Pixhawk 6X + TBS Crossfire Nano RX — "RC not found" despite Telemetry Signal 100% (CRSF on TELEM2)

ArduCopter Copter 4.7
1

Hi all,

I’m building a custom quadcopter with a Pixhawk 6X (baseboard V2) and a TBS Crossfire Nano RX, connected via CRSF to the TELEM2 port (SERIAL2/UART5). The Tango 2 and Nano RX are bound (solid green LED), but I’m getting persistent “RC not found” pre-arm despite telemetry appearing to work.

Hardware:

  • Pixhawk 6X (Holybro, baseboard V2A/V2B)

  • ArduCopter V4.6.3 (92b0cd78), Pixhawk6X-bdshot firmware

  • TBS Tango 2 (integrated Crossfire TX)

  • TBS Crossfire Nano RX — bound, solid green LED

  • Connected via hand-soldered JST-GH 1.25mm cable to TELEM2

Wiring (TELEM2 port):

  • Pin 1 (VCC) → Nano RX 5V (red wire)

  • Pin 2 (TX out) → Nano RX CH2/CRSF RX (yellow wire)

  • Pin 3 (RX in) → Nano RX CH1/CRSF TX (white wire)

  • Pin 6 (GND) → Nano RX GND (black wire)

Output mapping on Nano RX confirmed via TBS Agent Lite: CH1 = CRSF TX, CH2 = CRSF RX.

Parameters (current):

Parameter Value
SERIAL2_PROTOCOL 23 (RCIN)
SERIAL2_OPTIONS 0
SERIAL2_BAUD 57 (auto)
BRD_SER2_RTSCTS 0
RC_PROTOCOLS 512 (CRSF)

Key observation: In Mission Planner, the PreFlight tab shows “Telemetry Signal: 100%”, which suggests some form of CRSF communication is reaching the Pixhawk. However, RC input is not being decoded — no channel movement on the radio calibration screen, and “RC not found” persists.

What I’ve already tried:

  1. Verified and corrected BRD_SER2_RTSCTS (was 2, set to 0)

  2. Verified and corrected RC_PROTOCOLS (was 1/PPM, set to 512/CRSF, also tried 0/all)

  3. Tested SERIAL2_OPTIONS = 4 (TX/RX swap) — no change

  4. Tested on TELEM1 (SERIAL1) with matching config — same result

  5. Performed emergency firmware recovery on Nano RX (was double-blinking, now solid green)

  6. Multimeter continuity test on signal wires — both beep OK

  7. Reconnected a loose wire (white/CH1) — this is when Telemetry Signal 100% appeared

Suspected root causes (not yet tested):

  1. Pin offset in JST-GH connector — hand-crimped cable, possible off-by-one on the 1.25mm pitch connector. Continuity confirmed but pin mapping not yet verified pin-by-pin against the connector housing.

  2. Wrong port — ArduPilot wiki recommends SERIAL6/UART4 (USER port) for CRSF on the Pixhawk 6X. I’ve been using TELEM2 (SERIAL2/UART5). Could there be a hardware-level issue with CRSF on TELEM2 specifically?

Questions:

  1. Has anyone successfully run CRSF on TELEM2 (SERIAL2) on a Pixhawk 6X, or is SERIAL6 required?

  2. The “Telemetry Signal 100%” combined with “RC not found” — does this indicate a TX/RX line swap (FC receiving telemetry from RX but not sending/receiving RC channel data correctly)?

  3. Any other ideas given the symptoms?

Thanks for any help. Happy to provide logs or additional details.

**EDIT — 15 April 2026:**

Tested on UART4/SERIAL6 (the officially recommended port for CRSF on Pixhawk 6X) with a new cable. Configuration: SERIAL6_PROTOCOL = 23, SERIAL6_OPTIONS = 0. SERIAL2_PROTOCOL reverted to 2 (MAVLink2).

Result: same behavior — Telemetry Signal 100% in Mission Planner PreFlight, Nano RX solid green LED (bound), but still "RC not found" and zero channel movement on the Radio Calibration screen.

