# 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:

<table><thead><tr><th width="161.85693359375">Signal</th><th width="127.4285888671875">Status</th><th width="102.571044921875">Source</th><th width="351.571533203125">Notes</th></tr></thead><tbody><tr><td><strong>SBUS OUT</strong></td><td><mark style="color:orange;background-color:orange;"><strong>Not available</strong></mark></td><td>Pilot_PX</td><td>SBUS OUT pin shown in peripheral diagram is incorrect - diagram has an error</td></tr><tr><td><strong>SBUS IN</strong></td><td><mark style="color:orange;background-color:orange;"><strong>Not available</strong></mark></td><td>Pilot_PX</td><td>Only PPM peripheral is connected to the Pixhawk FMU on Pilot_PX</td></tr><tr><td><strong>PPM IN</strong></td><td><mark style="color:green;background-color:$success;"><strong>Available</strong></mark></td><td>SERIAL5 connector</td><td>Shared with the label 'PPM' on the adapter board</td></tr><tr><td><strong>SBUS-Servo OUT (ArduPilot)</strong></td><td><mark style="color:green;background-color:green;"><strong>Available</strong></mark></td><td>SERIAL5 connector</td><td>Exposed pin - ArduPilot only; configure SERIALX_PROTOCOL=15 for other serial ports</td></tr><tr><td><strong>FMU_DBG (JTAG)</strong></td><td><mark style="color:green;background-color:green;"><strong>Available</strong></mark></td><td>Pilot_PX board</td><td>Pinout in docs under Pilot_PX connectors - compatible standard Pixhawk JTAG tools</td></tr><tr><td><strong>I2S Audio</strong></td><td><mark style="color:orange;background-color:orange;"><strong>Not available</strong></mark></td><td>Adapter Default</td><td>Not routed to any connector on the default adapter board</td></tr></tbody></table>

***

### 3.2 PWM Output Access

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

<table><thead><tr><th width="221.427978515625">Source</th><th width="156.998779296875">Count</th><th width="365.5732421875">How to access</th></tr></thead><tbody><tr><td><strong>Cube MAIN outputs</strong></td><td>7</td><td><p>PWM1 connector on Adapter Default</p><p>(JST GH to JR adapter)</p></td></tr><tr><td><strong>Cube AUX outputs</strong></td><td>Not on Adapter Default</td><td>Available on B2B connector - requires custom adapter board or DCS2.VTOL board</td></tr><tr><td><strong>Secondary FMU PWM</strong></td><td>4</td><td>FMU_SEC connector on Pilot board - for secondary FMU only, not routed to Cube</td></tr><tr><td><strong>Orin GPIO (I2C expander)</strong></td><td>2 (GPIO_EXP4/5)</td><td>GPIO connector on Adapter Default - 3.3 V, not PWM-capable</td></tr></tbody></table>

{% hint style="info" %}
**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.
{% endhint %}

***

### 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:

<table><thead><tr><th width="124.14306640625">Connector</th><th width="148.5709228515625">ArduPilot Serial</th><th width="170.8570556640625">Default use</th><th width="294.71435546875">Notes</th></tr></thead><tbody><tr><td>SERIAL1</td><td>SERIAL1</td><td>Telemetry 1</td><td>Routed to Jetson — primary MAVLink endpoint</td></tr><tr><td>SERIAL5</td><td>SERIAL5</td><td>Telemetry 5 / SBUS</td><td>Contains UART + SBUS_OUT pin; SBUS-Servo out is ArduPilot-only</td></tr><tr><td>GPS1</td><td>SERIAL3</td><td>GPS</td><td>Standard JST GH GPS connector</td></tr><tr><td>GPS2</td><td>SERIAL4</td><td>GPS 2 / telemetry</td><td>Can be repurposed for telemetry if GPS2 is unused</td></tr><tr><td>ttyTHS0</td><td>-</td><td>Jetson↔Cube UART</td><td>Physical UART for mavlink-router; also accessible as ttyACM0 via USB</td></tr></tbody></table>

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.

***

### 3.4 Secondary (Onboard) FMU

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

<table><thead><tr><th width="255.142578125">Property</th><th>Detail</th></tr></thead><tbody><tr><td><strong>IMU</strong></td><td>BMI088</td></tr><tr><td><strong>Barometer</strong></td><td>BMP390</td></tr><tr><td><strong>Default firmware</strong></td><td>ArduPilot 4.5.0 with Airvolute bootloader</td></tr><tr><td><strong>USB access</strong></td><td>Shared with Cube — switch via fmu_cube_usb_switch.py fmu</td></tr><tr><td><strong>Serial access</strong></td><td>SERIAL1 and SERIAL2 on the FMU_SEC connector</td></tr><tr><td><strong>Typical use</strong></td><td>Flies standalone on FPV-class Patron drones (no Cube); on Stribog drones it is present but idle</td></tr><tr><td><strong>Pre-production boards</strong></td><td>Blue boards — secondary FMU is empty (no firmware)</td></tr></tbody></table>

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
```

***

### 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
```

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

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


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