Try to build the sim on the latest macos

To make it consistent with the documentation

.editorconfig

@@ -0,0 +1,15 @@
+root = true
+
+[*]
+end_of_line = lf
+insert_final_newline = true
+
+[*.{ino,cpp,c,h,hpp,sdf,world,json}]
+charset = utf-8
+indent_style = tab
+tab_width = 4
+trim_trailing_whitespace = true
+
+[{*.yml,*.yaml,CMakeLists.txt}]
+indent_style = space
+indent_size = 2

.gitattributes

@@ -0,0 +1,2 @@
+# https://github.com/github-linguist/linguist/blob/master/docs/overrides.md
+*.h linguist-language=C++

.github/workflows/build.yml

@@ -0,0 +1,99 @@
+name: Build
+
+on:
+  push:
+    branches: [ '*' ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  build_linux:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=/usr/local/bin sh
+    - name: Build firmware
+      run: make
+    - name: Check c_cpp_properties.json
+      run: tools/check_c_cpp_properties.py
+
+  build_macos:
+    runs-on: macos-14
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: brew install arduino-cli
+    - name: Build firmware
+      run: make
+    - name: Check c_cpp_properties.json
+      run: tools/check_c_cpp_properties.py
+
+  build_windows:
+    runs-on: windows-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Arduino CLI
+      run: choco install arduino-cli
+    - name: Install Make
+      run: choco install make
+    - name: Build firmware
+      run: make
+    - name: Check c_cpp_properties.json
+      run: python3 tools/check_c_cpp_properties.py
+
+  build_simulator:
+    runs-on: ubuntu-latest
+    steps:
+    - name: Install Arduino CLI
+      uses: arduino/setup-arduino-cli@v1.1.1
+    - uses: actions/checkout@v4
+    - name: Install Gazebo
+      run: curl -sSL http://get.gazebosim.org | sh
+    - name: Install SDL2
+      run: sudo apt-get install libsdl2-dev
+    - name: Build simulator
+      run: make build_simulator
+    - uses: actions/upload-artifact@v3
+      with:
+        name: gazebo-plugin-binary
+        path: gazebo/build/*.so
+        retention-days: 1
+
+  build_simulator_macos:
+    runs-on: macos-15
+    steps:
+    - name: Install Arduino CLI
+      run: brew install arduino-cli
+    - uses: actions/checkout@v4
+    - name: Clean up python binaries # Workaround for https://github.com/actions/setup-python/issues/577
+      run: |
+        rm -f /usr/local/bin/2to3*
+        rm -f /usr/local/bin/idle3*
+        rm -f /usr/local/bin/pydoc3*
+        rm -f /usr/local/bin/python3*
+        rm -f /usr/local/bin/python3*-config
+    - name: Install Gazebo
+      run: brew update && brew tap osrf/simulation && brew install gazebo11
+    - name: Install SDL2
+      run: brew install sdl2
+    - name: Build simulator
+      run: make build_simulator
+
+  install_gz_ionic_macos:
+    runs-on: macos-15
+    steps:
+    - name: Install Gazebo
+      run: brew update && brew tap osrf/simulation && brew install gz-ionic
+
+  install_gz_jetty_macos:
+    runs-on: macos-15
+    steps:
+    - name: Install Gazebo
+      run: brew update && brew tap osrf/simulation && brew install gz-jetty
+
+  install_gz_harmonic_macos:
+    runs-on: macos-15
+    steps:
+    - name: Install Gazebo
+      run: brew update && brew tap osrf/simulation && brew install gz-harmonic

.github/workflows/tools.yml

@@ -0,0 +1,33 @@
+name: Build tools
+
+on:
+  push:
+    branches: [ '*' ]
+  pull_request:
+    branches: [ master ]
+
+jobs:
+  csv_to_ulog:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Build csv_to_ulog
+      run: cd tools/csv_to_ulog && mkdir build && cd build && cmake .. && make
+    - name: Test csv_to_ulog
+      run: |
+        cd tools/csv_to_ulog/build
+        echo -e "t,x,y,z\n0,1,2,3\n1,4,5,6" > log.csv
+        ./csv_to_ulog log.csv
+        test $(stat -c %s log.ulg) -eq 196
+  python_tools:
+    runs-on: ubuntu-latest
+    steps:
+    - uses: actions/checkout@v4
+    - name: Install Python dependencies
+      run: pip install -r tools/requirements.txt
+    - name: Test csv_to_mcap tool
+      run: |
+        cd tools
+        echo -e "t,x,y,z\n0,1,2,3\n1,4,5,6" > log.csv
+        ./csv_to_mcap.py log.csv
+        test $(stat -c %s log.mcap) -eq 883

.gitignore

@@ -0,0 +1,12 @@
+*.hex
+*.elf
+build/
+tools/log/
+.dependencies
+.vscode/*
+!.vscode/settings.json
+!.vscode/c_cpp_properties.json
+!.vscode/tasks.json
+!.vscode/launch.json
+!.vscode/extensions.json
+!.vscode/intellisense.h

.vscode/c_cpp_properties.json

@@ -0,0 +1,147 @@
+{
+	"configurations": [
+		{
+			"name": "Linux",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				"${workspaceFolder}/gazebo",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.0.7/libraries/**",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32",
+				"~/.arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/**",
+				"~/.arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/dio_qspi/include",
+				"~/Arduino/libraries/**",
+				"/usr/include/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32/Arduino.h",
+				"~/.arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/util.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/.arduino15/packages/esp32/tools/esp-x32/2302/bin/xtensa-esp32-elf-g++",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		},
+		{
+			"name": "Mac",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				"${workspaceFolder}/gazebo",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.0.7/libraries/**",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32",
+				"~/Library/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/include/**",
+				"~/Library/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/dio_qspi/include",
+				"~/Documents/Arduino/libraries/**",
+				"/opt/homebrew/include/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32/Arduino.h",
+				"~/Library/Arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/util.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/Library/Arduino15/packages/esp32/tools/esp-x32/2302/bin/xtensa-esp32-elf-g++",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ARDUINO_FQBN=esp32:esp32:d1_mini32",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		},
+		{
+			"name": "Win32",
+			"includePath": [
+				"${workspaceFolder}/flix",
+				"${workspaceFolder}/gazebo",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.0.7/libraries/**",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32",
+				"~/AppData/Local/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/**",
+				"~/AppData/Local/Arduino15/packages/esp32/tools/esp32-arduino-libs/idf-release_v5.1-632e0c2a/esp32/dio_qspi/include",
+				"~/Documents/Arduino/libraries/**"
+			],
+			"forcedInclude": [
+				"${workspaceFolder}/.vscode/intellisense.h",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.0.7/cores/esp32/Arduino.h",
+				"~/AppData/Local/Arduino15/packages/esp32/hardware/esp32/3.0.7/variants/d1_mini32/pins_arduino.h",
+				"${workspaceFolder}/flix/cli.ino",
+				"${workspaceFolder}/flix/control.ino",
+				"${workspaceFolder}/flix/estimate.ino",
+				"${workspaceFolder}/flix/flix.ino",
+				"${workspaceFolder}/flix/imu.ino",
+				"${workspaceFolder}/flix/led.ino",
+				"${workspaceFolder}/flix/log.ino",
+				"${workspaceFolder}/flix/mavlink.ino",
+				"${workspaceFolder}/flix/motors.ino",
+				"${workspaceFolder}/flix/rc.ino",
+				"${workspaceFolder}/flix/time.ino",
+				"${workspaceFolder}/flix/util.ino",
+				"${workspaceFolder}/flix/wifi.ino"
+			],
+			"compilerPath": "~/AppData/Local/Arduino15/packages/esp32/tools/esp-x32/2302/bin/xtensa-esp32-elf-g++.exe",
+			"cStandard": "c11",
+			"cppStandard": "c++17",
+			"defines": [
+				"F_CPU=240000000L",
+				"ARDUINO=10607",
+				"ARDUINO_D1_MINI32",
+				"ARDUINO_ARCH_ESP32",
+				"ARDUINO_BOARD=D1_MINI32",
+				"ARDUINO_VARIANT=d1_mini32",
+				"ARDUINO_PARTITION_default",
+				"ARDUINO_FQBN=esp32:esp32:d1_mini32",
+				"ESP32",
+				"CORE_DEBUG_LEVEL=0",
+				"ARDUINO_USB_CDC_ON_BOOT="
+			]
+		}
+	],
+	"version": 4
+}

.vscode/extensions.json

@@ -0,0 +1,10 @@
+{
+	// See https://go.microsoft.com/fwlink/?LinkId=827846 to learn about workspace recommendations.
+	"recommendations": [
+		"ms-vscode.cpptools",
+		"twxs.cmake",
+		"ms-vscode.cmake-tools",
+		"ms-python.python"
+	],
+	"unwantedRecommendations": []
+}

.vscode/intellisense.h

@@ -0,0 +1,5 @@
+#ifdef __INTELLISENSE__
+	#pragma diag_suppress 144, 513
+	// diag 144: a value of type "enum <unnamed>" cannot be used to initialize an entity of type "enum <unnamed>"C/C++
+	// diag 513: a value of type "enum <unnamed>" cannot be assigned to an entity of type "enum <unnamed>"C/C++
+#endif

.vscode/launch.json

@@ -0,0 +1,25 @@
+{
+	"version": "0.2.0",
+	"configurations": [
+		{
+			"name": "Debug simulation",
+			"type": "cppdbg",
+			"request": "launch",
+			"program": "/usr/bin/gzserver",
+			"osx": {
+				"program": "/opt/homebrew/bin/gzserver",
+				"MIMode": "lldb",
+			},
+			"args": ["--verbose", "${workspaceFolder}/gazebo/flix.world"],
+			"stopAtEntry": false,
+			"cwd": "${fileDirname}",
+			"environment": [
+				{"name": "GAZEBO_MODEL_PATH", "value": "${workspaceFolder}/gazebo/models"},
+				{"name": "GAZEBO_PLUGIN_PATH", "value": "${workspaceFolder}/gazebo/build"}
+			],
+			"MIMode": "gdb",
+			"preLaunchTask": "Build simulator",
+			"externalConsole": true,
+		},
+	]
+}

.vscode/settings.json

@@ -0,0 +1,13 @@
+{
+	"C_Cpp.intelliSenseEngineFallback": "enabled",
+	"files.associations": {
+		"*.sdf": "xml",
+		"*.ino": "cpp",
+		"*.h": "cpp"
+	},
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.function": "newLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.block": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.lambda": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.namespace": "sameLine",
+	"C_Cpp.vcFormat.newLine.beforeOpenBrace.type": "sameLine"
+}

.vscode/tasks.json

@@ -0,0 +1,31 @@
+{
+	"tasks": [
+		{
+			"label": "Build firmware",
+			"type": "shell",
+			"command": "make",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false },
+		},
+		{
+			"label": "Upload firmware",
+			"type": "shell",
+			"command": "make upload",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false }
+		},
+		{
+			"label": "Build simulator",
+			"type": "shell",
+			"command": "make build_simulator",
+			"problemMatcher": [ "$gcc" ],
+			"presentation": { "clear": true, "showReuseMessage": false }
+		},
+		{
+			"label": "Clean",
+			"type": "shell",
+			"command": "make clean",
+		}
+	],
+	"version": "2.0.0"
+}

CNAME

@@ -1 +0,0 @@
-quadcopter.dev

Makefile

@@ -0,0 +1,43 @@
+BOARD = esp32:esp32:d1_mini32
+PORT := $(wildcard /dev/serial/by-id/usb-Silicon_Labs_CP21* /dev/serial/by-id/usb-1a86_USB_Single_Serial_* /dev/cu.usbserial-*)
+PORT := $(strip $(PORT))
+
+build: .dependencies
+	arduino-cli compile --fqbn $(BOARD) flix
+
+upload: build
+	arduino-cli upload --fqbn $(BOARD) -p "$(PORT)" flix
+
+monitor:
+	arduino-cli monitor -p "$(PORT)" -c baudrate=115200
+
+dependencies .dependencies:
+	arduino-cli core update-index --config-file arduino-cli.yaml
+	arduino-cli core install esp32:esp32@3.0.7 --config-file arduino-cli.yaml
+	arduino-cli lib update-index
+	arduino-cli lib install "FlixPeriph"
+	arduino-cli lib install "MAVLink"@2.0.12
+	touch .dependencies
+
+gazebo/build cmake: gazebo/CMakeLists.txt
+	mkdir -p gazebo/build
+	cd gazebo/build && cmake ..
+
+build_simulator: .dependencies gazebo/build
+	make -C gazebo/build
+
+simulator: build_simulator
+	GAZEBO_MODEL_PATH=$$GAZEBO_MODEL_PATH:${CURDIR}/gazebo/models \
+	GAZEBO_PLUGIN_PATH=$$GAZEBO_PLUGIN_PATH:${CURDIR}/gazebo/build \
+	gazebo --verbose ${CURDIR}/gazebo/flix.world
+
+log:
+	PORT=$(PORT) tools/grab_log.py
+
+plot:
+	plotjuggler -d $(shell ls -t tools/log/*.csv | head -n1)
+
+clean:
+	rm -rf gazebo/build flix/build flix/cache .dependencies
+
+.PHONY: build upload monitor dependencies cmake build_simulator simulator log clean

