STM32 Flight controller

Implementing a flight controller for a small quadcopter. UAV is controlled through ELRS transmitter.

What's done:

• single roll/pitch PID control loop, stabilization using gyroscope (accro mode) readings.
• double roll/pitch PID control loop, stabilization using accelerometer/gyroscope readings.
• yaw stabilization using gyroscope readings.
• yaw stabilization using magnetometer/gyroscope readings.
• acceleration stabilization using accelerometer readings.
• configuration through wi-fi.
• altitude hold.
• dshot-300 ESC control protocol.
• IRC Tramp VTX control.
• telemetry through eLRS.
• terminal configuration tool.
• Qt5 based GUI configuration tool.

Devices

• MCU: STM32F405RGT6
• Crystall oscillator: 20 Mhz
• DC-DC converter for control board and camera: TPS5430
• Control board voltage regulator: AMS1117-3.3
• Accelerometer/Gyroscope: ICM-42688-P
• Magnetometer: QMC5883L
• Remote control: ERLS CRSF receiver
• Telemetry/debug/config: ESP8285
• Barometer: HP206C

Project structure

• pcb -- the directory containing schematics for the flight controller and BEC:

  • bottom.png -- bottom side of flight controller board.
  • top.png -- top side of flight controller board.
  • ground.png -- ground layer of flight controller board.
  • power.png -- power layer of flight controller board.
  • tps5430.JPG -- DC-DC conveter used to convert battery voltage to 5 volts used by main board's input LDO and FPV camera.
  • conponentvalues.txt -- values and types for components on schematics.

• additional -- additional files

  • frame.dxf -- quadcopter frame outline.

• devices -- drivers for devices used by the flight controller:

  • device.h -- main interface for a character device. Used by almost all devices in devices directory.
  • uartconf.c and `uartconf.h -- driver that receives and sends data through one of UART's used for configuration and debugging.
  • bmp280.c and bmp280.h -- driver for a bmp280 barometer (currenty unused).
  • crsf.c and crsf.h -- driver for the CRSF protocol used by a ERLS receiver to interract with the main MCU through UART.
  • esp8266.c and esp8266.h -- driver used to exchange data with esp8285 through SPI.
  • hmc5883l.c and hmc5883l.h -- driver for an HMC5883L magnetometer (currently unused).
  • hp206c.c -- driver for a HP206C barometer.
  • mpu6500.c and mpu6500.h -- I2C driver for mpu6050 and mpu6500 IMUs (accelerometer + gyroscope).
  • qmc5883l.c and qmc5883l.h -- driver for an QMC5883L magnetometer.
  • icm42688.c and icm42688.h -- driver for an icm42688 IMU (accelerometer + gyroscope).
  • m10.c and m10.h -- driver for a M10 GNSS module.
  • w25.c and w25.h -- driver for a w25q SPI flash.
  • irc.c and irc.h -- driver for an IRC Tramp controlled VTX device.

• main.c -- all routines related to flight control.

• global.h -- global values used in many places in source code.

• crc.h -- CRC-8 implementation.

• stm32periph.c and stm32periph.h -- stm32 periphery initialization and error handling.

• util.c and util.h -- common utility functions that can be used in more than one source file.

• dsp.c and dsp.h -- functions for PID control and data filtering like low-pass filtering and complimentary filtering.

• command.c and command.h -- configuration and informational commands processing API.

• timev.c and timev.h -- periodic event processing API.

• uavconf/uavconf.c -- configuration tool that works through wi-fi AP created by flight controller using UDP protocol.

• uavconf_gui -- gui configuration tool:

  • main.cpp -- entry point for GUI configuration tool.
  • mainwidget.cpp -- implementation for Qt5 related functions.
  • mainwidget.h -- headers for Qt5 related functions.
  • uavconf.c and uavconf.h -- API for UDP interaction with UAV.

• all other .c, *.h and *.s files are generated by software.

UAV commands

Debug and configuration is performed through AP named copter created by this UAV. Listed commands should be sent using UDP/IP to address 192.168.3.1.

