Drone flight controller and autopilot for Raspberry Pi (Zero 2). It does not require any additional flight controller, the Raspberry Pi pinout is connected directly to ESCs and sensors. It has been developed from the scratch, the code for stabilisation and reaching waypoints is original. Here is a video of one of the first succesfull flights. PiFly is a project to build a DIY drone under 250g running Raspilot.
This project began as a professional assignment. The aim was to develop a flight controller and autopilot where it is easy to connect various hardware components such as experimental gyroscopes, barometers, distance sensors, positioning modules etc. and perform series of tests. Another goal was potentially unlimited precision (sub centimeter) of flight.
Unfortunately, the company that commissioned the software cancelled the project before it had reached its first milestone. By that time the most of the autopilot code had been written. I published it and maintain it on my own now.
Raspberry Pi fits the purpose of the project. It is powerful enough to support sensors that require a Linux operating system such as Intel Intellisense devices. The computer is light enough to be mounted on small drones. Raspbery Pi natively supports double precision floating-point arithmetic which we use for all our calculations.
Of course, there are obvious drawbacks to using Raspberry Pi. After connecting the battery, you have to wait until Linux boots. You have to shut down Linux before you disconnect the battery. And, of course, Linux is not a real-time operating system and precise timing can be a problem.
However, none of these points outweigh the advantages we have gained. Raspberry Pi offers plenty of processing power and a standard development and debugging environment. Connected via wifi we can edit, compile, run and debug the code directly on the drone. No need to flash the firmware every time we change the code. We can fly with new versions of our software again and again without physically touching the drone. We can put any debugging output to logs with no effort. We can connect any new sensor through a pipe immediately after having compiled its factory provided demo software.
Raspilot is a small software at the moment. It implements the necessary to allow a drone to fly and carry out its mission. The autopilot provides basic stabilisation, it reads sensors and sends commands to the motors. The overall architecture is similar to that of the PX4. Specialised routines that manipulate the sensors and motors are running in separate processes and are connected to the autopilot via Linux pipes and/or shared memory. Software runs asynchronously and the input is read as it comes. The autopilot itself runs an infinite loop at an adjustable frequency. Frequency is configurable and ranges between 50Hz and 5kHz. Less stable designs with the centre of gravity above propellers require higher frequency. Most of our drones (small and large) were operated at 200 Hz.
From the user point of view, the whole autopilot behaves like a library. The main program initialises the autopilot and then executes a mission for the drone to follow. The mission is a C function coded by the user. It basically calls autopilot functions like "goto_waypoint(X,Y,Z,Yaw)", which means that the drone will go to the point X,Y,Z and approach it with the yaw orientation. When the waypoint is reached, the function returns and the mission can continue. Such an architecture gives the user (who must be a C programmer) full control over all flight variables and configurations to perform any sophisticated computations he may wish during the flight.
The physics that Raspilot uses to stabilise drones is very rudimentary. Only inertia rules are taken into account. Changes in rotation and speed of movement are controlled by PID controllers.
At the moment Raspilot supports T265 Intel intellisense positioning and orientation sensor; MPU-6050 family of gyroscopes; BMI160 gyroscope; HC-SR04 distance sensor; Matek 3901 L0X sensor; NMEA GPS sensors and others. It implements PWM and DSHOT 150 protocols to control motor ESCs. To see all supported hardware go through subdirectories under 'tool' directory. If your hardware is not there, it is quite easy to add it. All you need to do is to hack a demo example that comes with the sensor and make it to print measurements to the standard output.
You need to have at least a basic understanding of Linux and C programming in order to use Raspilot. Different modules in ./tool directory use various 3rd party libraries. If you use those modules you will need to install corresponding libraries. That are common libraries like 'pigpio' and/or 'bcm2835'.
If you have the courage to compile and try Raspilot then:
1.) Clone Raspilot to your Raspberry Pi
git clone https://github.com/Marian-Vittek/raspilot.git
2.) Create/Edit configuration file for your drone in the directory "cfg". There are a few working configurations which can be used as templates. Then create a symbolic link to your configuration file in the "src" directory. The name of the link shall be "config.json".
cd raspilot/src
ln -s -f ../cfg/raspilot-myconfiguration.json config.json
3.) Compile Raspilot
make all
4.) Launch the autopilot with
make starttolog
Once the mission is completed, the log from the last flight can be seen in the file currentlog.txt. All logs from previous flights can be found in ../log directory. If you do not need log files, you can launch autopilot with:
make start
Good luck and do not hesitate to contact me.