Troubleshooting RC Failsafe

ArduCopter
,
1

Hi I’m having an issue with “RC Failsafe Low Throttle” or “No RC Receiver”.

I’m using an Frsky X9D transmitter using ACCST (required) and an XSR receiver (I’ve had the same issue with a Frsky Archer RS Plus receiver also).
I’m not using telemetry, one way communication only.
Receiver firmware is: XSR_ACCST_2.1.0_FCC.frk
Radio firmware is ISRM-S-X9D2019_2.1.0.frsk
Using SBUS out RX6 Serial 7 on Matek FC. No SBUS in as comms is one way only.

Looking at the logs the throttle doesn’t register a drop. I’m not sure why it is going into failsafe.
The problem is difficult to recreate.

I don’t think its connections bc this has occurred on 2 similar drones with different receivers. Although I’m not ruling it out. Could it be interference with the other 2.4GHz antenna, or other high current devices?

Perhaps its because I don’t have serial 7 protocol configured? I could change this to 23: RCIN.

See log below, the failsafe occurred at 25min 31s into the log.The distance between transmitter and drone was only 25m. The issue seems to be independent of distance as it has occurred on the bench. Using range test on the transmitter allows for a distance of 50m+.

2 
2024-08-09 22:11:39.019 Error: Subsys RADIO ECode RADIO_LATE_FRAME
2024-08-09 22:11:39.019 Error: Subsys FAILSAFE_RADIO ECode FAILSAFE_OCCURRED

From the wiki regarding the error:

Late Frame : no updates received from receiver for two seconds

I wouldn’t rule out interference of some sort. or the radio. Especially if this is happening on 2 other drones, that really points to the radio or some external factor, not the drone. Check the antennas and make sure they’re in good shape. Look in side your radio and make sure nothing strange is happening in there.

This drone is on old firmware, might be time to update it.