Drone (Frame & Flight Controller)¶
This page covers the airframe and the flight controller — the platform everything else (sensors, companion computer, drop mechanism) is built on. The step-by-step firmware installation and parameter setup lives in Initial Setup; tuning is covered in Tuning.
Components¶
| Component | Part |
|---|---|
| Frame | SpeedyBee BEE35 Pro 3.5" CineWhoop frame kit (ducted, with propeller guards) |
| Flight controller | Flywoo GOKU GN745 45A AIO 2-6S (STM32F745 @ 216 MHz, 1 MB flash), AM32 ESCs |
| Firmware | ArduCopter 4.6.3 (FlywooF745 target) — version is pinned, see Initial Setup |
| Motors | Emax Eco II 2004 3000KV (3-6S) |
| Propellers | Gemfan D90-5 90 mm 3.5" ducted 5-blade |
| Receiver | Radiomaster XR4 Gemini dual-band ELRS (see RC & FPV) |
| GPS / compass | HGLRC M100 with integrated compass |
| FPV camera / VTX | RunCam Phoenix 2 / SpeedyBee TX800 — removed from the current build (see RC & FPV) |
| Battery | 4S Li-Ion pack (16.4 V full, 11.2 V empty) |
| Additional | MicroAir MTF-01P (sensor page), Raspberry Pi Zero 2 WH (companion page) |
The GN745 is an all-in-one board: flight controller and 45 A 4-in-1 ESC on a single PCB. That keeps the CineWhoop build compact, but it also means one board failure can take out both flight control and motor drive.
Component details¶
SpeedyBee BEE35 Pro frame¶
The SpeedyBee BEE35 Pro 3.5" CineWhoop frame kit is designed for the DJI O3 Air Unit, with dedicated heat-dissipation hardware and support for other compatible 20×20 video transmitters as well as external action cameras. For this project its ducts/propeller guards are what matter: they make indoor flight near people and walls survivable and safe.
Flywoo GOKU GN745 45A AIO¶
The Flywoo GOKU GN745 45A AIO 2-6S AM32 combines the flight controller and a 4-in-1 ESC on a single 33.5 × 33.5 mm board, reducing wiring, weight and required frame space. At its core sits an STM32F745 32-bit processor at 216 MHz, paired with an onboard gyro, barometer, 16 MB blackbox storage and seven hardware UARTs. The integrated ESC supports 2S-6S packs, delivers 45 A continuous and runs AM32 firmware with protocols up to DShot1200 (we use DShot600).
FC quirks every rebuilder must know¶
These are properties of the FlywooF745 hardware definition that are easy to miss in the datasheet and that directly affected this project.
One I2C bus — baro and compass share it¶
The single I2C bus is a single point of failure
The FlywooF745 target exposes exactly one I2C bus. The onboard barometer (BMP280/SPL06/DPS310 at address 0x76) and the external compass inside the GPS module both hang off it. A fault anywhere on that bus — a shorted wire, a damaged connector, a dying peripheral — can hang the whole bus and take all I2C devices down at once.
This is exactly what happened after our crash on 2026-08-21: the GPS connector was torn off, and afterwards the FC no longer detected the barometer at all (plus "Bad Compass Health" errors). The hypothesis was confirmed on 2026-08-24: bent pins in the GPS connector had hung the shared bus. After straightening them, compass and barometer worked again — no chip had died. The full story: crash & barometer recovery.
16 MB SPI flash logging — no SD card slot¶
The board has no SD card slot. Dataflash logs go to a 16 MB SPI flash chip
(LOG_BACKEND_TYPE = 4), and 16 MB fills up fast:
- Keep
LOG_DISARMED = 0. Logging while disarmed silently eats the flash while the drone sits on the bench, and old logs get overwritten — after our crash the crash-day logs were retained (withLOG_DISARMED = 0, the default, the flash budget goes to actual flights). - Full batch-sampler IMU logging (needed for notch-filter tuning) is a lot of data; enable it only for tuning flights, not permanently.
- With the companion computer installed, logs can additionally be streamed over
MAVLink to the Pi (
LOG_BACKEND_TYPE = 2or6), whose SD card is effectively unlimited compared to 16 MB. See the logging section of Initial Setup.
UART map¶
Seven UARTs, all in use. This is the wiring as configured on our aircraft (SERIALn parameter numbering; details in Initial Setup):
| Port | Connected to | Protocol | Baud |
|---|---|---|---|
| SERIAL1 | Telemetry (DJI VTX pad) | MAVLink | 57600 |
| SERIAL2 | Radiomaster XR4 receiver | RCIN (CRSF) | auto |
| SERIAL3 | SpeedyBee TX800 VTX control (VTX removed from current build) | IRC Tramp | auto |
| SERIAL4 | Raspberry Pi Zero 2 WH | MAVLink2 | 921600 |
| SERIAL5 | MicroAir MTF-01P | MAVLink1 | 115200 |
| SERIAL6 | HGLRC M100 GPS (UART part) | GPS | 115200 |
| SERIAL7 | ESC telemetry (RX only) | ESC Telemetry | 115200 |
Note the split on the GPS module: the GPS receiver itself talks over UART (SERIAL6), while its integrated compass is on the shared I2C bus described above.
ESCs: AM32, DShot600, bi-directional¶
The integrated 4-in-1 ESC runs AM32 firmware and is driven with
DShot600 (MOT_PWM_TYPE = 6) — digital, so no ESC PWM calibration is
needed. The documented target setup uses bi-directional DShot (SERVO_BLH_BDMASK = 15,
SERVO_DSHOT_ESC = 1 for AM32, SERVO_BLH_POLES = 12 for the Eco II 2004's
12 magnets) so the ESCs report per-motor RPM back to the FC; that RPM feed
drives the harmonic notch filters (INS_HNTCH_MODE = 3). Full walk-through in
Initial Setup.
Related pages¶
- Initial Setup — firmware flash, mandatory hardware setup, serial ports, EKF sources, indoor failsafes
- Tuning — PID and filter tuning
- Incident 2026-08-21 — the crash analysis referenced throughout this page