Building a flight controller with Raspberry Pi RP2350B

Why RP2350B?

The Raspberry Pi Pico 2 (RP2350B) offers an appealing combination for flight controller development: dual ARM Cortex-M33 cores, 520 KB SRAM, and support for both ThreadX and NuttX RTOS. But the key question was whether BetaFlight — historically built around STM32 — could run on it well enough for actual flight.

We found the HELLBENDER_0001 board configuration in BetaFlight’s config repository. HellBender is a US-based company focused on computer vision as a service (CVaaS), and their RP2350A development board included an interesting MCU choice: the MAX7456 for on-screen display overlay on video streams. This was a familiar concept in the FPV world — a simple way to stack telemetry data directly on the video feed when digital transmission isn’t available.

The pin-out puzzle

The HELLBENDER_0001 configuration revealed an important detail: it used GPIO32 through GPIO48, which are only available on the RP2350B variant, not the original RP2350A (which only has GPIO0-GPIO31). This meant a standard Pico 2 wouldn’t work directly — we needed either to remap the pin-out or use an RP2350B development board.

Compiling BetaFlight for the HELLBENDER_0001 configuration was surprisingly fast:

FLASH:      340,186 B / 4,032 KB  (8.24%)
RAM:        383,016 B /  512 KB   (73.05%)

The build completed in about 33 seconds. The flash usage is very conservative — there’s plenty of headroom on the RP2350B’s 4 MB of external flash (or 2 MB internal).

FMU2350 design

We designed the FMU2350 board based on the RP2350B minimum system design from Raspberry Pi’s hardware design guide, extending it with the connectors and peripherals needed for a flight controller. The power design was inherited from the RP2350B mini board, so that portion was already validated.

Three potential directions emerged:

1. FPV racing: A BetaFlight-compatible board that looks like traditional flight controllers, with 2.54mm through-hole pins around the perimeter for easy layout and rapid production
2. Education: A simple drone that can hover in place with ~500 lines of Arduino code, small enough to take off from a desk and hover for a minute
3. Industrial: Full ArduPilot or PX4 integration, or a companion computer approach where an RP2350B handles low-level control while a CM4 runs high-level mission planning

Market context

While developing with the Pico, we tracked parallel market developments. DJI’s Neo drone teardown revealed interesting design choices, and Google’s Pigweed embedded framework added Pico 2 support. Pigweed — originally an internal Google project — now ships in millions of devices including Pixel phones, Nest thermostats, satellites, and autonomous delivery drones.

For simple projects, the Arduino-Pico framework by Earle F. Philhower remains our preferred path. It compiles incredibly fast and gives immediate access to the Pico’s full peripheral set.

The ESP32 connection

During development, we also explored using ESP32-C2-M1 chips as WiFi-serial bridges on the flight controller. For indoor cinewhoop drones with propeller guards, the combination of manual flight mode with optical flow hovering provides a good balance of pilot control and stability.

The PMW3901 optical flow sensor, for example, requires SPI rather than UART for meaningful data rates — its 35x35 frame buffer is simply too large for UART at useful frequencies. This reinforced the need for careful peripheral planning when designing a flight controller from scratch.

What’s next

The RP2350B platform is promising but still maturing in the BetaFlight ecosystem. The next step is PCB fabrication and bringing up the hardware — starting with the basics (IMU detection, motor output, receiver input) and progressively adding peripherals like optical flow sensors and GPS.