Severe crash with AC3.6.6, help needed

Hi,

I ask help from you guys, I do not know what to do…

Setup: modified F450 frame (arms changed to CF tubes, 16mm, diameter lowered to ~380mm), Micro Pix FCU, M8N GPS+Compass, LidarLite V3 as main altimeter sensor on I2C, Sonar (chinese) on I2C for back object detection. 1045 CF props, Sunnysky X2212 KV1400 motors, ZTW Spider 30A ESCs, motor output set to “Oneshot”, Hubsan X4Pro 7000mAh 11.1V battery.

Recently, (after installing the Lidarlite) the copter started to act strangely… In Stab mode, everything is fine. In AltHold mode, it banks forward, thus starts to go away, it reacts the stick orders a little bit slowly, but it is possible to control. In PosHold and Loiter, it kept the position, but the control was very sluggish… Also, landing detection was not functioning with FW AC3.6.7-3.6.8. Many times it turned over after a succesful landing, if the mode was not Stab.

So I decided to downgrade the FW to PX4 AC3.6.6 V2 because I have read here that it seems to be the last version with working landing detection. I needed to manually download the FW, my MP wanted either to upload the latest version, or the 3.5.7 version…

Today I made a test flight… Total destruction… Before it I have made all the necessary parameter checks, I reloaded the “surly working” param list, I checked everything again… Also, just for sure, I made the ACC calibration again and also the level cal as well. At the field, Stab mode worked as it should, nice soft flight, well controllable, no problems. In Althold, the forward banking happened again, and it reacted to the stick quite slowly… In PosHold, the craft rolled nearly uncontrollable to one side, than the other, but luckily I was able to set is back to Stab. In Loiter, the disaster happened… I had no control over my craft, if has flown around, rolled to right, I tried to use Break mode, but nothing happened, the craft flow through a tree, turned upside down and crashed, braking the GPS mast down. Still I was not able to disarm, when I lifted, one motor started to spin, cutting the GPS cable… I needed to use the QGroundControl app’s “Emergency stop” function to disarm the craft…

Link to the log file:

So, I have no idea, what to do… Recently I have broke four motor mounts, some leg tubes, and some props with these uncontrollable side-flying flyaways… I have no idea how to fix them… A month earlier, the craft has flown perfectly with the 3.6.7 FW, except the landing detection… Now, I have to rebuild again…

Is this a hardware fail, or have I set some parameters incorrectly?

Any help is highly appreciated!

Also, here is the parameter list as well:

10 2019.06.20. 13-16-50.bin.log.param (13.9 KB)

You have an important motor imbalance (motors 1 and 2 are working harder). Make sure your motors / propellers are perfectly tilted. It could also be that one motor is not working properly or ESC not calibrated.

Second, your copter is overpowered. Test with a bigger battery.

I hope you can fly soon.

Thank you for your suggestions!

Actually, when I switched the ESC setting from pwm to Oneshot I did the calibration. I will redo it. As I saw, the motors are paralell with each other, but I will check them again.

As for the power, you have right, in this setup, the copter is a little bit overpowered, but normally it is ment to carry a gimbal and a GoPro as well, approx. 160g more weight. Just for the test flights, I do not want it to be installed to avoid the unnecessary damage.