README.md

@@ -0,0 +1,156 @@
+# Flix
+
+**Flix** (*flight + X*) — making an open source ESP32-based quadcopter from scratch.
+
+<table>
+  <tr>
+    <td align=center><strong>Version 1</strong> (3D-printed frame)</td>
+    <td align=center><strong>Version 0</strong></td>
+  </tr>
+  <tr>
+    <td><img src="docs/img/flix1.jpg" width=500 alt="Flix quadcopter"></td>
+    <td><img src="docs/img/flix.jpg" width=500 alt="Flix quadcopter"></td>
+  </tr>
+</table>
+
+## Features
+
+* Simple and clean Arduino based source code.
+* Acro and Stabilized flight using remote control.
+* Precise simulation using Gazebo.
+* [In-RAM logging](docs/log.md).
+* Command line interface through USB port.
+* Wi-Fi support.
+* MAVLink support.
+* Control using mobile phone (with QGroundControl app).
+* Completely 3D-printed frame.
+* *Textbook and videos for students on writing a flight controller¹.*
+* *Position control and autonomous flights using external camera¹*.
+* [Building and running instructions](docs/build.md).
+
+*¹ — planned.*
+
+## It actually flies
+
+See detailed demo video (for version 0): https://youtu.be/8GzzIQ3C6DQ.
+
+<a href="https://youtu.be/8GzzIQ3C6DQ"><img width=500 src="https://i3.ytimg.com/vi/8GzzIQ3C6DQ/maxresdefault.jpg"></a>
+
+Version 1 test flight: https://t.me/opensourcequadcopter/42.
+
+<a href="https://t.me/opensourcequadcopter/42"><img width=500 src="docs/img/flight-video.jpg"></a>
+
+## Simulation
+
+The simulator is implemented using Gazebo and runs the original Arduino code:
+
+<img src="docs/img/simulator.png" width=500 alt="Flix simulator">
+
+See [instructions on running the simulation](docs/build.md).
+
+## Components (version 1)
+
+|Type|Part|Image|Quantity|
+|-|-|:-:|:-:|
+|Microcontroller board|ESP32 Mini|<img src="docs/img/esp32.jpg" width=100>|1|
+|IMU (and barometer²) board|GY‑91 (or other MPU‑9250/MPU‑6500 board), ICM‑20948³|<img src="docs/img/gy-91.jpg" width=90 align=center><img src="docs/img/icm-20948.jpg" width=100>|1|
+|Motor|8520 3.7V brushed motor (**shaft 0.8mm!**)|<img src="docs/img/motor.jpeg" width=100>|4|
+|Propeller|Hubsan 55 mm|<img src="docs/img/prop.jpg" width=100>|4|
+|MOSFET (transistor)|100N03A or [analog](https://t.me/opensourcequadcopter/33)|<img src="docs/img/100n03a.jpg" width=100>|4|
+|Pull-down resistor|10 kΩ|<img src="docs/img/resistor10k.jpg" width=100>|4|
+|3.7V Li-Po battery|LW 952540 (or any compatible by the size)|<img src="docs/img/battery.jpg" width=100>|1|
+|Li-Po Battery charger|Any|<img src="docs/img/charger.jpg" width=100>|1|
+|Screws for IMU board mounting|M3x5|<img src="docs/img/screw-m3.jpg" width=100>|2|
+|Screws for frame assembly|M1.4x5|<img src="docs/img/screw-m1.4.jpg" height=30 align=center>|4|
+|Frame bottom part|3D printed⁴:<br>[`flix-frame.stl`](docs/assets/flix-frame.stl) [`flix-frame.step`](docs/assets/flix-frame.step)|<img src="docs/img/frame1.jpg" width=100>|1|
+|Frame top part|3D printed:<br>[`esp32-holder.stl`](docs/assets/esp32-holder.stl) [`esp32-holder.step`](docs/assets/esp32-holder.step)|<img src="docs/img/esp32-holder.jpg" width=100>|1|
+|Washer for IMU board mounting|3D printed:<br>[`washer-m3.stl`](docs/assets/washer-m3.stl) [`washer-m3.step`](docs/assets/washer-m3.step)|<img src="docs/img/washer-m3.jpg" width=100>|1|
+|*RC transmitter (optional)*|*KINGKONG TINY X8 or other⁵*|<img src="docs/img/tx.jpg" width=100>|1|
+|*RC receiver (optional)*|*DF500 or other⁵*|<img src="docs/img/rx.jpg" width=100>|1|
+|Wires|28 AWG recommended|<img src="docs/img/wire-28awg.jpg" width=100>||
+|Tape, double-sided tape||||
+
+*² — barometer is not used for now.*<br>
+*³ — change `MPU9250` to `ICM20948` in `imu.ino` file if using ICM-20948 board.*<br>
+*⁴ — this frame is optimized for GY-91 board, if using other, the board mount holes positions should be modified.*<br>
+*⁵ — you may use any transmitter-receiver pair with SBUS interface.*
+
+Tools required for assembly:
+
+* 3D printer.
+* Soldering iron.
+* Solder wire (with flux).
+* Screwdrivers.
+* Multimeter.
+
+Feel free to modify the design and or code, and create your own improved versions of Flix! Send your results to the [official Telegram chat](https://t.me/opensourcequadcopterchat), or directly to the author ([E-mail](mailto:okalachev@gmail.com), [Telegram](https://t.me/okalachev)).
+
+## Schematics (version 1)
+
+### Simplified connection diagram
+
+<img src="docs/img/schematics1.svg" width=800 alt="Flix version 1 schematics">
+
+Motor connection scheme:
+
+<img src="docs/img/mosfet-connection.png" height=400 alt="MOSFET connection scheme">
+
+Complete diagram is Work-in-Progress.
+
+### Notes
+
+* Power ESP32 Mini with Li-Po battery using VCC (+) and GND (-) pins.
+* Connect the IMU board to the ESP32 Mini using VSPI, power it using 3.3V and GND pins:
+
+  |IMU pin|ESP32 pin|
+  |-|-|
+  |GND|GND|
+  |3.3V|3.3V|
+  |SCL *(SCK)*|SVP (GPIO18)|
+  |SDA *(MOSI)*|GPIO23|
+  |SAO *(MISO)*|GPIO19|
+  |NCS|GPIO5|
+
+* Solder pull-down resistors to the MOSFETs.
+* Connect the motors to the ESP32 Mini using MOSFETs, by following scheme:
+
+  |Motor|Position|Direction|Wires|GPIO|
+  |-|-|-|-|-|
+  |Motor 0|Rear left|Counter-clockwise|Black & White|GPIO12|
+  |Motor 1|Rear right|Clockwise|Blue & Red|GPIO13|
+  |Motor 2|Front right|Counter-clockwise|Black & White|GPIO14|
+  |Motor 3|Front left|Clockwise|Blue & Red|GPIO15|
+
+  Counter-clockwise motors have black and white wires and clockwise motors have blue and red wires.
+
+* Optionally connect the RC receiver to the ESP32's UART2:
+
+  |Receiver pin|ESP32 pin|
+  |-|-|
+  |GND|GND|
+  |VIN|VC (or 3.3V depending on the receiver)|
+  |Signal|GPIO4⁶|
+
+*⁶ — UART2 RX pin was [changed](https://docs.espressif.com/projects/arduino-esp32/en/latest/migration_guides/2.x_to_3.0.html#id14) to GPIO4 in Arduino ESP32 core 3.0.*
+
+### IMU placement
+
+Required IMU orientation on the drone is **FLU** (Forward, Left, Up)⁷:
+
+<img src="docs/img/flu.svg" width=400 alt="GY-91 axis">
+
+In case of using **FRD** orientation (Forward, Right, Down), use [the code for rotation](https://gist.github.com/okalachev/713db47e31bce643dbbc9539d166ce98).
+
+*⁷ — This X/Y/Z IMU axis orientation is used in the Flix IMU library, internal accel/gyro/mag axes differ.*
+
+## Version 0
+
+See the information on the obsolete version 0 in the [corresponding article](docs/version0.md).
+
+## Materials
+
+Subscribe to the Telegram channel on developing the drone and the flight controller (in Russian): https://t.me/opensourcequadcopter.
+
+Join the official Telegram chat: https://t.me/opensourcequadcopterchat.
+
+Detailed article on Habr.com about the development of the drone (in Russian): https://habr.com/ru/articles/814127/.

arduino-cli.yaml

@@ -0,0 +1,3 @@
+board_manager:
+  additional_urls:
+    - https://raw.githubusercontent.com/espressif/arduino-esp32/gh-pages/package_esp32_index.json

docs/assets/washer-m3.step

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docs/build.md

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+# Building and running
+
+To build the firmware or the simulator, you need to clone the repository using git:
+
+```bash
+git clone https://github.com/okalachev/flix.git
+cd flix
+```
+
+## Simulation
+
+### Ubuntu 20.04
+
+The latest version of Ubuntu supported by Gazebo 11 simulator is 20.04. If you have a newer version, consider using a virtual machine.
+
+1. Install Arduino CLI:
+
+   ```bash
+   curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=~/.local/bin sh
+   ```
+
+2. Install Gazebo 11:
+
+   ```bash
+   curl -sSL http://get.gazebosim.org | sh
+   ```
+
+   Set up your Gazebo environment variables:
+
+   ```bash
+   echo "source /usr/share/gazebo/setup.sh" >> ~/.bashrc
+   source ~/.bashrc
+   ```
+
+3. Install SDL2 and other dependencies:
+
+   ```bash
+   sudo apt-get update && sudo apt-get install build-essential libsdl2-dev
+   ```
+
+4. Add your user to the `input` group to enable joystick support (you need to re-login after this command):
+
+   ```bash
+   sudo usermod -a -G input $USER
+   ```
+
+5. Run the simulation:
+
+   ```bash
+   make simulator
+   ```
+
+### macOS
+
+1. Install Homebrew package manager, if you don't have it installed:
+
+   ```bash
+   /bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"
+   ```
+
+2. Install Arduino CLI, Gazebo 11 and SDL2:
+
+   ```bash
+   brew tap osrf/simulation
+   brew install arduino-cli
+   brew install gazebo11
+   brew install sdl2
+   ```
+
+   Set up your Gazebo environment variables:
+
+   ```bash
+   echo "source /opt/homebrew/share/gazebo/setup.sh" >> ~/.zshrc
+   source ~/.zshrc
+   ```
+
+3. Run the simulation:
+
+   ```bash
+   make simulator
+   ```
+
+### Setup and flight
+
+#### Control with smartphone
+
+1. Install [QGroundControl mobile app](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/getting_started/download_and_install.html#android) on your smartphone.
+2. Connect your smartphone to the same Wi-Fi network as the machine running the simulator.
+3. If you're using a virtual machine, make sure that its network is set to the **bridged** mode with Wi-Fi adapter selected.
+4. Run the simulation.
+5. Open QGroundControl app. It should connect and begin showing the virtual drone's telemetry automatically.
+6. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
+7. Use the virtual joystick to fly the drone!
+
+#### Control with USB remote control
+
+1. Connect your USB remote control to the machine running the simulator.
+2. Run the simulation.
+3. Calibrate the RC using `cr` command in the command line interface and stop the simulation.
+4. Copy the calibration results to the source code (`gazebo/joystick.h`).
+5. Run the simulation again.
+6. Use the USB remote control to fly the drone!
+
+## Firmware
+
+### Arduino IDE (Windows, Linux, macOS)
+
+1. Install [Arduino IDE](https://www.arduino.cc/en/software) (version 2 is recommended).
+2. Install ESP32 core, version 3.0.7 (version 2.x is not supported). See the [official Espressif's instructions](https://docs.espressif.com/projects/arduino-esp32/en/latest/installing.html#installing-using-arduino-ide) on installing ESP32 Core in Arduino IDE.
+3. Install the following libraries using [Library Manager](https://docs.arduino.cc/software/ide-v2/tutorials/ide-v2-installing-a-library):
+   * `FlixPeriph`, the latest version.
+   * `MAVLink`, version 2.0.12.
+4. Clone the project using git or [download the source code as a ZIP archive](https://codeload.github.com/okalachev/flix/zip/refs/heads/master).
+5. Open the downloaded Arduino sketch `flix/flix.ino` in Arduino IDE.
+6. [Build and upload](https://docs.arduino.cc/software/ide-v2/tutorials/getting-started/ide-v2-uploading-a-sketch) the firmware using Arduino IDE.
+
+### Command line (Windows, Linux, macOS)
+
+1. [Install Arduino CLI](https://arduino.github.io/arduino-cli/installation/).
+2. Windows users might need to install [USB to UART bridge driver from Silicon Labs](https://www.silabs.com/developers/usb-to-uart-bridge-vcp-drivers).
+3. Compile the firmware using `make`. Arduino dependencies will be installed automatically:
+
+   ```bash
+   make
+   ```
+
+   You can flash the firmware to the board using command:
+
+   ```bash
+   make upload
+   ```
+
+   You can also compile the firmware, upload it and start serial port monitoring using command:
+
+   ```bash
+   make upload monitor
+   ```
+
+See other available Make commands in the [Makefile](../Makefile).
+
+### Setup and flight
+
+Before flight you need to calibrate the accelerometer:
+
+1. Open Serial Monitor in Arduino IDE (use use `make monitor` command in the command line).
+2. Type `ca` command there.
+3. Copy calibration results to the source code (`flix/imu.ino`).
+
+#### Control with smartphone
+
+1. Install [QGroundControl mobile app](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/getting_started/download_and_install.html#android) on your smartphone.
+2. Power the drone using the battery.
+3. Connect your smartphone to the appeared `flix` Wi-Fi network.
+4. Open QGroundControl app. It should connect and begin showing the drone's telemetry automatically.
+5. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
+6. Use the virtual joystick to fly the drone!
+
+#### Control with remote control
+
+Before flight using remote control, you need to calibrate it:
+
+1. Open Serial Monitor in Arduino IDE (use use `make monitor` command in the command line).
+2. Type `cr` command there.
+3. Copy calibration results to the source code (`flix/rc.ino`).
+
+Then you can use your remote control to fly the drone!
+
+> [!NOTE]
+> If something goes wrong, go to the [Troubleshooting](troubleshooting.md) article.
+
+### Firmware code structure
+
+See [firmware overview](firmware.md) for more details.

docs/firmware.md

@@ -0,0 +1,37 @@
+# Firmware overview
+
+## Dataflow
+
+<img src="img/dataflow.svg" width=800 alt="Firmware dataflow diagram">
+
+The main loop is running at 1000 Hz. All the dataflow is happening through global variables (for simplicity):
+
+* `t` *(float)* — current step time, *s*.
+* `dt` *(float)* — time delta between the current and previous steps, *s*.
+* `gyro` *(Vector)* — data from the gyroscope, *rad/s*.
+* `acc` *(Vector)* — acceleration data from the accelerometer, *m/s<sup>2</sup>*.
+* `rates` *(Vector)* — filtered angular rates, *rad/s*.
+* `attitude` *(Quaternion)* — estimated attitude (orientation) of drone.
+* `controls` *(float[])* — user control inputs from the RC, normalized to [-1, 1] range.
+* `motors` *(float[])* — motor outputs, normalized to [-1, 1] range; reverse rotation is possible.
+
+## Source files
+
+Firmware source files are located in `flix` directory. The key files are:
+
+* [`flix.ino`](../flix/flix.ino) — main entry point, Arduino sketch. Includes global variables definition and the main loop.
+* [`imu.ino`](../flix/imu.ino) — reading data from the IMU sensor (gyroscope and accelerometer), IMU calibration.
+* [`rc.ino`](../flix/rc.ino) — reading data from the RC receiver, RC calibration.
+* [`estimate.ino`](../flix/estimate.ino) — drone's attitude estimation, complementary filter.
+* [`control.ino`](../flix/control.ino) — drone's attitude and rates control, three-dimensional two-level cascade PID controller.
+* [`motors.ino`](../flix/motors.ino) — PWM motor outputs control.
+
+Utility files include:
+
+* [`vector.h`](../flix/vector.h), [`quaternion.h`](../flix/quaternion.h) — project's vector and quaternion libraries implementation.
+* [`pid.h`](../flix/pid.h) — generic PID controller implementation.
+* [`lpf.h`](../flix/lpf.h) — generic low-pass filter implementation.
+
+## Building
+
+See build instructions in [build.md](build.md).

