If you want to see a 76 meter crash onto pavement

I had been very smug with my new TBS discovery. After crashing my way through an apm or two and some dubious chinese clone parts - I popped for a pixhawk and a new taranis. Was like night and day - loving every minute. About 20 successful flights. Flashed 3.2rc3 to do compassmot. Was successful and it flew even better.

I was going to try to do some autotune - show my wife my success and tried two 3s 2200 batteries in parallel to give me 4400mah. Was not quite what I hoped for.

Started - autotrimmed. Hovered for what felt like 30 seconds. Disarmed, and then flew on. Probably didn’t wait long enough for the trimming to stick. But I flew on - total flight time about 2:30. Switched to rtl to show my wife (had tested it with a single 3s many times previously).

And it fell out of the sky. 75 meters of freefall. Total loss of power. Destroyed my nice tbs frame, one motor and two batteries and three props. All the arms survived. Fell on its butt.

Quite likely to believe it was operator error, but even my wife noticed that it just shut itself off at about 76.9 meters (relative).

I have been a lurker for quite a while. I’ve read about troubleshooting logs. But I can’t find a cause. The pixhawk is still intact, as is the gps. I’ve ordered another discovery but I don’t want to risk flying again until I can find out what caused the crash.


http://api.ning.com:80/files/3t6avD66wnD5p2dQ5lMLAzXk1oKCo-YXwWA1zbnPpA5Ht1R3znVA9nTZ7ppl9vXTf*fnwWG2Y4TL0aWEJ3N5RadFDlLRBhQ8/20140721182304.logfor log.

and http://youtu.be/pEf-PO9LTmM for video.

Please see attached log and video. Basically - hit rtl on 3.0.2 rc3 (pixhawk, apm power module) and got stuck in loiter. Switched back to stabilize to try to manually lower - then there was a double beep (from video) and it fell 75 meters to pavement. Only out two batteries, one motor, 3 props and a frame. Even the gopro still works.

After getting clearance from my so, I’ve already ordered replacement parts. What I’m most concerned with is avoiding/fixing this issue going forwards. The logs just show no power/finis. The double beep (heard in audio from video) concerns me - does it signal disarm - if so what caused it? Should I backup the apm with a bec and a separate 3S I planned on using for my vtx?

Hi HeadGeek,

Your log is not matching the sequence of events like you are describing in the text…

If you select a filter on MODE you’ll find that you tookoff in Stabilize, Hit Land around line 21967, and immidiately triggered RTL at line 22088…

Also your GPS (RelAlt) stays around the 75 meters directly following the RTL command till the end of the log, so I don’t see any drop in altitude there…

On the Current and PixHawk Power side nothing strange as well (no drop in voltage, VCC, or current indicating a power loss…

Try to get the BIN log which is on the SD card, as I think your current log is incomplete…,


At work - but I’ll pull my bin later.

Was wondering if I stumbled into this


Some FRSky tx/rx systems receivers can only be set-up to modify all channels including the flight mode channel (channel 5) when a failsafe event occurs. For these receivers it is important to setup the receiver’s channel 5 failsafe value so that the APM is switched into RTL, Loiter or LAND. This is critical because there is a very short period of time (3/50ths of a second) between when the receiver pulls the throttle low and when the APM initiates the RTL or LAND. During this time, if the receiver also switches the flight mode channel to stabilize or acro the APM may switch to stabilize momentarily and then because the copter is in stabilize with throttle at zero it will disarm the copter (i.e. Test #2).

In the video you can hear the pixhawk disarm (two beeps) I think.


You might be correct there…

The log will confirm, if you pull the correct Bin.