Overview

This page will explain the overview of the crazyflie ROS 2 nodes:

Explanation per node

In the source code of the Crazyswarm2 (Crazyflie ROS 2) project, there are several packages that we will explain here:

• crazyflie/: The package that contains the crazyflie server nodes and the crazyflies.yaml.

• crazyflie_py/: The package that contains the python library that wraps around the ROS 2 services and topics that connects with the crazyflie server nodes.

• crazyflie_examples/: The package that contains examples of using the crazyflie ROS 2 package. See ROS 2 Tutorials.

• crazyflie_interfaces/: The package that contain all msgs and srvs for the crazyflie ROS 2 project.

Crazyflie server

The crazyflie server node connects multiple Crazyflies with on or more Crazyradio PA dongles.

It has two backends that you can choose from:

• cpp: This is based on the crazyflie-link-cpp on the lowest layer.

• cflib: This is based on the crazyflie-lib-python up until the logging, parameter, and command sending handling.

It handles several low level communication aspects with the Crazyflies:

• Parameter to ROS 2 parameters handling: It receives the parameter ToC from the Crazyflie, transforms it into ROS 2 parameters, and sets the CF2 parameters based on the crazyflies.yaml input.

• Logging to ROS 2 topics handling: The server sets up logblocks for data streaming in the crazyflie, and transforms the received variables into ROS 2 topics.

• Run-time configuration: Both parameters and logging can be configured in run-time while the server is connected with the Crazyflies. Please check Usage.

It also setups several flight command services:

• Takeoff / Land / GoTo: With a single service command and a given height or coordinate, you can make the connected crazyflies take off, go to a position and land.

• Upload / Start trajectory: You can upload a predefined trajectory and indicate if the Crazyflies need to start flying it.

• Emergency : To turn off the motors in case something goes wrong.

• /all or /cf2 : The services are setup either for all crazyflies to respond to, or each individual crazyflie, depended on the prefix.

Simulation

The simulator uses the Crazyflie firmware as a software-in-the-loop (SIL). It provides the same ROS interface as the server and therefore can be used with C++ or Python user code.

Currently, the desired setpoint is visualized in rviz (see Usage). However, the code is prepared to support physics-based simulation in the future as well.

Support functionality with backends

Functionality	Cpp	CFlib	Sim
Parameters	Yes	Yes	No
Logging
default: pose	Yes	Yes	No
default: scan	Yes	Yes	No
default: odom	No	Yes	No
custom	Yes	Yes	No
Add/Remove Srv	No	Yes	No
Broadcasts	Yes	No	n/a
Manual control
cmd_full_state	Yes	No	Yes
cmd_position	Yes	No	No
cmd_hover	No	Yes	No
High-level control
takeoff/land	Yes	Yes	Yes
go_to	Yes	Yes	Yes
upload/start traj	Yes	No	Yes
Positioning System
Motion Capture	Yes	Yes	No
Flow Deck	Yes	Yes	No
LightHouse	Yes	Yes	No
LPS	Yes	Yes	No