Many updates to documentation

Updates to main readme. Add much more info to usage article. Move simulator building to simulation's readme. Improve assembly article. Many fixes. Updates in diagrams.
2026-01-09 12:36:49 +00:00 · 2025-11-06 13:46:25 +03:00
parent 2e7330d2f5
commit f1b993d719
14 changed files with 344 additions and 186 deletions
--- a/README.md
+++ b/README.md
@@ -1,6 +1,6 @@
 # Flix

-**Flix** (*flight + X*) — making an open source ESP32-based quadcopter from scratch.
+**Flix** (*flight + X*) — open source ESP32-based quadcopter made from scratch.

 <table>
  <tr>
@@ -52,25 +52,27 @@ The simulator is implemented using Gazebo and runs the original Arduino code:

 <img src="docs/img/simulator1.png" width=500 alt="Flix simulator">

-## Articles
+## Documentation

 * [Assembly instructions](docs/assembly.md).
 * [Usage: build, setup and flight](docs/usage.md).
 * [Troubleshooting](docs/troubleshooting.md).
-* [Firmware architecture overview](docs/firmware.md).
-* [Python library tutorial](tools/pyflix/README.md).
+* [Simulation](gazebo/README.md).
+* [Firmware architectural overview](docs/firmware.md).
+* [Python library](tools/pyflix/README.md).
 * [Log analysis](docs/log.md).
 * [User builds gallery](docs/user.md).
+* [Version 0 (obsolete)](docs/version0.md).

 ## Components

 |Type|Part|Image|Quantity|
 |-|-|:-:|:-:|
 |Microcontroller board|ESP32 Mini|<img src="docs/img/esp32.jpg" width=100>|1|
-|IMU (and barometer²) board|GY‑91, MPU-9265 (or other MPU‑9250/MPU‑6500 board)<br>ICM20948V2 (ICM‑20948)³<br>GY-521 (MPU-6050)³⁻¹|<img src="docs/img/gy-91.jpg" width=90 align=center><br><img src="docs/img/icm-20948.jpg" width=100><br><img src="docs/img/gy-521.jpg" width=100>|1|
-|<span style="background:yellow">Buck-boost converter</span> (recommended)|To be determined, output 5V or 3.3V, see [user-contributed schematics](https://miro.com/app/board/uXjVN-dTjoo=/?moveToWidget=3458764612179508274&cot=14)|<img src="docs/img/buck-boost.jpg" width=100>|1|
-|Motor|8520 3.7V brushed motor (shaft 0.8mm).<br>Motor with exact 3.7V voltage is needed, not ranged working voltage (3.7V — 6V).|<img src="docs/img/motor.jpeg" width=100>|4|
-|Propeller|Hubsan 55 mm|<img src="docs/img/prop.jpg" width=100>|4|
+|IMU (and barometer¹) board|GY‑91, MPU-9265 (or other MPU‑9250/MPU‑6500 board)<br>ICM20948V2 (ICM‑20948)³<br>GY-521 (MPU-6050)³⁻¹|<img src="docs/img/gy-91.jpg" width=90 align=center><br><img src="docs/img/icm-20948.jpg" width=100><br><img src="docs/img/gy-521.jpg" width=100>|1|
+|Boost converter (optional, for more stable power supply)|5V output|<img src="docs/img/buck-boost.jpg" width=100>|1|
+|Motor|8520 3.7V brushed motor.<br>Motor with exact 3.7V voltage is needed, not ranged working voltage (3.7V — 6V).<br>Make sure the motor shaft diameter and propeller hole diameter match!|<img src="docs/img/motor.jpeg" width=100>|4|
+|Propeller|55 mm (alternatively 65 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|
@@ -78,19 +80,17 @@ The simulator is implemented using Gazebo and runs the original Arduino code:
 |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 main part|3D printed⁴:<br>[`flix-frame-1.1.stl`](docs/assets/flix-frame-1.1.stl) [`flix-frame-1.1.step`](docs/assets/flix-frame-1.1.step)<br>Recommended settings: layer 0.2 mm, line 0.4 mm, infill 100%.|<img src="docs/img/frame1.jpg" width=100>|1|
+|Frame main part|3D printed²:<br>[`flix-frame-1.1.stl`](docs/assets/flix-frame-1.1.stl) [`flix-frame-1.1.step`](docs/assets/flix-frame-1.1.step)<br>Recommended settings: layer 0.2 mm, line 0.4 mm, infill 100%.|<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>|2|
 |Controller (recommended)|CC2500 transmitter, like BetaFPV LiteRadio CC2500 (RC receiver/Wi-Fi).<br>Two-sticks gamepad (Wi-Fi only) — see [recommended gamepads](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/setup_view/joystick.html#supported-joysticks).<br>Other⁵|<img src="docs/img/betafpv.jpg" width=100><img src="docs/img/logitech.jpg" width=80>|1|
-|*RC receiver (optional)*|*DF500 or other⁵*|<img src="docs/img/rx.jpg" width=100>|1|
+|*RC receiver (optional)*|*DF500 or other³*|<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` or `MPU6050` in `imu.ino` file for using the appropriate boards.*<br>
-*³⁻¹ — MPU-6050 supports I²C interface only (not recommended). To use it change IMU declaration to `MPU6050 IMU(Wire)`.*<br>
-*⁴ — this frame is optimized for GY-91 board, if using other, the board mount holes positions should be modified.*<br>
-*⁵ — you also may use any transmitter-receiver pair with SBUS interface.*
+*¹ — barometer is not used for now.*<br>
+*² — this frame is optimized for GY-91 board, if using other, the board mount holes positions should be modified.*<br>
+*³ — you also may use any transmitter-receiver pair with SBUS interface.*

