1.Electronics

STM32-Quadcopter: Low-cost Quadcopter Design

Description

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This is a quadcopter design based on the STM32F411CEU Blackpill flight controller. The flight controller is compatible with INAV 6.0 firmware. The flight controller uses an MPU6500 for inertial measurements and a BMP280 for altitude sensing, and also supports an optional GPS and magnetometer module.

The frame is composed mostly of 2D parts cut from carbon-fiber sheets. Alternatively, you can 3D-print parts in carbon-fiber-reinforced filaments (PET-CF, PAHT-CF, PA6-CF, PPS-CF), with less-critical components in ABS.

Table of Contents

• Introduction
• Frame
  • CF Components
  • ABS Components
  • Mechanical Components BOM
• Electronics
  • Electronics BOM
  • SMD Components
  • Pins
  • Sample Diagram
  • GPS (UART1) Wiring
  • Capacitor for Spike Filtering
• Firmware
  • Build
    • Prerequisites
    • Clone INAV
    • Add Target
    • Patch Code
    • Build
  • Flash
  • MPU9250 Issue
• Configuration and Setting Up

Frame

Use the assembled CAD model in the 3.Models/ folder as a reference to build.

CF Components

All files are under 3.Models/. Add dogbones and tolerances for manufacturability.

ABS Components

Recommend using a 0.4 mm or 0.6 mm high-strength print profile.

Mechanical Components BOM

Electronics

Structure

1. Electronics/
  ├── Extra/
  │   ├── *.step
  │   └── ...
  ├── Hardware-backups/
  │   └── ...
  ├── Production/           ← Gerber output for fabrication
  │   ├── Hardware-B_Cu.gbl
  │   └── ...
  ├── Hardware.kicad_pcb    ← KiCAD PCB file
  ├── Hardware.kicad_sch    ← KiCAD Schematics file
  ├── Hardware.kicad_pro    ← KiCAD project
  ├── JLCPCB.kicad_dru      ← Rules for JLCPCB manufacturing
  ├── Production.zip        ← Gerber
  └── Schematics.pdf        ← Schematics

Electronics BOM

SMD Components

Gerber files and BOM are available under the electronics folder.

Pins

Sample Diagram

Diagram only; not actual wiring. Please follow the strict pin assignments.

GPS (UART1) Wiring

Ensure connectors are wired correctly according to the pinout. Note that RX should connect to TX: RX1 → GPS TX, TX1 → GPS RX.

Capacitor for Spike Filtering

One or more bulk electrolytic capacitor is recommended to protect against voltage spikes. Use an electrolytic capacitor such as 330 µF @ 50 V and place it between VBAT and GND near the input. For extra protection, a TVS diode clampeing at ~12 V is ideal.

Firmware

Build

The firmware used is INAV v6.0.0 (github link). This project does not support INAV v7+ currently due to USB issue. If one wants to modify the target file or other configurations of the firmware, they must rebuild the binary. Follow this guide to build:

Prerequisites

• CMake ≥ 3.15
• Ninja
• gcc-arm-none-eabi toolchain

Clone INAV

git clone https://github.com/iNavFlight/inav.git
cd inav
git checkout 6.0

Add Target

Copy the entire 2.Firmware/GYW_BLACKPILL_F411 folder into the local INAV repository under src/main/target/ so that it ends up as:

inav/
└── src/
    └── main/
        └── target/
            ├──  GYW_BLACKPILL_F411/
            └── ...

Patch Code

INAV 6.0 doesn’t support a 25 MHz HSE clock by default, so if your board (like the Blackpill F411) uses a 25 MHz crystal, you must update the PLL setup in src/main/target/system_stm32f4xx.c as follows:

In system_stm32f4xx.c, locate the PLL setup region and modify it as follows:

#if defined(STM32F40_41xxx) || defined(STM32F427_437xx) || defined(STM32F429_439xx) || defined(STM32F401xx) || defined(STM32F469_479xx) || defined(STM32F446xx) || defined(STM32F410xx) || defined(STM32F411xE)
+   #if HSE_VALUE == 25000000
+       #define PLL_M   25
+   #elif HSE_VALUE == 24000000
-   #if HSE_VALUE == 24000000
        #define PLL_M   24
    #elif HSE_VALUE == 16000000
        #define PLL_M   16
    #elif HSE_VALUE == 8000000
        #define PLL_M   8
    #else
        #error Invalid HSE_VALUE
    #endif
#else
    #error Undefined CPU
#endif

Build

Ensure that you have installed all dependencies. Inside the inav root repository execute:

mkdir -p build && cd build
cmake .. -G Ninja \
  -DBOARD=GYW_BLACKPILL_F411 \
  -DCMAKE_TOOLCHAIN_FILE=../tools/cmake/toolchain-arm-none-eabi.cmake
ninja

The firmware binary should be at build/inav_6.0.0_GYW_BLACKPILL_F411.hex.

Flash

First, download the INAV Configurator v6.0.0 from this link. Once installed, launch INAV Configurator and connect to the Blackpill via USB. Cut the red wire in the USB cable to prevent it from powering the Blackpill. Instead, power the flight controller using an external 3S battery.

To enter DFU mode, hold the BOOT button on the Blackpill while powering it on. Alternatively, you can press RESET while holding the BOOT button. When in DFU mode, the blue LED on the Blackpill will be off, and the board should appear in the INAV Configurator’s drop-down menu as a DFU device. Move to the Firmware Flasher tab on the left. Click Load Firmware, select the file inav_6.0.0_GYW_BLACKPILL_F411.hex (found in the firmware folder), then click Flash Firmware.

A progress bar will appear during firmware flash.

When the firmware is successfully flashed, click connect. The configuration menu should show up.

MPU9250 Issue

If you are using a MPU9250 module, you may encounter the problem that INAV does not recognize the accelerometer. This is due to many boards labeled MPU9250 actually house only an MPU6500 (omitting or substituting the magnetometer). Since drones often use an external magnetometer, this usually isn’t critical if your accelerometer and gyro (MPU6500) work.

To identify your chip, read the WHO_AM_I register (0x75) via I²C (use an Arduino or something similar to do this part). Example Arduino code:

#include <Wire.h>
const uint8_t MPU_ADDR     = 0x68; // I²C address
const uint8_t WHO_AM_I_REG = 0x75;
void setup() {
  Serial.begin(115200);
  Wire.begin();
  delay(100);
  Wire.beginTransmission(MPU_ADDR);
  Wire.write(WHO_AM_I_REG);
  if (Wire.endTransmission(false) != 0) {
    Serial.println(F("no device found")); while (1);
  }
  Wire.requestFrom(MPU_ADDR, (uint8_t)1);
  if (Wire.available()) {
    uint8_t id = Wire.read();
    Serial.print(F("WHO_AM_I = 0x"));
    Serial.println(id, HEX);
  } else {
    Serial.println(F("no data returned"));
  }
}

If it prints 0x71, it’s MPU6500; 0x73 indicates MPU9250.

The current binary file and target is configured for MPU6500. To use MPU9250, comment out the block for MPU6500 and uncomment the MPU9250 block in the target file. Rebuild the binary and flash. It looks like this:

#define USE_IMU_MPU9250
#define IMU_MPU9250_ALIGN   CW0_DEG
#define MPU9250_CS_PIN      PB12
#define MPU9250_SPI_BUS     BUS_SPI2

Configuration and Setting Up

Follow standard inav configuration procedures.