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docs/log.md

@@ -0,0 +1,72 @@
+# Log analysis
+
+Flix quadcopter uses RAM to store flight log data. The default log capacity is 10 seconds at 100 Hz. This configuration can be adjusted in the `log.ino` file.
+
+To perform log analysis, you need to download the log right after the flight without powering off the drone. Then you can use several tools to analyze the log data.
+
+## Log download
+
+To download the log, connect the ESP32 using USB right after the flight and run the following command:
+
+```bash
+make log
+```
+
+Logs are stored in `tools/log/*.csv` files.
+
+## Analysis
+
+### PlotJuggler
+
+The recommended tool for log analysis is PlotJuggler.
+
+<img src="img/plotjuggler.png" width="500">
+
+1. Install PlotJuggler using the [official instructions](https://github.com/facontidavide/PlotJuggler?tab=readme-ov-file#installation).
+
+2. Run PlotJuggler and drag'n'drop the downloaded log file there. Choose `t` column to be used as X axis.
+
+   You can open the most recent downloaded file using the command:
+
+   ```bash
+   make plot
+   ```
+
+   You can perform both log download and run PlotJuggler in one command:
+
+   ```bash
+   make log plot
+   ```
+
+### FlightPlot
+
+FlightPlot is a powerful tool for analyzing logs in [ULog format](https://docs.px4.io/main/en/dev_log/ulog_file_format.html). This format is used in PX4 and ArduPilot flight software.
+
+<img src="img/flightplot.png" width="500">
+
+1. [Install FlightPlot](https://github.com/PX4/FlightPlot).
+2. Flix repository contains a tool for converting CSV logs to ULog format. Build the tool using [the instructions](../tools/csv_to_ulog/README.md) and convert the log you want to analyze.
+3. Run FlightPlot and drag'n'drop the converted ULog-file there.
+
+### Foxglove Studio
+
+Foxglove is a tool for visualizing and analyzing robotics data with very rich functionality. It can import various formats, but mainly focuses on its own format, called [MCAP](https://mcap.dev).
+
+<img src="img/foxglove.png" width="500">
+
+1. Install Foxglove Studio from the [official website](https://foxglove.dev/download).
+
+2. Flix repository contains a tool for converting CSV logs to MCAP format. First, install its dependencies:
+
+   ```bash
+   cd tools
+   pip install -r requirements.txt
+   ```
+
+3. Convert the log you want to analyze:
+
+   ```bash
+   csv_to_mcap.py log_file.csv
+   ```
+
+4. Open the log in Foxglove Studio using *Open local file* command.

docs/troubleshooting.md

@@ -0,0 +1,32 @@
+# Troubleshooting
+
+## The sketch doesn't compile
+
+Do the following:
+
+* **Check ESP32 core is installed**. Check if the version matches the one used in the [tutorial](build.md#firmware).
+* **Check libraries**. Install all the required libraries from the tutorial. Make sure there are no MPU9250 or other peripherals libraries that may conflict with the ones used in the tutorial.
+
+## The drone doesn't fly
+
+Do the following:
+
+* **Check the battery voltage**. Use a multimeter to measure the battery voltage. It should be in range of 3.7-4.2 V.
+* **Check if there are some startup errors**. Connect the ESP32 to the computer and check the Serial Monitor output. Use the Reset button to make sure you see the whole ESP32 output.
+* **Make sure correct IMU model is chosen**. If using ICM-20948 board, change `MPU9250` to `ICM20948` everywhere in the `imu.ino` file.
+* **Check if the CLI is working**. Perform `help` command in Serial Monitor. You should see the list of available commands.
+* **Configure QGroundControl correctly before connecting to the drone** if you use it to control the drone. Go to the settings and enable *Virtual Joystick*. *Auto-Center Throttle* setting **should be disabled**.
+* **Make sure you're not moving the drone several seconds after the power on**. The drone calibrates its gyroscope on the start so it should stay still for a while.
+* **Check the IMU sample rate**. Perform `imu` command. The `rate` field should be about 1000 (Hz).
+* **Check the IMU data**. Perform `imu` command, check raw accelerometer and gyro output. The output should change as you move the drone.
+* **Calibrate the accelerometer.** if is wasn't done before. Perform `ca` command and put the results to `imu.ino` file.
+* **Check the attitude estimation**. Connect to the drone using QGroundControl. Rotate the drone in different orientations and check if the attitude estimation shown in QGroundControl is correct.
+* **Check the motors**. Perform the following commands using Serial Monitor:
+  * `mfr` — should rotate front right motor (counter-clockwise).
+  * `mfl` — should rotate front left motor (clockwise).
+  * `mrl` — should rotate rear left motor (counter-clockwise).
+  * `mrr` — should rotate rear right motor (clockwise).
+* **Calibrate the RC** if you use it. Perform `rc` command and put the results to `rc.ino` file.
+* **Check the RC data** if you use it. Use `rc` command, `Control` should show correct values between -1 and 1, and between 0 and 1 for the throttle.
+* **Check the IMU output using QGroundControl**. Connect to the drone using QGroundControl on your computer. Go to the *Analyze* tab, *MAVLINK Inspector*. Plot the data from the `SCALED_IMU` message. The gyroscope and accelerometer data should change according to the drone movement.
+* **Check the gyroscope only attitude estimation**. Comment out `applyAcc();` line in `estimate.ino` and check if the attitude estimation in QGroundControl. It should be stable, but only drift very slowly.

docs/version0.md

@@ -0,0 +1,30 @@
+# Flix version 0
+
+Flix version 0 (obsolete):
+
+<img src="img/flix.jpg" width=500 alt="Flix quadcopter">
+
+## Components list
+
+|Type|Part|Image|Quantity|
+|-|-|-|-|
+|Microcontroller board|ESP32 Mini|<img src="img/esp32.jpg" width=100>|1|
+|IMU and barometer² board|GY-91 (or other MPU-9250 board)|<img src="img/gy-91.jpg" width=100>|1|
+|Quadcopter frame|K100|<img src="img/frame.jpg" width=100>|1|
+|Motor|8520 3.7V brushed motor (**shaft 0.8mm!**)|<img src="img/motor.jpeg" width=100>|4|
+|Propeller|Hubsan 55 mm|<img src="img/prop.jpg" width=100>|4|
+|Motor ESC|2.7A 1S Dual Way Micro Brush ESC|<img src="img/esc.jpg" width=100>|4|
+|RC transmitter|KINGKONG TINY X8|<img src="img/tx.jpg" width=100>|1|
+|RC receiver|DF500 (SBUS)|<img src="img/rx.jpg" width=100>|1|
+|~~SBUS inverter~~*||<img src="img/inv.jpg" width=100>|~~1~~|
+|Battery|3.7 Li-Po 850 MaH 60C|||
+|Battery charger||<img src="img/charger.jpg" width=100>|1|
+|Wires, connectors, tape, ...|||
+
+*\* — not needed as ESP32 supports [software pin inversion](https://github.com/bolderflight/sbus#inverted-serial).*
+
+## Schematics
+
+<img src="img/schematics.svg" width=800 alt="Flix schematics">
+
+You can also check a user contributed [variant of complete circuit diagram](https://miro.com/app/board/uXjVN-dTjoo=/) of the drone.

flix/cli.ino

@@ -0,0 +1,169 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Implementation of command line interface
+
+#include "pid.h"
+#include "vector.h"
+
+extern PID rollRatePID, pitchRatePID, yawRatePID, rollPID, pitchPID;
+extern LowPassFilter<Vector> ratesFilter;
+
+const char* motd =
+"\nWelcome to\n"
+" _______  __       __  ___   ___\n"
+"|   ____||  |     |  | \\  \\ /  /\n"
+"|  |__   |  |     |  |  \\  V  /\n"
+"|   __|  |  |     |  |   >   <\n"
+"|  |     |  `----.|  |  /  .  \\\n"
+"|__|     |_______||__| /__/ \\__\\\n\n"
+"Commands:\n\n"
+"help - show help\n"
+"show - show all parameters\n"
+"<name> <value> - set parameter\n"
+"ps - show pitch/roll/yaw\n"
+"psq - show attitude quaternion\n"
+"imu - show IMU data\n"
+"rc - show RC data\n"
+"mot - show motor data\n"
+"log - dump in-RAM log\n"
+"cr - calibrate RC\n"
+"cg - calibrate gyro\n"
+"ca - calibrate accel\n"
+"mfr, mfl, mrr, mrl - test motor\n"
+"reset - reset drone's state\n";
+
+const struct Param {
+	const char* name;
+	float* value;
+	float* value2;
+} params[] = {
+	{"rp", &rollRatePID.p, &pitchRatePID.p},
+	{"ri", &rollRatePID.i, &pitchRatePID.i},
+	{"rd", &rollRatePID.d, &pitchRatePID.d},
+
+	{"ap", &rollPID.p, &pitchPID.p},
+	{"ai", &rollPID.i, &pitchPID.i},
+	{"ad", &rollPID.d, &pitchPID.d},
+
+	{"yp", &yawRatePID.p, nullptr},
+	{"yi", &yawRatePID.i, nullptr},
+	{"yd", &yawRatePID.d, nullptr},
+
+	{"lpr", &ratesFilter.alpha, nullptr},
+	{"lpd", &rollRatePID.lpf.alpha, &pitchRatePID.lpf.alpha},
+
+	{"ss", &loopRate, nullptr},
+	{"dt", &dt, nullptr},
+	{"t", &t, nullptr},
+};
+
+void doCommand(String& command, String& value) {
+	if (command == "help" || command == "motd") {
+		Serial.println(motd);
+	} else if (command == "show") {
+		showTable();
+	} else if (command == "ps") {
+		Vector a = attitude.toEulerZYX();
+		Serial.printf("roll: %f pitch: %f yaw: %f\n", a.x * RAD_TO_DEG, a.y * RAD_TO_DEG, a.z * RAD_TO_DEG);
+	} else if (command == "psq") {
+		Serial.printf("qx: %f qy: %f qz: %f qw: %f\n", attitude.x, attitude.y, attitude.z, attitude.w);
+	} else if (command == "imu") {
+		printIMUInfo();
+		Serial.printf("gyro: %f %f %f\n", rates.x, rates.y, rates.z);
+		Serial.printf("acc: %f %f %f\n", acc.x, acc.y, acc.z);
+		printIMUCal();
+		Serial.printf("rate: %f\n", loopRate);
+	} else if (command == "rc") {
+		Serial.printf("Raw: throttle %d yaw %d pitch %d roll %d armed %d mode %d\n",
+			channels[RC_CHANNEL_THROTTLE], channels[RC_CHANNEL_YAW], channels[RC_CHANNEL_PITCH],
+			channels[RC_CHANNEL_ROLL], channels[RC_CHANNEL_ARMED], channels[RC_CHANNEL_MODE]);
+		Serial.printf("Control: throttle %f yaw %f pitch %f roll %f armed %f mode %f\n",
+			controls[RC_CHANNEL_THROTTLE], controls[RC_CHANNEL_YAW], controls[RC_CHANNEL_PITCH],
+			controls[RC_CHANNEL_ROLL], controls[RC_CHANNEL_ARMED], controls[RC_CHANNEL_MODE]);
+		Serial.printf("Mode: %s\n", getModeName());
+	} else if (command == "mot") {
+		Serial.printf("MOTOR front-right %f front-left %f rear-right %f rear-left %f\n",
+			motors[MOTOR_FRONT_RIGHT], motors[MOTOR_FRONT_LEFT], motors[MOTOR_REAR_RIGHT], motors[MOTOR_REAR_LEFT]);
+	} else if (command == "log") {
+		dumpLog();
+	} else if (command == "cr") {
+		calibrateRC();
+	} else if (command == "cg") {
+		calibrateGyro();
+	} else if (command == "ca") {
+		calibrateAccel();
+	} else if (command == "mfr") {
+		cliTestMotor(MOTOR_FRONT_RIGHT);
+	} else if (command == "mfl") {
+		cliTestMotor(MOTOR_FRONT_LEFT);
+	} else if (command == "mrr") {
+		cliTestMotor(MOTOR_REAR_RIGHT);
+	} else if (command == "mrl") {
+		cliTestMotor(MOTOR_REAR_LEFT);
+	} else if (command == "reset") {
+		attitude = Quaternion();
+	} else {
+		float val = value.toFloat();
+		// TODO: on error returns 0, check invalid value
+
+		for (uint8_t i = 0; i < sizeof(params) / sizeof(params[0]); i++) {
+			if (command == params[i].name) {
+				*params[i].value = val;
+				if (params[i].value2 != nullptr) *params[i].value2 = val;
+				Serial.print(command);
+				Serial.print(" = ");
+				Serial.println(val, 4);
+				return;
+			}
+		}
+		Serial.println("Invalid command: " + command);
+	}
+}
+
+void showTable() {
+	for (uint8_t i = 0; i < sizeof(params) / sizeof(params[0]); i++) {
+		Serial.print(params[i].name);
+		Serial.print(" ");
+		Serial.println(*params[i].value, 5);
+	}
+}
+
+void cliTestMotor(uint8_t n) {
+	Serial.printf("Testing motor %d\n", n);
+	motors[n] = 1;
+	delay(50); // ESP32 may need to wait until the end of the current cycle to change duty https://github.com/espressif/arduino-esp32/issues/5306
+	sendMotors();
+	delay(3000);
+	motors[n] = 0;
+	sendMotors();
+	Serial.println("Done");
+}
+
+void parseInput() {
+	static bool showMotd = true;
+	static String command;
+	static String value;
+	static bool parsingCommand = true;
+
+	if (showMotd) {
+		Serial.println(motd);
+		showMotd = false;
+	}
+
+	while (Serial.available()) {
+		char c = Serial.read();
+		if (c == '\n') {
+			parsingCommand = true;
+			if (!command.isEmpty()) {
+				doCommand(command, value);
+			}
+			command.clear();
+			value.clear();
+		} else if (c == ' ') {
+			parsingCommand = false;
+		} else {
+			(parsingCommand ? command : value) += c;
+		}
+	}
+}