 Tools required for assembly:

@@ -100,7 +100,7 @@ Tools required for assembly:
 * 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)).
+Feel free to modify the design and or code, and create your own improved versions. 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

@@ -108,7 +108,7 @@ Feel free to modify the design and or code, and create your own improved version

 <img src="docs/img/schematics1.svg" width=700 alt="Flix version 1 schematics">

-*(Dashed is optional).*
+*(Dashed elements are optional).*

 Motor connection scheme:

@@ -135,14 +135,15 @@ See [assembly guide](docs/assembly.md) for instructions on assembling the drone.
 * 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 (*TDI*)|
-  |Motor 1|Rear right|Clockwise|Blue & Red|GPIO13 (*TCK*)|
-  |Motor 2|Front right|Counter-clockwise|Black & White|GPIO14 (*TMS*)|
-  |Motor 3|Front left|Clockwise|Blue & Red|GPIO15 (*TD0*)|
+  |Motor|Position|Direction|Prop type|Motor wires|GPIO|
+  |-|-|-|-|-|-|
+  |Motor 0|Rear left|Counter-clockwise|B|Black & White|GPIO12 (*TDI*)|
+  |Motor 1|Rear right|Clockwise|A|Blue & Red|GPIO13 (*TCK*)|
+  |Motor 2|Front right|Counter-clockwise|B|Black & White|GPIO14 (*TMS*)|
+  |Motor 3|Front left|Clockwise|A|Blue & Red|GPIO15 (*TD0*)|

-  Counter-clockwise motors have black and white wires and clockwise motors have blue and red wires.
+  Clockwise motors have blue & red wires and correspond to propeller type A (marked on the propeller).
+  Counter-clockwise motors have black & white wires correspond to propeller type B.

 * Optionally connect the RC receiver to the ESP32's UART2:

@@ -154,28 +155,14 @@ See [assembly guide](docs/assembly.md) for instructions on assembling the drone.

