FakeFC

An emulated Betaflight flight controller running on an ESP32. FakeFC lets you use Betaflight Configurator and ELRS Configurator without a real flight controller — ideal for integration testing ExpressLRS (ELRS) receivers and flashing their firmware via the Betaflight Passthrough method.

Features

• MSP v1 / v2 protocol — responds to Betaflight Configurator queries so it appears as a real Betaflight 4.3 FC
• CRSF RC receiver — reads 16 RC channels from an ExpressLRS receiver at 420000 baud
• Serial passthrough — bridges USB ↔ ELRS receiver UART so ELRS Configurator can flash receiver firmware through the standard Betaflight Passthrough workflow
• DTR forwarding (ESP32-S2 only) — forwards the USB DTR signal to the ELRS receiver's reset pin so esptool can trigger bootloader mode automatically
• Web dashboard — live HTTP page showing all 16 RC channel values, served from a built-in WiFi access point

Hardware Requirements

Component	Details
Microcontroller	ESP32-S2 Mini (LOLIN S2 Mini) or ESP32 WROOM 32
ELRS receiver	Any ExpressLRS receiver with a UART CRSF output

Recommended board: ESP32-S2 Mini — it has native USB CDC, which enables automatic DTR forwarding for hands-free ELRS firmware flashing. The WROOM 32 works too but requires manually resetting the ELRS receiver before flashing.

Wiring

Signal	ESP32 GPIO	ELRS Receiver pin
CRSF RX (ESP32 receives)	GPIO 25	TX
CRSF TX / Reset (ESP32 sends)	GPIO 26	RX / RST

The USB port of the ESP32 connects to your computer and is used for both Betaflight Configurator communication (MSP) and ELRS firmware flashing (passthrough).

Pin numbers are defined in src/crsf.h (CRSF_RX_PIN / CRSF_TX_PIN) and can be changed to match your board layout.

Getting Started

Prerequisites

Install PlatformIO (CLI or the VS Code extension).

Build & Flash

# Clone the repository
git clone https://github.com/Akceptor/FakeFC.git
cd FakeFC

# Flash to ESP32-S2 Mini (recommended)
platformio run --environment lolin_s2_mini --target upload

# Flash to ESP32 WROOM 32
platformio run --environment esp32_wroom_32 --target upload

Monitor Serial Output

platformio device monitor --speed 115200

Usage

Betaflight Configurator

1. Connect the ESP32 to your computer via USB.
2. Open Betaflight Configurator.
3. Select the correct COM/serial port and click Connect.
4. FakeFC identifies itself as Betaflight 4.3 and responds to all standard MSP queries (board info, RC channels, serial config, etc.).

The Receiver tab will show live RC channel values streamed from the ELRS receiver.

ELRS Receiver Firmware Flashing (Betaflight Passthrough)

1. Wire the ELRS receiver to the ESP32 as described in the Wiring section.
2. Open ELRS Configurator and select the Betaflight Passthrough flashing method.
3. ELRS Configurator will:
   • Query FakeFC via MSP to discover UART1 (CRSF receiver port)
   • Enter CLI mode and issue serialpassthrough 1 420000
4. FakeFC bridges USB ↔ UART1, allowing esptool to flash the receiver.
5. On ESP32-S2, DTR changes are forwarded automatically to reset the receiver into bootloader mode. On WROOM 32, reset the receiver manually when prompted.
6. Power-cycle the ESP32 after flashing to return to normal operation.

Web Dashboard

After power-on, FakeFC creates a WiFi access point:

Setting	Value
SSID	FakeFC
Password	(none — open network)
Dashboard URL	http://192.168.4.1

Connect to the FakeFC network and open the URL in a browser to see a live bar graph of all 16 RC channels, updated every 100 ms.

The endpoint GET /channels returns a JSON array of the 16 channel values (1000–2000 µs range) for programmatic access:

[1500, 1500, 1000, 1500, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000, 1000]

Project Structure

FakeFC/
├── platformio.ini          # PlatformIO build configuration
└── src/
    ├── main.cpp            # Setup & main loop
    ├── crsf.h / crsf.cpp   # CRSF protocol decoder (AlfredoCRSF wrapper)
    ├── msp.h / msp.cpp     # MSP v1 / v2 state machine and command handlers
    ├── passthrough.h / passthrough.cpp  # CLI parser and UART passthrough bridge
    └── web.h / web.cpp     # WiFi AP, HTTP server and RC channel dashboard

Board Comparison

Feature	ESP32-S2 Mini	ESP32 WROOM 32
USB	Native USB CDC (TinyUSB)	UART-to-USB bridge (CP2102 / CH340)
Automatic DTR forwarding	✅ Yes	❌ No — manual receiver reset required
Build environment	lolin_s2_mini	esp32_wroom_32

License

This project does not currently include a license file. Please contact the repository owner for usage terms.