flix/control.ino

@@ -0,0 +1,177 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Flight control
+
+#include "vector.h"
+#include "quaternion.h"
+#include "pid.h"
+#include "lpf.h"
+
+#define PITCHRATE_P 0.05
+#define PITCHRATE_I 0.2
+#define PITCHRATE_D 0.001
+#define PITCHRATE_I_LIM 0.3
+#define ROLLRATE_P PITCHRATE_P
+#define ROLLRATE_I PITCHRATE_I
+#define ROLLRATE_D PITCHRATE_D
+#define ROLLRATE_I_LIM PITCHRATE_I_LIM
+#define YAWRATE_P 0.3
+#define YAWRATE_I 0.0
+#define YAWRATE_D 0.0
+#define YAWRATE_I_LIM 0.3
+#define ROLL_P 4.5
+#define ROLL_I 0
+#define ROLL_D 0
+#define PITCH_P ROLL_P
+#define PITCH_I ROLL_I
+#define PITCH_D ROLL_D
+#define YAW_P 3
+#define PITCHRATE_MAX radians(360)
+#define ROLLRATE_MAX radians(360)
+#define YAWRATE_MAX radians(360)
+#define MAX_TILT radians(30)
+
+#define RATES_D_LPF_ALPHA 0.2 // cutoff frequency ~ 40 Hz
+
+enum { MANUAL, ACRO, STAB, USER } mode = STAB;
+enum { YAW, YAW_RATE } yawMode = YAW;
+bool armed = false;
+
+PID rollRatePID(ROLLRATE_P, ROLLRATE_I, ROLLRATE_D, ROLLRATE_I_LIM, RATES_D_LPF_ALPHA);
+PID pitchRatePID(PITCHRATE_P, PITCHRATE_I, PITCHRATE_D, PITCHRATE_I_LIM, RATES_D_LPF_ALPHA);
+PID yawRatePID(YAWRATE_P, YAWRATE_I, YAWRATE_D);
+PID rollPID(ROLL_P, ROLL_I, ROLL_D);
+PID pitchPID(PITCH_P, PITCH_I, PITCH_D);
+PID yawPID(YAW_P, 0, 0);
+
+Quaternion attitudeTarget;
+Vector ratesTarget;
+Vector torqueTarget;
+float thrustTarget;
+
+void control() {
+	interpretRC();
+	failsafe();
+	if (mode == STAB) {
+		controlAttitude();
+		controlRate();
+		controlTorque();
+	} else if (mode == ACRO) {
+		controlRate();
+		controlTorque();
+	} else if (mode == MANUAL) {
+		controlTorque();
+	}
+}
+
+void interpretRC() {
+	armed = controls[RC_CHANNEL_THROTTLE] >= 0.05 && controls[RC_CHANNEL_ARMED] >= 0.5;
+
+	// NOTE: put ACRO or MANUAL modes there if you want to use them
+	if (controls[RC_CHANNEL_MODE] < 0.25) {
+		mode = STAB;
+	} else if (controls[RC_CHANNEL_MODE] < 0.75) {
+		mode = STAB;
+	} else {
+		mode = STAB;
+	}
+
+	thrustTarget = controls[RC_CHANNEL_THROTTLE];
+
+	if (mode == ACRO) {
+		yawMode = YAW_RATE;
+		ratesTarget.x = controls[RC_CHANNEL_ROLL] * ROLLRATE_MAX;
+		ratesTarget.y = controls[RC_CHANNEL_PITCH] * PITCHRATE_MAX;
+		ratesTarget.z = -controls[RC_CHANNEL_YAW] * YAWRATE_MAX; // positive yaw stick means clockwise rotation in FLU
+
+	} else if (mode == STAB) {
+		yawMode = controls[RC_CHANNEL_YAW] == 0 ? YAW : YAW_RATE;
+
+		attitudeTarget = Quaternion::fromEulerZYX(Vector(
+			controls[RC_CHANNEL_ROLL] * MAX_TILT,
+			controls[RC_CHANNEL_PITCH] * MAX_TILT,
+			attitudeTarget.getYaw()));
+		ratesTarget.z = -controls[RC_CHANNEL_YAW] * YAWRATE_MAX; // positive yaw stick means clockwise rotation in FLU
+
+	} else if (mode == MANUAL) {
+		// passthrough mode
+		yawMode = YAW_RATE;
+		torqueTarget = Vector(controls[RC_CHANNEL_ROLL], controls[RC_CHANNEL_PITCH], -controls[RC_CHANNEL_YAW]) * 0.01;
+	}
+
+	if (yawMode == YAW_RATE || !motorsActive()) {
+		// update yaw target as we don't have control over the yaw
+		attitudeTarget.setYaw(attitude.getYaw());
+	}
+}
+
+void controlAttitude() {
+	if (!armed) {
+		rollPID.reset();
+		pitchPID.reset();
+		yawPID.reset();
+		return;
+	}
+
+	const Vector up(0, 0, 1);
+	Vector upActual = attitude.rotate(up);
+	Vector upTarget = attitudeTarget.rotate(up);
+
+	Vector error = Vector::angularRatesBetweenVectors(upTarget, upActual);
+
+	ratesTarget.x = rollPID.update(error.x, dt);
+	ratesTarget.y = pitchPID.update(error.y, dt);
+
+	if (yawMode == YAW) {
+		float yawError = wrapAngle(attitudeTarget.getYaw() - attitude.getYaw());
+		ratesTarget.z = yawPID.update(yawError, dt);
+	}
+}
+
+void controlRate() {
+	if (!armed) {
+		rollRatePID.reset();
+		pitchRatePID.reset();
+		yawRatePID.reset();
+		return;
+	}
+
+	Vector error = ratesTarget - rates;
+
+	// Calculate desired torque, where 0 - no torque, 1 - maximum possible torque
+	torqueTarget.x = rollRatePID.update(error.x, dt);
+	torqueTarget.y = pitchRatePID.update(error.y, dt);
+	torqueTarget.z = yawRatePID.update(error.z, dt);
+}
+
+void controlTorque() {
+	if (!armed) {
+		memset(motors, 0, sizeof(motors));
+		return;
+	}
+
+	motors[MOTOR_FRONT_LEFT] = thrustTarget + torqueTarget.x - torqueTarget.y + torqueTarget.z;
+	motors[MOTOR_FRONT_RIGHT] = thrustTarget - torqueTarget.x - torqueTarget.y - torqueTarget.z;
+	motors[MOTOR_REAR_LEFT] = thrustTarget + torqueTarget.x + torqueTarget.y - torqueTarget.z;
+	motors[MOTOR_REAR_RIGHT] = thrustTarget - torqueTarget.x + torqueTarget.y + torqueTarget.z;
+
+	motors[0] = constrain(motors[0], 0, 1);
+	motors[1] = constrain(motors[1], 0, 1);
+	motors[2] = constrain(motors[2], 0, 1);
+	motors[3] = constrain(motors[3], 0, 1);
+}
+
+bool motorsActive() {
+	return motors[0] > 0 || motors[1] > 0 || motors[2] > 0 || motors[3] > 0;
+}
+
+const char* getModeName() {
+	switch (mode) {
+		case MANUAL: return "MANUAL";
+		case ACRO: return "ACRO";
+		case STAB: return "STAB";
+		case USER: return "USER";
+		default: return "UNKNOWN";
+	}
+}

flix/estimate.ino

@@ -0,0 +1,44 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Attitude estimation from gyro and accelerometer
+
+#include "quaternion.h"
+#include "vector.h"
+#include "lpf.h"
+
+#define ONE_G 9.807f
+#define WEIGHT_ACC 0.5f
+#define RATES_LFP_ALPHA 0.2 // cutoff frequency ~ 40 Hz
+
+LowPassFilter<Vector> ratesFilter(RATES_LFP_ALPHA);
+
+void estimate() {
+	applyGyro();
+	applyAcc();
+}
+
+void applyGyro() {
+	// filter gyro to get angular rates
+	rates = ratesFilter.update(gyro);
+
+	// apply rates to attitude
+	attitude *= Quaternion::fromAngularRates(rates * dt);
+	attitude.normalize();
+}
+
+void applyAcc() {
+	// test should we apply accelerometer gravity correction
+	float accNorm = acc.norm();
+	bool landed = !motorsActive() && abs(accNorm - ONE_G) < ONE_G * 0.1f;
+
+	if (!landed) return;
+
+	// calculate accelerometer correction
+	Vector up = attitude.rotate(Vector(0, 0, 1));
+	Vector correction = Vector::angularRatesBetweenVectors(acc, up) * dt * WEIGHT_ACC;
+
+	// apply correction
+	attitude *= Quaternion::fromAngularRates(correction);
+	attitude.normalize();
+}

flix/failsafe.ino

@@ -0,0 +1,22 @@
+// Copyright (c) 2024 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Fail-safe for RC loss
+
+#define RC_LOSS_TIMEOUT 0.2
+#define DESCEND_TIME 3.0 // time to descend from full throttle to zero
+
+void failsafe() {
+	if (t - controlsTime > RC_LOSS_TIMEOUT) {
+		descend();
+	}
+}
+
+void descend() {
+	// Smooth descend on RC lost
+	mode = STAB;
+	controls[RC_CHANNEL_ROLL] = 0;
+	controls[RC_CHANNEL_PITCH] = 0;
+	controls[RC_CHANNEL_YAW] = 0;
+	controls[RC_CHANNEL_THROTTLE] -= dt / DESCEND_TIME;
+}

flix/flix.ino

@@ -0,0 +1,67 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Main firmware file
+
+#include "vector.h"
+#include "quaternion.h"
+
+#define SERIAL_BAUDRATE 115200
+
+#define WIFI_ENABLED 1
+
+#define RC_CHANNELS 16
+#define RC_CHANNEL_ROLL 0
+#define RC_CHANNEL_PITCH 1
+#define RC_CHANNEL_THROTTLE 2
+#define RC_CHANNEL_YAW 3
+#define RC_CHANNEL_ARMED 4
+#define RC_CHANNEL_MODE 5
+
+#define MOTOR_REAR_LEFT 0
+#define MOTOR_REAR_RIGHT 1
+#define MOTOR_FRONT_RIGHT 2
+#define MOTOR_FRONT_LEFT 3
+
+float t = NAN; // current step time, s
+float dt; // time delta from previous step, s
+float loopRate; // loop rate, Hz
+int16_t channels[RC_CHANNELS]; // raw rc channels
+float controls[RC_CHANNELS]; // normalized controls in range [-1..1] ([0..1] for throttle)
+float controlsTime; // time of the last controls update
+Vector gyro; // gyroscope data
+Vector acc; // accelerometer data, m/s/s
+Vector rates; // filtered angular rates, rad/s
+Quaternion attitude; // estimated attitude
+float motors[4]; // normalized motors thrust in range [-1..1]
+
+void setup() {
+	Serial.begin(SERIAL_BAUDRATE);
+	Serial.println("Initializing flix");
+	disableBrownOut();
+	setupLED();
+	setupMotors();
+	setLED(true);
+#if WIFI_ENABLED == 1
+	setupWiFi();
+#endif
+	setupIMU();
+	setupRC();
+
+	setLED(false);
+	Serial.println("Initializing complete");
+}
+
+void loop() {
+	readIMU();
+	step();
+	readRC();
+	estimate();
+	control();
+	sendMotors();
+	parseInput();
+#if WIFI_ENABLED == 1
+	processMavlink();
+#endif
+	logData();
+}

