Flix

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

Features

• Dedicated for education and research.
• Made from general-purpose components.
• Simple and clean source code in Arduino (<2k lines firmware).
• Control using USB gamepad, remote control or smartphone.
• Wi-Fi and MAVLink support.
• Wireless command line interface and analyzing.
• Precise simulation with Gazebo.
• Python library.
• Textbook on flight control theory and practice (in development).
• Position control (using external camera) and autonomous flights¹.

¹ — planned.

It actually flies

See detailed demo video: https://youtu.be/hT46CZ1CgC4.

Version 0 demo video: https://youtu.be/8GzzIQ3C6DQ.

Usage in education (RoboCamp): https://youtu.be/Wd3yaorjTx0.

See the user builds gallery:

Simulation

The simulator is implemented using Gazebo and runs the original Arduino code:

Articles

• Assembly instructions.
• Usage: build, setup and flight.
• Troubleshooting.
• Firmware architecture overview.
• Python library tutorial.
• Log analysis.
• User builds gallery.

Components

Type	Part	Image	Quantity
Microcontroller board	ESP32 Mini		1
IMU (and barometer²) board	GY‑91, MPU-9265 (or other MPU‑9250/MPU‑6500 board)ICM20948V2 (ICM‑20948)³GY-521 (MPU-6050)³⁻¹		1
Buck-boost converter (recommended)	To be determined, output 5V or 3.3V, see user-contributed schematics		1
Motor	8520 3.7V brushed motor (shaft 0.8mm).Motor with exact 3.7V voltage is needed, not ranged working voltage (3.7V — 6V).		4
Propeller	Hubsan 55 mm		4
MOSFET (transistor)	100N03A or analog		4
Pull-down resistor	10 kΩ		4
3.7V Li-Po battery	LW 952540 (or any compatible by the size)		1
Battery connector cable	MX2.0 2P female		1
Li-Po Battery charger	Any		1
Screws for IMU board mounting	M3x5		2
Screws for frame assembly	M1.4x5		4
Frame main part	3D printed⁴:flix-frame-1.1.stl flix-frame-1.1.stepRecommended settings: layer 0.2 mm, line 0.4 mm, infill 100%.		1

² — barometer is not used for now. ³ — change MPU9250 to ICM20948 or MPU6050 in imu.ino file for using the appropriate boards. ³⁻¹ — MPU-6050 supports I²C interface only (not recommended). To use it change IMU declaration to MPU6050 IMU(Wire). ⁴ — this frame is optimized for GY-91 board, if using other, the board mount holes positions should be modified. ⁵ — you also 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, or directly to the author (E-mail, Telegram).

Schematics

Simplified connection diagram

(Dashed is optional).

Motor connection scheme:

You can see a user-contributed variant of complete circuit diagram of the drone.

See assembly guide for instructions on assembling the drone.

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 (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)

  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	VCC (or 3.3V depending on the receiver)
  Signal (TX)	GPIO4⁶

⁶ — UART2 RX pin was changed to GPIO4 in Arduino ESP32 core 3.0.

IMU placement

Default IMU orientation in the code is LFD (Left-Forward-Down):

In case of using other IMU orientation, modify the rotateIMU function in the imu.ino file.

See FlixPeriph documentation 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.

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.

⚠️ The author is not responsible for any damage, injury, or loss resulting from the use of this project. Use at your own risk!