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FSG-A // CLUSTER 1 — CONSTRUCTION // 1.6

WIRING SCHEMATICS
STANDARD DRONE WIRING DIAGRAMS

KEY TAKEAWAY

Every drone follows the same basic wiring pattern: battery → power distribution → ESC → motors, and FC → serial ports → peripherals (receiver, GPS, companion computer, telemetry). The key is knowing which UART (serial port) goes to which device. SpeedyBee F405 V4 has 6 UARTs. Standard assignment: UART1=telemetry, UART2=Jetson companion, UART6=MANET radio module.

SPEEDYBEE F405 V4 — UART ASSIGNMENT

UART1 (SERIAL1)

MAVLink telemetry output (to GCS via ELRS passthrough)

UART2 (SERIAL2)

Jetson companion computer (MAVLink, 921600 baud)

UART3 (SERIAL3)

GPS (if installed — often unused in EW zone)

UART4 (SERIAL4)

Rangefinder (VL53L1X for optical flow assist)

UART5 (SERIAL5)

Reserved / spare

UART6 (SERIAL6)

MANET radio module (CRSF protocol, RC input)

Power Distribution

Battery (6S LiPo, 22.2V) connects to the power distribution board (PDB) or ESC power input via XT60 connector. The ESC distributes power to all 4 motors and provides a regulated 5V BEC output for the flight controller and peripherals. The Jetson Orin Nano requires a separate 5V 3A supply — use a dedicated BEC (Matek UBEC-5V, €8) connected directly to the battery, NOT through the ESC's BEC (insufficient current). The VTX requires 9V or 12V depending on model — use the ESC's 9V output or a second BEC.

UART Assignment — The Communication Backbone

The SpeedyBee F405 V4 has six UART ports. UART1 (TX1/RX1) connects to the Silvus StreamCaster MANET radio at 115200 baud running MAVLink 2.0 — this is the primary command and telemetry link to the ground station and Lisa 26 network. UART2 (TX2/RX2) connects to the Jetson Orin Nano companion computer at 921600 baud — high-speed link for AI inference results, camera commands, and ORB-SLAM3 position updates. UART6 is reserved for telemetry logging to SD card. UARTs 3, 4, and 5 are disabled (SERIAL3_PROTOCOL=-1) as part of firmware hardening — each open port is an attack surface.

Baud rate selection matters: 115200 baud on the MANET link is sufficient for MAVLink telemetry (30 Hz update rate, approximately 2 kB/s) but insufficient for video streaming. Video goes through the Silvus StreamCaster's dedicated Ethernet port, not through the UART. The 921600 baud Jetson link supports both MAVLink and custom high-frequency data (100 Hz SLAM updates at 200 bytes each = 20 kB/s) with margin for burst traffic.

Power Distribution — Separate BEC Per Subsystem

The single most common cause of in-flight companion computer crashes is shared power regulation. A Jetson Orin Nano draws 7-15 watts depending on AI workload — when YOLOv8 inference peaks coincide with ORB-SLAM3 feature matching, current draw spikes to 3A at 5V for 50-100 milliseconds. If this spike occurs on a BEC shared with the flight controller, the Pixhawk experiences a 200-400mV voltage sag. Below 4.5V, the Pixhawk triggers a brownout reset — all servo outputs freeze for 200ms while the processor reboots. At flight speed, 200ms of frozen outputs means uncontrolled flight.

Solution: dedicated BEC per subsystem. BEC1 (5V 3A) powers ONLY the flight controller, FPV camera, and VTX. BEC2 (5V 5A) powers ONLY the Jetson. Both BECs draw from the main battery bus but regulate independently. A current spike on BEC2 cannot affect BEC1 voltage. This costs €3 for the additional BEC and adds 5 grams of weight — negligible insurance against the most common avionics failure mode in companion-computer drone builds.

Connector Reliability and Field Expedients

JST-SH connectors (1.0mm pitch) are the standard signal connector on SpeedyBee F405 for UART, I2C, and SPI interfaces. These connectors are designed for consumer electronics — vibration in a drone environment loosens the friction fit over 20-50 flight hours. Hot glue on every JST connector after insertion is mandatory: the glue acts as a vibration-resistant lock that holds the connector in place without making it permanent (peel-able for maintenance). XT60 power connectors are mechanically robust but the spring contacts weaken after 500+ insertion cycles — replace XT60 connectors preventively every 6 months on heavily used drones.

