Nicholas Rehm's dRehmFlight — the teaching-oriented VTOL flight controller — ported to STM32 and evolved into a multi-board flight stack. The control law is untouched: every change is in the I/O boundary, loop architecture, sensor-axis handling, or configuration UX, never the PID math. The repo carries the full evolution as diffable in-repo stages:

Build and fly dRehmFlight_STM32_SCHED_MSP_INI. It is the maintained, flight-validated configuration; the earlier stages are kept as lineage artifacts for study and diffing. Full stage-by-stage change record: doc/DF_EVOLUTION.md.

Companion: dRehm Configurator — a browser-based configurator PWA (Chrome/Edge, Web Serial; source: geosmall/dRehm-configurator) that speaks this firmware's MSP telemetry and CLI. Connect over USB to watch live status/attitude, RC channels, and sensor graphs; set parameters in the grouped PID/filter editor and save them to the board; or use its CLI terminal to enter the bootloader (bl) and reflash from the Arduino IDE (once the UF2 bootloader is present on the board).

Board is selected via the Arduino board menu (pnum). "Persistence" = tuning survives reboot (internal-flash config region); RAM-only boards lose set changes at power-off.

Flight-validated: BEFH_BETAFPVG473 (Air75 whoop) and BEFH_BETAFPVF405 (Pavo Pico II). Other targets are build-verified and bench-tested to varying degrees — see doc/BOARD_ALIGNMENT_REQUIREMENTS.md for the honest per-target validation ledger before trusting one in the air.

Requires the STM32_Robotics Arduino core, robo-2.1.0 or later (geosmall/Arduino_Core_STM32 — a fork of the STM32 Arduino core with type-safe pins, peripheral-aware bus constructors, DShot, and UF2 bootloader support).

Arduino IDE: Preferences → Additional Board Manager URLs → https://github.com/geosmall/BoardManagerFiles/raw/main/package_stm32_robotics_index.json, then Boards Manager → install "STM32 Robotics Core", pick your board under Tools, open Versions/dRehmFlight_STM32_SCHED_MSP_INI/dRehmFlight_STM32_SCHED_MSP_INI.ino. (Works on Windows, macOS, and Linux. arduino-cli users: the same index URL and core work from the command line — full steps in the sketch README.)

Flashing flight controllers with the UF2 bootloader installed: enter the bootloader (CLI bl command, or MSP reboot-to-bootloader), a UF2 drive appears, then upload with upload_method=bootuf2Method or drag the built .uf2. The UF2 bootloader binaries and first-time installation / recovery documentation live in the core repository (bootloaders/, doc/).

This is firmware for spinning blades. Work through these in order; skipping them is how flyaways happen:

1. IMU alignment bench check (doc/IMU_ALIGNMENT_BENCH_PROCEDURE.md, tools/imu_align_check.py) — props off, read-only. Run before the first flight of ANY new or changed board alignment. A wrong axis sign flips a correction into an amplification the moment the craft leaves the ground.
2. Motor order / direction check (tools/motor_order_check.py, or the CLI motor <1-4> <pct> single-motor bench test) — props off, verify pad→position mapping and spin direction against your frame.
3. Props-off arm test — arm, verify throttle response and throttle-cut on all four motors, verify disarm.
4. First hover — props on only after 1–3 pass, in a safe area, low, brief.

The align_board_* and motor_output_reordering parameters are runtime (set/save) — most boards can be adapted without recompiling, but every alignment change re-triggers gate 1.

• All gains and filters are runtime CLI parameters: # enters the CLI, set, save, diff all (Betaflight-style paste-back). See Versions/dRehmFlight_STM32_SCHED_MSP_INI/README.md and Versions/dRehmFlight_STM32_SCHED_MSP_INI/QUAD_TUNING.md.
• The dRehm Configurator (see top) offers the same parameter editing and CLI from the browser.
• tools/ — host-side helpers that talk to the firmware over USB serial: blackbox fetch (bb_fetch.py), MSP queries, restrained-rig test, tune capture with build provenance (save_tune.sh).
• tunes/ — reference tunes for the flight-validated craft, self-stamped with the exact firmware commit they flew on.

GPL v3, same as upstream dRehmFlight (LICENSE). The bundled INav-derived scheduler is likewise GPL. Copyright original work Nicholas Rehm; STM32 port and flight-stack evolution by the maintainers of this fork.