Drone demo in ROS 2/Gazebo/RVIZ 2

This repository contains the contents for a drone demonstration.

It is running Gazebo, PX4, QGroundControl and some other ROS 2 nodes.

Video + Pictures

A video and screenshots of the demo can be seen in the ROS wiki:

Requirements

This demo has been tested on Ubuntu Bionic (18.04)

• An X server
• Docker
• nvidia-docker2
• The current user is a member of the docker group or other group with docker execution rights.
• rocker

See the prerequisite instructions here:

There are also some notes about how to make it work without an nvidia card as well. Mileage may vary.

Running

To run the demo from the hosted docker images you can simply invoke

rocker --x11 --nvidia --user --home --pulse tfoote/drone_demo

An RVIZ window will open showing the drones, sensor output and an interactive marker and some buttons to control the drones. A gazebo window will appear showing the simulation.

Modifying or building your own

See the Dockerfiles and docs in the docker_deploy branch:

What you'll see when you launch

By default it will launch gazebo headless, QGroundControl, and a small python script that will prompt you for how many of what type of drones to launch.

You can select up to 4 total drones.

After that gazebo models of the instances will be spawned with appropriately parameterized PX4 autopilots connected. Once they have initialized you can interact with them via QGroundControl or RVIZ2.

Changing Behavior

If you'd like to change behavior you can pass argumets with a command like this:

rocker --x11 --nvidia --user --home --pulse tfoote/drone_demo ros2 launch sitl_launcher demo.launch.py use_rviz:=true use_qgroundcontrol:=true gui:=true verbose:=true sitl_world:=yosemite

gui:=true will enable the Gazebo head verbose:=true will enable Gazebo debug traces use_qgroundcontrol:=true will enable QGrounControl use_rviz:=true use_rviz:=true

Other valid sitl_worlds are: mcmillan, ksql, and baylands.

You can also pass arguments via drone_args to skip the drone selector gui and immediately start the selected drones.

The script is here: https://github.com/osrf/drone_demo/blob/master/sitl_launcher/scripts/launch_drone_ros2.py

Docs

This drone demonstrator runs Gazebo, PX4, QGroundcontrol and some other ROS 2 components. In this section we will provide some details about the inner ROS 2 architecture.

Gazebo and PX4

The launchfile demo.launch.py creates the Gazebo world and also it launches an GUI to select the drones that you want to include in the world. The GUI has the following aspect:

When you have selected the drones and clicked in the "Done Selecting" button, this node will expand in the world the drones. Each one of the drones will launch a PX4 instance. These instances connect with a bridge called ros2_to_serial_bridge with converts the uORB messages into ROS 2 px4_msgs messages.

Inside PX4 code there is a file called uorb_rtps_message_ids.yaml which defines the publishers and subscribers that the bridge will connect. For example, the battery_status message will be send by the PX4 uORB publisher and the bridge will republish this message into the ROS 2 network using px4_msgs/BatteryStatus message. Something similar happens with subscriber like vehicle_command which is defined as receive, the bridge will create a subscriber with px4_msgs/VehicleCommand message and this will be republish into the PX4 uORB network.

- msg: battery_status
  id: 6
  send: true
...
- msg: vehicle_command
  id: 89
  receive: true

Gazebo launches some nodes thanks to some of the plugins running for each drone. It creates a camera node and joint state publisher node which will allow us to visualize the model in RVIZ2.

NOTES

• In the official documentation of PX4 you can find more details
• If you want to understand how the ros2_to_serial_bridge works there is an extense readme.

ROS 2

ros2_to_serial_bridge

Based on the section above we will have a node publishing some topics:

• /iris_0/vehicle_gps_position: GPS position in WGS84 coordinates.
• /iris_0/vehicle_attitude: it contains the rotation from XYZ body frame to NED earth frame.
• /iris_0/vehicle_status: it contains internal information about the drone such us arming state, flight mode, etc
• /iris_0/battery_status: it contains data about the voltage, cells, etc
• /iris_0/vehicle_land_detected: it contains information about the landing state
• /iris_0/vehicle_odometry: Vehicle odometry. It fits ROS REP 147 for aerial vehicles

and one subscription to:

• /iris_0/vehicle_command: it allows us to send commands to the drone

drone_odom_broadcast

This node is subscribed to vehicle_odometry topic from ros2_to_serial_bridge node. This node publish the odom topic and broadcast the corresponding transforms to tf.

drone_node

This node converts the px4_msgs/BatteryStatus messages generated by the ros2_to_serial_bridge node to REP 147 messages

Publishers:

• battery_status publish sensor_msgs/BaterryState message.
• flight_mode publish proposed_aerial_msgs::msg::FlightMode
• vehicle_status publish proposed_aerial_msgs::msg::VehicleStatus
• odometry publish nav_msgs::msg::Odometry
• vehicle_gps_position publish sensor_msgs::msg::NavSatFix
• attitude publish proposed_aerial_msgs::msg::Attitude

Subscribers:

• command_pose is subscribed to geometry_msgs::msg::PoseStamped

Actions

• set_flight_mode creates the action proposed_aerial_msgs::action::SetFlightMode

RVIZ 2

RVIZ2 is subscribed to topics coming from drone_node node and tf. Using the interface you can also send some commands.

There is more documentation about how to use rviz_aerial_plugins here

The hole system graph:

The ROS 2 graph using one Iris and one plane:

The drone demonstrator allows to use multirobot. As you can see each drone in the system has its own namespace.

• Iris namespace is iris_0
• plane namespace is plane_1