This has now been tested on three different UARTs (TELEM1/SERIAL1, TELEM2/SERIAL2, UART4/SERIAL6) with the same result each time. The telemetry path (Pixhawk TX → Nano RX) works on every port, but the RC path (Nano RX TX → Pixhawk RX) never gets decoded.

Parameters currently set: SERIAL6_PROTOCOL = 23, SERIAL6_OPTIONS = 0, RC_PROTOCOLS = 512, BRD_ALT_CONFIG = 0.

**EDIT 2 — 15 April 2026:**

Further testing and investigation:

1. Tested on UART4/SERIAL6 (officially recommended port for CRSF on Pixhawk 6X) with new cable. SERIAL6_PROTOCOL = 23, SERIAL6_OPTIONS = 0. Same result: Telemetry Signal 100%, solid green LED, but "RC not found" and zero channel movement in Radio Calibration.

2. This has now been tested on THREE different UARTs (TELEM1, TELEM2, UART4) — identical behavior every time. This rules out port and cable issues.

3. Nano RX output mapping confirmed correct via TBS Agent Lite on Tango 2: Output 1 = CRSF TX, Output 2 = CRSF RX.

4. Receiver is a TBS Crossfire **Nano Diversity** RX (not standard Nano RX). Pinout verified — same CH1/CH2 mapping for CRSF.

5. Tango 2 Crossfire firmware is **V4.10** (current latest is V6.48). This is significantly outdated. Unable to update at this time due to a TBS Agent server-side bug affecting firmware downloads (confirmed by other users in TBS Crossfire SOS Group on Facebook, 15 April 2026).

**Current theory:** The V4.10 Crossfire firmware may not be fully compatible with ArduCopter V4.6.3 CRSF implementation, or the Nano Diversity RX hardware revision may require V6.10+ firmware. However, this is unconfirmed — the firmware update is currently blocked by the TBS Agent issue.

**Question remains:** Has anyone experienced "Telemetry 100% but RC not found" specifically caused by outdated Crossfire firmware? Or could there be another cause I'm missing?

2

Upgrade to the latest TBS firmware

1 Like
3

EDIT 3 — 3 May 2026: Tango 2 firmware updated to V6.48 — RC still not found

Following @andyp1per’s advice, I contacted TBS support to upgrade the Tango 2 firmware from V4.10 to V6.48. This turned out to be a two-week process — TBS had a server-side bug that affected ~40 users whose Agent IDs were accidentally removed from their database. After multiple rounds of testing, videos, and screenshots exchanged with TBS support, they identified and fixed the issue. Firmware list finally appeared and I successfully flashed V6.48.

After the flash, I re-bound the Tango 2 with the Crossfire Nano Diversity RX — binding confirmed, solid green LED on the RX.

However: RC not found persists. No channel movement on the Radio Calibration screen.

Current setup:

  • Pixhawk 6X (baseboard V2), ArduCopter V4.6.3 (Pixhawk6X-bdshot)
  • TBS Tango 2, firmware V6.48 (freshly updated)
  • TBS Crossfire Nano Diversity RX, bound (solid green LED)
  • Connected to UART4/SERIAL6 via hand-soldered JST-GH cable

Parameters (unchanged, verified):

Parameter Value
SERIAL6_PROTOCOL 23 (RCIN)
SERIAL6_OPTIONS 0
SERIAL6_BAUD 57
RC_PROTOCOLS 512 (CRSF)

Symptoms (unchanged):

  • Telemetry Signal: 100% in Mission Planner PreFlight
  • RC not found pre-arm error
  • Zero channel movement in Radio Calibration
  • Tested on 3 different UARTs (TELEM1, TELEM2, UART4) — same result every time

So the outdated firmware was not the cause. The telemetry uplink (Pixhawk TX → Nano RX) clearly works on every port, but the RC data (Nano RX TX → Pixhawk RX) is never decoded.

At this point I’m suspecting a wiring issue on my hand-crimped JST-GH cable — possibly the RX pin on the Pixhawk side is not actually making contact, or there’s a pin offset in the connector housing. The fact that telemetry works (one direction) but RC doesn’t (other direction) would be consistent with only one signal wire being connected properly.

