Assembling a 5-inch digital FPV drone requires connecting a 4-in-1 ESC, a Flight Controller (FC), a Digital Air Unit, an ExpressLRS (ELRS) Receiver, and 4 Brushless Motors.
System Wiring Schematic
[ 4x Brushless Motors ]
(3 Phase Wires per Motor)
│
▼
[ 4-in-1 ESC Board ]
[ + ] [ - ] <-- Main XT60 Power Cable
│ │ (+ Low-ESR Capacitor)
└─────┬─────┘
│ (8-Pin JST Wiring Harness)
▼
[ Flight Controller (FC) ]
┌───────────────────────────┼───────────────────────────┐
│ UART 1 │ UART 2 │ Power Out (9V/VBAT)
▼ ▼ ▼
[ ELRS Receiver ] [ Digital VTX / Air Unit ] [ GPS Module ]
(Tx, Rx, 5V, GND) (Tx, Rx, 9V/VBAT, GND, (Tx, Rx, 5V, GND,
SBus/Video) SDA, SCL)
Pin-by-Pin Wiring Diagram
1. Main Power System (Battery & ESC)
- Battery Lead: Solder the XT60 cable (12AWG or 14AWG) directly to the main VBAT (+) and GND (-) pads on the 4-in-1 ESC.
- Capacitor (Crucial): Solder a 35V 1000µF Low-ESR Electrolytic Capacitor across the ESC power pads. Match polarity: Long leg/striped side is Negative (-).
2. Motor to ESC Connections
- Solder the 3 wires from each motor to the 3 pads on their respective ESC corner. Motor rotation direction will be adjusted later in Betaflight/BLHeli software.
3. ESC-to-FC Interconnect
- Connect the included 8-pin or 10-pin JST harness between the ESC and FC ports. This passes:
- VBAT (Power to FC)
- GND (Ground reference)
- M1, M2, M3, M4 (Motor control signals)
- CURRENT (Current sensor output)
- TELEMETRY (ESC Telemetry data)
4. Digital Air Unit / VTX
Connect the Air Unit to an available UART on the FC (commonly UART 2 or UART 6):
| Air Unit Wire Color | FC Pad Connection | Function |
|---|---|---|
| Red | 9V / 10V / VBAT | Power (Ensure pad provides ≥9V and 2A+) |
| Black | GND | Ground |
| White (Tx) | RX2 | DisplayPort OSD Data In |
| Gray (Rx) | TX2 | DisplayPort OSD Data Out |
| Brown | GND | Signal Ground |
| Yellow | SBUS (Optional) | DJI Remote controller signal (Skip if using ELRS) |
5. ExpressLRS (ELRS) 2.4GHz Receiver
Connect the ELRS receiver to an unused UART (e.g., UART 1):
| Receiver Pad | FC Pad Connection | Function |
|---|---|---|
| +5V / VCC | 5V | Receiver Power |
| GND | GND | Ground |
| TX | RX1 | Serial RX data to FC |
| RX | TX1 | Telemetry back to Receiver |
Step-by-Step Soldering & Assembly Checklist
- Tin All Pads First: Apply a high-quality rosin-core leaded solder (63/37) and set your soldering iron to 380°C–400°C. Apply heat briefly and tin every wire end and FC pad.
- Mount the ESC: Install the ESC on the frame’s mounting stack using rubber anti-vibration grommets. Ensure the arrow on the ESC points toward the front of the frame.
- Connect Motors: Solder motor wires flat against the ESC pads. Ensure no stray wire strands touch adjacent pads or the carbon frame.
- Wire FC & Peripherals: Solder the Receiver and Air Unit harnesses to the FC pads according to the pinout table above.
- Mount the FC: Place the FC on top of the stack separated by isolation standoffs. Check that the FC arrow points forward.
Initial Power-On & Safety Verification
- Smoke Stopper Test: Before plugging in a LiPo battery for the first time, ALWAYS plug in a current-limiting Smoke Stopper between the battery and the drone. If the LED turns red or trips, you have a short circuit.
- Continuity Check: Use a multimeter in Continuity Mode (
beep) to verify there is no short between the XT60 positive and negative leads. - Betaflight Initial Configuration:
- Open Betaflight Configurator and connect via USB.
- Under the Ports tab:
- Set UART 1 Serial Receiver to ON for your ELRS receiver.
- Set UART 2 Peripherals to
MSP / DisplayPortfor the Digital VTX OSD.
- Under Receiver tab: Set Receiver Type to
CRSF(Crossfire/ELRS protocol). - Under Motors tab: Verify motor spin direction and enable DShot600 with Bidirectional DShot enabled for RPM filtering.