Telemetry lost...

[sande005]

The hardware:
X9D, OpenTX 2.2.2
Plane 1: RX8R Pro, with X4R redundant (RSSI and RxV)
Plane 2: G-RX6 Vario (RSSI, RxV, Alt, VSpd)

Both planes, I get occasional "Telemetry Lost/Telemetry Recovered" prompts during a flight. Much more frequent on plane 1.
For the last flight of the day on plane 1, I turned on logging, interval of 1/2 sec. Got the prompt 2 times while flying, and once after landing when the plane was about 10 ft away. No failsafe kicking in detected. Log doesn't show much - lowest RSSI was 45, average around 60-70. At the end of the log, about when the last prompt occured while I was on the ground, RSSI and RxV both had a dip for one timeslice to 0.

Should I speed up logging to better "trap" any incidents? For plane 1, any way to determine whether I have failed over momentarily to the redundant RX or not?

Plane 1 did not have this issue when using my X9D+ SE (in for repairs, currently), although Plane 2 did.

Looking for suggestions on a process to narrow down the possibilities of the causes....

 

[Scott Page]

There is no reason not to use 0.1 second logging. The log files are not memory limited and our SD cards are plenty big for a zillion (hyperbole) hours of logging. Of course RSSI is signal up to the aircraft, and "telemetry lost" is for signal back down to the TX . That said - it might be a antenna orientation issue -- or not. In any case - you probably know that the null area on the Tx antenna is directly outside of the end and in the opposite direction. For this reason I point my antenna directly at my face and the signal null is then behind my head (where I'm not flying I hope) and into the ground directly in front of me.

 

[sande005]

Thanks Scott - since the log is only trapping the data coming back to the Tx, I was kind of hoping to see some kind of precursor - like RSSI getting really low, then a dead spot in the log, then everything coming back. In the one incident in the log, the before and after RSSI's were above 70. I'll try a faster log rate, to see if anything shows up. At least failsafe never appears to kick-in, so I'm suspecting downlink issues, more than uplink.
Would be nice to be able to not only see signal strength at the RX (RSSI) as we can now, but also signal strength of the telemetry as received at the TX. And while I'm wishing, a counter in the RX to log/report missed frames.

 

[Wayne]

Lost frame counter - With Spektrum, this seems to always have some lost frames, but with FrSky, typically no lost frames for a normal flight. If you are pushing the limits out past the "critical" warnings, then yes you may risk some packets.

 

[Woodstock1]

Where do I look for these lost packets I am not familiar with this. Kiwi4

 

[HENNY]

The hardware:
X9D, OpenTX 2.2.2
Plane 1: RX8R Pro, with X4R redundant (RSSI and RxV)
Plane 2: G-RX6 Vario (RSSI, RxV, Alt, VSpd)

Your OTX version 2.2.2 is very old. It dates back to 2018.

Telemetry lost normally means the return link from the receiver to the transmitter is weak. Or antenna placement is shielded or even inside a carbon fiber fuz. It would be interesting to know if the RSSI is also weak. RSSI is the up-link between the TX and receiver, Telemetry lost is the down link. So they are different measurements.

I recall there were some fixes in this area along the way. So upgrade your OTX to version v2.3.14 is a starting point. You can find it here. https://www.open-tx.org/

 

[sande005]

Ummm...the original post was from 2018, so I was pretty current back then.

After getting my repaired X9DSE back, I would still have it happen, but only on X8R receivers. Swapped many out, rerouted antenna, etc. Tried completely different trainer-style planes with nothing else in common. Still happened after updates to v2.1 for the RX's., and using OTX 2.3.12.
Primary use was for a club trainer, and we never got further out than I was comfortable letting a beginner fly.
The interesting point - I switched my main radio to a Horus X10SE, and it all stopped being an issue.
Had a fly away with the X9DSE - fail safe didn't, and never in that case got a "telemetry lost" even when it was finally coming down 2.5 miles away (found it the next day!). That radio is now here at my desk relegated to the "bad boy" corner. Maybe I'll send it in over the winter.
Have not retried the original X9D - that is usually the buddy box, or used for BNF Spektrum box planes I seem to be accumulating....

 

[HENNY]

You may simply have a weak or damaged antenna or RF output stage in your X9D radio, it's getting quite old these days.

 

[Landru]

Had a fly away with the X9DSE - fail safe didn't, and never in that case got a "telemetry lost" even when it was finally coming down 2.5 miles away (found it the next day!). That radio is now here at my desk relegated to the "bad boy" corner. Maybe I'll send it in over the winter.

This thread caught my eye but I realize I'm very late to the discussion.

My interest arises from my own experience of fly-aways with two different brands of gear.

In one case, the problem was understood and corrected by the manufacturer (a brand I won't mention but not FrSky). The issue turned out to be a receiver fault that caused the control link to be irrecoverable after it was interrupted by RF interference, no matter how briefly.

The other cases concerned R9 ACCESS. The symptoms were exactly as reported above: a loss of control without any telemetry lost warning. In my cases, the incidents all occurred at close range, about 20-100m or so. Using an onboard S.bus data logger, I discovered that the issue was not a one-off occurrence. Rather, I logged several more brief occurrences in a subsequent flight after the initial incident, which lasted 27-seconds. The cause remains a mystery. However, I was able to rule out brownout as the culprit via the onboard data logger. Incidentally, I wonder if brownout might have been a factor in your incidents, @sande005.

@HENNY mentioned the possibility of a hardware fault. That certainly seems plausible to me. In fact, a hardware fault may have been the cause of my R9 failures. However, I think RF interference might also have been involved. At least, I'm not sure it can be ruled out. In the case of the 'non-FrSky' fly-away, the manufacturer shared with me the details of a RF stress-testing program they implemented for their products. It was impressive. It made me wonder what steps other manufacturers take to test RF reliability.

Well, this post is more of a musing than a call to action. If there is any easy action to suggest, it would be to test for a brownout.