3 palnes,3 pixhawk,3 crashes. with logs

I need your help, 3 planes of my crashed in a row…the same simptomes on the 3 crashes, the plane loss of height very fast with no option to control, twice it was on manual mode. I attached the 3 logs from these flights please help me to discover what happened…

the logs here


If you’re crashing during manual mode then it’s not an autopilot problem, probably hardware.

Things I noticed in the logs:

  • Your aircraft seems to be balanced well - good CG.
  • airspeed is around 16m/s, can you confirm that isn’t near the stall speed of your aircraft?
  • it doesn’t look like a motor problem. Your throttle goes up and your battery current goes up so the motor appears to be working
  • temperature looked OK. Hovering around 38C so that’s well within normal range.
  • you’re flying Plane v3.5, why such an old version?
  • some more info would be helpful. What kind of plane?

how exactly do you see that ? - what data are you plotting to verify CG ?

the plane is ZETA FX-79, the CG was good, the speed is good…this plane can fly much solwer, I use v3.5 because in v3.7.1 I get Bad AHRS and I can`t solve it for some reason, if you have solution for me it will be helpful by the way.
how I can be sure that the powe from the pixhawk is good for my servos during the flight, I use savox digital mini servo (I need to check to give the model).
any other option to investigate those problems.

PIDP.I (pitch integrator) was close to zero, the autopilot was not having to drive any constant pitch up/down to maintain normal flight.

how I can be sure that the powe from the pixhawk is good
dataflash log (.bin on SD card) CURR is from the power module. Check value CURR.Volt and CURR.Curr. You can also look at the POWR.Vcc/VServo which are analog voltage readings on the pixhawk for the two power rails.

I thought so, just needed to ask, I’ve seen many bad builds where level flight is set up with some degrees up/down elevator (so trim elevator to AP was actually already up/down), So it’s not a perfectly accurate method of knowing if the CG is good, or if the user already assembled so that some up/down elevator is applied at all time, resulting in a more speed-sensitive “trim”. (and integrator values more affected by speed) I have no reason to doubt it’s good in this case. - just tried to learn a new trick if there was one :slight_smile:

Ok I’ll check. And about the bed AHRS on v.3.7.1 do you have any idea how to solve it. I suspect the bec of my esc with the power supply for the servos. I want to check with external ubec.
Do you think this is what caused the problem…?
Thanksfor your help very appreciate

have you tried v3.8beta?

No…it’s stable? I have a stable version. I work with those planes…

Hi Omri,
I am also struggling to know the reason for several crashed with two planes, so I share your pain :sweat:
I am just starting to learn how to analyze the logs, but I see something that could be related. for plane 1, if you plot the “mechanical failure” during FbwA, there is a huge offset between desired and real roll and pitch, in my logs when a plane is flying ok, they have similar values and trend. for example, in your log for plane 1:

roll is mostly negative but demand is positive. Looking at the parameters, RLL2SRV_P and PTCH2SRV_P are both 0.4, which seems to me a very low value (it is around 1 for most models, I think). For X8, which is a simmilar airframe , RLL2SRV_P is recommended at 0.8 (http://ardupilot.org/plane/docs/configuration-files-for-common-airframes.html)
Maybe the P value is too low and the I value is not enough to reach the demanded bank in a reasonable time?
Did you tried autotune?

good luck,

Hi again,
I have just read your problen of “bad AHRS”. I had the same problem and the reason was that the two GPS with compass that I was using had the compass chip rotated. That is, the “COMPASS_ORIENT= NONE” was not the rigth orientation for the compas with the arrow printed on the GPS case pointing forward. I had to disasembly the GPS and check the HMC5883 chip datasheet to discover that. However, the calibration and orientation of the plane seemed perfect when checked on the ground, but once in flight, measurements from IMU, GPS and internal and external compasses started to diverge and got the “bad AHRS” message (and several crashses too)
Hope that helps,

On both plane1&2 that was the first fly. I just checked the fbwa on plan 1. Iand it wasn’t very good I know. But on plane 2 I was only on manual and I had the same problem. I do wanted to do autotune but the first flight was the last too. How can I know the tuning before the first flight. This set up works very well on older planes. And I can remember just one of them that did autotune. But I’ll check it. Thanks for your help

My compass is disabled. The compass isn’t necessary for a plane as i know.
And another question. I want to use external bec not from the esc so it is possible to do? And if my power sensor also includes bec I nees to avoid from the bec in the esc?

Here an owner of a fx-79 with many flights. I would recommend to enable both magnetometers ( the built in and the GPS’s one) and calibrate, also update firmware and run autotune as soon as possible.
I don’t have external bec for servos, and are the same cheap 9g than the first day. I’M NOT AN EXPERT IN ELECTRONICS, DO AT YOUR OWN RISK, but If you still want to add a dedicated bec, remove the red cable from the ESC plug into the pixhawk and connect the bec to the pixhawk. Keep in mind that all the GND need to be connected.
I will give Param for if requested, but i have to say that will have many weird settings, as i have tried many different settings, like differential spoilers, banking angles, camera triggering options and so on.

first thanks for your help…I think it will be helpful if you will send me your param file. I will compare with my param. I change from the 9g servo to savox digital servo because I had a lot of problems form slow servo. I know about the needs to disconnect the red wire in case of external bec but thanks for the noteis…I also did a lot of flight with the fx-79 but I also had some same problems like thus 3 on old planes but now it was on new plans and new setup and 3 in a row…so I have to know what cause this.

Never felt that my servos were slow, and I’m flying with 10.000mah and a Sony alpha Nex 7, my plane goes really heavy.
Maybe failsafe settings? I had problems in another plane and it was related to failsafes and a broken receiver antenna…

fx-79-2017-02-07 15-00-13.param (107 Bytes)

Thanks. I have only battery failsafe on the pixhawk. The radio failsafe set on the radio but I’ll check it too.

I have another question. …can you please send me you hardware setup.? I need recommendation to esc and ubec as well. …thanks

The you have a video of my fx-79 “Frankenstein”, I have my “flaps” configured as differential spoilers, (channels 5 and 6 with functions 16 and 17) but disabling the differential spoilers main function (differential spoilers rudder rate=0) therefore those surfaces mimic the elevons movements.
Don’t take into account the dust, and the dirt and messi build, I’ve learnt to fly with this!

Thanks you use with the esc bec.?