flix/imu.ino

@@ -0,0 +1,128 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Work with the IMU sensor
+// IMU is oriented FLU (front-left-up) style.
+// In case of FRD (front-right-down) orientation of the IMU, use this code:
+// https://gist.github.com/okalachev/713db47e31bce643dbbc9539d166ce98.
+
+#include <SPI.h>
+#include <MPU9250.h>
+
+#define ONE_G 9.80665
+
+// NOTE: use 'ca' command to calibrate the accelerometer and put the values here
+Vector accBias(0, 0, 0);
+Vector accScale(1, 1, 1);
+
+MPU9250 IMU(SPI);
+Vector gyroBias;
+
+void setupIMU() {
+	Serial.println("Setup IMU");
+	bool status = IMU.begin();
+	if (!status) {
+		while (true) {
+			Serial.println("IMU begin error");
+			delay(1000);
+		}
+	}
+	configureIMU();
+	calibrateGyro();
+}
+
+void configureIMU() {
+	IMU.setAccelRange(IMU.ACCEL_RANGE_4G);
+	IMU.setGyroRange(IMU.GYRO_RANGE_2000DPS);
+	IMU.setDLPF(IMU.DLPF_MAX);
+	IMU.setRate(IMU.RATE_1KHZ_APPROX);
+}
+
+void readIMU() {
+	IMU.waitForData();
+	IMU.getGyro(gyro.x, gyro.y, gyro.z);
+	IMU.getAccel(acc.x, acc.y, acc.z);
+	// apply scale and bias
+	acc = (acc - accBias) / accScale;
+	gyro = gyro - gyroBias;
+}
+
+void calibrateGyro() {
+	const int samples = 1000;
+	Serial.println("Calibrating gyro, stand still");
+	IMU.setGyroRange(IMU.GYRO_RANGE_250DPS); // the most sensitive mode
+
+	gyroBias = Vector(0, 0, 0);
+	for (int i = 0; i < samples; i++) {
+		IMU.waitForData();
+		IMU.getGyro(gyro.x, gyro.y, gyro.z);
+		gyroBias = gyroBias + gyro;
+	}
+	gyroBias = gyroBias / samples;
+
+	printIMUCal();
+	configureIMU();
+}
+
+void calibrateAccel() {
+	Serial.println("Calibrating accelerometer");
+	IMU.setAccelRange(IMU.ACCEL_RANGE_2G); // the most sensitive mode
+
+	Serial.setTimeout(60000);
+	Serial.print("Place level [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("Place nose up [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("Place nose down [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("Place on right side [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("Place on left side [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+	Serial.print("Place upside down [enter] "); Serial.readStringUntil('\n');
+	calibrateAccelOnce();
+
+	printIMUCal();
+	configureIMU();
+}
+
+void calibrateAccelOnce() {
+	const int samples = 1000;
+	static Vector accMax(-INFINITY, -INFINITY, -INFINITY);
+	static Vector accMin(INFINITY, INFINITY, INFINITY);
+
+	// Compute the average of the accelerometer readings
+	acc = Vector(0, 0, 0);
+	for (int i = 0; i < samples; i++) {
+		IMU.waitForData();
+		Vector sample;
+		IMU.getAccel(sample.x, sample.y, sample.z);
+		acc = acc + sample;
+	}
+	acc = acc / samples;
+
+	// Update the maximum and minimum values
+	if (acc.x > accMax.x) accMax.x = acc.x;
+	if (acc.y > accMax.y) accMax.y = acc.y;
+	if (acc.z > accMax.z) accMax.z = acc.z;
+	if (acc.x < accMin.x) accMin.x = acc.x;
+	if (acc.y < accMin.y) accMin.y = acc.y;
+	if (acc.z < accMin.z) accMin.z = acc.z;
+	Serial.printf("acc %f %f %f\n", acc.x, acc.y, acc.z);
+	Serial.printf("max %f %f %f\n", accMax.x, accMax.y, accMax.z);
+	Serial.printf("min %f %f %f\n", accMin.x, accMin.y, accMin.z);
+	// Compute scale and bias
+	accScale = (accMax - accMin) / 2 / ONE_G;
+	accBias = (accMax + accMin) / 2;
+}
+
+void printIMUCal() {
+	Serial.printf("gyro bias: %f, %f, %f\n", gyroBias.x, gyroBias.y, gyroBias.z);
+	Serial.printf("accel bias: %f, %f, %f\n", accBias.x, accBias.y, accBias.z);
+	Serial.printf("accel scale: %f, %f, %f\n", accScale.x, accScale.y, accScale.z);
+}
+
+void printIMUInfo() {
+	Serial.printf("model: %s\n", IMU.getModel());
+	Serial.printf("who am I: 0x%02X\n", IMU.whoAmI());
+}

flix/led.ino

@@ -0,0 +1,27 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Board's LED control
+
+#define BLINK_PERIOD 500000
+
+#ifndef LED_BUILTIN
+#define LED_BUILTIN 2 // for ESP32 Dev Module
+#endif
+
+void setupLED() {
+	pinMode(LED_BUILTIN, OUTPUT);
+}
+
+void setLED(bool on) {
+	static bool state = false;
+	if (on == state) {
+		return; // don't call digitalWrite if the state is the same
+	}
+	digitalWrite(LED_BUILTIN, on ? HIGH : LOW);
+	state = on;
+}
+
+void blinkLED() {
+	setLED(micros() / BLINK_PERIOD % 2);
+}

flix/log.ino

@@ -0,0 +1,53 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// In-RAM logging
+
+#define LOG_RATE 100
+#define LOG_DURATION 10
+#define LOG_PERIOD 1.0 / LOG_RATE
+#define LOG_SIZE LOG_DURATION * LOG_RATE
+#define LOG_COLUMNS 14
+
+float logBuffer[LOG_SIZE][LOG_COLUMNS]; // * 4 (float)
+int logPointer = 0;
+
+void logData() {
+	if (!armed) return;
+
+	static float logTime = 0;
+	if (t - logTime < LOG_PERIOD) return;
+	logTime = t;
+
+	logBuffer[logPointer][0] = t;
+	logBuffer[logPointer][1] = rates.x;
+	logBuffer[logPointer][2] = rates.y;
+	logBuffer[logPointer][3] = rates.z;
+	logBuffer[logPointer][4] = ratesTarget.x;
+	logBuffer[logPointer][5] = ratesTarget.y;
+	logBuffer[logPointer][6] = ratesTarget.z;
+	logBuffer[logPointer][7] = attitude.toEulerZYX().x;
+	logBuffer[logPointer][8] = attitude.toEulerZYX().y;
+	logBuffer[logPointer][9] = attitude.toEulerZYX().z;
+	logBuffer[logPointer][10] = attitudeTarget.toEulerZYX().x;
+	logBuffer[logPointer][11] = attitudeTarget.toEulerZYX().y;
+	logBuffer[logPointer][12] = attitudeTarget.toEulerZYX().z;
+	logBuffer[logPointer][13] = thrustTarget;
+
+	logPointer++;
+	if (logPointer >= LOG_SIZE) {
+		logPointer = 0;
+	}
+}
+
+void dumpLog() {
+	Serial.printf("t,rates.x,rates.y,rates.z,ratesTarget.x,ratesTarget.y,ratesTarget.z,"
+		"attitude.x,attitude.y,attitude.z,attitudeTarget.x,attitudeTarget.y,attitudeTarget.z,thrustTarget\n");
+	for (int i = 0; i < LOG_SIZE; i++) {
+		if (logBuffer[i][0] == 0) continue; // skip empty records
+		for (int j = 0; j < LOG_COLUMNS - 1; j++) {
+			Serial.printf("%f,", logBuffer[i][j]);
+		}
+		Serial.printf("%f\n", logBuffer[i][LOG_COLUMNS - 1]);
+	}
+}

flix/lpf.h

@@ -0,0 +1,38 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Low pass filter implementation
+
+#pragma once
+
+template <typename T> // Using template to make the filter usable for scalar and vector values
+class LowPassFilter {
+public:
+	float alpha; // smoothing constant, 1 means filter disabled
+	T output;
+
+	LowPassFilter(float alpha): alpha(alpha) {};
+
+	T update(const T input) {
+		if (alpha == 1) { // filter disabled
+			return input;
+		}
+
+		if (!initialized) {
+			output = input;
+			initialized = true;
+		}
+		return output = output * (1 - alpha) + input * alpha;
+	}
+
+	void setCutOffFrequency(float cutOffFreq, float dt) {
+		alpha = 1 - exp(-2 * PI * cutOffFreq * dt);
+	}
+
+	void reset() {
+		initialized = false;
+	}
+
+private:
+	bool initialized = false;
+};

flix/mavlink.ino

@@ -0,0 +1,107 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// MAVLink communication
+
+#if WIFI_ENABLED == 1
+
+#include <MAVLink.h>
+
+#define SYSTEM_ID 1
+#define PERIOD_SLOW 1.0
+#define PERIOD_FAST 0.1
+#define MAVLINK_CONTROL_SCALE 0.7f
+#define MAVLINK_CONTROL_YAW_DEAD_ZONE 0.1f
+
+void processMavlink() {
+	sendMavlink();
+	receiveMavlink();
+}
+
+void sendMavlink() {
+	static float lastSlow = 0;
+	static float lastFast = 0;
+
+	mavlink_message_t msg;
+	uint32_t time = t * 1000;
+
+	if (t - lastSlow >= PERIOD_SLOW) {
+		lastSlow = t;
+
+		mavlink_msg_heartbeat_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, MAV_TYPE_QUADROTOR,
+			MAV_AUTOPILOT_GENERIC, MAV_MODE_FLAG_MANUAL_INPUT_ENABLED | (armed ? MAV_MODE_FLAG_SAFETY_ARMED : 0),
+			0, MAV_STATE_STANDBY);
+		sendMessage(&msg);
+	}
+
+	if (t - lastFast >= PERIOD_FAST) {
+		lastFast = t;
+
+		const float zeroQuat[] = {0, 0, 0, 0};
+		Quaternion attitudeFRD = FLU2FRD(attitude); // MAVLink uses FRD coordinate system
+		mavlink_msg_attitude_quaternion_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg,
+			time, attitudeFRD.w, attitudeFRD.x, attitudeFRD.y, attitudeFRD.z, rates.x, rates.y, rates.z, zeroQuat);
+		sendMessage(&msg);
+
+		mavlink_msg_rc_channels_scaled_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, time, 0,
+			controls[0] * 10000, controls[1] * 10000, controls[2] * 10000,
+			controls[3] * 10000, controls[4] * 10000, controls[5] * 10000,
+			INT16_MAX, INT16_MAX, UINT8_MAX);
+		sendMessage(&msg);
+
+		float actuator[32];
+		memcpy(actuator, motors, sizeof(motors));
+		mavlink_msg_actuator_output_status_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, time, 4, actuator);
+		sendMessage(&msg);
+
+		mavlink_msg_scaled_imu_pack(SYSTEM_ID, MAV_COMP_ID_AUTOPILOT1, &msg, time,
+			acc.x * 1000, acc.y * 1000, acc.z * 1000,
+			gyro.x * 1000, gyro.y * 1000, gyro.z * 1000,
+			0, 0, 0, 0);
+		sendMessage(&msg);
+	}
+}
+
+void sendMessage(const void *msg) {
+	uint8_t buf[MAVLINK_MAX_PACKET_LEN];
+	int len = mavlink_msg_to_send_buffer(buf, (mavlink_message_t *)msg);
+	sendWiFi(buf, len);
+}
+
+void receiveMavlink() {
+	uint8_t buf[MAVLINK_MAX_PACKET_LEN];
+	int len = receiveWiFi(buf, MAVLINK_MAX_PACKET_LEN);
+
+	// New packet, parse it
+	mavlink_message_t msg;
+	mavlink_status_t status;
+	for (int i = 0; i < len; i++) {
+		if (mavlink_parse_char(MAVLINK_COMM_0, buf[i], &msg, &status)) {
+			handleMavlink(&msg);
+		}
+	}
+}
+
+void handleMavlink(const void *_msg) {
+	mavlink_message_t *msg = (mavlink_message_t *)_msg;
+	if (msg->msgid == MAVLINK_MSG_ID_MANUAL_CONTROL) {
+		mavlink_manual_control_t manualControl;
+		mavlink_msg_manual_control_decode(msg, &manualControl);
+		controls[RC_CHANNEL_THROTTLE] = manualControl.z / 1000.0f;
+		controls[RC_CHANNEL_PITCH] = manualControl.x / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controls[RC_CHANNEL_ROLL] = manualControl.y / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controls[RC_CHANNEL_YAW] = manualControl.r / 1000.0f * MAVLINK_CONTROL_SCALE;
+		controls[RC_CHANNEL_MODE] = 1; // STAB mode
+		controls[RC_CHANNEL_ARMED] = 1; // armed
+		controlsTime = t;
+
+		if (abs(controls[RC_CHANNEL_YAW]) < MAVLINK_CONTROL_YAW_DEAD_ZONE) controls[RC_CHANNEL_YAW] = 0;
+	}
+}
+
+// Convert Forward-Left-Up to Forward-Right-Down quaternion
+inline Quaternion FLU2FRD(const Quaternion &q) {
+	return Quaternion(q.w, q.x, -q.y, -q.z);
+}
+
+#endif

flix/motors.ino

@@ -0,0 +1,39 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Motors output control using MOSFETs
+// In case of using ESC, use this version of the code: https://gist.github.com/okalachev/8871d3a94b6b6c0a298f41a4edd34c61.
+// Motor: 8520 3.7V
+
+#define MOTOR_0_PIN 12 // rear left
+#define MOTOR_1_PIN 13 // rear right
+#define MOTOR_2_PIN 14 // front right
+#define MOTOR_3_PIN 15 // front left
+
+#define PWM_FREQUENCY 200
+#define PWM_RESOLUTION 8
+
+void setupMotors() {
+	Serial.println("Setup Motors");
+
+	// configure pins
+	ledcAttach(MOTOR_0_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_1_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_2_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+	ledcAttach(MOTOR_3_PIN, PWM_FREQUENCY, PWM_RESOLUTION);
+
+	sendMotors();
+	Serial.println("Motors initialized");
+}
+
+uint8_t signalToDutyCycle(float control) {
+	float duty = mapff(control, 0, 1, 0, (1 << PWM_RESOLUTION) - 1);
+	return round(constrain(duty, 0, (1 << PWM_RESOLUTION) - 1));
+}
+
+void sendMotors() {
+	ledcWrite(MOTOR_0_PIN, signalToDutyCycle(motors[0]));
+	ledcWrite(MOTOR_1_PIN, signalToDutyCycle(motors[1]));
+	ledcWrite(MOTOR_2_PIN, signalToDutyCycle(motors[2]));
+	ledcWrite(MOTOR_3_PIN, signalToDutyCycle(motors[3]));
+}