 *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
+## Resources

-Default IMU orientation in the code is **LFD** (Left-Forward-Down):
-
-<img src="docs/img/gy91-lfd.svg" width=400 alt="GY-91 axes">
-
-In case of using other IMU orientation, modify the `rotateIMU` function in the `imu.ino` file.
-
-See [FlixPeriph documentation](https://github.com/okalachev/flixperiph?tab=readme-ov-file#imu-axes-orientation) to learn axis orientation of other IMU boards.
-
-## 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/.
-
-See the information on the obsolete version 0 in the [corresponding article](docs/version0.md).
+* Telegram channel on developing the drone and the flight controller (in Russian): https://t.me/opensourcequadcopter.
+* 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/.

 ## Disclaimer

-This is a fun DIY project, and I hope you find it interesting and useful. However, it's not easy to assemble and set up, and it's provided "as is" without any warranties. There’s no guarantee that it will work perfectly — or even work at all.
+This is a DIY project, and I hope you find it interesting and useful. However, it's not easy to assemble and set up, and it's provided "as is" without any warranties. There's no guarantee that it will work perfectly, or even work at all.

 ⚠️ The author is not responsible for any damage, injury, or loss resulting from the use of this project. Use at your own risk!
--- a/docs/assembly.md
+++ b/docs/assembly.md
@@ -27,3 +27,27 @@ Soldered components ([schematics variant](https://miro.com/app/board/uXjVN-dTjoo
 <br>Assembled drone:

 <img src="img/assembly/7.jpg" width=600>
+
+## Motor directions
+
+> [!WARNING]
+> The drone above is an early build, and it has **inversed** motor directions scheme. The photos only illustrate the assembly process in general.
+
+Use standard motor directions scheme:
+
+<img src="img/motors.svg" width=200>
+
+Motors connection table:
+
+|Motor|Position|Direction|Prop type|Motor wires|GPIO|
+|-|-|-|-|-|-|
+|Motor 0|Rear left|Counter-clockwise|B|Black & White|GPIO12 (*TDI*)|
+|Motor 1|Rear right|Clockwise|A|Blue & Red|GPIO13 (*TCK*)|
+|Motor 2|Front right|Counter-clockwise|B|Black & White|GPIO14 (*TMS*)|
+|Motor 3|Front left|Clockwise|A|Blue & Red|GPIO15 (*TD0*)|
+
+## Motors tightening
+
+Motors should be installed very tightly — any vibration may lead to bad attitude estimation and unstable flight. If motors are loose, use tiny tape pieces to fix them tightly as shown below:
+
+<img src="img/motor-tape.jpg" width=600>
--- a/docs/book/firmware.md
+++ b/docs/book/firmware.md
@@ -12,8 +12,8 @@
 * `acc` *(Vector)* — данные с акселерометра, *м/с<sup>2</sup>*.
 * `rates` *(Vector)* — отфильтрованные угловые скорости, *рад/с*.
 * `attitude` *(Quaternion)* — оценка ориентации (положения) дрона.
-* `controlRoll`, `controlPitch`, ... *(float[])* — команды управления от пилота, в диапазоне [-1, 1].
-* `motors` *(float[])* — выходные сигналы на моторы, в диапазоне [0, 1].
+* `controlRoll`, `controlPitch`, `controlYaw`, `controlThrottle`, `controlMode` *(float)* — команды управления от пилота, в диапазоне [-1, 1].
+* `motors` *(float[4])* — выходные сигналы на моторы, в диапазоне [0, 1].

 ## Исходные файлы

--- a/docs/build.md
+++ b/docs/build.md
@@ -1 +0,0 @@
-usage.md
--- a/docs/build.md
+++ b/docs/build.md
@@ -0,0 +1,2 @@
+<!-- markdownlint-disable MD041 -->
+Build instructions are moved to [usage article](usage.md).
--- a/docs/firmware.md
+++ b/docs/firmware.md
@@ -6,7 +6,7 @@ The firmware is a regular Arduino sketch, and it follows the classic Arduino one

 <img src="img/dataflow.svg" width=600 alt="Firmware dataflow diagram">

-The main loop is running at 1000 Hz. All the dataflow goes through global variables (for simplicity):
+The main loop is running at 1000 Hz. The dataflow goes through global variables, including:

