Log Analysis Help!

Hi every one, I have been some problems with my drone, and I cant find the problem in the log.

I was making a Guided Mode flying, 30mts on the ground, some RTL too. On the last Guided fly the drone sudenly fall. I could see and Im almost sure the was a problem with a motor.

So, Im looking the log, and I cant find the problem with the motor. And some strange thing I found

For example, here you can see the DALT and the ALT at the crash moment, and as I understand, the DALT in this case (As i was in a guided mode at 30mt) is the altitude the drone must be, but you can see went down.


The flight mode was never changed until the drone touch the ground. So, if im not wrong, someting give the instruction to the drone to go down, right?

In the other hand, in the next picture I have the desire Climb rate and the real one, as you can see are oposite, and you can see how fast went down.

So the next picture, the motors, im very sure the motor number 3 was the one I saw failing, but I cant really see a number here give me the reason.

So im very confuse, I cant understand what happend, so I would like your help to determinate what whas the problem.

Im using a pixhawk 2.1, quadcopter, 12Amps 6S battery, 23V aprox at the moment, enought battery to fly. I have checked the voltage the battery after and before with a voltage meter and was ok. The drone weight almost 4.3Kg, each motor can handdle 2.2KG (Arris 4010, 380KV).

Here is the log file

I really will apreciatte your help!


Motor 1 seems to be the one which failed; the flight controller is commanding full power from motor 1 and minimum power from motor 2, which makes sense because it is opposite of motor 1.

The climb rate graph shows that the flight controller wanted to go up, but the drone was falling; this is enough information to know that the descent was not intentional. The desired altitude goes down because it can get “dragged” down by the actual altitude. If you zoom in, you will see that the desired altitude is higher than the actual altitude while the drone is falling.

This “dragging” behavior is normal; the desired altitude (or attitude, or position) does not always stay at the final target. For example, you will see in Position Control graphs (PSC) that if you give it a waypoint 1000 meters away, the desired position doesn’t change by 1000 meters. This is a safety feature that can prevent the drone from doing crazy things because there is a huge difference between desired and actual state. That is why the desired altitude gets dragged down by altitude, even though the real altitude target is still 30 meters.

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Hi Rick!

Thanks! I appreciate your help! You are right, Im doing the autopsy to the drone, and I have run all the motors, all runs, but the number 1, if I move the ESC, the motor stop…

I appreciate you comments about the DALT, is very helpfull to a better understanding of the logs.

What software do you use to review de logs? MP?


Hi Rick, sorry to bother you, but can you pls check this another log? I have lend an Hexa drone to a friend, and he told me he took off in loiter, and some seconds later, the drone start to go down, fast, but steady. Finaly it crash and the drone turn over on the flor.

I was looking the Log, and I cant find any strange, just the behavor of the motor number 3 and 4, those are like to the limit (one to full TH, the other to min TH) over 8 meters of altitude. I was looking another HexaLogs and there is no that kind of behavor. Im thinking may be my friend put those 2 props in the wrong motor (motor 3 is CW and he use the CCW prop, the same with the motor number 4…). I think its posible to fly with those props changed in loiter. What do you think?

here is the log

I don’t think it was the wrong props, because the flight was normal at first.

These are the rate controller outputs, which are basically a measure of how hard the flight controller is trying to control the drone. In stable flight, they should be near 0. It looks pretty normal at first, except that yaw is at 20% instead of . This usually means that the drone’s motors are not aligned perfectly.

In the last third of the flight, the pilot issues a yaw command (you can see the rate spike at 34:08), but the drone loses control soon afterwards. It appears to have been a mechanical problem. Vibrations and IMU clipping go crazy right as this happens:

So I think something must have broken in flight or something was not secured properly. Maybe a motor mount or arm came loose.

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Wow Rick, nice deduction… Tomorrow I will have the drone in may hands and I will check if there are something lose.

Let you know!

Hey Rick, me again.

I have the drone, and beside the parts are broken because the hard landing, it seems to be there is no mechanical issues with the drone. Motors are good and running, arms supports are stady and firm, so no losen parts.

What I found was the user was using a foldable prop, and one of them was a little lose, here is a video


Do you think this could be the problem?


I’m not sure because I’ve never seen or experienced that before. However, it certainly seems like a possibility, because the propeller might “flap” as it spins. If you want to be sure, you can do a short flight with the bad prop (if you think it is safe), then do another flight after replacing the propeller to see if the vibrations improve.

Thanks Rick

I have try the prop on my bench test, and the table start to shake a lot! I think that was the problem. I really dont want to fly it with that lose prop.

Hi Rick, how are you? Hope you are doing well!

I had another problem, dificult to deduct whats going on… Cheking the log, the only strange I can see is this battery behavor, seems to be a kind of shortcut for a little time, then the drone start to fall, but not faster, start to decend fast, but not like a rock.

About the short, if the FC didnt reset or power off, I think the short was made on the ESC circuit or someting outside the BECs (12 and 5V), em i right?

here is the complete log, can you pls chek it and give me your comments? thanks!


And if another one wants to help me will be appreciate it