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S900 + A2 sudden fall
1619 7 2015-3-23
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dariodm
lvl.1

Italy
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Hi All!
Just two days ago my new S900 with A2 board had fallen suddenly during an autonomous flight with waypoints.
Luckily i've installed a cut-off system with parachute. They worked well and the s900 is almost safe (only a landing skid broken).
I'm investigating on the cause of this accident but i need your support.

The log shows a voltage drop. But why? Any suggestion?

The battery was a Kypom K6 series 16000 mAh, charged and balanced well. Outside temperature was 13° C.

And this is the log.



Thanks

D

main voltage log

main voltage log
2015-3-23
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fabien
lvl.2

France
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Hi, this can be either a main connector problem ( battery  connector), either a PMU problem.
I would suggest to check with care all the XT60 connectors and your battery connectors, including with slightly bending the frames, in case this would be a coper circuit broken or damaged ( very rade but can happen).
In your logs, is the BEC and Canbus voltage also at 0 ? Because one thing is a bit disturbing : how can the IOSD continue to log events if it is powered by main power and there is a voltage drop ? Normally you have this curve fall when you disconnect the battery and it stops recording almost instantly ?
If you have a copy of your logs, do not hesitate to send it to me with retransfer ( you can send the link via PM) and i will give  a look.
Best regards,
Fabien
2015-3-23
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dariodm
lvl.1

Italy
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fabien@e-copter Posted at 2015-3-24 07:44
Hi, this can be either a main connector problem ( battery  connector), either a PMU problem.
I woul ...

Hi Fabien,
thanks for your response.
I sent you the link to download my log via pm.
Bec and canbus are not at 0. Can voltage has a little drop (0,3 v) and canbus is quite normal till the end.
I've noticed that in other logs the disconnection of battery causes an immediate stop in recording the log so there is not the same curve drop.
Best regards

Darius
2015-3-24
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fabien
lvl.2

France
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Hi Darius,
thanks for the info, did you have the chance to check for what i suggested by email  ?
Best regards,
Fabien
2015-3-26
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dariodm
lvl.1

Italy
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Hi Fabien,
sorry for the long delay in the response.
I'm still investigating. I've disassembled the s900 totally and now i'm rebuilding it.
No issues found in cables or connections.
I'm waiting for a response from the cut-off producer.
I'll update this post if i find a solution. Thanks.

Darius
2015-4-18
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dylan
lvl.2
United States
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Certainly an argument for the parachute. Do you have the DJI version or third party? Obviously happy with that purchase!
2015-4-28
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dariodm
lvl.1

Italy
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dylan@dylangloc Posted at 2015-4-29 05:23
Certainly an argument for the parachute. Do you have the DJI version or third party? Obviously happy ...

I've a third party Cut-off system with an opale parachute.

and maybe i've solved the mistery!!!!

I totally disassembled the s900  and re-assembled it. 2 days ago i was doing some flight test and then when i tried the battery that was onboard during the fall i noticed that the A2 showed a 2 voltage alarm.
I use a voltage monitor to look at the value and it was 24,9v.
Then i connected the battery to a pro-charger and it showed an abnormal resistance of the battery. 300 mO instead a normal value between 8 and 16 mO.
The battery is a Kypom K6 series 16000 mAh. The battery was'nt damaged in the fall because it was a slow fall thanks to the parachute so i think the battery was failed before the damned flight.

Now i can't charge/discharge that battery. So i think that the fall of the s900 was caused by a battery failure.

The lesson: be aware of batteries!!!


2015-5-6
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fabien
lvl.2

France
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Hi,

ouch ! This is not the first time i see this with Kypom batteries unfortunately.
Also i notices since a few weeks that many customers using Tattu had batteries 16 000 and more capacity with very long balancing during the first charge, especially on 22 000, with pretty high unbalance with 2 or more cells. But after first charge at 0,25 C with slow balancing, and proper breaking in flights ( 6 or 7) all is perfect..

At least, you have a valid crash explanation, this is better than not know what happened. Definitely something to add in the " check list" items to check internal resistance before flights . Thank you very much for taking the time to post the informations
2015-5-6
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