3. Flight Controller Reference

3.1 Pilot_PX Board — Signal Availability

Several documentation errors and omissions have been identified in the Pilot_PX peripherals page. The table below reflects confirmed hardware reality:

Signal	Status	Source	Notes
SBUS OUT	Not available	Pilot_PX	SBUS OUT pin shown in peripheral diagram is incorrect - diagram has an error
SBUS IN	Not available	Pilot_PX	Only PPM peripheral is connected to the Pixhawk FMU on Pilot_PX
PPM IN	Available	SERIAL5 connector	Shared with the label 'PPM' on the adapter board
SBUS-Servo OUT (ArduPilot)	Available	SERIAL5 connector	Exposed pin - ArduPilot only; configure SERIALX_PROTOCOL=15 for other serial ports
FMU_DBG (JTAG)	Available	Pilot_PX board	Pinout in docs under Pilot_PX connectors - compatible standard Pixhawk JTAG tools
I2S Audio	Not available	Adapter Default	Not routed to any connector on the default adapter board

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3.2 PWM Output Access

A recurring source of confusion is how many PWM outputs are accessible and from which port.

Source	Count	How to access
Cube MAIN outputs	7	PWM1 connector on Adapter Default (JST GH to JR adapter)
Cube AUX outputs	Not on Adapter Default	Available on B2B connector - requires custom adapter board or DCS2.VTOL board
Secondary FMU PWM	4	FMU_SEC connector on Pilot board - for secondary FMU only, not routed to Cube
Orin GPIO (I2C expander)	2 (GPIO_EXP4/5)	GPIO connector on Adapter Default - 3.3 V, not PWM-capable

Note:

The DCS2.VTOL board (see docs.airvolute.com/autopilots/dcs2/.vtol-board) combines adapter and PDB functionality and exposes the full set of MAIN and AUX PWM outputs. It supports up to 14S battery input and is optimised for VTOL airframes. A new Adapter Default revision adding AUX support is also in development.

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3.3 Serial / UART Port Reference

The following ports are physically accessible on the DCS2 Adapter Default board and can be configured in ArduPilot as telemetry, GPS, RCIN, or SBUS-Servo out:

Connector	ArduPilot Serial	Default use	Notes
SERIAL1	SERIAL1	Telemetry 1	Routed to Jetson — primary MAVLink endpoint
SERIAL5	SERIAL5	Telemetry 5 / SBUS	Contains UART + SBUS_OUT pin; SBUS-Servo out is ArduPilot-only
GPS1	SERIAL3	GPS	Standard JST GH GPS connector
GPS2	SERIAL4	GPS 2 / telemetry	Can be repurposed for telemetry if GPS2 is unused
ttyTHS0	-	Jetson↔Cube UART	Physical UART for mavlink-router; also accessible as ttyACM0 via USB

For PX4 / NuttX: consult the PX4 serial-port mapping for your specific FMU hardware version (e.g. CUAV Pixhawk V6X) at docs.px4.io to correlate SERIAL numbers with /dev/ttyS* device nodes.

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3.4 Secondary (Onboard) FMU

Every DCS2 production board (green boards) contains an onboard secondary FMU in addition to the Cube autopilot socket.

Property	Detail
IMU	BMI088
Barometer	BMP390
Default firmware	ArduPilot 4.5.0 with Airvolute bootloader
USB access	Shared with Cube — switch via fmu_cube_usb_switch.py fmu
Serial access	SERIAL1 and SERIAL2 on the FMU_SEC connector
Typical use	Flies standalone on FPV-class Patron drones (no Cube); on Stribog drones it is present but idle
Pre-production boards	Blue boards — secondary FMU is empty (no firmware)

To switch the shared USB bus between Cube and secondary FMU:

# Switch to secondary FMU
python3 fmu_cube_usb_switch.py fmu
 
# Verify with lsusb — look for 'Generic Airvolute-DCS2'
lsusb
 
# Switch back to Cube
python3 fmu_cube_usb_switch.py cube

To flash firmware to the secondary FMU, connect via a GCS after switching USB, or use the ArduPilot bootloader uploader directly from Jetson:

python3 px_uploader.py --port /dev/ttyACM0 arducopter.apj

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3.5 ARKV6X Flight Controller Setup

Users integrating the ARK Electronics FMUV6X in place of the Cube should follow this sequence:

1. Flash the DCS2 using dcs-deploy as normal

2. Install mavlink-router

3. Build PX4 for ARKV6X default config and upload:

python3 px_uploader.py --port /dev/ttyACM0 ark_fmu-v6x_default.px4

1. Configure mavlink-router with the ARKV6X endpoint (note: 115200 baud, not 921600):

[UartEndpoint cube]
Device = /dev/ttyACM0
Baud = 115200