Gazebo Model for the Uvify IFO-S with PX4 Software-in-the-Loop

Simulated quadcopter vs the real quadcopter, running the same code.

This repo is a collection of ROS packages, Gazebo models, Gazebo plugins, as well as the PX4-Autopilot source code contained as a git submodule. It does not contain the Gazebo simulator itself, or ROS. These are all dependencies that must be installed as per the instructions below.

Currently, this simulator is intended for Ubuntu 18.04 with ROS Melodic

This model uses the Iris quadcopter model available in the PX4-SITL_gazebo repo as a starting point, which is then modified to have the same sensor configuration as the Uvify IFO-S

Folder structure

• ./docs/ : A directory for any files related to documentation.
• ./cpr_office_gazebo/ : A copy of the Clearpath Robotics' "Office World".
• ./ifo_description/ : Folder containing CAD meshes and URDF/Xacro files that describe the actual gazebo model
• ./ifo_gazebo/ : Gazebo-specific config files, launch files, and a ROS node that emulates a motion capture system VRPN server.
• ./PX4-Autopilot/ : A submodule containing the PX4 source code.
• ./realsense_gazebo_plugin/ : A submodule of a realsense plugin made by PAL Robotics.

TODO

1. Add bottom-facing 1D Lidar and camera

Pre-requisites

1. Gazebo + ROS Melodic (follow standard install instructions for the desktop-full option here)
2. Python catkin tools (installable with sudo apt-get install python3-catkin-tools)

Getting Started

This repo is a collection of ROS packages that contains everything you need to create a simulated version of the Uvify IFO-S quadcopter in Gazebo with ROS.

The PX4-Autopilot repo, which contains the software of the Uvify IFO-S flight controller, is stored as submodule of this repo. This allows the PX4 directory to be fixed relative to the gazebo model, which simplifies the simulator start-up procedure since the user no longer needs to specify the location of PX4 source code. Moreover, this gives us control of the exact version of PX4-Autopilot, meaning this repo will not break if the PX4 developers push a new commit to the PX-Autopilot repo. The PX4-Autopilot repo has lots of submodules itself, so it is critical to clone this repo with the --recursive flag. Start by creating the folder ~/catkin_ws/src/. Then

cd ~/catkin_ws/src
git clone [email protected]:decarsg/ifo_gazebo.git --recursive

Feel free to change the above URL to one appropriate for SSH-keys. Alternatively, you can clone this repo regularly and then run git submodule update --init --recursive.

Next, we must blacklist the PX4-Autopilot directory in the catkin tools, so that the catkin build command does not compile the PX4 source code (since it fails). PX4 must be built manually. While inside your catkin workspac, add the px4 package to the blacklist,

catkin config --blacklist px4

You can now run

catkin build

and test to see that all the packages get built successfully, with the px4 package being skipped.

Note: We prefer catkin build instead of catkin_make to build a ROS workspace, but catkin_make should also be possible. Check out the documentation for catkin.

Building the PX4-Autopilot Source Code

To compile PX4 manually, we must first install the toolchain. Thankfully PX4 provides an install script which installs everything required. The PX4 documentation cites that their installation scripts, are intended for a clean Ubuntu 18.04 installation. It might still work for a non-fresh installation, but it is recommended to run rm -rf ~/.ros beforehand.

bash ~/catkin_ws/src/ifo_gazebo/PX4-Autopilot/Tools/setup/ubuntu.sh

Reboot your computer when complete. Technically, at this point, your computer is also outfitted with a development environment to modify the PX4 source code itself, and do some basic software-in-the-loop (SITL) testing in simulation. Now, build the PX4 code.

cd ~/catkin_ws/src/ifo_gazebo/PX4-Autopilot
make px4_sitl gazebo

This can take a long time, and can fail multiple times with a C++ compiler failure. The reason of failure is apparently due to your computer running out of RAM. Nevertheless, the build process gets a little further every time, so the solution is just to keep running make px4_sitl gazebo until it succeeds. Once successful, you should see the PX4 app start up in the terminal and the Gazebo GUI launching. You should only need to do this build step once, provided that you never modify the PX4 source code.

See PX4's Ubuntu Development Environment instructions for reference.

Installing ROS, Gazebo, MAVROS

Next, the PX4 documentation conveniently provides an install script which will install all the required software for ROS/Gazebo simulation including ROS Melodic, Gazebo 9, MAVROS and more

cd ~
wget https://raw.githubusercontent.com/PX4/Devguide/master/build_scripts/ubuntu_sim_ros_melodic.sh
bash ubuntu_sim_ros_melodic.sh

See PX4's ROS/Gazebo installation instructions for reference.

Note that this will create some additional folders under ~/catkin_ws/src/ such as ~/catkin_ws/src/mavros/. If you have no need to modify the source code of these packages, feel free to delete these folders so they arn't compiled every time with catkin build. If you do this, install MAVROS dependencies with

sudo apt-get install ros-melodic-mavros ros-melodic-mavros-extras

As per the official MAVROS installation instructions, we also need to install some geographic dataset dependency for proper reference frame conversions.

cd ~
wget https://raw.githubusercontent.com/mavlink/mavros/master/mavros/scripts/install_geographiclib_datasets.sh
sudo bash ./install_geographiclib_datasets.sh
rm install_geographiclib_datasets.sh     # Delete the file once done.

Launching the simulator

Finally, we need to source the usual setup script in catkin_ws/devel/setup.bash, but also a custom script setup_ifo_gazebo.bash located in this repo, which manually specifies the paths to relevant dependencies inside the PX4 source using environment variables. These two scripts need to be run for every new terminal. Alternatively, adding them to ~/.bashrc will automatically execute them with every new terminal

echo "source ~/catkin_ws/devel/setup.bash" >> ~/.bashrc
echo "source ~/catkin_ws/src/ifo_gazebo/setup_ifo_gazebo.bash suppress" >> ~/.bashrc

Restart your terminal. Then, you should be ready to fire up the simulator

roslaunch ifo_gazebo ifo_empty_world_1.launch

The PX4 app should be running in the terminal, and the Gazebo GUI should have started, displaying a single quadcopter located at the origin. You can run rostopic list and you should see a large list of topics. You can see it in action by typing

commander takeoff

in the same terminal you used to type the previous command (the one with all the PX4 printout). Watch the quadcopter take off and immediately land. You can also open a second terminal and type rostopic echo /mavros/local_position/pose to view the state estimate in real time.

Launching multiple drones

An example can be seen here, which will launch 3 drones.

roslaunch ifo_gazebo ifo_empty_world_3.launch

Or alternatively, this can be launch in the Clearpath Office World with

roslaunch ifo_gazebo ifo_office_world_3.launch

Changing master branch to main

We recently changed the master branch to main. If you have an old clone that still has master as the default branch, run

git branch -m master main
git fetch origin
git branch -u origin/main main
git remote set-head origin -a