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Flight controller · In design

NAVIX X427 Mini

The X427, made small.

An STM32F427 at 180 MHz, an IMU, a barometer, CAN and eight PWM outputs, on a 36 x 36 mm board with the standard 30.5 mm mounting pattern.

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Read the docs
NAVIX X427 Mini flight controller, top view at an angle

The same processor, on a board a quarter the size.

The X427 Mini is a four-layer flight controller built around the same STM32F427 as the X427. Compared with the X427 it has one IMU instead of up to three, eight PWM outputs instead of fourteen, and onboard flash instead of a microSD slot. It is in design: this page describes the schematic and board layout, not a built board.

180MHz
Cortex-M4F
8PWM
motor outputs
16MB
onboard flash
36 x 36mm
4-layer board

What it does

Six things worth knowing.

  • The same core as the X427.

    An STM32F427VGT6 runs a Cortex-M4F at 180 MHz with 1 MB of flash and 256 KB of SRAM, from an 8 MHz crystal. 58 of its 82 I/O pins are in use.

    • 180 MHz
    • 1 MB flash
    • 192 + 64 KB SRAM
    • 58 of 82 I/O used

  • An IMU, a barometer and flash for logs.

    An LSM6DSOX IMU on SPI1 and a BMP585 barometer on I2C. A 16 MB flash chip on its own SPI bus takes the place of the X427's microSD slot. There is no compass on the board: use the one in your GPS module.

    • LSM6DSOX
    • BMP585
    • 16 MB flash
    • No onboard compass

  • Two power inputs, one clear order.

    A power mux gives the power module on POWER1 priority over USB, with no back-feed between them. Each input is cut off above about 5.6 V to protect the regulators behind it. Two switched 5 V ports report faults and can be turned off from firmware.

    • POWER1 over USB
    • Over-voltage cut-off
    • 2 switched 5 V ports

  • The ports a small flight stack asks for.

    Eight motor outputs, GPS with safety-switch and buzzer lines, telemetry with flow control, one RC port for SBUS, iBUS, CRSF and DSM, a spare serial port, I2C, CAN, an analogue input, USB-C and a debug port.

    • 8 PWM
    • CAN
    • SBUS / CRSF / DSM
    • USB-C

  • Small, on the standard mounting pattern.

    The board is 36 x 36 mm with four M3 holes on the standard 30.5 x 30.5 mm pattern. Soft-mount it: the IMU wants vibration isolation. Ports are 2 mm solder pads, so wires go straight to the board.

    • 36 x 36 mm
    • 30.5 mm mount
    • 4 layers
    • 6 test pads

  • Built for the NavHAL / VaiOS / VAYU family.

    The Mini uses the same STM32F4-family, Cortex-M4 architecture as the X427 and as the NAVIXSM-F401RE our stack already runs on.

    • STM32F4
    • Cortex-M4F
    • NavHAL
    • VaiOS
    • VAYU
Full specifications

The platform

From silicon to flight code, one stack.

The X427 Mini uses the same STM32F4-family, Cortex-M4 architecture as the X427 and the NAVIXSM-F401RE our stack already runs on. Here is the software family it is meant for, each layer with its own documentation.

  1. VAYUFlight softwareEstimation, control, mixing and failsafes, with a simulator built from the same code.
  2. VaiOSReal-time kernelA preemptive RTOS for Cortex-M, aimed at hard-real-time work such as a 1 kHz flight controller.
  3. NavHALHardware abstractionOne frozen hal_* C API over layered arch, vendor, family and board sources.
  4. NAVIX X427 Mini flight controller, top view at an angleHardwareNAVIX X427 MiniSTM32F427 flight controller, STM32F4 family, Cortex-M4F

For developers

Tools that go with the board.

Status

Where it stands.

The X427 Mini is in design. The schematic is at Rev A and the board layout is still being finished, so no board has been built or tested and nothing here is a measured result.

Join the X427 Mini waitlist to be added to the list, or enquire to talk to an engineer about it.

Enquire

Enquire about NAVIX X427 Mini

Your message goes to an engineer, and the reply comes from one.

Reference

Full specifications.

