2 crashes in a morning,Pix shut off 80% power while AltHold

Log Analysis -- deprecated Copter Logs -- deprecated
1

Hello all,
[color=#FF0000][size=150]Sorry for my English, I’m Chinese.[/size][/color]

Pixhawk autopilot running AC 3.2.
550 frame
2216-800KV
20 amp esc
Futaba t8fg
Futaba 6303 Receiver
3DR GPS
Power module
3s 5300mah battery
1147 Propellers

I recently had 2 crashes in a morning. 2 crashes are same issues.
[color=#FF0000]The second crash:
[/color]I pushed Throttle stick slowly up to taking off and switch to AltHold mode. I was flying about 5 meters in front of me and about 30 meters high in AltHold mode. During the flight the copter was flying fine for the first two minutes, but then started losing altitude and sudden falling, I immediately increased the throttle stick position to full (and hold it in that position almost till the end). No reaction at all. I noticed that it didn’t listen to the Throttle stick and did not respond to throttle increase resulting in an ugly crash, fell down horizontal from about 30 meters…
Because crash was horizontal, the Gopro3+, gimbal was a total wreck. Frame, motors, propellers remained intact without damage. Suddenly the copter was skimming the ground with full throttle automatically bashed against the garden railing more than a dozen meters away. (at this time the transmitter’s throttle stick keep bottom)

[attachment=0]secondcrash_resize.jpg[/attachment]

[color=#FF0000]The first crash [/color]was same issue, the Pix shut off the power during AutoTune, and Fortunately there was no damage in the first crash.

I first thought of a battery issue but there appear to be plenty of juice left in the battery after crash. The problem still occurs when using a different battery after first crash.

You can see in the log that ThrottleOut was going down, while ThrottleOut kept on the top.

Here is video from the Gopro3+, log file and a graph are attached to the post, I cannot access YouTube in China, so I upload the video to Youku.
http://v.youku.com/v_show/id_XODcwNzAzMTA0.html

[attachment=1]SecondCrash.rar[/attachment]

PS:
The year of Gopro3+ set wrong, it should be 2015, not 2014
Log bitmask: Default+IMU

Could you please take a look on what I wrote here and help me, if you see the reason of the issue? I’m really scared now to have any flight, until I’m 100% sure that the issue is resolved.

Looking forward to your assistance. Thanks in advance!

2

I’m not sure you can watch the video outside of China

3

It might be a voltage or power problem. At line 30271 it looks like your voltage drops to 9.97v and that is the same time things start to go wrong. I’m not sure if that is an cause but it is something I noticed.

4

battery does look pretty low…lower than i’d like. Voltage dips pretty quick too.

Was the battery properly charged? If you are charging at less than 1C, are you sure your charger is not terminating on a cpacity limit rather than till its actually fully charged?

I have to restart my charger for my bigger batteries as my PSU doesn;t not allow 1C charging.

5

Let me thank you for taking the time to look this over as well as giving me advice. But I think the battery here is not a fact of the crash, during the whole flight there is no brownout or power interruption. The battery is an ‘old battery’, the internal resistance gets higher than a new one, so the voltage during flight is lower.Although voltage drops to 9.97v, according to the factory datasheet, even at 7.4v each motor can generate 510g thrust, sum of four motors are 510*4=2040g, My copter weight is just 1560g. At that time I push full throttle stick.
[attachment=0]Clip.jpg[/attachment]

The first crash with the same issue, the Pix shut off the power during AutoTune. The two crashes at that morning used different battery, The first crash at the falling time the voltage is 10.45v.
[attachment=1]firstcrash_resize.jpg[/attachment]

[size=150][color=#FF0000]The first crash log is here[/color][/size]
[attachment=2]Firstcrash.rar[/attachment]

For the test I discharger this battery with 20a current 8 minute can draw more than 3500 mah. Then measure the open circuit voltage is about 3.72/cell, each cell has good balance.
I had also tested many times in stabilize mode with same battery it worked perfectly.
I also changed the Flight controller to ‘Dji naza lite’ everything is doing what it should and functional.

What is strange is that in all the cases why the Pixhawk make ThrottleOut going down, while ThrottleIn kept on the top?

6

[quote=“RabbitStu”]battery does look pretty low…lower than i’d like. Voltage dips pretty quick too.

Was the battery properly charged? If you are charging at less than 1C, are you sure your charger is not terminating on a cpacity limit rather than till its actually fully charged?

I have to restart my charger for my bigger batteries as my PSU doesn;t not allow 1C charging.[/quote]

Thank you for the reply, I’m sure the battery is being charged properly with a balance charger within 1c current. The charger has not capacity limit, by the end of charge total voltage is 12.6v each cell is 4.2v, each cell has good balance. The battery is an ‘old battery’, the internal resistance gets higher than a new one, so the voltage during flight is lower. There appear to be plenty of juice left in the battery after crash. The problem still occurs when using a better different battery in the first crash.

7

Crash is very similar to this bug
[attachment=0]111850j9gxblxx31tx9tl9.jpg[/attachment]

8

[youtube]http://youtu.be/XXTHElKVnUE[/youtube]

9

[color=#FF0000][size=150]youtube video:
PS:
The year of Gopro3+ set wrong, it should be 2015, not 2014
[/size][/color]

[youtube]https://www.youtube.com/watch?v=XXTHElKVnUE[/youtube]

10

Looking forward to your assistance. Thanks in advance!

11

Nobody?

12

watching your video I don’t think its that bug you posted as its still trying to self level, if it thought it had landed I would think it would have shut the motors off all together anf fall like a stone.

If you had rcout logs it might pin point the issue more.

I still think its a battery issue. 10V is just too low under load in my opinion. it must be really hot after use if it is high resistance as you say.