This repository contains the flight controller firmware for an autonomous quadcopter designed to track a sport climber (as a part of an engineering thesis). The system runs on an STM32F411 microcontroller with FreeRTOS, providing deterministic real-time performance for sensor fusion, state estimation, and low-level control. It communicates with a companion computer (Raspberry Pi) via MAVLink and implements comprehensive safety features.
- Real‑time multitasking with FreeRTOS – tasks for sensor reading, state estimation, control, and communication.
- Error‑State Kalman Filter (ESKF) for attitude, velocity, and position estimation using IMU, magnetometer, barometer, and GNSS data.
- Cascade PID control – rate, angle, and velocity loops for precise and stable flight.
- Multi‑sensor integration:
- MPU6050 (IMU) – gyroscope & accelerometer
- QMC5883L (magnetometer)
- BMP280 (barometer)
- L76K (GNSS)
- 6 × HC‑SR04 (ultrasonic distance sensors)
- MAVLink communication with companion computer for high‑level commands and telemetry.
- Safety state machine – arming checks, failsafe on connection loss, low battery, excessive tilt, and automatic landing.
- DMA‑driven UART/I²C for low‑CPU‑load sensor reading and radio communication (CRSF protocol).
- Custom 2‑layer PCB designed for noise immunity and compact integration.
- Crossfire protocol support for ExpressLRS control and telemetry
| Component | Model / Specification |
|---|---|
| Microcontroller | STM32F411CEU6 (WeAct Studio MiniF4) |
| IMU | MPU6050 |
| Magnetometer | QMC5883L |
| Barometer | BMP280 |
| GNSS | L76K |
| Distance Sensors | 6 × HC‑SR04 |
| Radio Receiver | Radiomaster RP3 (CRSF protocol) |
| Power Regulation | Pololu D24V50F5 (5V, 5A step‑down) |
| Frame | GEPRC Mark4 (7‑inch) |
| Motors / ESCs | T‑Motor Velox V3008 / T‑Motor P60A |
Fig. 1: FreeRTOS task structure and data flow.
The firmware is modular, with each hardware interface and algorithm isolated in its own driver or module. Tasks are prioritized as follows:
| Task | Frequency | Priority | Description |
|---|---|---|---|
| Sensor Acquisition | 1 kHz | High | Read IMU, barometer, magnetometer |
| State Estimation | 500 Hz | High | ESKF update and prediction |
| Control Loop | 500 Hz | High | Cascade PID (rate → angle → velocity) |
| Distance Sensing | 10 Hz | Medium | Poll HC‑SR04 sensors |
| MAVLink RX/TX | Event‑driven | Medium | Communicate with companion computer |
| Radio RX | Event‑driven | High | Decode CRSF frames |
| Safety Monitor | 10 Hz | Low | Check battery, tilt, connection |
All inter‑task communication uses FreeRTOS queues and mutexes to avoid race conditions. Memory allocation is static.
- ARM GCC toolchain (
arm-none-eabi-gcc) - CMake (≥ 3.10)
- OpenOCD or ST‑Link utility
git clone https://github.com/mboiar/FreeRTOS_FlightController.git
cd FreeRTOS_FlightController
mkdir build && cd build
cmake ..
make -j4