 * `t` *(float)* — current step time, *s*.
 * `dt` *(float)* — time delta between the current and previous steps, *s*.
@@ -14,12 +14,12 @@ The main loop is running at 1000 Hz. All the dataflow goes through global variab
 * `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.
-* `controlRoll`, `controlPitch`, ... *(float[])* — pilot control inputs, range [-1, 1].
-* `motors` *(float[])* — motor outputs, range [0, 1].
+* `controlRoll`, `controlPitch`, `controlYaw`, `controlThrottle`, `controlMode` *(float)* — pilot control inputs, range [-1, 1].
+* `motors` *(float[4])* — motor outputs, range [0, 1].

 ## Source files

-Firmware source files are located in `flix` directory. The core files are:
+Firmware source files are located in `flix` directory.

 * [`flix.ino`](../flix/flix.ino) — Arduino sketch main file, entry point.Includes some global variable definitions and the main loop.
 * [`imu.ino`](../flix/imu.ino) — reading data from the IMU sensor (gyroscope and accelerometer), IMU calibration.
@@ -28,6 +28,7 @@ Firmware source files are located in `flix` directory. The core files are:
 * [`control.ino`](../flix/control.ino) — control subsystem, three-dimensional two-level cascade PID controller.
 * [`motors.ino`](../flix/motors.ino) — PWM motor output control.
 * [`mavlink.ino`](../flix/mavlink.ino) — interaction with QGroundControl or [pyflix](../tools/pyflix) via MAVLink protocol.
+* [`cli.ino`](../flix/cli.ino) — serial and MAVLink console.

 Utility files:

@@ -45,12 +46,22 @@ Pilot inputs are interpreted in `interpretControls()`, and then converted to the
 * `torqueTarget` *(Vector)* — target torque, range [-1, 1].
 * `thrustTarget` *(float)* — collective thrust target, range [0, 1].

-Control command is processed in `controlAttitude()`, `controlRates()`, `controlTorque()` functions. Each function may be skipped if the corresponding target is set to `NAN`.
+Control command is handled in `controlAttitude()`, `controlRates()`, `controlTorque()` functions. Each function may be skipped if the corresponding control target is set to `NAN`.

 <img src="img/control.svg" width=300 alt="Control subsystem diagram">

 Armed state is stored in `armed` variable, and current mode is stored in `mode` variable.

-## Building
+### Console
+
+To write into the console, `print()` function is used. This function sends data both to the Serial console and to the MAVLink console (which can be accessed wirelessly in QGroundControl). The function supports formatting:
+
+```cpp
+print("Test value: %.2f\n", testValue);
+```
+
+In order to add a console command, modify the `doCommand()` function in `cli.ino` file.
+
+## Building the firmware

