Overview

ROS2 Crash course

Task 1 Create your new workspace

mkdir -p /home/usr/ros2/workspaces/ros2_crash_ws/src
cd /home/usr/ros2/workspaces/ros2_crash_ws/src

Task 2 Get teleop ros package and modify it

1) Clone the ros package repo
	cd /home/usr/ros2/workspaces/ros2_crash_ws/src/
	git clone [email protected]:ros2/teleop_twist_keyboard.git
	source /opt/ros/foxy/setup.bash
2) Compile the workspace
	cd /home/usr/ros2/workspaces/ros2_crash_ws/
	colcon build
3) Run the binary teleop_twist_keyboard.py and play with it! 
	ros2 run teleop_twist_keyboard teleop_twist_keyboard

Q1: How can we test our program? Hint: ros topics!

4) Add a customized print message in the file teleop_twist_keyboard.py and run it again

Q2: What happened? Hint: underlay vs overlay

5) Modify the binary teleop_twist_keyboard.py to generate the following motions:

	Linear motions: 

	u: left-front
	i: front
	o: right-front
	j: left
	k: stop
	l: right
	m: left-back
	,: back
	.: right-back

	Angular Motions:
	w: counter-clockwise
	e: stop
	r: clock-wise

	Speed:

	+ increase linear speed +0.1
	- decrease linear speed -0.1
	* increase angular speed +0.1
	/ decrease angular speed -0.1

6) Test your new binary
	Open a new terminal and source your workspace
	cd /home/usr/ros2/workspaces/ros2_crash_ws/
	source install/setup.bash
	ros2 run teleop_twist_keyboard teleop_twist_keyboard --ros-args --remap /cmd_vel:=turtle_twist

Q3: Does it work?

Task 3 Create a new ros2 cpp package named "turtle_msg"

1) Use the ros2 create package function 
	cd /home/usr/ros2/workspaces/ros2_crash_ws/src
	ros2 pkg create --build-type ament_cmake turtle_msgs
2) Compile the workspace
	colcon build --symlink-install --merge-install --cmake-args -DCMAKE_EXPORT_COMPILE_COMMANDS=1

Q4: Any problems? Do you notice any difference with the additional compiling arguments?

3) Add msg/TurtleState.msg and modify CMakeLists.txt, package.xml
4) Compile your workspace
5) Verify that your new message has been created, using ros2 interface.

Q5: Can you find your new message? Hint: overlay

Task 4 Create a new ros2 cpp package "turtle_ctrl"

1) Use the ros2 create package function 
	cd /home/dean/ros2/workspaces/ros2_crash_ws/src
	ros2 pkg create --build-type ament_cmake turtle_ctrl
2) Compile your workspace
3) Copy the TurtleVis class files TurtleVis.h and TurtleVis.cpp to their corresponding folders
4) Modify the CMakeFile to create a shared library with the TurtleVis class
5) Copy the application file turtle_vis.cpp
6) Modify the CMakeFile to create a new binary (Exec)
7) Compile your workspace (or single ros package)
8) Copy the file "turtle.rviz" into turtle_ctr/rviz/turtle.rviz
9) Test your application. You will need 3 terminals
	T1) Run the turtle visualization 
		ros2 run turtle_ctrl turtle_vis
	T2) Run rviz
		ros2 run rviz2 rviz2 -d src/turtle_ctrl/rviz/turtle.rvi
	T3) Publish a TurtleState message and check the rviz window
		ros2 topic pub --rate 1 /turtle_pose turtle_msgs/msg/TurtleStateStamped "{pose: {x: 1, y: 1, theta: 0}}"

Q6: What can you see?

Task 5 Let's create a lunch file to automate the above process

1) Copy the file "turtle_vis_test_launch.py" into the folder turtle_ctrl/launch/
2) Run the new launch file
	ros2 launch turtle_ctrl turtle_vis_test_launch.py

Q7: Does it work? What happened?

Task 6 Create the controller

1) Copy the class files  TurtleCtrl.cpp and TurtleCtrl.h to its corresponding folders
2) Modify the CMakeFile to create a shared library with the control class
3) Copy the application file turtle_control.cpp
4) Modify the CMakeFile to create a new binary (Exec)
5) Compile your workspace (or single ros package) 
6) Test your application
	T1) Copy the launch file turtle_vis_test_launch.py and renamed as turtle_test_launch.py
		Modify the new launch file to include the control node

Q8: How can you test your application?

Task 7 Trajectory generator

We will implement two methods to generate the commanded turtle pose for the controller.
First, transform the Twist (turtle velocity) message generated from the node teleop_twist_keyboard to continuous 
commanded turtle poses. 
Second, we will create a node that provides a service to request a desired turtle pose. This node will use the
requested turtle pose and generate a continuous smooth trajectory for the commanded turtle pose. 
The output of both nodes is a TurtleStateStamped message, which is connected to the controller to change the 
pose of the turtle
1) Create a new ros python package "turtle_trajectory_generator"
	ros2 pkg create --build-type ament_python turtle_trajectory_generator
2) Fix the ros package configuration files to use the new package, e.g. package.xml, resource, setup.py, etc.
3) Copy the file teleop_twist_keyboard.py from the ros package teleop_twist_keyboard to this new package
4) Compile the workspace. This is needed to create the symbolic links to the python files. 
	colcon build --symlink-install --merge-install --cmake-args -DCMAKE_EXPORT_COMPILE_COMMANDS=1
5) Create the trajectory generator module. Use the file trajectory_generator_class.py 
6) Compile again the workspace
7) Create the application nodes
	a) applications/poly_trajectories.py: Generates the smooth trajectory for the commanded turtle pose (TurtleStateStamped message)
	b) applications/twist2cmd.py: Converts from Twist message to commanded turtle pose (TurtleStateStamped message)
8) Compile your workspace 
7) Test your applications

Q9: How can you test the trajectory generator nodes only? Hint: ros2 run rqt_plot rqt_plot Q9: Does it work? Hint: did you configure your setup.py file?

Running Demo

Turtle Ctrl + Vis

T1) cd /home/dean/ros2/workspaces/ros2_crash_ws/

source install/setup.bash

ros2 launch turtle_ctrl turtle_test_launch.py

T2) ros2 topic pub --rate 1 /turtle_pose turtle_msgs/msg/TurtleStateStamped "{pose: {x: 0, y: 1, theta: 0}}"

Turtle Trajectory + Ctrl + Vis

ros2 launch turtle_ctrl turtle_test_launch.py

Keyboard commands (Velocity reference)

T1) ros2 run turtle_trajectory_generator twist2cmd

T2) ros2 run turtle_trajectory_generator teleop_twist_keyboard --ros-args --remap /cmd_vel:=turtle_twist

Spline (Smooth Position Commands)

T1) ros2 run turtle_trajectory_generator poly_trajectory

T2) ros2 service call /set_desired_pose turtle_msgs/srv/SetDesiredPose "{ turtle_d:{x: 1, y: 0, theta: 0}, time: 1}"

Owner
Emmanuel Dean
Emmanuel Dean
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