Pixhawk flips on take off

Hi, I am trying to help a friend with his copter. I ve been successfully flying apm and pixhawk for over a year now but can not figure out this problem.
His copter flips over, pitches forward, when trying to take off. I told him to recalibrate everything (esc, gyro, acc,…) and double check motor order and prop rotation direction. He assured me that everything was done properly (I do not have physical acces to the copter as he lives too far).
I am trying to understand the problem from a logfile he sent, but cant seem to find anything. Except maybe that the TRIM_THROTTLE param is way too high.
Could someone more experienced with logfile analysis maybe check the logs briefly and let me know if there is something weird?


also a video of the problem

Thank you.

Strongly suspect a motor order or motor direction issue. Please post a closeup photo of the quad.

Accidental reversion of the pitch channel?

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Hi, thanks for your suggestions.
As i wrote before, I have no access to the copter, so it is quite hard to know what is really going on…
But he assures me that everything is recalibrated and connected correctly - motor order, prop direction (according to photos is OK), RC channels reaction is tested in hand - pitch, roll, yaw react correctly to radio input, Terminal - Setup - Motors test works OK…

Here are some pictures:

Motors are connected according to this http://www.axnzero.com/wp/wp-content/uploads/2014/02/

Some more tech details:
Motors Emax MT 3510 600Kv, ESC DJI 30A Opto, 4S 4000 40C batt, 13x4 and 14x4,7 props, FW 3.1.5.

However there seems to be a problem with ESC calibration. After arming the copter only 1-2 motors start spinning. After applying throttle a bit all start to spin, when throttle is set to zero again only some remain spinning.
MOT_SPIN_ARMED is raised from 70 to 100 , MIN_THROTTLE is 130.

I have the same motors on my X8 setup and MOT_SPIN_ARMED at 70 and everything spins as it should.
I had the same problem, that only some motors were spinning after arming the copter, but calibration solved it. Here it does not seem to help much.
So could there be something else to try?

Could there perhaps be a problem with the sbus to ppm decoder which he apparently uses?

The other guy is right, the pitch channel is probably reversed. When the thing fell over the first time, it had a pitch command in that direction. It did overshoot it, but the landing gear was touching the ground. Being a pretty tall copter, it’ll be kind of touchy that way. If it were autotuned, it would probably have less of that trouble, but I still suspect pitch is reversed.

Thanks again for all your input.
Will do a test flight on weekend if the weather allows it.

BTW Where did you get such a nice graph from? Is it from APM planner?

[quote=“azrael_sk”]Thanks again for all your input.
Will do a test flight on weekend if the weather allows it.

BTW Where did you get such a nice graph from? Is it from APM planner?[/quote]

That’s a matplotlib graph from pymavlink’s mavgraph tool.

Assuming the inputs are reversed how is this corrected?

I believe I’m having similar issues but with Roll (see post titled IRIS tips on takeoff)

Maybe not the place to ask but how do I pull reports and graph them? I’m very new to pixhawk…

Motor rotation looks fine make sure your inputs are correct motor wise.
Do radio calibration look and make sure your radio is set up correctly and none of the channels servos are reversed.
Drop all your pid values top numbers from the facrory 4.5 ro 2.5 it will feel sluggish but may solve it. Those are big props on there and it may be trying to compensate too quickly. copter.ardupilot.com/wiki/tuning/
Start with 2.5 and go up from there.
At 3.0 evoking auto tune my copter would literally fall out of the sky.

Also here are the motor numbers and outputs copter.ardupilot.com/wiki/connec … nd-motors/

If the input direction is reversed you change that in your radio.
I’m assuming that you have a good computer radio of some sort.

Also once you get the radio calibrated drop your pitch and roll dual rates to 50 percent for starter.

I have my rates set for 40% for takeoff 60% flies good and fast. 100% is stupid fast and hard to control

For now, just reverse the pitch channel in your radio and redo radio calibration and see if that fixes the problem. No need to mess with PIDs.