Crazyflie can be controlled through a number of host devices over BLE or a Crazyradio communication channel. A BLE link to Crazyflie limits the flying range to 20 meters. The best communications link, Crazyradio PA, extends the communication range to 1000 meters. Either communication method is supported by the Crazyflie Python client (PC) software available for computers running Linux, Windows, or MAC OS. Bitcraze has also configured its own Virtual Machine (VM) that imports into the Oracle VirtualBox to make it easy to start on Crazyflie development projects. For more information on the Bitcraze VM, visit https://wiki.bitcraze.io/projects:virtualmachine:index.

For the latest release of the Crazyflie PC client, visit https://github.com/bitcraze/crazyflie-clients-python/releases.

Instructions for installing the Crazyflie PC client can be found at https://github.com/bitcraze/crazyflie-clients-python.

The Crazyflie PC client can be used to upgrade and flash the Crazyflie firmware over the Crazyradio link. Refer to the following website for instructions: https://wiki.bitcraze.io/projects:crazyflie2:upgrading:index.

Application software also exists for controlling the Crazyflie from an Android OS (4.4 or newer) or iOS (7.1 or newer) device. Refer to the appropriate app store for the Crazyflie software:

For Android users: https://play.google.com/store/apps/details?id=se.bitcraze.crazyfliecontrol2.

For iOS users: https://itunes.apple.com/us/app/crazyflie-2.0/id946151480?mt=8.

For Raspberry Pi enthusiasts, check out the client version of software for Raspbian at https://wiki.bitcraze.io/projects:crazyflie:binaries:raspberrypi#download.

For user input control, Crazyflie can use any gamepad with a minimum of four analog axes. The primary joystick controllers are the Xbox 360 USB controller, the PS 3 USB controller and the PS4 USB controller. Other controllers can be configured to work with the Crazyflie by modifying the Crazyflie client software.

In order to use Crazyflie 2.0 with ROS, a Crazyradio or Crazyradio PA is necessary to provide wireless radio communication to the Crazyflie. The Crazyradio resides on a small circuit board mounted on a USB dongle to interface with a computer, tablet, or smart phone. It has radio amplification to 20 dBm power output and a line-of-sight (LOS) range of greater than 1 kilometer. The design is based on the nRF24LU1+ chip from Nordic Semiconductor that operates at the 2.4 GHz band of radio communications. It provides 125 radio channels and offers 2 Megabits per second (Mbps), 1Mbps, and 250Kbps communication data rates. Firmware for the Crazyradio is open source and is upgradeable through a bootloader that comes embedded with the hardware.

The following figure shows the Crazyradio PA with its antenna extended. Additional information on the Crazyradio PA can be found at https://www.bitcraze.io/crazyradio-pa.

For the latest stable release of the Crazyradio firmware, go to https://github.com/bitcraze/crazyradio-firmware/releases.

Crazyradio PA

The next sections will focus on using ROS to command and control the flight of the Crazyflie quadrotor. A ROS metapackage for the Crazyflie has been developed by Wolfgang Hoenig with current information found at the GitHub site: https://github.com/whoenig/crazyflie_ros.

We thank Mr. Hoenig for his generous support in helping us prepare this section.

This software supports both the Crazyflie 1.0 and the Crazyflie 2.0 quadrotors embedded with stock firmware.

The Crazyflie ROS software for Crazyflie can be added to the catkin workspace catkin_ws created in Chapter 1, Getting Started with ROS, and then used in Chapter 2, Creating Your First Two-Wheeled ROS Robot (in Simulation), for our package ros_robotics. However, we provide instructions here to install the crazyflie metapackage into a catkin workspace of its own identified as crazyflie_ws. This workspace will provide you with the chance to examine the existing Crazyflie ROS packages and be a development space for new software you might wish to create. If you wish to use the catkin_ws workspace for your Crazyflie ROS software, skip to the step where the command sudo apt-get update is issued. (Afterwards, remember to replace the crazyflie_ws name in each of the command lines with catkin_ws.)

To create the Crazyflie workspace crazyflie_ws, type the following commands:

$ mkdir -p ~/crazyflie_ws/src
$ cd ~/crazyflie_ws/src
$ catkin_init_workspace

Build and install the Crazyflie workspace:

$ cd ~/crazyflie_ws
$ catkin_make

Next, source the setup.bash file within the Crazyflie workspace to overlay this workspace on top of the ROS environment for the workstation:

$ source ~/crazyflie_ws/devel/setup.bash

Remember to add this source command to your .bashrc file:

$ echo "source ~/crazyflie_ws/devel/setup.bash" >> ~/.bashrc

Make sure the ROS_PACKAGE_PATH environment variable includes the path you just sourced:

$ echo $ROS_PACKAGE_PATH

The path /home/<username>/crazyflie_ws/src should be displayed as one of the paths on the screen.

