tello_ros

tello_ros is a ROS2 driver for Tello and Tello EDU drones.

Packages

There are 4 ROS packages:

• tello_driver is a C++ ROS node that connects to the drone
• tello_msgs is a set of ROS messages
• tello_description contains robot description (URDF) files
• tello_gazebo can be used to simulate a Tello drone in Gazebo, see the README.md in that package for details

Interface

Overview

The driver is designed to very simple while making it easy to integrate Tello drones into the ROS ecosystem.

The driver communicates with the drone using the Tello SDK, which has several advantages:

• The SDK is documented, and there's quite a bit of development activity around it, so it's likely to be stable.
• The SDK is text-based, which means that tello_ros can be simple but still provide full access to the SDK by passing arbitrary strings to the drone.

Many Tello commands (e.g., takeoff and land) are long-running, and the drone returns ok or error on completion. The driver provides the ROS service tello_command to initiate commands, and the corresponding ROS topic tello_response to indicate command completion.

Per ROS convention, the driver also responds to Twist messages on the cmd_vel topic. These are translated into rc commands and sent to the drone. Velocity values are arbitrarily mapped from [-1.0, 1.0] to [-100, 100]. This may change in the future.

The driver parses telemetry data and sends it on the flight_data topic. The presence of telemetry data is a good indicator that the drone is connected.

The driver parses the video stream and sends images on the image_raw topic. Camera information is sent on the camera_info topic.

The Tello drones have a sophisticated visual odometry system and an onboard IMU, but there's minimal access to these internal systems. The driver does not publish odometry.

Additional notes:

• Only one command may be running at a time.
• If a command (other than rc) is currently running, incoming cmd_vel messages are ignored.
• Tello drones do not send responses for rc commands, and neither does the driver.
• The driver sends command and streamon commands at startup to initiate telemetry and video.
• If telemetry or video stops, the driver will attempt to restart by sending command and streamon commands.
• Roll (Twist.angular.x) and pitch (Twist.angular.y) are ignored in cmd_vel messages.
• The driver doesn't keep track of state, so it will happily send rc messages to the drone even if it's on the ground. The drone just ignores them.
• You can send arbitrary strings to the drone via the tello_command service.
• Tello drones auto-land if no commands are received within 15 seconds. The driver sends a rc 0 0 0 0 command after 12 seconds of silence to avoid this.

Services

• ~tello_action tello_msgs/TelloAction

Subscribed topics

• ~cmd_vel geometry_msgs/Twist

Published topics

• ~tello_response std_msgs/String
• ~flight_data tello_msgs/FlightData
• ~image_raw sensor_msgs/Image
• ~camera_info sensor_msgs/CameraInfo

Parameters

The defaults work well for a single Tello drone.

Installation

1. Set up your Linux environment

Set up a Ubuntu 20.04 box or VM.

Also install asio:

sudo apt install libasio-dev

2. 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

3. Install tello_ros

Download, compile and install tello_ros:

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

Teleop

The driver provides a simple launch file that will allow you to fly the drone using a wired XBox One gamepad.

Turn on the drone, connect to TELLO-XXXXX via wi-fi, and launch ROS:

cd ~/tello_ros_ws
source install/setup.bash
ros2 launch tello_driver teleop_launch.py

Hit the XBox One menu button to take off, and the view button to land.

If you don't have an XBox One gamepad, you can send commands using the ROS2 CLI:

ros2 service call /tello_action tello_msgs/TelloAction "{cmd: 'takeoff'}"
ros2 service call /tello_action tello_msgs/TelloAction "{cmd: 'rc 0 0 0 20'}"
ros2 service call /tello_action tello_msgs/TelloAction "{cmd: 'land'}"
ros2 service call /tello_action tello_msgs/TelloAction "{cmd: 'battery?'}"

You can also send cmd_vel messages:

ros2 topic pub /cmd_vel geometry_msgs/Twist  # Sends rc 0 0 0 0
ros2 topic pub /cmd_vel geometry_msgs/Twist "{linear: {x: 0.0, y: 0.0, z: 0.0}, angular: {x: 0.0, y: 0.0, z: 0.2}}"

Devices tested

• Tello
  • Firmware v01.04.35.01, SDK v1.3
• Tello EDU
  • Firmware v02.04.69.03, SDK v2.0

Versions and branches

tello_ros was developed along with several other projects while ROS2 was rapidly changing. All of the related projects adopted similar conventions around branch names:

• the master branch works with the latest ROS2 release (Foxy as of this writing)
• there may be branches for older ROS2 versions, such as crystal, dashing or eloquent

The following projects and branches were tested together:

• ROS2 Foxy with fiducial_vlam:
  • git clone https://github.com/ptrmu/ros2_shared.git
  • git clone https://github.com/ptrmu/fiducial_vlam.git
  • git clone https://github.com/clydemcqueen/tello_ros.git
  • git clone https://github.com/clydemcqueen/flock2.git

Credits

The h264decoder is from: https://github.com/DaWelter/h264decoder

Resources

• Tello User Manual 1.4
• SDK 1.3 for Tello, see the errata below
• SDK 2.0 for Tello EDU, see the errata below
• Tello EDU Mission Pad Guide (SDK 2.0) for Tello EDU
• Tello Pilots Developer Forum is a good developer community

Tello SDK errata

• Tello drones do not respond to rc commands (the SDK suggests that they return ok or error)