• r -- turn off motors
• c [altitude] -- recalibrate and set altitude reference value.
• calib mag (on|off) -- enter/escape magnetometer calibration mode
• flash write -- write settings into MCU's internal flash.
• info (mpu | qmc | hp | | dev | values | pid | gnss | ctrl | filter) -- get various values and infomation:
  • mpu -- ICM-42688-P IMU data.
  • qmc -- QMC5883L magnetometer data.
  • dev -- all devices status.
  • values -- configuration values.
  • pid -- PID values.
  • gnss -- M10 GNSS data.
  • ctrl -- eLRS remote configuration values.
  • filter -- complimentary and LPF filters configuration values.
• log set {l} -- set log length to {l} records and if {l} greater than 0 start logging. If {l} is 0, stop logging.
• log rget {b} {e} -- get log records whose number starts from {b} and end with {e} - 1.
• log bget {n1}...{nN} -- get batch of log records with numbers {n1}...{nN}.
• pid (tilt|yaw) mode (single/double) -- switch to single/double PID loop mode for tilt/yaw
• pid (tilt|stilt|yaw|syaw|throttle/climbrate/altitude) (p|i|d) {val} -- set PID controller values:
  • tilt -- tilt PID controler P/I/D value.
  • stilt -- pitch/roll rotation speed PID controller P/I/D value.
  • yaw -- yaw PID controller P/I/D value.
  • syaw -- yaw rotation speed PID controller P/I/D value.
  • throttle -- acceleration PID controller P/I/D value.
  • climbrate -- climb speed PID controller P/I/D value.
  • altitude -- altitude PID controller P/I/D value.
• compl (attitude/yaw/climbrate/altitude) {val} -- set complimentary filters time constants:
  • attitude -- filter that mixing accelerometer and gyroscope data to get pitch/roll value.
  • yaw -- filter that mixing gyroscope and magnetometer data to get yaw value.
  • climb rate -- filter that mixing acceleromter interated data and barometer data to get climb speed value.
  • altitude -- filter that mixing climb rate value and barometer data to get altitude value.
• lpf (climb|vaccel/altitude) {val} -- set low-pass filter's time constant for climb speed/vertical acceleration/altitude.
• adj (rollthrust/pitchthrust) {val} -- adjust motors thrust.
• adj (roll|pitch|yaw) {val} -- set offset for roll/pitch/yaw (only for dual PID loop mode).
• adj acc (x|y|z) {val} -- set x/y/z offset for acceleromter
• adj gyro (x|y|z) {val} -- set x/y/z offset for gyroscope
• adj mag (x0|y0|z0|xscale|yscale|zscale|decl) {val} -- set x/y/z offset, x/y/z scale or magnetic declination for magnetometer
• ctrl (roll|pitch) {val} -- set maximum roll/pitch tilt value in radians.
• ctrl (syaw|yaw) {val} -- set yaw rotation speed for single/double loop mode in radians.
• ctrl accel {val} -- set maximum acceleration for throttle loop.
• ctrl climbrate {val} -- set maximum climb rate in m/s.
• ctrl altmax {val} -- set maximum altitude in meters.

Log format

Log records got by commands log rget and log bget are just lines with set of space separated numeric strings and have such format:

    {CRC} {number} {v0} ... {v31}

, where {CRC} is CRC-8 sum of record line, {number} -- record number and {v0} ... {v31} -- 31 record values.

Log records sampled 64 times per second, so it is possible to get exact time from log start for each record, by it's number. For example, record with number 1234 was sampled at 45763 / 64 = 715.04 seconds from logging start, or, at 11 minutes and 55.04 seconds.

Record values store various values that have meaning during flight. They are listed below:

number	value
0	accelerometer scaled raw X value
1	accelerometer scaled raw Y value
2	accelerometer scaled raw Z value
3	gyroscope scaled raw X value
4	gyroscope scaled raw Y value
5	gyroscope scaled raw Z value
6	magnetometer raw X value
7	magnetometer raw Y value
8	magnetometer raw Z value
9	barometer temperature
10	barometer altitude
11	filtered accelerometer X value
12	filtered accelerometer Y value
13	filtered accelerometer Z value
14	calculated roll value
15	calculated pitch value
16	calculated yaw value
17	calculated climb rate
18	calculated altitude
19	left-forward motor's thrust
20	left-backward motor's thrust
21	right-forward motor's thrust
22	right-backward motor's thrust
23	eLRS channel 0 value
24	eLRS channel 1 value
25	eLRS channel 2 value
26	eLRS channel 3 value
27	eLRS channel 4 value
28	eLRS channel 5 value
29	eLRS channel 6 value
30	eLRS channel 7 value
31	battery voltage

Quadcopter parameters

• Motors: 1404, 3800 kV
• Props: 3030
• Battery: 14.8v (4s), 1300 mAh, 120c
• Frame: carbon fiber

Quadcopter Weight

• PCB and camera: 20g
• ESC: 30g
• Motors + props: 48g
• Battery: 148g
• BEC: ~6g
• Antenna: 10g
• Frame: ~114g
• Total weight: 376g