Processor6 items
MCU
STM32F427VGT6 in LQFP100, 14 x 14 mm, 0.5 mm pitch
Core
Cortex-M4F at 180 MHz
Memory
1 MB flash, 192 KB SRAM plus 64 KB CCM SRAM
I/O
82 on the package, 58 used
Clock
8 MHz crystal; no RTC crystal fitted
Debug
SWD, plus a UART7 console
Sensors and storage4 items
IMU
LSM6DSOX on SPI1
Barometer
BMP585 on I2C1
Compass
Not on the board. Use the compass in the GPS module, over I2C2
Flash
W25Q128JV, 16 MB serial NOR flash on its own SPI bus (SPI2). There is no microSD slot
Indicators and controls3 items
Status
A blue status LED and an addressable RGB LED
Buttons
BOOT and RESET
Buzzer and safety switch
Their driver and input lines are on the GPS1 port; the board carries neither a buzzer nor a switch
Ports and interfaces11 items
PWM MAIN
10 pads: a servo-rail pin, channels 1 to 8 (motor outputs on timers 1 and 4), ground
GPS1
10 pads: USART1, I2C2, safety switch and LED lines, buzzer driver, 3.3 V and switched 5 V
POWER1
6 pads: power module input with battery voltage and current sense
TELEM1
6 pads: USART2 with flow control (CTS and RTS), on its own switched 5 V
RC
4 pads: USART6, with an inverter for SBUS and a pass-through for iBUS, CRSF and DSM
SERIAL4
6 pads: UART4 and I2C2. Second GPS, a UART rangefinder or a companion computer
I2C
4 pads, on I2C2
CAN
4 pads through a TJA1051T/3 transceiver. The bus termination parts are not fitted
ADC
3 pads, 6.6 V analogue input
USB-C
Device mode, full speed
Debug
6 pads: SWD and a UART7 console
Power design7 items
Inputs
POWER1 (the power module's 5 V) and USB-C VBUS
Priority
A TPS2121 power mux gives POWER1 priority over USB. The inputs cannot back-feed each other, and the firmware can read which source is powering the board
Over-voltage
Each input is cut off at about 5.36 to 5.86 V (nominal 5.64 V) to protect the regulators behind it
Logic supply
Two 3.3 V LDOs (TLV757P), one dedicated to the sensors
Servo rail
Does not power the board. Feed POWER1 from a flight-controller BEC
Peripheral 5 V
Two switched 5 V ports, one for peripherals and one for telemetry, each with a fault flag and firmware control. Both are on at reset
Budget
The two switched ports together are budgeted at 1.5 A or less, so that POWER1 (two 1 A contacts) stays at 2 A or less
Mechanical5 items
Outline
36.0 x 36.0 mm, 3 mm corner radius
Stack-up
4-layer, 1.6 mm, with an inner ground plane
Mount
Four M3 holes (3.2 mm) on the standard 30.5 x 30.5 mm pattern. Use rubber grommets or soft standoffs: the IMU needs vibration isolation, so do not hard-mount
Ports
2.00 mm solder-pad groups along the edges, each named in silkscreen
Bring-up
6 test pads: VBUS, 5 V, 3.3 V, battery voltage, battery current and ground

Questions.

Is it available?

Not yet. The X427 Mini is in design and no board has been built. You can join the X427 Mini waitlist, or enquire and an engineer will reply.

How is it different from the X427?

The same STM32F427 and the same stack, on a 36 x 36 mm board. It has one IMU instead of up to three, eight PWM outputs instead of fourteen, one I2C port instead of three, no SPI port, no microSD slot (16 MB onboard flash instead) and 6 test pads instead of 36.

Which software is it built for?

The in-house NavHAL, VaiOS and VAYU stack, on the same STM32F4 family and Cortex-M4 architecture as the X427 and the NAVIXSM-F401RE.

Does it have a compass?

Not on the board. Use the compass in your GPS module, which connects over the I2C2 bus on the GPS1 port.

How many motors can it drive?

Eight, on the PWM MAIN pads.

Does it log to a microSD card?

No. Logs go to a 16 MB flash chip on the board.

Can I use SBUS and CRSF receivers?

Yes. The RC port passes the signal through an XOR gate so inverted SBUS and non-inverted protocols share one port.

Join the Mini waitlist.

It is in design. Join the waitlist to be on the list, or write with your questions and an engineer will reply.

Enquire

Enquire about NAVIX X427 Mini

Your message goes to an engineer, and the reply comes from one.

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