I’m attaching photos of my wiring for review. Can anyone confirm:

  1. The correct pin mapping for CRSF on the UART4 & I2CB connector of the Pixhawk 6X baseboard V2?
  2. Whether the “Telemetry 100% + RC not found” pattern definitively points to a missing/broken RX line?

Any help appreciated — I’ve been stuck on this for over three weeks now.

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4

Wiring order looks correct. And at a glance the paramaters look correct as well. Double check the wire with a multi-meter to make sure it’s working. Those pins can be a bugger to crimp if you don’t have the right tools.

1 Like
5

Did you check the pins are set to CRSF in TBS agent?

6

I double check to be sure, but yes

  1. Output 1 = CRSF TX
  2. Output 2 = CRSF RX
7

To summarize where things stand after all checks:

Verified OK:

  • Tango 2 firmware updated from V4.10 to V6.48 (confirmed working)
  • Nano Diversity RX bound — solid green LED
  • Output map in TBS Agent Lite: Output 1 = CRSF TX, Output 2 = CRSF RX
  • Wiring on UART4 & I2C port: Pin 1 (VCC) → 5V, Pin 2 (TX4 out) → CH2 (CRSF RX), Pin 3 (RX4 in) → CH1 (CRSF TX), Pin 7 (GND) → GND
  • Multimeter continuity confirmed on all 4 wires, including the RX line (pin 3 → CH1)
  • Parameters: SERIAL6_PROTOCOL = 23, SERIAL6_OPTIONS = 0, SERIAL6_BAUD = 57, RC_PROTOCOLS = 512, BRD_SER2_RTSCTS = 0
  • Tested on 3 different UARTs (TELEM1, TELEM2, UART4) — same result every time

Symptoms (unchanged since day one):

  • Mission Planner shows Telemetry Signal: 100%
  • “RC not found” pre-arm persists
  • Zero channel movement in Radio Calibration screen

The telemetry path (Pixhawk TX → Nano RX) works on every port, which confirms wiring direction is correct. But the RC path (Nano RX TX → Pixhawk RX) is never decoded.

At this point I’m running out of ideas. Could this be a hardware issue with the Nano Diversity RX itself (TX output not actually transmitting)? Or is there a parameter I’m missing?

Happy to provide logs or run any test you suggest.

8

Something fundamentally wrong here because I am wiring a Pixhawk6X up the whole time to TBS RX without issue.

9

Hang on - what is that picture? What is the connector wired into? Doesn’t look like a telemetry port.

Please post all your params

10

Hi Andy,

Thanks for taking another look.

Regarding the photo — the connector is plugged into the UART4 & I2C port on the Pixhawk Baseboard V2. It’s the 7-pin JST-GH connector on the upper edge of the board. Note that the silkscreen on this baseboard revision is printed upside-down on that edge, which may make it look unfamiliar in the photo. I chose this port based on the ArduPilot Pixhawk 6X documentation recommending SERIAL6 (UART4) for CRSF.

Wiring on that 7-pin connector:

  • Pin 1 (VCC +5V) → red wire → Nano RX 5V
  • Pin 2 (TX4 out) → yellow wire → Nano RX CH2 (CRSF RX)
  • Pin 3 (RX4 in) → white wire → Nano RX CH1 (CRSF TX)
  • Pin 7 (GND) → black wire → Nano RX GND
  • Pins 4, 5, 6 not connected

I’ve also tested on TELEM1 (SERIAL1) and TELEM2 (SERIAL2) with the same result each time — Telemetry Signal 100%, but RC not found and zero channel movement in Radio Calibration.

Full parameter file attached.

For reference, here’s what has been verified so far:

  • TBS Crossfire Nano Diversity RX, bound (solid green LED)
  • Tango 2 firmware updated to V6.48 (was V4.10 previously)
  • Output mapping confirmed via TBS Agent Lite: Output 1 = CRSF TX, Output 2 = CRSF RX
  • Continuity tested on all 4 wires with multimeter — all OK
  • SERIAL6_PROTOCOL = 23, SERIAL6_OPTIONS = 0, RC_PROTOCOLS = 512
  • Tested on 3 different UARTs — identical behavior on all

Happy to run any additional tests you suggest.

Thanks,
Alexandre

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ParamList.param (17.9 KB)