Crazyflie Interface package

This package provides a basic interface to use low-level control (roll, pitch, yaw rate, thrust) to interface with the crazyflie 2.1. It is meant as the base package upon which more elaborate controllers can be built.

The template_controller.py file provides the template to inherit for creating one owns controller. It can be imported as follows: from crazyflie_interface_py.template_controller import TemplateController.

• We provide a basic lqr_controller.py to showcase how to inherit from the TemplateController.
• The template_controller.py has the following base functionality (which can be overridden) implemented:
  • Keeps track of self.state (subscribed from the cf_interface/state topic)
  • Provides a wrapper around __call__(self, state); publish_control.py which converts the control commands to ROS2 message and publishes to the cf_interface/control topic.
  • Sets the control rate & associated timer.

The base functionality (ros2 launch crazyflie_interface launch.py) does the following:

• Command line arguments: backend (currently: sim, cflib), uri (the robot id, for cflib backend)
• Launches the crazyflie launch.py launch file with the given backend and uri. This initiates:
  • Motion capture tracking (if cflib backend)
  • Connection to the crazyflie (if cflib backend)
  • Basic simulation engine (if sim backend)
• Launches the cf_interface.py node which:
  • Subscribes to the relevant crazyflie state topic, converts to standard form (see below) and publishes it to cf_interface/state topic.
  • Subscribes to the cf_interface/control topic, converts to crazyflie format and publishes the low-level control commands to the crazyflie
  • Provides the cf_interface/command service for high-level interface to crazyflie: takeoff, land
    • Example call: ros2 service call /cf_interface/command crazyflie_interface/srv/Command "{command: 'takeoff'}"

Standard form

State message is as follows: [x, y, z, vx, vy, vz, q_x, q_y, q_z, q_w, wx, wy, wz]

• Linear velocities are in world frame
• Angular velocities are in body frame

Control message is as follows: [roll, pitch, yaw_rate, thrust]

• Roll, pitch are in radians
• Yaw rate is in radians per second
• Thrust is in Newtons per kilogram (same as gravity)

Getting started

Dependencies

• UCSD SASLab's crazyswarm2 package.
• Tested on ROS2 Humble only.

Installation

• colcon build --packages-select crazyflie_interface from ros2_ws directory.
• source install/setup.bash from ros2_ws directory.

Running base functionality (sim)

1. ros2 launch crazyflie_interface base_controller_launch.py backend:=sim for simulation backend.
2. ros2 service call /cf_interface/command crazyflie_interface/srv/Command "{command: 'takeoff'}" to takeoff.
3. It will start flying to random position targets.
4. ros2 service call /cf_interface/command crazyflie_interface/srv/Command "{command: 'land'}" to land.

Running base functionality (hardware)

1. Identify drone URI (# under drone)
2. ros2 launch crazyflie_interface base_controller_launch.py backend:=cflib uri:=uri for hardware backend.
3. ros2 service call /cf_interface/command crazyflie_interface/srv/Command "{command: 'takeoff'}" to takeoff.
4. It will start flying to random targets
5. ros2 service call /cf_interface/command crazyflie_interface/srv/Command "{command: 'land'}" to land.

TODOs

• Add GUI for command service.
• Add gym_pybullet_drones interface for simulation backend.
• Provide option for running rviz with gym_pybullet_drones.
• Add time to state message.
• Add calibration as part of command service in cf_interface.py.