flix/pid.h

@@ -0,0 +1,48 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// PID controller implementation
+
+#pragma once
+
+#include "lpf.h"
+
+class PID {
+public:
+	float p = 0;
+	float i = 0;
+	float d = 0;
+	float windup = 0;
+
+	float derivative = 0;
+	float integral = 0;
+
+	LowPassFilter<float> lpf; // low pass filter for derivative term
+
+	PID(float p, float i, float d, float windup = 0, float dAlpha = 1) : p(p), i(i), d(d), windup(windup), lpf(dAlpha) {};
+
+	float update(float error, float dt) {
+		integral += error * dt;
+
+		if (isfinite(prevError) && dt > 0) {
+			// calculate derivative if both dt and prevError are valid
+			derivative = (error - prevError) / dt;
+
+			// apply low pass filter to derivative
+			derivative = lpf.update(derivative);
+		}
+
+		prevError = error;
+
+		return p * error + constrain(i * integral, -windup, windup) + d * derivative; // PID
+	}
+
+	void reset() {
+		prevError = NAN;
+		integral = 0;
+		derivative = 0;
+	}
+
+private:
+	float prevError = NAN;
+};

flix/quaternion.h

@@ -0,0 +1,187 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Lightweight rotation quaternion library
+
+#pragma once
+
+#include "vector.h"
+
+class Quaternion : public Printable {
+public:
+	float w, x, y, z;
+
+	Quaternion(): w(1), x(0), y(0), z(0) {};
+
+	Quaternion(float w, float x, float y, float z): w(w), x(x), y(y), z(z) {};
+
+	static Quaternion fromAxisAngle(float a, float b, float c, float angle) {
+		float halfAngle = angle * 0.5;
+		float sin2 = sin(halfAngle);
+		float cos2 = cos(halfAngle);
+		float sinNorm = sin2 / sqrt(a * a + b * b + c * c);
+		return Quaternion(cos2, a * sinNorm, b * sinNorm, c * sinNorm);
+	}
+
+	static Quaternion fromAngularRates(const Vector& rates) {
+		if (rates.zero()) {
+			return Quaternion();
+		}
+		return Quaternion::fromAxisAngle(rates.x, rates.y, rates.z, rates.norm());
+	}
+
+	static Quaternion fromEulerZYX(const Vector& euler) {
+		float cx = cos(euler.x / 2);
+		float cy = cos(euler.y / 2);
+		float cz = cos(euler.z / 2);
+		float sx = sin(euler.x / 2);
+		float sy = sin(euler.y / 2);
+		float sz = sin(euler.z / 2);
+
+		return Quaternion(
+			cx * cy * cz + sx * sy * sz,
+			sx * cy * cz - cx * sy * sz,
+			cx * sy * cz + sx * cy * sz,
+			cx * cy * sz - sx * sy * cz);
+	}
+
+	static Quaternion fromBetweenVectors(Vector u, Vector v) {
+		float dot = u.x * v.x + u.y * v.y + u.z * v.z;
+		float w1 = u.y * v.z - u.z * v.y;
+		float w2 = u.z * v.x - u.x * v.z;
+		float w3 = u.x * v.y - u.y * v.x;
+
+		Quaternion ret(
+			dot + sqrt(dot * dot + w1 * w1 + w2 * w2 + w3 * w3),
+			w1,
+			w2,
+			w3);
+		ret.normalize();
+		return ret;
+	}
+
+	void toAxisAngle(float& a, float& b, float& c, float& angle) {
+		angle = acos(w) * 2;
+		a = x / sin(angle / 2);
+		b = y / sin(angle / 2);
+		c = z / sin(angle / 2);
+	}
+
+	Vector toEulerZYX() const {
+		// https://github.com/ros/geometry2/blob/589caf083cae9d8fae7effdb910454b4681b9ec1/tf2/include/tf2/impl/utils.h#L87
+		Vector euler;
+		float sqx = x * x;
+		float sqy = y * y;
+		float sqz = z * z;
+		float sqw = w * w;
+		// Cases derived from https://orbitalstation.wordpress.com/tag/quaternion/
+		float sarg = -2 * (x * z - w * y) / (sqx + sqy + sqz + sqw);
+		if (sarg <= -0.99999) {
+			euler.x = 0;
+			euler.y = -0.5 * PI;
+			euler.z = -2 * atan2(y, x);
+		} else if (sarg >= 0.99999) {
+			euler.x = 0;
+			euler.y = 0.5 * PI;
+			euler.z = 2 * atan2(y, x);
+		} else {
+			euler.x = atan2(2 * (y * z + w * x), sqw - sqx - sqy + sqz);
+			euler.y = asin(sarg);
+			euler.z = atan2(2 * (x * y + w * z), sqw + sqx - sqy - sqz);
+		}
+		return euler;
+	}
+
+	float getYaw() const {
+		// https://github.com/ros/geometry2/blob/589caf083cae9d8fae7effdb910454b4681b9ec1/tf2/include/tf2/impl/utils.h#L122
+		float yaw;
+		float sqx = x * x;
+		float sqy = y * y;
+		float sqz = z * z;
+		float sqw = w * w;
+		double sarg = -2 * (x * z - w * y) / (sqx + sqy + sqz + sqw);
+		if (sarg <= -0.99999) {
+			yaw = -2 * atan2(y, x);
+		} else if (sarg >= 0.99999) {
+			yaw = 2 * atan2(y, x);
+		} else {
+			yaw = atan2(2 * (x * y + w * z), sqw + sqx - sqy - sqz);
+		}
+		return yaw;
+	}
+
+	void setYaw(float yaw) {
+		// TODO: optimize?
+		Vector euler = toEulerZYX();
+		euler.z = yaw;
+		(*this) = Quaternion::fromEulerZYX(euler);
+	}
+
+	Quaternion& operator *= (const Quaternion& q) {
+		Quaternion ret(
+			w * q.w - x * q.x - y * q.y - z * q.z,
+			w * q.x + x * q.w + y * q.z - z * q.y,
+			w * q.y + y * q.w + z * q.x - x * q.z,
+			w * q.z + z * q.w + x * q.y - y * q.x);
+		return (*this = ret);
+	}
+
+	Quaternion operator * (const Quaternion& q) {
+		return Quaternion(
+			w * q.w - x * q.x - y * q.y - z * q.z,
+			w * q.x + x * q.w + y * q.z - z * q.y,
+			w * q.y + y * q.w + z * q.x - x * q.z,
+			w * q.z + z * q.w + x * q.y - y * q.x);
+	}
+
+	Quaternion inversed() const {
+		float normSqInv = 1 / (w * w + x * x + y * y + z * z);
+		return Quaternion(
+			w * normSqInv,
+			-x * normSqInv,
+			-y * normSqInv,
+			-z * normSqInv);
+	}
+
+	float norm() const {
+		return sqrt(w * w + x * x + y * y + z * z);
+	}
+
+	void normalize() {
+		float n = norm();
+		w /= n;
+		x /= n;
+		y /= n;
+		z /= n;
+	}
+
+	Vector conjugate(const Vector& v) {
+		Quaternion qv(0, v.x, v.y, v.z);
+		Quaternion res = (*this) * qv * inversed();
+		return Vector(res.x, res.y, res.z);
+	}
+
+	Vector conjugateInversed(const Vector& v) {
+		Quaternion qv(0, v.x, v.y, v.z);
+		Quaternion res = inversed() * qv * (*this);
+		return Vector(res.x, res.y, res.z);
+	}
+
+	// Rotate vector by quaternion
+	inline Vector rotate(const Vector& v) {
+		return conjugateInversed(v);
+	}
+
+	inline bool finite() const {
+		return isfinite(w) && isfinite(x) && isfinite(y) && isfinite(z);
+	}
+
+	size_t printTo(Print& p) const {
+		size_t r = 0;
+		r += p.print(w, 15) + p.print(" ");
+		r += p.print(x, 15) + p.print(" ");
+		r += p.print(y, 15) + p.print(" ");
+		r += p.print(z, 15);
+		return r;
+	}
+};

flix/rc.ino

@@ -0,0 +1,55 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Work with the RC receiver
+
+#include <SBUS.h>
+
+// NOTE: use 'cr' command to calibrate the RC and put the values here
+int channelNeutral[] = {995, 883, 200, 972, 512, 512, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+int channelMax[] = {1651, 1540, 1713, 1630, 1472, 1472, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+
+SBUS RC(Serial2); // NOTE: Use RC(Serial2, 16, 17) if you use the old UART2 pins
+
+void setupRC() {
+	Serial.println("Setup RC");
+	RC.begin();
+}
+
+void readRC() {
+	if (RC.read()) {
+		SBUSData data = RC.data();
+		memcpy(channels, data.ch, sizeof(channels)); // copy channels data
+		normalizeRC();
+		controlsTime = t;
+	}
+}
+
+void normalizeRC() {
+	for (uint8_t i = 0; i < RC_CHANNELS; i++) {
+		controls[i] = mapf(channels[i], channelNeutral[i], channelMax[i], 0, 1);
+	}
+}
+
+void calibrateRC() {
+	Serial.println("Calibrate RC: move all sticks to maximum positions within 4 seconds");
+	Serial.println("··o     ··o\n···     ···\n···     ···");
+	delay(4000);
+	for (int i = 0; i < 30; i++) readRC(); // ensure the values are updated
+	for (int i = 0; i < RC_CHANNELS; i++) {
+		channelMax[i] = channels[i];
+	}
+	Serial.println("Calibrate RC: move all sticks to neutral positions within 4 seconds");
+	Serial.println("···     ···\n···     ·o·\n·o·     ···");
+	delay(4000);
+	for (int i = 0; i < 30; i++) readRC(); // ensure the values are updated
+	for (int i = 0; i < RC_CHANNELS; i++) {
+		channelNeutral[i] = channels[i];
+	}
+	printRCCal();
+}
+
+void printRCCal() {
+	printArray(channelNeutral, RC_CHANNELS);
+	printArray(channelMax, RC_CHANNELS);
+}

flix/time.ino

@@ -0,0 +1,27 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Time related functions
+
+void step() {
+	float now = micros() / 1000000.0;
+	dt = now - t;
+	t = now;
+
+	if (!(dt > 0)) {
+		dt = 0; // assume dt to be zero on first step and on reset
+	}
+
+	computeLoopRate();
+}
+
+void computeLoopRate() {
+	static float windowStart = 0;
+	static uint32_t rate = 0;
+	rate++;
+	if (t - windowStart >= 1) { // 1 second window
+		loopRate = rate;
+		windowStart = t;
+		rate = 0;
+	}
+}

flix/util.ino

@@ -0,0 +1,42 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Utility functions
+
+#include <math.h>
+#include <soc/soc.h>
+#include <soc/rtc_cntl_reg.h>
+
+float mapf(long x, long in_min, long in_max, float out_min, float out_max) {
+	return (float)(x - in_min) * (out_max - out_min) / (float)(in_max - in_min) + out_min;
+}
+
+float mapff(float x, float in_min, float in_max, float out_min, float out_max) {
+	return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
+}
+
+// Wrap angle to [-PI, PI)
+float wrapAngle(float angle) {
+	angle = fmodf(angle, 2 * PI);
+	if (angle > PI) {
+		angle -= 2 * PI;
+	} else if (angle < -PI) {
+		angle += 2 * PI;
+	}
+	return angle;
+}
+
+template <typename T>
+void printArray(T arr[], int size) {
+	Serial.print("{");
+	for (uint8_t i = 0; i < size; i++) {
+		Serial.print(arr[i]);
+		if (i < size - 1) Serial.print(", ");
+	}
+	Serial.println("}");
+}
+
+// Disable reset on low voltage
+void disableBrownOut() {
+	WRITE_PERI_REG(RTC_CNTL_BROWN_OUT_REG, 0);
+}

flix/vector.h

@@ -0,0 +1,98 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Lightweight vector library
+
+#pragma once
+
+class Vector : public Printable {
+public:
+	float x, y, z;
+
+	Vector(): x(0), y(0), z(0) {};
+
+	Vector(float x, float y, float z): x(x), y(y), z(z) {};
+
+	float norm() const {
+		return sqrt(x * x + y * y + z * z);
+	}
+
+	bool zero() const {
+		return x == 0 && y == 0 && z == 0;
+	}
+
+	void normalize() {
+		float n = norm();
+		x /= n;
+		y /= n;
+		z /= n;
+	}
+
+	Vector operator * (const float b) const {
+		return Vector(x * b, y * b, z * b);
+	}
+
+	Vector operator / (const float b) const {
+		return Vector(x / b, y / b, z / b);
+	}
+
+	Vector operator + (const Vector& b) const {
+		return Vector(x + b.x, y + b.y, z + b.z);
+	}
+
+	Vector operator - (const Vector& b) const {
+		return Vector(x - b.x, y - b.y, z - b.z);
+	}
+
+	// Element-wise multiplication
+	Vector operator * (const Vector& b) const {
+		return Vector(x * b.x, y * b.y, z * b.z);
+	}
+
+	// Element-wise division
+	Vector operator / (const Vector& b) const {
+		return Vector(x / b.x, y / b.y, z / b.z);
+	}
+
+	inline bool operator == (const Vector& b) const {
+		return x == b.x && y == b.y && z == b.z;
+	}
+
+	inline bool operator != (const Vector& b) const {
+		return !(*this == b);
+	}
+
+	inline bool finite() const {
+		return isfinite(x) && isfinite(y) && isfinite(z);
+	}
+
+	static float dot(const Vector& a, const Vector& b) {
+		return a.x * b.x + a.y * b.y + a.z * b.z;
+	}
+
+	static Vector cross(const Vector& a, const Vector& b) {
+		return Vector(a.y * b.z - a.z * b.y, a.z * b.x - a.x * b.z, a.x * b.y - a.y * b.x);
+	}
+
+	static float angleBetweenVectors(const Vector& a, const Vector& b) {
+		return acos(constrain(dot(a, b) / (a.norm() * b.norm()), -1, 1));
+	}
+
+	static Vector angularRatesBetweenVectors(const Vector& a, const Vector& b) {
+		Vector direction = cross(a, b);
+		if (direction.zero()) {
+			// vectors are opposite, return any perpendicular vector
+			return cross(a, Vector(1, 0, 0));
+		}
+		direction.normalize();
+		float angle = angleBetweenVectors(a, b);
+		return direction * angle;
+	}
+
+	size_t printTo(Print& p) const {
+		return
+			p.print(x, 15) + p.print(" ") +
+			p.print(y, 15) + p.print(" ") +
+			p.print(z, 15);
+	}
+};

