Discussions

Pixhawk Crash Analysis

Date:19-05-2017

Time: 4 – 7 p.m.

Weather: Calm, sunny day & with no or little wind

Temp: 37-32 C

Plane: Volantex Ranger

Board: 3DR Pixhawk loaded with plane 3.7.1

Battery: DIY 3s pack 20400Mah made from Panasonic ncr18650b

After programming the board, today was the first test flight. I took off in manual mode, trimmed the plane and flown it for almost 10 to 15 minutes in manual mode without any problem.

Then I switched to FBWA mode the plane handled the flight very well with the stock parameters and without any tuning at all. Then I switched to FBWB mode and the result was great flight. After that I switched to cruise mode where I faced only one issue: The plane was holding the flight path really well but with some roller coaster motion (something that I know is having to do with tuning). After that I switched to loiter and the plane started performing good circles thought I haven’t calibrated the airspeed yet. Only then and after making sure that the plane can fly itself I switched to RTL mode and the plane came back to me and started loitering at 200m altitude which I had set for RTL altitude.

Now it was the right time to start the auto tuning progress. I went ahead and did the roll tuning, then the pitch tuning and everything was good. After that I checked the tuning page on my mission planner and the parameters were changed to the new set of the auto tuning. Afterwards I started applying rudder inputs to tune the yaw and here the problem started. After few rudder inputs the plane stopped responding and went into a turn towards the ground with the rudder stock in one end. While the plane was going down I switched out of Auto tune and tried all the modes but without getting any response from the plane even in manual mode.

It was at that moment when the plane sat on the green field about 500 meters away from me. When the plane hit the ground the radio announced “RSSI CRITICAL”.

When I reached the plane opened the canopy the led indicator of Pixhawk was indicating failsafe. The plane wasn’t damaged at all and I didn’t notice any damage to the electronics as well. Of course I haven’t checked anything yet.

I had the screen recorder on my laptop recording the screen and now when I came to see the last seconds before the crash I realized few things that I wasn’t aware of as I had the sound muted on my laptop.

31’ 20”                    in to the flight                        started the yaw tuning

31’ 27”                    in to the flight                        3 yaw inputs so far

31’ 28”                    in to the flight                        bad AHRS

31’ 29”                    in to the flight                        error caused vert variance   

31’ 36”                    in to the flight                        6 yaw inputs and I realized that something is not OK with plane

31’ 39”                    in to the flight                        warning no data for 10 seconds

31’ 40”                    in to the flight                        changed to other modes

31’ 44”                    in to the flight                        earning no data for 15 seconds

31’ 46”                    in to the flight                        I was sure that the plane is not responding at all

31’ 55”                    in to the flight                        warning no data for 25 seconds

32’ 05”                    in to the flight                        RSSI critical (from Taranis)

32’ 08”                    in to the flight                        Telemetry lost (from Taranis)

32’ 21”                    in to the flight                        Telemetry recovered (from Taranis)

32’ 23”                    in to the flight                        Telemetry lost (from Taranis)

32’ 42”                    in to the flight                        No RC Receiver

                                                                                 Error caused vert variance

                                                                                 Bad AHRS

                                                                                 Error compass variance      

Same errors continued for several minutes till I reached the plane and turned it off.

                                                                                 Telemetry Recovered, RSSI critical, Telemetry Lost, ….

Now when I connect the Pixhawk to the PC I get a solid red light and I cannot get it to connect to mission planner.

I’ll try to go through all the components one by one to see if I can detect any error or issue starting from tonight.

Guys, please give me your thoughts and ideas on what could be the cause

Many Thanks