RC Transmitter beeps intermittently - No power issue

Last weekend I ran into an anomaly with the RC transmitter of my IRIS: It started beeping intermittently.
Once I heard only a single short beep, during another flight I heard a short beep, followed by two more short beeps in a different tone.

During one flight I was using the stock AA batteries provide by 3DR. In another flight I used rechargable Nimh batteries. But in both flights the battery voltage in the RC transmitter was above 10V and thus well above the alarm voltage of 8.9V of the FS-TH9X.

Also at this point IRIS was 60 ft / 20 m high across and about 300 ft / 100 m away from me. In both cases I kept flying without any issues at all.

Unfortunately 3DR doesn’t provide a manual with the remote that explains what the beeps mean. And the manuals of the FS-TH9X that I found on the internet didn’t mention anything about beeps or buzers other than the voltage alarm.

I have to admit that these beeps did make me a bit nervous. I would therefore like to know what they mean. Does anyone have an idea?


I opened a support case with 3DR, asking what the beeps mean.
Now they want me to ship everything (IRIS + RC transmitter + LiPo) back to them for inspection.

To me that looks a little bit like an overreaction to the simple question of what the RC transmitter beeps mean. Especially as my IRIS has been flying very nicely last weekend and I don’t really want to see it be gone for 1-2 weeks while it’s being serviced.

But the reaction from 3DR does raise a little suspicion, that there might be more behind these inconspicuous beeps.

Any thoughts?

After poking around some more I was able to reproduce the RC transmitter beeps: It appears to have been the range / RSSI warning.
Initiating the range test on the FrSky module and walking into another room triggered the alarm. Also in regular operational mode, walking into the elevator and going to another floor also triggered the alarm.

I will need to do some range tests outside today.

When the alarm happened in the field I wasn’t very far away from the TX with IRIS. But it was a new location in the middle of the city. Could have been that he 2.4 GHz range is particularly noisy there.

WHOA!!! This is very interesting, because the very first thing that happened right before my IRIS fell out of the sky was that the transmitter started beeping! I remember very distinctly that it beeped, and then the IRIS just turned off and crashed. This is that doomed flight I wrote - the one where you were helping me with the logs. Interesting… very interesting. I could not have been THAT far away for it to be beyond radio range, unless the range is not that good from the stock equipment. Hmm… now I am really going to be keeping it very close to me. The weird thing is that one of my logs showed that it hit the GEOFENCE setting in altitude and it was WAY farther UP than the drone was vertically away from me when it dropped.

I wonder if there is something I can set if RC range is exceeded, like initiate a loiter or something like that.

What mode were you flying in, when the crash occurred? Stabilize?

It’s possible that the RC transmitter went out of range and triggered an RC receiver failsafe That failsafe is different from the Arducopter failsafe. With the RC failsafe configured the receiver will send out a predefined stick setting. If that stick setting was configured to be in the zero position, IRIS would indeed drop from the air like a stone.

But to be fair: Your logs don’t show any indication of that. The logs rather point towards a brownout.
But as part of the brownout the RC receiver would also be underserved with electricity, which would cause the RC range warning to go off.