flix/wifi.ino

@@ -0,0 +1,37 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Wi-Fi support
+
+#if WIFI_ENABLED == 1
+
+#include <WiFi.h>
+#include <WiFiAP.h>
+#include <WiFiUdp.h>
+
+#define WIFI_SSID "flix"
+#define WIFI_PASSWORD "flixwifi"
+#define WIFI_UDP_IP "255.255.255.255"
+#define WIFI_UDP_PORT 14550
+
+WiFiUDP udp;
+
+void setupWiFi() {
+	Serial.println("Setup Wi-Fi");
+	WiFi.softAP(WIFI_SSID, WIFI_PASSWORD);
+	IPAddress myIP = WiFi.softAPIP();
+	udp.begin(WIFI_UDP_PORT);
+}
+
+void sendWiFi(const uint8_t *buf, int len) {
+	udp.beginPacket(WIFI_UDP_IP, WIFI_UDP_PORT);
+	udp.write(buf, len);
+	udp.endPacket();
+}
+
+int receiveWiFi(uint8_t *buf, int len) {
+	udp.parsePacket();
+	return udp.read(buf, len);
+}
+
+#endif

gazebo/Arduino.h

@@ -0,0 +1,141 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Partial implementation of Arduino API for simulation
+
+#pragma once
+
+#include <cmath>
+#include <string>
+#include <stdint.h>
+#include <stdio.h>
+#include <unistd.h>
+#include <sys/poll.h>
+
+#define PI 3.1415926535897932384626433832795
+#define DEG_TO_RAD 0.017453292519943295769236907684886
+#define RAD_TO_DEG 57.295779513082320876798154814105
+#define radians(deg) ((deg)*DEG_TO_RAD)
+#define degrees(rad) ((rad)*RAD_TO_DEG)
+
+#define constrain(amt,low,high) ((amt)<(low)?(low):((amt)>(high)?(high):(amt)))
+
+long map(long x, long in_min, long in_max, long out_min, long out_max) {
+	const long run = in_max - in_min;
+	const long rise = out_max - out_min;
+	const long delta = x - in_min;
+	return (delta * rise) / run + out_min;
+}
+
+class __FlashStringHelper;
+
+// Arduino String partial implementation
+// https://www.arduino.cc/reference/en/language/variables/data-types/stringobject/
+class String: public std::string {
+public:
+	long toInt() const { return atol(this->c_str()); }
+	float toFloat() const { return atof(this->c_str()); }
+	bool isEmpty() const { return this->empty(); }
+};
+
+class Print;
+
+class Printable {
+public:
+	virtual size_t printTo(Print& p) const = 0;
+};
+
+class Print {
+public:
+	size_t printf(const char *format, ...) {
+		va_list args;
+		va_start(args, format);
+		size_t result = vprintf(format, args);
+		va_end(args);
+		return result;
+	}
+
+	size_t print(int n) {
+		return printf("%d", n);
+	}
+
+	size_t print(float n, int digits = 2) {
+		return printf("%.*f", digits, n);
+	}
+
+	size_t println(float n, int digits = 2) {
+		return printf("%.*f\n", digits, n);
+	}
+
+	size_t print(const char* s) {
+		return printf("%s", s);
+	}
+
+	size_t println() {
+		return print("\n");
+	}
+
+	size_t println(const char* s) {
+		return printf("%s\n", s);
+	}
+
+	size_t println(const Printable& p) {
+		return p.printTo(*this) + print("\n");
+	}
+
+	size_t print(const String& s) {
+		return printf("%s", s.c_str());
+	}
+
+	size_t println(const std::string& s) {
+		return printf("%s\n", s.c_str());
+	}
+
+	size_t println(const String& s) {
+		return printf("%s\n", s.c_str());
+	}
+};
+
+class HardwareSerial: public Print {
+public:
+	void begin(unsigned long baud) {
+		// server is running in background by default, so doesn't have access to stdin
+		// https://github.com/gazebosim/gazebo-classic/blob/d45feeb51f773e63960616880b0544770b8d1ad7/gazebo/gazebo_main.cc#L216
+		// set foreground process group to current process group to allow reading from stdin
+		// https://stackoverflow.com/questions/58918188/why-is-stdin-not-propagated-to-child-process-of-different-process-group
+		signal(SIGTTOU, SIG_IGN);
+		tcsetpgrp(STDIN_FILENO, getpgrp());
+		signal(SIGTTOU, SIG_DFL);
+	};
+
+	int available() {
+		// to implement for Windows, see https://stackoverflow.com/a/71992965/6850197
+		struct pollfd pfd = { .fd = STDIN_FILENO, .events = POLLIN };
+		return poll(&pfd, 1, 0) > 0;
+	}
+
+	int read() {
+		if (available()) {
+			char c;
+			size_t res = ::read(STDIN_FILENO, &c, 1); // use raw read to avoid C++ buffering
+			// https://stackoverflow.com/questions/45238997/does-getchar-function-has-its-own-buffer-to-store-remaining-input
+			return c;
+		}
+		return -1;
+	}
+
+	void setRxInvert(bool invert) {};
+};
+
+HardwareSerial Serial, Serial2;
+
+void delay(uint32_t ms) {
+	std::this_thread::sleep_for(std::chrono::milliseconds(ms));
+}
+
+unsigned long __micros;
+unsigned long __resetTime = 0;
+
+unsigned long micros() {
+	return __micros + __resetTime; // keep the time monotonic
+}

gazebo/CMakeLists.txt

@@ -0,0 +1,22 @@
+cmake_minimum_required(VERSION 3.5 FATAL_ERROR)
+project(flix_gazebo)
+
+# === gazebo plugin
+find_package(gazebo REQUIRED)
+find_package(SDL2 REQUIRED)
+include_directories(${GAZEBO_INCLUDE_DIRS})
+link_directories(${GAZEBO_LIBRARY_DIRS})
+list(APPEND CMAKE_CXX_FLAGS "${GAZEBO_CXX_FLAGS}")
+
+set(FLIX_SOURCE_DIR ../flix)
+include_directories(${FLIX_SOURCE_DIR})
+
+set(CMAKE_BUILD_TYPE RelWithDebInfo)
+add_library(flix SHARED simulator.cpp)
+target_link_libraries(flix ${GAZEBO_LIBRARIES} ${SDL2_LIBRARIES})
+target_include_directories(flix PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+target_compile_options(flix PRIVATE -Wno-address-of-packed-member) # disable unneeded mavlink warnings
+
+# Include dir for MAVLink-Arduino library
+target_include_directories(flix PUBLIC $ENV{HOME}/Arduino/libraries/MAVLink)
+target_include_directories(flix PUBLIC $ENV{HOME}/Documents/Arduino/libraries/MAVLink)

gazebo/README.md

@@ -0,0 +1,15 @@
+# Gazebo Simulation
+
+<img src="../docs/img/simulator.png" width=500 alt="Flix simulator">
+
+## Building and running
+
+See [building and running instructions](../docs/build.md#simulation).
+
+## Code structure
+
+Flix simulator is based on [Gazebo Classic](https://classic.gazebosim.org) and consists of the following components:
+
+* Physical model of the drone: [`models/flix/flix.sdf`](models/flix/flix.sdf).
+* Plugin for Gazebo: [`simulator.cpp`](simulator.cpp). The plugin is attached to the physical model. It receives stick positions from the controller, gets the data from the virtual sensors, and then passes this data to the Arduino code.
+* Arduino imitation: [`Arduino.h`](Arduino.h). This file contains partial implementation of the Arduino API, that is working within Gazebo plugin environment.

gazebo/SBUS.h

@@ -0,0 +1,25 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// SBUS library mock to make it possible to compile simulator with rc.ino
+
+#include "joystick.h"
+
+struct SBUSData {
+	int16_t ch[16];
+};
+
+class SBUS {
+public:
+	SBUS(HardwareSerial& bus, const bool inv = true) {};
+	SBUS(HardwareSerial& bus, const int8_t rxpin, const int8_t txpin, const bool inv = true) {};
+	void begin() {};
+	bool read() { return joystickGet(); };
+	SBUSData data() {
+		SBUSData data;
+		for (uint8_t i = 0; i < 16; i++) {
+			data.ch[i] = channels[i];
+		}
+		return data;
+	};
+};

gazebo/flix.h

@@ -0,0 +1,62 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Declarations of some functions and variables in Arduino code
+
+#include <cmath>
+#include <stdio.h>
+#include "vector.h"
+#include "quaternion.h"
+#include "Arduino.h"
+#include "wifi.h"
+
+#define RC_CHANNELS 16
+
+#define MOTOR_REAR_LEFT 0
+#define MOTOR_FRONT_LEFT 3
+#define MOTOR_FRONT_RIGHT 2
+#define MOTOR_REAR_RIGHT 1
+
+#define WIFI_ENABLED 1
+
+float t = NAN;
+float dt;
+float loopRate;
+float motors[4];
+int16_t channels[16]; // raw rc channels
+float controls[RC_CHANNELS];
+float controlsTime;
+Vector acc;
+Vector gyro;
+Vector rates;
+Quaternion attitude;
+
+// declarations
+void computeLoopRate();
+void applyGyro();
+void applyAcc();
+void control();
+void interpretRC();
+void controlAttitude();
+void controlRate();
+void controlTorque();
+void showTable();
+bool motorsActive();
+void cliTestMotor(uint8_t n);
+void printRCCal();
+void processMavlink();
+void sendMavlink();
+void sendMessage(const void *msg);
+void receiveMavlink();
+void handleMavlink(const void *_msg);
+void failsafe();
+void descend();
+inline Quaternion FLU2FRD(const Quaternion &q);
+
+// mocks
+void setLED(bool on) {};
+void calibrateGyro() { printf("Skip gyro calibrating\n"); };
+void calibrateAccel() { printf("Skip accel calibrating\n"); };
+void sendMotors() {};
+void printIMUCal() { printf("cal: N/A\n"); };
+void printIMUInfo() {};

gazebo/flix.world

@@ -0,0 +1,29 @@
+<?xml version="1.0"?>
+<sdf version="1.4">
+	<world name="default">
+		<scene>
+			<ambient>1 1 1 1</ambient>
+			<sky/>
+			<origin_visual>false</origin_visual>
+			<grid>false</grid>
+		</scene>
+		<gui>
+			<camera name="user_camera">
+				<pose>-2.3 0 1.1 0 0.3 0</pose>
+			</camera>
+		</gui>
+		<physics type="ode">
+			<max_step_size>0.001</max_step_size>
+		</physics>
+		<include>
+			<uri>model://floor</uri>
+		</include>
+		<include>
+			<uri>model://sun</uri>
+		</include>
+		<include>
+			<uri>model://flix</uri>
+			<pose>0 0 0.3 0 0 0</pose>
+		</include>
+	</world>
+</sdf>

gazebo/joystick.h

@@ -0,0 +1,56 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Joystick support for simulation
+
+#include <SDL2/SDL.h>
+#include <gazebo/gazebo.hh>
+#include <iostream>
+
+// simulation calibration overrides, NOTE: use `cr` command and replace with the actual values
+const int channelNeutralOverride[] = {-258, -258, -27349, 0, -27349, 0};
+const int channelMaxOverride[] = {27090, 27090, 27090, 27090, -5676, 1};
+
+#define RC_CHANNEL_ROLL 0
+#define RC_CHANNEL_PITCH 1
+#define RC_CHANNEL_THROTTLE 2
+#define RC_CHANNEL_YAW 3
+#define RC_CHANNEL_ARMED 5
+#define RC_CHANNEL_MODE 4
+
+SDL_Joystick *joystick;
+bool joystickInitialized = false, warnShown = false;
+
+void normalizeRC();
+
+void joystickInit() {
+	SDL_Init(SDL_INIT_JOYSTICK);
+	joystick = SDL_JoystickOpen(0);
+	if (joystick != NULL) {
+		joystickInitialized = true;
+		gzmsg << "Joystick initialized: " << SDL_JoystickNameForIndex(0) << std::endl;
+	} else if (!warnShown) {
+		gzwarn << "Joystick not found, begin waiting for joystick..." << std::endl;
+		warnShown = true;
+	}
+
+	// apply calibration overrides
+	extern int channelNeutral[RC_CHANNELS];
+	extern int channelMax[RC_CHANNELS];
+	memcpy(channelNeutral, channelNeutralOverride, sizeof(channelNeutralOverride));
+	memcpy(channelMax, channelMaxOverride, sizeof(channelMaxOverride));
+}
+
+bool joystickGet() {
+	if (!joystickInitialized) {
+		joystickInit();
+		return false;
+	}
+
+	SDL_JoystickUpdate();
+
+	for (uint8_t i = 0; i < 8; i++) {
+		channels[i] = SDL_JoystickGetAxis(joystick, i);
+	}
+	return true;
+}

