flock2

flock2 can fly a swarm of DJI Tello drones. flock2 is built on top of ROS2, fiducial_vlam, and tello_ros.

Installation

1. Set up your Linux environment

Set up a Ubuntu 20.04 box or VM.

2. Set up your Python environment

Use your favorite Python package manager to set up Python 3.6+ and the following packages:

• numpy 1.15.2
• transformations 2018.9.5

3. Set up your ROS environment

Install ROS2 Foxy with the ros-foxy-desktop option.

If you install binaries, be sure to also install the development tools and ROS tools from the source installation instructions.

Install these additional packages:

sudo apt install ros-foxy-cv-bridge ros-foxy-camera-calibration-parsers ros-foxy-gazebo-ros

4. Install dependencies

Download, compile and install the following packages:

mkdir -p ~/flock2_ws/src
cd ~/flock2_ws/src
git clone https://github.com/clydemcqueen/flock2.git
git clone https://github.com/clydemcqueen/tello_ros.git
git clone https://github.com/ptrmu/fiducial_vlam.git
git clone https://github.com/ptrmu/ros2_shared.git
cd ..
source /opt/ros/foxy/setup.bash
# If you didn't install Gazebo, avoid building tello_gazebo:
colcon build --event-handlers console_direct+ --packages-skip tello_gazebo

Running

Flying a single drone

launch_one.py will allow you to fly a drone using a wired XBox One gamepad.

Turn on the drone, connect to TELLO-XXXXX via wifi, and launch ROS2:

cd ~/flock2_ws
source install/setup.bash
ros2 launch flock2 launch_one.py

Gamepad controls:

• menu button to take off
• view button to land
• B to start mission
• A to stop mission

Flying multiple drones

launch_two.py provides an example for flying multiple drones.

Key elements of multi-drone missions:

• All drones must be networked together. One way to do this is to connect to each drone’s wifi using a Raspberry Pi 3 or similar device, and forward all UDP packets from the Pi to the host computer. See udp_forward for an example using 2 Tello drones.
• Global nodes such as flock_base should have exactly 1 instance running. Per-drone nodes such as drone_base should have 1 instance running per drone.
• Each drone has it’s own ROS topic namespace. The default namespace for 1 drone is solo.
• Each drone must have it’s own URDF file with the appropriate coordinate frames.
• The joystick controls one drone at a time. Hit the right bumper to select a different drone.
• All drones participate in the mission.

Design

Coordinate frames

ROS world coordinate frames are ENU (East, North, Up).

There are 3 significant coordinate frames in flock2:

• The world frame is map
• Each drone has a base coordinate frame. The default for 1 drone is base_link
• Each drone has a camera coordinate frame. The default for 1 drone is camera_frame

The arena

An arena is a right rectangular prism defined by 2 points: (x1=0, y1=0, z1=0) and (x2, y2, z2). z1 defines the ground, so z2 must be positive. The ground must be flat.

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