Hexa garage hover crash has me losing sleep

Hey guys, I’m really hoping you can help shed some light on this one. It’s driving my nuts and I can’t seem to find the culprit. I have a hexa that I’ve flown for the past year with Pixhawk. I recently upgraded the gimbal and am carrying a Nex-5 beneath. The hexa hovers between 50-60% throttle. I’ve been hovering in the garage over the past week to get some of the gimbal settings dialed in. Last night I was doing a hover test and the hexa basically fell backwards and would not respond to my stick input to pitch forward. I immediately had to cut throttle and let it crash into a wall. Thankfully not too much damage. The kicker is I’ve spent about 5 hours looking through the log and reading different howtos, but can’t find any sign of what went wrong.

Here is a link to the dataflash log:


And let me share some analysis I’ve done just in case it raises any ideas. This first screen is a plot of the pitch vs despitch to see if there were any potential ESC/motor issues as mentioned here:

copter.ardupilot.com/wiki/common … sing-logs/

Also, note at the bottom of the image I’ve filtered on “EV”. This test was a series of three different hovers. Notice on line 16 where it takes off and never lands?


In the next image I charted my RC inputs to make sure something wasn’t going on with the receiver causing the hexa to pitch back. You’ll see CH4 rudder sequence to arm the motors and the CH3 throttle increase to about 50% where it begins to hover. But you never see it come back down. What’s even more interesting is I know I cut throttle with the hexa started to pitch backwards but none of that is shown in the logs.


The third image below shows the RC outputs just to see if somehow Pixhawk told any of the ESCs to pitch backwards. I don’t see anything like it.


That’s what I know so far and will continue to investigate. I’m just frustrated because I’ve lost confidence in this rig and don’t want to take a bunch of $$$ equipment in the air only to have this happen again. My next test is going to be to remove the gimbal and camera to see if I can reproduce this.

Any insight would be very much appreciated.

Many thanks,

What RC are you using? Flying indoors can be problematic as the radio link can drop. If that triggers failsafe in your rc receiver, the channels may lock to the failsafe you have set, hence for the throttle not dropping.

Also you should set AHRS_USE_GPS to off indoors, since GPS may cause an issue. Even in Stabilize mode.

Thanks for getting back to me. I’m using the FrSky Taranis with X8R receiver. I will check the RX failsafe settings and report back. I would still expect to see something that indicates the behavior of the hexa pitching backwards.

I will look into disabling AHRS_USE_GPS while indoors. I appreciate the tip.