Using STM32 to produce multi-rotor UAV (Unmanned Aerial Vehicle)

Using STM32 microcontrollers to develop a multi-rotor UAV (Unmanned Aerial Vehicle) is a popular choice due to their real-time processing capabilities, peripheral support, and robustness. Below is a structured guide on how to approach this project:

1. Hardware Selection

A. STM32 MCU Options

• STM32F4/F7/H7 Series (High Performance, Floating-Point Support)

  • Recommended for advanced flight controllers (e.g., STM32F405, STM32F745, STM32H743).

• STM32G4 Series (Balanced Performance & Power Efficiency)

• STM32F1/F0 Series (Basic Quadcopters, Less Complex Control)

B. Essential Components

• Flight Controller Board (Custom PCB or Development Board like Nucleo-STM32H743)

• IMU (Inertial Measurement Unit) – MPU6050 (Accel + Gyro), BMI270, ICM-42605, or BNO055 (9-DOF)

• Barometer (MS5611, BMP280) – For altitude hold

• Magnetometer (HMC5883L, QMC5883) – For heading

• ESC (Electronic Speed Controller) – BLHeli_S / BLHeli_32 (for Brushless Motors)

• Motors & Propellers – KV rating depends on UAV size (e.g., 1000KV for 5" drones)

• Battery – LiPo (3S-6S, depending on motor requirements)

• Radio Receiver (PPM/SBUS/CRSF – e.g., FrSky X4R, ELRS)

• Telemetry (Optional) – ESP8266/NRF24L01 for wireless data

2. Software Development

A. Firmware Development

• RTOS (Real-Time OS) – Use FreeRTOS or ChibiOS for task scheduling.

• Sensor Fusion – Implement Madgwick/Mahony AHRS or Kalman Filter for attitude estimation.

• PID Control – For motor stabilization (Roll, Pitch, Yaw).

• PWM Output – Use STM32 TIMER + DMA for ESC control (OneShot125, DShot protocol).

• Communication Protocols:

  • I2C/SPI (IMU, Barometer)

  • UART (GPS, Telemetry, Receiver)

  • CAN Bus (Advanced ESCs)

B. Development Tools

• IDE: STM32CubeIDE (Free, HAL/LL Support)

• Libraries:

  • STM32 HAL/LL (Hardware Abstraction Layer)

  • Betaflight/INAV (Open-Source Reference) (Study their STM32 implementations)

• Debugging: ST-Link, Logic Analyzer, UART Printf

3. Flight Control Algorithm

A. Basic Control Loop

1. Read Sensors (IMU, Barometer, Magnetometer)

2. Sensor Fusion (Compute Roll, Pitch, Yaw)

3. PID Controller (Adjust motor speeds based on error)

4. ESC Signal Generation (PWM/DShot)

B. Advanced Features (Optional)

• GPS Navigation (Waypoint Following, Return-to-Home)

• Obstacle Avoidance (Ultrasonic/LiDAR)

• Computer Vision (OpenMV, ESP32-CAM)

• Wireless Telemetry (MAVLink Protocol)

4. Example Code Snippet (STM32 + MPU6050 + PID)

// STM32 HAL-based PID Motor Control (Simplified)
#include "stm32f4xx_hal.h"
#include "mpu6050.h"  // MPU6050 Driver

// PID Gains
float Kp = 1.2, Ki = 0.5, Kd = 0.1;
float roll_error, pitch_error, yaw_error;

void IMU_Update() {
  MPU6050_Read_Data(&accel, &gyro);  // Read IMU
  MadgwickAHRSupdate(gyro.x, gyro.y, gyro.z, accel.x, accel.y, accel.z); // Sensor Fusion
}

void PID_Control() {
  roll_error = target_roll - current_roll;
  pitch_error = target_pitch - current_pitch;
  yaw_error = target_yaw - current_yaw;
  
  // Compute PID Output
  float roll_output = Kp * roll_error + Ki * roll_integral + Kd * (roll_error - prev_roll_error);
  float pitch_output = Kp * pitch_error + Ki * pitch_integral + Kd * (pitch_error - prev_pitch_error);
  
  // Adjust Motor Speeds (4 Motors)
  motor1 = throttle + roll_output + pitch_output;
  motor2 = throttle - roll_output + pitch_output;
  motor3 = throttle - roll_output - pitch_output;
  motor4 = throttle + roll_output - pitch_output;
  
  // Apply PWM to ESCs
  __HAL_TIM_SET_COMPARE(&htim3, TIM_CHANNEL_1, motor1);
  __HAL_TIM_SET_COMPARE(&htim3, TIM_CHANNEL_2, motor2);
  // ... (Other Motors)
}

int main(void) {
  HAL_Init();
  MPU6050_Init();
  while (1) {
    IMU_Update();
    PID_Control();
    HAL_Delay(2);  // ~500Hz Loop
  }
}

5. Testing & Calibration

• Motor Testing – Ensure correct spin direction.

• PID Tuning – Start with small gains, increase gradually.

• IMU Calibration – Eliminate bias in gyro/accel.

• Radio Calibration – Verify stick inputs (1000-2000µs PWM range).

6. Safety Considerations

• Fail-Safes (Signal Loss → Hover/Land)

• Battery Monitoring (Voltage Check)

• Propeller Guards (For Indoor Testing)

Conclusion

Building a multi-rotor UAV with STM32 involves:
✅ Selecting the right STM32 MCU (F4/F7/H7 recommended)
✅ Integrating IMU, ESCs, and Radio Receiver
✅ Writing firmware with Sensor Fusion + PID Control
✅ Testing and tuning for stable flight

For faster development, consider studying open-source flight controllers like Betaflight, iNav, or ArduPilot (many use STM32).