PLAIN LANGUAGE: DRONE WIRING

Think of it like house wiring. The battery is the power company. The PDB is the fuse box. Each motor gets its own circuit through the ESC. The flight controller, camera, and radio get low-voltage circuits (5V) through voltage regulators. The Jetson computer is power-hungry — it gets its own dedicated regulator. If you wire the Jetson to the same regulator as the radio receiver, voltage drops when the Jetson processes AI inference, and the radio drops out. Separate power for sensitive electronics. That is the number one wiring rule.

Fischer 26 Avionics Wiring

PIXHAWK 6C UART ASSIGNMENT (FISCHER 26)

TELEM1 (SERIAL1)

Silvus SL5200 MANET (MAVLink2, 921600 baud)

TELEM2 (SERIAL2)

Jetson Orin Nano companion (MAVLink2, 921600 baud)

GPS1 (SERIAL3)

Disconnected (GPS-denied ops)

GPS2 (SERIAL4)

PMW3901 optical flow + VL53L1X rangefinder (via I2C adapter)

SERIAL5

Reserved for future SDR spectrum sensor

RC IN

MANET radio RC channel (via Silvus serial output)

Power distribution: main battery (2×6S 10Ah) → PDB → motor ESC (direct, no regulator), Pixhawk (5V BEC, 2A), Jetson (5V dedicated BEC, 4A, separate from Pixhawk), Starlink (12V regulator, 8A peak), servos (6V BEC from PDB, 5A). Critical rule: Jetson and Pixhawk on SEPARATE BECs. If Jetson's AI inference causes voltage dip on shared BEC, Pixhawk may brownout and crash the flight controller.

← Del av Component Architecture

External source: Kretskort – Wikipedia

Implementation

# UART Assignment — SpeedyBee F405 V4
UART_CONFIG = {
    "SERIAL1": {
        "port": "UART1 (TX1/RX1)",
        "protocol": "MAVLink 2.0",
        "baud": 115200,
        "device": "Silvus SL5200 MANET",
        "param": "SERIAL1_PROTOCOL=2, SERIAL1_BAUD=115"
    },
    "SERIAL2": {
        "port": "UART2 (TX2/RX2)",
        "protocol": "MAVLink 2.0",
        "baud": 921600,
        "device": "Jetson Orin Nano companion",
        "param": "SERIAL2_PROTOCOL=2, SERIAL2_BAUD=921"
    },
    "I2C": {
        "devices": [
            {"name": "BMP390", "addr": "0x77", "function": "barometer"},
            {"name": "PMW3901", "addr": "0x47", "function": "optical flow"},
        ]
    },
    "POWER": {
        "BEC1": "5V 3A → FC + FPV camera + VTX",
        "BEC2": "5V 5A → Jetson ONLY (NEVER shared with FC)",
        "WARNING": "Shared BEC = voltage sag under AI load = crash"
    }
}

Swedish Supply Chain

SUPPLY CHAIN & SECURITY RISK

Flight Controller

⚠ RISK — Electrokit.com (Malmö) — SpeedyBee F405. STM32 MCU manufactured by STMicroelectronics (FR/IT factory) but wafers from TSMC (

Jetson Orin Nano

⚠ RISK — Arrow Electronics (Kista), Mouser.se. NVIDIA designar (US), TSMC tillverkar (TW). Exportkontroll ITAR/EAR kan blockera

NATIONAL SECURITY RISK

Flight Controller: STM32 MCU manufactured by STMicroelectronics (FR/IT factory) but wafers from TSMC ( Jetson Orin Nano: NVIDIA designar (US), TSMC tillverkar (TW). Exportkontroll ITAR/EAR kan blockera Recommendation: Swedish Armed Forces should establish strategic stockpiles and evaluate European alternatives.

Related Chapters

Soldering & Field Repair

Tactical Build: EW-Hardened FPV

Component Architecture: FC, ESC, IMU, RF

Fiber-Optic FPV: Jam-Proof

Sources

See the categorized source sections earlier on this page for specific citations supporting each claim. Cross-referenced technical baselines: ArduPilot developer documentation; ExpressLRS hardware documentation; NATO STANAG 4609 Ed. 4 (motion imagery metadata), 4671 (UAV airworthiness), 2022 (intelligence evaluation); Watling & Reynolds, "Meatgrinder: Russian Tactics in the Second Year of Its Invasion of Ukraine", RUSI (2023); ISW daily campaign assessments at understandingwar.org (archive). FSG-A has no own operational experience.