 See build instructions in [usage.md](usage.md).
--- a/docs/img/control.svg
+++ b/docs/img/control.svg
--- a/docs/img/dataflow.svg
+++ b/docs/img/dataflow.svg
--- a/docs/img/motor-tape.jpg
+++ b/docs/img/motor-tape.jpg
--- a/docs/img/motors.svg
+++ b/docs/img/motors.svg
@@ -0,0 +1,89 @@
+<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 355.49 357.47">
+  <defs>
+    <style>
+      .a, .e {
+        fill: none;
+        stroke-miterlimit: 10;
+      }
+
+      .a {
+        stroke: #d5d5d5;
+        stroke-width: 31px;
+      }
+
+      .b {
+        fill: #c1c1c1;
+      }
+
+      .c {
+        fill: #ff9400;
+      }
+
+      .d {
+        opacity: 0.12;
+      }
+
+      .e {
+        stroke: #cc5200;
+        stroke-width: 8px;
+      }
+
+      .f {
+        fill: #cc5200;
+      }
+
+      .g {
+        font-size: 50px;
+        fill: #fff;
+      }
+
+      .g, .h {
+        font-family: Tahoma;
+      }
+
+      .h {
+        font-size: 20px;
+      }
+
+      .i {
+        letter-spacing: 0em;
+      }
+    </style>
+  </defs>
+  <g>
+    <g>
+      <line class="a" x1="77" y1="279.14" x2="277" y2="78.14"/>
+      <line class="a" x1="78" y1="79.14" x2="278" y2="280.14"/>
+      <circle class="b" cx="177.5" cy="178.64" r="41.5"/>
+      <circle class="c" cx="77.57" cy="78.64" r="77.95"/>
+      <circle class="c" cx="277.13" cy="78.42" r="77.95"/>
+      <circle class="c" cx="276.13" cy="279.42" r="77.95"/>
+      <circle class="c" cx="77.13" cy="279.42" r="77.95"/>
+    </g>
+    <path class="d" d="M173.89,164.07l-8.44,26.05a4.31,4.31,0,0,0,4.1,5.65h16.9a4.32,4.32,0,0,0,4.11-5.65l-8.45-26.05A4.32,4.32,0,0,0,173.89,164.07Z"/>
+    <g>
+      <path class="e" d="M307.07,123A52.66,52.66,0,1,0,235,47"/>
+      <polygon class="f" points="228.28 38.98 227.04 59.68 245.59 50.41 228.28 38.98"/>
+    </g>
+    <g>
+      <path class="e" d="M42.57,237.58a52.66,52.66,0,1,0,72.08,76"/>
+      <polygon class="f" points="121.36 321.6 122.6 300.9 104.05 310.17 121.36 321.6"/>
+    </g>
+    <g>
+      <path class="e" d="M311.89,237.58a52.66,52.66,0,1,1-72.08,76"/>
+      <polygon class="f" points="250.41 310.17 231.86 300.9 233.1 321.6 250.41 310.17"/>
+    </g>
+    <g>
+      <path class="e" d="M47.71,122.69a52.66,52.66,0,1,1,72.08-75.95"/>
+      <polygon class="f" points="109.19 50.1 127.74 59.38 126.5 38.67 109.19 50.1"/>
+    </g>
+    <text class="g" transform="translate(64.5 99.24)">3</text>
+    <text class="g" transform="translate(63.52 297.27)">0</text>
+    <text class="g" transform="translate(263.52 298.27)">1</text>
+    <text class="g" transform="translate(260.52 99.27)">2</text>
+    <text class="h" transform="translate(65.66 129.73)">p<tspan class="i" x="11.05" y="0">r</tspan><tspan x="18.16" y="0">op A</tspan></text>
+    <text class="h" transform="translate(233.66 245.73)">p<tspan class="i" x="11.05" y="0">r</tspan><tspan x="18.16" y="0">op A</tspan></text>
+    <text class="h" transform="translate(232.15 129.42)">p<tspan class="i" x="11.05" y="0">r</tspan><tspan x="18.16" y="0">op B</tspan></text>
+    <text class="h" transform="translate(67.15 245.42)">p<tspan class="i" x="11.05" y="0">r</tspan><tspan x="18.16" y="0">op B</tspan></text>
+  </g>
+</svg>
--- a/docs/img/qgc-attitude.png
+++ b/docs/img/qgc-attitude.png
--- a/docs/img/schematics1.svg
+++ b/docs/img/schematics1.svg
--- a/docs/troubleshooting.md
+++ b/docs/troubleshooting.md
@@ -32,6 +32,8 @@ Do the following:
  * `mfl` — should rotate front left motor (clockwise).
  * `mrl` — should rotate rear left motor (counter-clockwise).
  * `mrr` — should rotate rear right motor (clockwise).
+* **Check the propeller directions are correct**. Make sure your propeller types (A or B) are installed as on the picture:
+  <img src="img/user/peter_ukhov-2/1.jpg" width="200">
 * **Check the remote control**. Using `rc` command, check the control values reflect your sticks movement. All the controls should change between -1 and 1, and throttle between 0 and 1.
 * If using SBUS receiver, **calibrate the RC**. Type `cr` command in Serial Monitor and follow the instructions.
 * **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.
--- a/docs/usage.md
+++ b/docs/usage.md
@@ -1,130 +1,36 @@
 # Usage: build, setup and flight

-To use Flix, you need to build the firmware and upload it to the ESP32 board. For simulation, you need to build and run the simulator.
+To fly Flix quadcopter, you need to build the firmware, upload it to the ESP32 board, and set up the drone for flight.