Now that the Crazyflie catkin workspace has been created, update the system information on the newest versions of packages and their dependencies:

$ sudo apt-get update

Next, move to the Crazyflie workspace source directory and download the software from GitHub:

$ cd ~/crazyflie_ws/src
$ git clone https://github.com/whoenig/crazyflie_ros.git

Move to the root of the Crazyflie workspace and build the packages:

$ cd ~/crazyflie_ws
$ catkin_make

These instructions install the latest version of the crazyflie metapackage, which has no dependencies on the Bitcraze Crazyflie SDK. To be able to fly Crazyflie with a joystick, ensure that the hector_quadrotor software is also installed. The instructions were presented earlier in this chapter.

$ export ROS_MASTER_URI=http://localhost:11311

ROS packages from the crazyflie metapackage are described here:

$ su –
$ apt-get install sudo

$ sudo groupadd plugdev
$ sudo usermod -a -G plugdev <username>

SUBSYSTEM=="usb", ATTRS{idVendor}=="1915", ATTRS{idProduct}=="7777", MODE="0664", GROUP="plugdev"

SUBSYSTEM=="usb", ATTRS{idVendor}=="0483", ATTRS{idProduct}=="5740", MODE="0664", GROUP="plugdev"

It is advisable to mark the right front (M1) leg of the Crazyflie with something bright. This marking will help you keep track of the forward direction for your Crazyflie. Due to the symmetrical design, it is easy to lose the orientation of the Crazyflie.

The Crazyflie should be placed on a stable surface. As you will see, the startup sequence involves spinning the motors and sensor calibration. In the following figure of Crazyflie, identify the on/off power button (near the M1 leg) and push it on.

Top view of Crazyflie

After the Crazyflie is powered on, the power-on sequence will spin all four propellers in order. If a propeller does not spin, be sure to check the motor connections. The blue LED lights on the rear of the UAV should be lit to indicate that the power is on. The front right red LED light should be pulsing at 1 Hz to indicate the vehicle's heartbeat. When Crazyradio communication is established with the Crazyflie, the red and green LED lights on the front left will be flashing to indicate communication is being exchanged.

Next, insert the Crazyradio into a USB 2.0 slot on your computer and the joystick controller into another USB slot. Check that the joystick knobs are in their center positions so that the throttle is set to zero. You are now ready to start the Crazyflie ROS software.

Before flying Crazyflie for the first time, it is recommended to tie the UAV to a heavy object, attaching string to the mounting holes on either side of the Printed Circuit Board (PCB) body.

Before communicating with your Crazyflie, you need to find the Uniform Resource Identifier (URI). This URI is associated with the communication protocol of the nRF51 MCU. The format for the URI is as follows:

Interface Type:// Interface Id/Interface Channel/Interface Speed

For the radio interface, this sequence is as follows:

radio://USB dongle number/radio channel number/radio speed

The package crazyflie_tools provides the program scan to identify all the URIs that are transmitting. Open a terminal window on your computer workstation and enter the following command:

$ rosrun crazyflie_tools scan

The output will be similar to the following two lines:

Configured Dongle with version 0.53

radio://0/80/250K

The URI for your Crazyflie may be different. For our Crazyflie, the USB dongle number is 0, the radio channel is 80, and the radio speed is 250K. This means that our communication link is over a 2480 MHz channel.

The package crazyflie_demo contains a spectrum of example launch files to use with Crazyflie. Launch files are given for using the Xbox 360 controller or the PS3 controller to teleoperate the Crazyflie. To fly your Crazyflie with an Xbox 360 controller, type the command:

$ roslaunch crazyflie_demo teleop_xbox360.launch uri:=<CrazyflieURI>

Replace <CrazyflieURI> with the URI found from the scan command. In the screen, look for the message:

SYS: Crazyflie is up and running!

You should see something similar to this:

Starting screen for the teleop_xbox360.launch

The window on the left is running rviz and the two rqt_plot windows on the right are for temperature and battery data. In rviz, IMU sensor data will be displayed on the grid.

If you are anxious to feel the joystick controls in your hands, proceed to using the left and right stick controls to navigate your Crazyflie. The stick controls are similar to those used for Hector Quadrotor:

You are now ready to use the Xbox 360 joystick to fly your Crazyflie around!

