Custom simulation setup

Note: It is assumed that QGroundControl is installed. This guide uses version v4.4.2.

Clone ‘final-demo’ branch from main repository 

git clone -b final-demo --single-branch --recursive git@github.com:CatScanners/find-my-kitten.git

Install ROS2 Gazebo Bridge

Install the ROS2 Gazebo bridge package:

sudo apt install ros-humble-ros-gzharmonic

Before running the simulation, start the image bridge:

ros2 run ros_gz_image image_bridge /camera

This command publishes images from Gazebo as ROS2 topics.

After cloning the repository, navigate to the simulation directory and run the setup script, which initializes submodules and PX4-Autopilot and Micro-XRCE-DDS-Agent directories.

cd find-my-kitten/ros2_ws/src/simulation/
./setup.sh

Setup QGroundControl Communication

Windows:

  1. Open QGroundControl.
  2. Click the logo in the upper-left corner.
  3. Go to Application Settings → Comm Links.
  4. Click Add to create a new communication link for Gazebo.
  5. Provide a name (e.g., Gazebo Link).
  6. Set Type to UDP.
  7. Set Port to 18570.
  8. Click OK and Connect.

Linux or WSL2:

In Linux QGroundControl should connect automatically to Gazebo simulator, when simulator is running.

Start Micro-XRCE-DDS Agent

Navigate to the Micro-XRCE-DDS-Agent/build directory and start the agent:

cd Micro-XRCE-DDS-Agent/build
MicroXRCEAgent udp4 -p 8888

Run PX4 SITL Simulation

Open a new terminal and navigate to PX4-Autopilot. Run one of the following commands:

cd PX4-Autopilot
make px4_sitl gz_x500_gimbal
  • To launch a world with trees, use:
make px4_sitl gz_x500_gimbal_baylands

A GUI window should appear with the simulated drone. If you want to see other worlds or models, please go to find-my-kitten/simulation/PX4-Autopilot/Tools/simulation/gz/. In this directory, you will find folders for models and worlds that can be used in the simulation. To use them, replace x500_gimbal with the model you want and baylands with the world you want.

If you want to modify predefined models and worlds, please do so in this repository: PX4 Gazebo Models.

Remember to update submodules after making changes to the PX4-gazebo-models repository to apply the latest changes.

Actions startup

Open a new terminal window and navigate to find-my-kitten/ros2_ws directory.

cd find-my-kitten/ros2_ws

Build ros2 directories.

colcon build

Remember to source after build.

source install/setup.bash
  1. Start a node receiving offboard messages and then sending those periodically to PX4 simulator. ros2 run px4_handler offboard_control. By default just sends current coordinates.
  2. Turn on offboard node from QGroundControl. Now the drone is flying with our ROS2 messges, currently just staying in its current position. Again, if you don’t have QGC, please refer to the Common problems -section.
  3. Star vision package to detect the ball. ros2 run vision_package object_detector.py --ros-args -p input_topic_name:="camera" -p output_topic_name:="detections"
  4. a - Start ballfinder node to start searching for the ball: ros2 run px4_handler ball_finder.py, or b - Start predefined motions with two speeds: ros2 run px4_handler hard_motions.py.
  5. a - With default code, the drone should search an area of 8m x 12m and stop and go a bit down when it sees a sports ball, or b - Does a few predefined motions in two different speeds.

Errors Encountered and Possible Fixes

Sometimes, PX4-Autopilot might fail to start properly. Below is an example error message you may see:

INFO  [gz_bridge] Requested Model Position: 0,0,0,0,0,0
WARN  [gz_bridge] Service call timed out. Check GZ_SIM_RESOURCE_PATH is set correctly.
ERROR [gz_bridge] Task start failed (-1)
ERROR [init] gz_bridge failed to start and spawn model
ERROR [px4] Startup script returned with return value: 256

Quick Fix

If you encounter this error, try stopping the execution of make px4_sitl gz_x500_gimbal and running it again.

Full Reset (If the Issue Persists)

If restarting doesn’t help, try cleaning the build environment before rebuilding PX4:

make clean          # Remove compiled binaries but keep configuration files
make distclean      # Remove all compiled files and reset configuration
make px4_sitl       # Rebuild PX4 SITL
make px4_sitl gz_x500_gimbal  # Start the simulation again

If this does not help either, then run this command in terminal

ps aux | grep gz

You will see something like this

user     776531  0.0  0.1  38840 25204 pts/0    S+   10:23   0:00 /usr/bin/python3 /opt/ros/humble/bin/ros2 run ros_gz_image image_bridge /camera
user     776532 16.1  0.7 1094372 113480 pts/0  Sl+  10:23  28:07 /opt/ros/humble/lib/ros_gz_image/image_bridge /camera
👉 user     817310 91.2  4.3 2070316 686916 pts/7  Rl   13:16   0:13 gz sim --verbose=1 -r -s /home/user/src/find-my-kitten/ros2_ws/src/simulation/PX4-Autopilot/Tools/simulation/gz/worlds/baylands.sdf
user     817443  0.0  0.0   6932  2224 pts/7    S+   13:17   0:00 grep --color=auto gz

You should look for processes similar to ‘817310’. These processes sometimes are left running in the background and causes issues as shown above. Stop these processes

kill -9 817310

where ‘817310’ should be replaced with the actual PID.

After this try to run the simulation again.