-For the start, clone the repository using git:
+To get the firmware sources, clone the repository using git:

 ```bash
-git clone https://github.com/okalachev/flix.git
-cd flix
+git clone https://github.com/okalachev/flix.git && cd flix
 ```

-## Simulation
+Beginners can [download the source code as a ZIP archive](https://github.com/okalachev/flix/archive/refs/heads/master.zip).

-### Ubuntu
+## Building the firmware

-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
-   sudo sh -c 'echo "deb http://packages.osrfoundation.org/gazebo/ubuntu-stable `lsb_release -cs` main" > /etc/apt/sources.list.d/gazebo-stable.list'
-   wget https://packages.osrfoundation.org/gazebo.key -O - | sudo apt-key add -
-   sudo apt-get update
-   sudo apt-get install -y gazebo11 libgazebo11-dev
-   ```
-
-   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
-
-#### 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. For **iOS**, use [QGroundControl build from TAJISOFT](https://apps.apple.com/ru/app/qgc-from-tajisoft/id1618653051).
-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.
-4. Run the simulation again.
-5. Use the USB remote control to fly the drone!
-
-## Firmware
+You can build and upload the firmware using either **Arduino IDE** (easier for beginners) or a **command line**.

 ### Arduino IDE (Windows, Linux, macOS)

 1. Install [Arduino IDE](https://www.arduino.cc/en/software) (version 2 is recommended).
-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).
+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. Install ESP32 core, version 3.2.0. 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.
 4. 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 2.0.16.
-5. Clone the project using git or [download the source code as a ZIP archive](https://codeload.github.com/okalachev/flix/zip/refs/heads/master).
-6. Open the downloaded Arduino sketch `flix/flix.ino` in Arduino IDE.
-7. Connect your ESP32 board to the computer and choose correct board type in Arduino IDE (*WEMOS D1 MINI ESP32* for ESP32 Mini) and the port.
-8. [Build and upload](https://docs.arduino.cc/software/ide-v2/tutorials/getting-started/ide-v2-uploading-a-sketch) the firmware using Arduino IDE.
+5. Open the `flix/flix.ino` sketch from downloaded firmware sources in Arduino IDE.
+6. Connect your ESP32 board to the computer and choose correct board type in Arduino IDE (*WEMOS D1 MINI ESP32* for ESP32 Mini) and the port.
+7. [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/).

-   On Linux, use:
+   On Linux, install it like this:

   ```bash
   curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=~/.local/bin sh
@@ -149,19 +55,84 @@ The latest version of Ubuntu supported by Gazebo 11 simulator is 20.04. If you h
   make upload monitor
   ```

-See other available Make commands in the [Makefile](../Makefile).
+See other available Make commands in [Makefile](../Makefile).

 > [!TIP]
-> You can test the firmware on a bare ESP32 board without connecting IMU and other peripherals. The Wi-Fi network `flix` should appear and all the basic functionality including CLI and QGroundControl connection should work.
+> You can test the firmware on a bare ESP32 board without connecting IMU and other peripherals. The Wi-Fi network `flix` should appear and all the basic functionality including console and QGroundControl connection should work.

-### Setup
+## Before first flight
+
+### Choose the IMU model
+
+In case if using different IMU model than MPU9250, change `imu` variable declaration in the `imu.ino`:
+
+```cpp
+ICM20948 imu(SPI);  // For ICM-20948
+MPU6050 imu(Wire);  // For MPU-6050
+```
+
+### Setup the IMU orientation
+
+The IMU orientation is defined in `rotateIMU` function in the `imu.ino` file. Change it so it converts the IMU axes to the drone's axes correctly. **Drone axes are X forward, Y left, Z up.**
+
+See various [IMU axes orientations table](https://github.com/okalachev/flixperiph/?tab=readme-ov-file#imu-axes-orientation) to help you set up the correct orientation.
