Why This Build
The 4" build is our testbed for new flight controller firmware, ArduPilot params, and ELRS configurations before committing to the 7" autonomous platform. The JHEMCU F745 runs ArduPilot Copter 4.6.2 — same firmware as our 7" build. Everything tuned here transfers directly.
Parts List
JHEMCU F745 NOXE Stack (FC + 60A BL32 ESC)
H7 processor flight controller + 60A 4-in-1 ESC stack. Solid UART count for GPS + companion + RC + telemetry simultaneously. 30×30mm.
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iFlight Xing2 2809 1250KV Motors (4-Pack)
Our motors. Cinelifter-grade 2809 stators. Smooth, quiet, efficient on 6S. Handles 4" × 4.5" tri-blade props well.
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SparkFun GPS-RTK2 Board (ZED-F9P)
RTK GPS with centimeter-level accuracy. UART interface to FC SERIAL3. ArduPilot GPS_TYPE=17. Essential for precision auto-landing testing.
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RadioMaster RP3 ELRS 2.4GHz Receiver
The exact receiver on our build. Diversity nano, UFL antennas. Binds with SERIAL7_PROTOCOL=23, RC_PROTOCOLS=512 (ELRS). Confirmed working.
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Matek Systems H743-Slim V3 Flight Controller
Alternative FC option — our 7" build runs this. STM32H743, 8 UARTs, 30×30. More UARTs than JHEMCU if you need extra serial ports.
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DJI O3 Air Unit
HD digital FPV — 1080p/60fps, ultra-low latency, on-board video storage. Pairs with DJI Goggles 2. Step up from analog.
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Tattu R-Line V4.0 6S 1300mAh 130C (2-Pack)
Premium 6S packs with consistent IR. Our choice for the 4" build. ~6 min flight time at 50% throttle. Buy two packs minimum.
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Tenergy LiPo Safe Bags (2-Pack)
Always charge and store 6S packs in fire-retardant bags. Non-negotiable. A thermal event on a 6S pack is catastrophic without containment.
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Key Wiring Notes
- SERIAL7 (T6/R6 pads) RadioMaster RP3 — SERIAL7_PROTOCOL=23, RC_PROTOCOLS=512 (ELRS, NOT 1024)
- SERIAL3 (TX2/RX2) ZED-F9P UART1 — SERIAL3_PROTOCOL=5, SERIAL3_BAUD=38, GPS_TYPE=17
- ESC signal S1–S4 pads → AM32 ESC. S2 is 3.3V tolerant only
- Power No BEC on ESC — use FC 4V5 pad for GPS and receiver power
- USB power Motors will NOT spin on USB alone — battery must be connected (>10V)
Once this is tuned and flying autonomously, step up to the 7" guard drone.