O4 Air Unit Pro — install (UL8 + ArduPilot + ELRS)

Digital FPV on the UL8 — install from the DJI manual, adapted to our Pixhawk/ELRS stack

The O4 Air Unit Pro was on the bench and the manual said: connect S.Bus, enable Canvas Mode, done. Fine — if you fly Betaflight + DJI radio. We don’t. Pixhawk 6X Mini + ExpressLRS on the AOS UL8 V5. Same hardware, different order, and a few wires we leave open on purpose.

Source: DJI O4 Air Unit Series User Manual (also local in part 23/media).

The problem we’re solving

We want picture in the goggles without breaking the radio stack. O4 = eyes. ELRS = stick link. ArduPilot = brains. Mixing those (S.Bus and ELRS, or OSD on a busy UART) is how beginners lose weekends.

What we expect:

• Video to DJI goggles — standalone (power + antennas + link)
• RC via ELRS XR4 on TELEM2 — not via O4
• Yellow S.Bus wire — open
• OSD (MSP DisplayPort) — optional later, once a UART is free
• Power — direct 6S from the Y-splitter (Pro: 7.4–26.4 V)

1. Power & 3-in-1 cable

From the DJI manual wiring page. Pro range: 7.4–26.4 V.

How it fits together: red/black feed the air unit. White/grey/brown are for optional UART to the FC (OSD). Yellow is DJI’s RC path — we ignore it.

Color	Function	Our choice
Red VCC	Pack / BEC	XT60 branch of the Y (6S OK on Pro)
Black GND	Power GND	Same rail GND
White UART_RX	FC OSD TX	Later → free UART (not TELEM1/2)
Grey UART_TX	FC OSD RX	Later → crossed with white
Brown GND	Signal GND	With UART
Yellow S.Bus	DJI HDL	Open — ELRS owns RC

If using a BEC instead of pack: Pro wants ≥ 13.5 W (e.g. 9 V / 1.5 A). We prefer pack rail via Y — one plug, fewer mysteries.

Full power architecture (incl. CAN Hub): power & capacitors.

2. Mounting (camera + air unit + antennas)

Pro: keep the heatsink clear; adhesive only on the flat side without fins.

Why this matters: a hot air unit drops out. Antennas against carbon = weak link. Antenna against the GPS helical = weird sat counts. We follow the manual, applied to UL8:

1. Camera: up mark correct. Soft-mount in the UL8 camera cage.
2. Air unit: do not overtighten. Keep the heatsink cool (not in a sealed box).
3. Antennas: ≥ 5 cm from air unit/camera/carbon/metal. Pro antennas preferably ~90° apart. Visible from front and rear.
4. Route coax carefully — no kinks against ESC/props.

Keep clear of the F9P helical and H-Flow (RF + EMI). Exact AOS adapter prints: see Rosser’s mount video in the product post — we’re not 100 % sure of our print setup yet. Soft-mount first.

3. Activation & firmware

This felt like having to “claim” a phone before it really works. Roughly accurate.

1. Props off.
2. Power the air unit. USB-C to PC.
3. DJI Assistant 2 (FPV Series) → account → activate.
4. Update firmware on the air unit (+ goggles when available).
5. Link in the goggles.

Without activation: TX power capped (≤20 mW) and menus locked. Good to know before you decide the unit is broken.

EU/NL: set CE transmit power in the goggles.

4. ExpressLRS alongside

• XR4 stays on TELEM2 / SERIAL2, PROTOCOL=23 (CRSF) — see ELRS setup.
• O4 and ELRS do not share a UART for RC.
• 5.8 GHz video vs 2.4 GHz ELRS: separate antennas. Nothing stuck to carbon.
• Goggles are not a TX16S failsafe replacement. Digital video ≠ radio failsafe. We don’t mix those up.

5. ArduPilot OSD (optional, later)

DJI “Canvas Mode” in the manual is Betaflight-oriented. On ArduPilot, MSP DisplayPort works (community confirmed with O4 + Goggles 3).

Do not use fpv.wtf / WTFOS — it does not support O4 / Goggles 3. Full write-up + steps: fpv.wtf & native OSD.

Parameter	Value
SERIALn_PROTOCOL	42 (DisplayPort)
SERIALn_BAUD	115
OSD_TYPE	5 (MSP_DISPLAYPORT)
OSD_TYPE2	5 (often required on Goggles 3)
MSP_OPTIONS	font bit (often 4 = Betaflight font on Goggles 3)

Wiring: crossed TX↔RX (white/grey), common GND. Use a free port — not TELEM1 (LD-06) or TELEM2 (ELRS). On the Mini: e.g. a free GPS/UART line or AUX serial if available. Otherwise postpone OSD until we revisit port budget — and that’s fine. Picture without OSD first.

Reference: ArduPilot DisplayPort OSD.

Do not use O4 S.Bus while ELRS already owns arming. Dual RC sources = chaos.

6. Bench order

We do this in small steps on purpose. If something fails, you know where.

1. Pack → Y → O4 only: picture in goggles?
2. Antennas fixed, CE power.
3. FC + ELRS without O4 UART.
4. MSP DisplayPort only once a UART is free.

Reference — expectations in one table

Function	On our build
Video to DJI goggles	Yes — standalone
RC / sticks	No — ELRS on TELEM2
S.Bus (yellow)	Open
OSD (MSP DisplayPort)	Later, free UART
Power	6S via Y (7.4–26.4 V)

Read next

• fpv.wtf & native OSD
• O4 Air Unit Pro — product
• XT60 Y + adapters
• Power & capacitors (O4 + CAN Hub XT30)
• Ports & wiring
• Step 2 — FC & power

Choice log

What	Install guide for DJI O4 Air Unit Pro on our ArduPilot/ELRS UL8
Why	Mount, power, activate safely — without DJI RC or WTFOS
Our pick	Pack power via Y. ELRS keeps RC. OSD only with a free UART.

Photos