+
+### Connect using QGroundControl
+
+QGroundControl is a ground control station software that can be used to monitor and control the drone.
+
+1. Install mobile or desktop version of [QGroundControl](https://docs.qgroundcontrol.com/master/en/qgc-user-guide/getting_started/download_and_install.html).
+2. Power up the drone.
+3. Connect your computer or smartphone to the appeared `flix` Wi-Fi network (password: `flixwifi`).
+4. Launch QGroundControl app. It should connect and begin showing the drone's telemetry automatically
+
+### Access console
+
+The console is a command line interface (CLI) that allows to interact with the drone, change parameters, and perform various actions. There are two ways of accessing the console: using **serial port** or using **QGroundControl (wirelessly)**.
+
+To access the console using serial port:
+
+1. Connect the ESP32 board to the computer using USB cable.
+2. Open Serial Monitor in Arduino IDE (or use `make monitor` command in the command line).
+3. In Arduino IDE, make sure the baudrate is set to 115200.
+
+To access the console wirelessly using QGroundControl:
+
+1. Connect to the drone using QGroundControl app.
+2. Go to the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Analyze Tools* ⇒ *MAVLink Console*.
+   <img src="img/cli.png" width="400">
+
+Use `help` command to see the list of available commands.
+
+### Calibrate accelerometer

 Before flight you need to calibrate the accelerometer:

-1. Open Serial Monitor in Arduino IDE (or use `make monitor` command in the command line).
+1. Access the console using QGroundControl (more convenient) or Serial Monitor.
 2. Type `ca` command there and follow the instructions.

-#### Control with smartphone
+### Check everything works
+
+1. Check the IMU is working: perform `imu` command and check its output:
+   * The `status` field should be `OK`.
+   * The `rate` field should be about 1000 (Hz).
+   * The `accel` and `gyro` fields should change as you move the drone.
+
+2. 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. Attitude indicator in QGroundControl is shown below:
+
+   <img src="img/qgc-attitude.png" height="200">
+
+3. Perform motor tests in the console. **Remove the propellers before this!** Use the following commands:
+   * `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).
+
+## Setup remote control
+
+There are several ways to control the drone's flight: using **smartphone** (Wi-Fi), using **standard radio remote control**, or using **USB remote control** (Wi-Fi).
+
+### 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.
@@ -173,7 +144,7 @@ Before flight you need to calibrate the accelerometer:
 > [!TIP]
 > Decrease `TILT_MAX` parameter when flying using the smartphone to make the controls less sensitive.

-#### Control with remote control
+### Control with remote control

 Before flight using remote control, you need to calibrate it:

@@ -181,7 +152,7 @@ Before flight using remote control, you need to calibrate it:
 2. Type `cr` command there and follow the instructions.
 3. Use the remote control to fly the drone!

-#### Control with USB remote control (Wi-Fi)
+### Control with USB remote control

 If your drone doesn't have RC receiver installed, you can use USB remote control and QGroundControl app to fly it.

@@ -193,9 +164,6 @@ If your drone doesn't have RC receiver installed, you can use USB remote control
 6. Go the the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Joystick*. Calibrate you USB remote control there.
 7. Use the USB remote control to fly the drone!

-> [!NOTE]
-> If something goes wrong, go to the [Troubleshooting](troubleshooting.md) article.
-
 ## Flight

 For both virtual sticks and a physical joystick, the default control scheme is left stick for throttle and yaw and right stick for pitch and roll:
@@ -214,6 +182,9 @@ When finished flying, **disarm** the drone, moving the left stick to the bottom

 <img src="img/disarming.svg" width="150">

+> [!NOTE]