gazebo/models/flix/flix.sdf

@@ -0,0 +1,95 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="flix">
+		<link name="body">
+			<inertial>
+				<mass>0.065</mass>
+				<inertia>
+					<ixx>3.55E-5</ixx>
+					<iyy>4.23E-5</iyy>
+					<izz>7.47E-5</izz>
+				</inertia>
+			</inertial>
+			<collision name="collision">
+				<geometry>
+					<box>
+						<size>0.095 0.095 0.0276</size>
+					</box>
+				</geometry>
+			</collision>
+			<sensor name="imu" type="imu">
+				<always_on>1</always_on>
+				<visualize>1</visualize>
+				<update_rate>1000</update_rate>
+				<imu>
+					<angular_velocity>
+						<x>
+							<noise type="gaussian">
+								<stddev>0.00174533</stddev><!-- 0.1 degrees per second -->
+							</noise>
+						</x>
+						<y>
+							<noise type="gaussian">
+								<stddev>0.00174533</stddev>
+							</noise>
+						</y>
+						<z>
+							<noise type="gaussian">
+								<stddev>0.00174533</stddev>
+							</noise>
+						</z>
+					</angular_velocity>
+					<linear_acceleration>
+						<x>
+							<noise type="gaussian">
+								<stddev>0.0784</stddev><!-- 8 mg -->
+							</noise>
+						</x>
+						<y>
+							<noise type="gaussian">
+								<stddev>0.0784</stddev>
+							</noise>
+						</y>
+						<z>
+							<noise type="gaussian">
+								<stddev>0.0784</stddev>
+							</noise>
+						</z>
+					</linear_acceleration>
+				</imu>
+			</sensor>
+			<visual name="body">
+				<geometry>
+					<mesh><uri>model://flix/flix.stl</uri></mesh>
+				</geometry>
+				<material>
+					<ambient>0.5 0.5 0.6 1</ambient>
+					<diffuse>0.5 0.5 0.6 1</diffuse>
+					<specular>0 0 0 1</specular>
+					<emissive>0 0 0 1</emissive>
+				</material>
+			</visual>
+			<visual name="prop0"><!-- rear left -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>-0.04243 0.04243 0.0142 0 0 0</pose>
+				<material><ambient>0.8 0.3 0.3 0.5</ambient><diffuse>0.8 0.3 0.3 0.5</diffuse></material>
+			</visual>
+			<visual name="prop1"><!-- rear right -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>-0.04243 -0.04243 0.0142 0 0 0</pose>
+				<material><ambient>0.8 0.3 0.3 0.5</ambient><diffuse>0.8 0.3 0.3 0.5</diffuse></material>
+			</visual>
+			<visual name="prop2"><!-- front right -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>0.04243 -0.04243 0.0142 0 0 0</pose>
+				<material><ambient>1 1 1 0.5</ambient><diffuse>1 1 1 0.5</diffuse></material>
+			</visual>
+			<visual name="prop3"><!-- front left -->
+				<geometry><cylinder><radius>0.0275</radius><length>0</length></cylinder></geometry>
+				<pose>0.04243 0.04243 0.0142 0 0 0</pose>
+				<material><ambient>1 1 1 0.5</ambient><diffuse>1 1 1 0.5</diffuse></material>
+			</visual>
+		</link>
+		<plugin name="flix" filename="libflix.so"/>
+	</model>
+</sdf>

gazebo/models/flix/model.config

@@ -0,0 +1,14 @@
+<?xml version="1.0"?>
+<model>
+    <name>flix</name>
+    <version>1.0</version>
+    <sdf version="1.5">flix.sdf</sdf>
+    <author>
+        <name>Oleg Kalachev</name>
+        <email>okalachev@gmail.com</email>
+    </author>
+    <license>Unknown</license>
+    <description>
+        Flix quadrotor
+    </description>
+</model>

gazebo/models/floor/floor.sdf

@@ -0,0 +1,31 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="floor">
+		<static>true</static>
+		<link name="link">
+			<pose>0 0 -0.02 0 0 0</pose>
+			<collision name="collision">
+				<geometry>
+					<box>
+						<size>200 200 .02</size>
+					</box>
+				</geometry>
+			</collision>
+			<visual name="visual">
+				<cast_shadows>false</cast_shadows>
+				<geometry>
+					<box>
+						<size>200 200 .02</size>
+					</box>
+				</geometry>
+				<material>
+					<script>
+						<uri>model://floor/materials/scripts</uri>
+						<uri>model://floor/materials/textures</uri>
+						<name>parquet</name>
+					</script>
+				</material>
+			</visual>
+		</link>
+	</model>
+</sdf>

gazebo/models/floor/materials/scripts/floor.material

@@ -0,0 +1,20 @@
+material parquet
+{
+	technique
+	{
+		pass
+		{
+			ambient 0.5 0.5 0.5 1.0
+			diffuse 0.5 0.5 0.5 1.0
+			specular 0.2 0.2 0.2 1.0 12.5
+
+			texture_unit
+			{
+				texture floor.jpg
+				filtering anistropic
+				max_anisotropy 16
+				scale 0.01 0.01
+			}
+		}
+	}
+}

gazebo/models/floor/model.config

@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+
+<model>
+  <name>Floor</name>
+  <version>1.0</version>
+  <sdf version="1.5">floor.sdf</sdf>
+
+  <author>
+    <name>Oleg Kalachev</name>
+    <email>okalachev@gmail.com</email>
+  </author>
+
+  <license>Unknown</license>
+
+  <description>
+    Floor.
+  </description>
+
+</model>

gazebo/models/linnmon/linnmon.sdf

@@ -0,0 +1,23 @@
+<?xml version="1.0"?>
+<sdf version="1.5">
+	<model name="table1">
+		<static>true</static>
+		<link name="link">
+			<pose>0 0 0 0 0 0</pose>
+			<collision name="mesh">
+				<geometry>
+					<mesh>
+						<uri>model://linnmon/linnmon.dae</uri>
+					</mesh>
+				</geometry>
+			</collision>
+			<visual name="visual">
+				<geometry>
+					<mesh>
+						<uri>model://linnmon/linnmon.dae</uri>
+					</mesh>
+				</geometry>
+			</visual>
+		</link>
+	</model>
+</sdf>

gazebo/models/linnmon/model.config

@@ -0,0 +1,19 @@
+<?xml version="1.0"?>
+
+<model>
+  <name>linnmon</name>
+  <version>1.0</version>
+  <sdf version="1.5">linnmon.sdf</sdf>
+
+  <author>
+    <name>Oleg Kalachev</name>
+    <email>okalachev@gmail.com</email>
+  </author>
+
+  <license>Unknown</license>
+
+  <description>
+    Linnmon table from https://3dlancer.net/en/producermodels/tables-coffee-tables/3dmodel-table-with-ikea-linnmon-36059
+  </description>
+
+</model>

gazebo/simulator.cpp

@@ -0,0 +1,134 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// Gazebo plugin for running Arduino code and simulating the drone
+
+#include <functional>
+#include <cmath>
+#include <gazebo/gazebo.hh>
+#include <gazebo/physics/physics.hh>
+#include <gazebo/common/common.hh>
+#include <gazebo/sensors/sensors.hh>
+#include <gazebo/msgs/msgs.hh>
+#include <ignition/math/Vector3.hh>
+#include <ignition/math/Pose3.hh>
+#include <iostream>
+#include <fstream>
+
+#include "Arduino.h"
+#include "flix.h"
+#include "util.ino"
+#include "rc.ino"
+#include "time.ino"
+#include "estimate.ino"
+#include "control.ino"
+#include "log.ino"
+#include "cli.ino"
+#include "mavlink.ino"
+#include "failsafe.ino"
+#include "lpf.h"
+
+using ignition::math::Vector3d;
+using namespace gazebo;
+using namespace std;
+
+class ModelFlix : public ModelPlugin {
+private:
+	physics::ModelPtr model;
+	physics::LinkPtr body;
+	sensors::ImuSensorPtr imu;
+	event::ConnectionPtr updateConnection, resetConnection;
+	transport::NodePtr nodeHandle;
+	transport::PublisherPtr motorPub[4];
+	LowPassFilter<Vector> accFilter = LowPassFilter<Vector>(0.1);
+
+public:
+	void Load(physics::ModelPtr _parent, sdf::ElementPtr /*_sdf*/) {
+		this->model = _parent;
+		this->body = this->model->GetLink("body");
+		this->imu = dynamic_pointer_cast<sensors::ImuSensor>(sensors::get_sensor(model->GetScopedName(true) + "::body::imu")); // default::flix::body::imu
+		this->updateConnection = event::Events::ConnectWorldUpdateBegin(std::bind(&ModelFlix::OnUpdate, this));
+		this->resetConnection = event::Events::ConnectWorldReset(std::bind(&ModelFlix::OnReset, this));
+		initNode();
+		Serial.begin(0);
+		gzmsg << "Flix plugin loaded" << endl;
+	}
+
+	void OnReset() {
+		attitude = Quaternion(); // reset estimated attitude
+		__resetTime += __micros;
+		gzmsg << "Flix plugin reset" << endl;
+	}
+
+	void OnUpdate() {
+		__micros = model->GetWorld()->SimTime().Double() * 1000000;
+		step();
+
+		// read virtual imu
+		gyro = Vector(imu->AngularVelocity().X(), imu->AngularVelocity().Y(), imu->AngularVelocity().Z());
+		acc = this->accFilter.update(Vector(imu->LinearAcceleration().X(), imu->LinearAcceleration().Y(), imu->LinearAcceleration().Z()));
+
+		// read rc
+		readRC();
+		controls[RC_CHANNEL_MODE] = 1; // 0 acro, 1 stab
+		controls[RC_CHANNEL_ARMED] = 1; // armed
+
+		estimate();
+
+		// correct yaw to the actual yaw
+		attitude.setYaw(this->model->WorldPose().Yaw());
+
+		control();
+		parseInput();
+		processMavlink();
+
+		applyMotorForces();
+		publishTopics();
+		logData();
+	}
+
+	void applyMotorForces() {
+		// thrusts
+		const double dist = 0.035355; // motors shift from the center, m
+		const double maxThrust = 0.03 * ONE_G; // ~30 g, https://youtu.be/VtKI4Pjx8Sk?&t=78
+
+		const float scale0 = 1.0, scale1 = 1.1, scale2 = 0.9, scale3 = 1.05; // imitating motors asymmetry
+		float mfl = scale0 * maxThrust * motors[MOTOR_FRONT_LEFT];
+		float mfr = scale1 * maxThrust * motors[MOTOR_FRONT_RIGHT];
+		float mrl = scale2 * maxThrust * motors[MOTOR_REAR_LEFT];
+		float mrr = scale3 * maxThrust * motors[MOTOR_REAR_RIGHT];
+
+		body->AddLinkForce(Vector3d(0.0, 0.0, mfl), Vector3d(dist, dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mfr), Vector3d(dist, -dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mrl), Vector3d(-dist, dist, 0.0));
+		body->AddLinkForce(Vector3d(0.0, 0.0, mrr), Vector3d(-dist, -dist, 0.0));
+
+		// torque
+		const double maxTorque = 0.0024 * ONE_G; // ~24 g*cm
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale0 * maxTorque * motors[MOTOR_FRONT_LEFT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale1 * -maxTorque * motors[MOTOR_FRONT_RIGHT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale2 * -maxTorque * motors[MOTOR_REAR_LEFT]));
+		body->AddRelativeTorque(Vector3d(0.0, 0.0, scale3 * maxTorque * motors[MOTOR_REAR_RIGHT]));
+	}
+
+	void initNode() {
+		nodeHandle = transport::NodePtr(new transport::Node());
+		nodeHandle->Init();
+		string ns = "~/" + model->GetName();
+		// create motors output topics for debugging and plotting
+		motorPub[0] = nodeHandle->Advertise<msgs::Int>(ns + "/motor0");
+		motorPub[1] = nodeHandle->Advertise<msgs::Int>(ns + "/motor1");
+		motorPub[2] = nodeHandle->Advertise<msgs::Int>(ns + "/motor2");
+		motorPub[3] = nodeHandle->Advertise<msgs::Int>(ns + "/motor3");
+	}
+
+	void publishTopics() {
+		for (int i = 0; i < 4; i++) {
+			msgs::Int msg;
+			msg.set_data(static_cast<int>(round(motors[i] * 1000)));
+			motorPub[i]->Publish(msg);
+		}
+	}
+};
+
+GZ_REGISTER_MODEL_PLUGIN(ModelFlix)

gazebo/soc/rtc_cntl_reg.h

@@ -0,0 +1 @@
+// Dummy file to make it possible to compile simulator with util.ino

gazebo/soc/soc.h

@@ -0,0 +1,3 @@
+// Dummy file to make it possible to compile simulator with util.ino
+
+#define WRITE_PERI_REG(addr, val) {}

gazebo/wifi.h

@@ -0,0 +1,44 @@
+// Copyright (c) 2023 Oleg Kalachev <okalachev@gmail.com>
+// Repository: https://github.com/okalachev/flix
+
+// sendWiFi and receiveWiFi implementations for the simulation
+
+#include <arpa/inet.h>
+#include <netinet/in.h>
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <unistd.h>
+#include <sys/poll.h>
+#include <gazebo/gazebo.hh>
+
+#define WIFI_UDP_PORT_LOCAL 14580
+#define WIFI_UDP_PORT_REMOTE 14550
+
+int wifiSocket;
+
+void setupWiFi() {
+	wifiSocket = socket(AF_INET, SOCK_DGRAM, 0);
+	sockaddr_in addr; // local address
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = INADDR_ANY;
+	addr.sin_port = htons(WIFI_UDP_PORT_LOCAL);
+	bind(wifiSocket, (sockaddr *)&addr, sizeof(addr));
+	int broadcast = 1;
+	setsockopt(wifiSocket, SOL_SOCKET, SO_BROADCAST, &broadcast, sizeof(broadcast)); // enable broadcast
+	gzmsg << "WiFi UDP socket initialized on port " << WIFI_UDP_PORT_LOCAL << " (remote port " << WIFI_UDP_PORT_REMOTE << ")" << std::endl;
+}
+
+void sendWiFi(const uint8_t *buf, int len) {
+	if (wifiSocket == 0) setupWiFi();
+	sockaddr_in addr; // remote address
+	addr.sin_family = AF_INET;
+	addr.sin_addr.s_addr = INADDR_BROADCAST; // send UDP broadcast
+	addr.sin_port = htons(WIFI_UDP_PORT_REMOTE);
+	sendto(wifiSocket, buf, len, 0, (sockaddr *)&addr, sizeof(addr));
+}
+
+int receiveWiFi(uint8_t *buf, int len) {
+	struct pollfd pfd = { .fd = wifiSocket, .events = POLLIN };
+	if (poll(&pfd, 1, 0) <= 0) return 0; // check if there is data to read
+	return recv(wifiSocket, buf, len, 0);
+}