Details of teleop_xbox360.launch

The teleop_xbox360.launch file performs a number of operations to launch ROS nodes, pass arguments, and set ROS parameters. The following list highlights the tasks performed:

• The crazyflie_server.launch file in the crazyflie_driver package is executed. This file launches the node crazyflie_server. This server handles communication with the Crazyflie as soon as it is dynamically added by the crazyflie_add.launch file.
• The crazyflie_add.launch file in the crazyflie_driver package is executed. This file launches the node crazyflie_add using the URI parameter that is passed into teleop_xbox360.launch. Other parameters that are set are as follows:
  • tf_prefix: This is the tf prefix for the Crazyflie frame(s)
  • roll_trim: This is the roll trim in degrees (negative value if drift is to the left)
  • pitch_trim: This is the pitch trim in degrees (negative value if drift is forward)
  • enable_logging: This is the flag to log data
• The joy node is launched to handle the joystick controller input.
• The xbox360.launch file is included to launch the node quadrotor_teleop (in the hector_quadrotor_teleop package) and set the parameters for the joystick controller. These parameters include x_axis, y_axis, z_axis, yaw_axis, x_velocity_max, y_velocity_max, z_velocity_max, and yaw_velocity_max.
• The crazyflie_demo_controller node in the crazyflie_demo package is launched via the script controller.py.
• The rviz node in package rviz is launched and the crazyflie.rviz configuration file in the crazyflie_demo package launch directory is used to configure rviz.
• Two rqt_plot nodes from package rqt_plot are launched. One node plots the temperature of the Crazyflie, and the other node plots the battery level.

Take a look at this figure to see some of the relationships between the nodes and topics. The large rectangle marked Crazyflie is the namespace for the enclosed nodes and topics:

Crazyflie ROS teleop nodes and topics

A number of ROS parameters are initialized at the start of this program. Of particular interest are the roll_trim and pitch_trim parameter values set by the crazyflie_add.launch file.

When first flying your Crazyflie, use the roll_trim and pitch_trim values in the crazyflie_add.launch file to adjust the response of your craft. Begin with a straight forward push on the Left Stick of the joystick (throttle). The Crazyflie should lift straight up into the air. If not, adjust these two parameters accordingly and try it again. (The battery may also be moved forward and back to change the pitch balance. It is recommended to mark the battery position when you get it into the desired spot.)

Prior to flying the Crazyflie, using the rostopic list command allows us to see the names of the topics that are available. Of primary importance is the /crazyflie/cmd_vel topic that is similar to the same topic for Hector. This topic is published by the quadrotor_teleop node and the data fields for this topic are as follows:

• angular.z: The yaw rate value is -200 to 200 degrees per second
• linear.x: The pitch value is -30 to 30 degrees
• linear.y: The roll value is -30 to 30 degrees
• linear.z: The thrust value is 10,000 to 60,000 for pulse-width modulation (PWM) output

The crazyflie_server node publishes sensor data from the Crazyflie as sensor_msgs:

• The imu topic contains gyroscope and accelerometer data and updates every 10 milliseconds (ms). The covariance matrices and orientation fields are not set.
• The temperature topic contains data from the barometer in degrees Celsius. This message is updated every 100 ms.
• The magnetic_field topic contains data from the magnetometer and is updated every 100 ms.
• The pressure topic contains readings from the pressure sensor in hectopascals (hPa) or millibars (mbar). This message is updated every 100 ms.
• The battery topic contains readings from the battery in volts and is updated every 100 ms. The stock battery is a 3.7 volt 240 mAh Lithium Polymer battery.

From this point, feel free to try the rostopic echo command with any of the topics listed previously to see the data being passed, especially between the computer and the Crazyflie. The ROS tool rqt can also be used to monitor these topics (Topic Monitor) and publish messages (Message Publisher) to the Crazyflie.

The crazyflie_demo package contains launch files to use the Crazyflie with external motion capture systems like VICON or Virtual-Reality Peripheral Network (VRPN). With an external motion capture system, you can get your Crazyflie to hover at a given location or navigate autonomously to a set of waypoints. For example, to get Crazyflie to hover a meter above its starting location using a VICON system, use the following command:

$ roslaunch crazyflie_demo hover_vicon.launch uri:=<CrazyflieURI>
frame:=<CrazyflieTFframe> x:=0 y:=0 z:=1

Replace <CrazyflieURI> with your Crazyflie's URI and <CrazyflieTFframe> is the tf-frame of your Crazyflie. The hover_vicon.launch file will automatically run vicon_bridge.

The crazyflie_demo package also contains launch files for flying multiple Crazyflies at the same time. To accomplish this, each Crazyflie must have a different address. If Crazyflies are to share communication on the same Crazyradio USB dongle, they should share the same channel and data rate to provide optimum performance. Up to three Crazyflies have been successfully flown over one Crazyradio dongle. Performance degrades as the number of Crazyflies increase due to limitations in bandwidth.

To command and control multiple Crazyflies using the Xbox 360 joystick controller, use the following command:

$ roslaunch crazyflie_demo multi_teleop_xbox360.launch uri1:=radio://0/100/2M/E7E7E7E7E7 uri2:=radio://0/100/2M/E7E7E7E705

The URIs used in the multi_teleop_xbox360.launch command are left as examples of the duplication of the radio channel and data rate but the difference in the address.