+> If something goes wrong, go to the [Troubleshooting](troubleshooting.md) article.
+
 ### Flight modes

 Flight mode is changed using mode switch on the remote control or using the command line.
@@ -241,12 +212,6 @@ If the pilot moves the control sticks, the drone will switch back to *STAB* mode

 ## Adjusting parameters

-You can adjust some of the drone's parameters (include PID coefficients) in QGroundControl app. In order to do that, go to the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Parameters*.
+You can adjust some of the drone's parameters (include PID coefficients) in QGroundControl. In order to do that, go to the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Parameters*.

 <img src="img/parameters.png" width="400">
-
-## CLI access
-
-In addition to accessing the drone's command line interface (CLI) using the serial port, you can also access it with QGroundControl using Wi-Fi connection. To do that, go to the QGroundControl menu ⇒ *Vehicle Setup* ⇒ *Analyze Tools* ⇒ *MAVLink Console*.
-
-<img src="img/cli.png" width="400">
--- a/gazebo/README.md
+++ b/gazebo/README.md
@@ -1,15 +1,96 @@
-# Gazebo Simulation
+# Simulation

-<img src="../docs/img/simulator.png" width=500 alt="Flix simulator">
+The Flix drone simulator is based on Gazebo 11 and runs the firmware code in virtual physical environment.

-## Building and running
+Gazebo 11 works on **Ubuntu 20.04** and used to work on macOS. However, on the recent macOS versions it seems to be broken, so Ubuntu 20.04 is recommended.

-See [building and running instructions](../docs/usage.md#simulation).
+<img src="../docs/img/simulator1.png" width=600 alt="Flix simulator">
+
+## Installation
+
+1. Clone the Flix repository using it:
+
+   ```bash
+   git clone https://github.com/okalachev/flix.git && cd flix
+   ```
+
+2. Install Arduino CLI:
+
+   ```bash
+   curl -fsSL https://raw.githubusercontent.com/arduino/arduino-cli/master/install.sh | BINDIR=~/.local/bin sh
+   ```
+
+3. Install Gazebo 11:
+
+   ```bash
+   sudo sh -c 'echo "deb http://packages.osrfoundation.org/gazebo/ubuntu-stable `lsb_release -cs` main" > /etc/apt/sources.list.d/gazebo-stable.list'
+   wget https://packages.osrfoundation.org/gazebo.key -O - | sudo apt-key add -
+   sudo apt-get update
+   sudo apt-get install -y gazebo11 libgazebo11-dev
+   ```
+
+   Set up your Gazebo environment variables:
+
+   ```bash
+   echo "source /usr/share/gazebo/setup.sh" >> ~/.bashrc
+   source ~/.bashrc
+   ```
+
+4. Install SDL2 and other dependencies:
+
+   ```bash
+   sudo apt-get update && sudo apt-get install build-essential libsdl2-dev
+   ```
+
+5. 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
+   ```
+
+6. Run the simulation:
+
+   ```bash
+   make simulator
+   ```
+
+## Usage
+
+Just like the real drone, the simulator can be controlled using a USB remote control or a smartphone.
+
+### 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. For **iOS**, use [QGroundControl build from TAJISOFT](https://apps.apple.com/ru/app/qgc-from-tajisoft/id1618653051).
+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.
+4. Use the USB remote control to fly the drone!
+
+### Piloting
+
+To start the flight, arm the drone moving the throttle stick to the bottom right position:
+
+<img src="../docs/img/arming.svg" width="150">
+
+To disarm, move the throttle stick to the bottom left position:
+
+<img src="../docs/img/disarming.svg" width="150">
+
+See other piloting and usage details in general [usage article](../docs/usage.md).

 ## Code structure

-Flix simulator is based on [Gazebo Classic](https://classic.gazebosim.org) and consists of the following components:
+Flix simulator consists of the following components:

-* Physical model of the drone: [`models/flix/flix.sdf`](models/flix/flix.sdf).
+* Physical model of the drone in Gazebo format: [`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.
+* Arduino emulation: [`Arduino.h`](Arduino.h). This file contains partial implementation of the Arduino API, that is working within Gazebo plugin environment.