Power cut to props during flight

[JohnChap]

Today I was doing my weekly flying session and on returning thought I would use up some of the remaining battery by taking some pics near me, then when it dropped to 12% brought it in to almost land but paused while my wife took some photos of it hovering near me. Anyway she takes a few pics, and suddenly the props stop and it drops a metre (3 ft) to the hard ground. I wasn't doing anything with the controls the battery power was at 10% when it happened. What made it stop as if it thought it had landed?? Could it happen again at a higher altitude?

 

[Starz]

What aircraft? Flight logs are probably the answer.

 

[new2mavic]

You may follow this thread to share the .TXT and .DAT flight log data : Flight log retrieval and analysis guide

 

[JohnChap]

What aircraft? Flight logs are probably the answer.

How remiss of me. A mavic pro platinum.

 

[Aragorn3]

My following comment may or may not apply, but it may help someone.

I don't know the age of this battery or how many recharge cycles its undergone or how often it just sets on a shelf, but in general as a lithium battery ages it offers diminishing time for operation. Further it becomes less reliable at reporting when it is about to die during your operation. An older battery or one approaching end of life may show 15 percent, when it is actually about to drop out.

On a side note: Very cold temperatures will also affect your battery's performance even on a battery that's not that old.

Knowing this about how lithium batteries age, some try to re-calibrate their batteries through thorough discharging and recharging, but "in general" it means it's time for a replacement. One failing cell is all it takes and this can even occur on a new battery as well, but then it was likely defective at the start. If your battery fits what I've described due to age, just know that for now you should land your craft when the battery is at 25% and get a new one soon.

 

[JohnChap]

Here are the DAT file and TXT files. Any interpretation help would be greatly appreciated.
I have used the batteries a lot. I have three which I use in turn. It will be a really worry if the reported % left is not the actual one. I'm usually flying over water! :-/

 

[Deleted member 94047]

The two logs do not mach; the corresponding DAT file to the txt log is FLY142.DAT.

DAT is from a flight on 2020-1-19 (10:34 GMT) whereas the txt log is from a flight on 2020-1-18 (15:12)

Having said that, if the DAT file is the correct one for the flight with the incident, there appears to have been a battery error at the end.

 

[JohnChap]

The two logs do not mach; the corresponding DAT file to the txt log is FLY142.DAT.

DAT is from a flight on 2020-1-19 (10:34 GMT) whereas the txt log is from a flight on 2020-1-18 (15:12)

Having said that, if the DAT file is the correct one for the flight with the incident, there appears to have been a battery error at the end.

Thanks and sorry for the wrong TXT file. But I think you have identified the issue - a battery error, which begs the question what the error could be given it was just hovering merrily at the time.
I have had a look at the underneath of the battery and it has a slight swelling at the front area of the flat area. Perhaps that is an indicator of decay?

 

[Deleted member 94047]

Thanks and sorry for the wrong TXT file. But I think you have identified the issue - a battery error, which begs the question what the error could be given it was just hovering merrily at the time.

One of the battery cells collapsing for example. I couldn't find the battery cell voltage readings in the DAT file (which is odd). Upload the correct txt and DAT files for the flight and it wouldn't be hard to find out.

 

[JohnChap]

One of the battery cells collapsing for example. I couldn't find the battery cell voltage readings in the DAT file (which is odd). Upload the correct txt and DAT files for the flight and it wouldn't be hard to find out.

 

[new2mavic]

One of the three cells had the voltage dropped gradually to a super low level before a total black out occurred. The power to everything was cut so instantly that the stopping of the motors could not be recorded in the .DAT file.

 

[JohnChap]

Thanks so much for that analysis. I will dispose of that battery and request a new one for my birthday coming shortly!
How can I perform that analysis, so I can do so from time to time as a battery health check. With Excel I only see gobbledy gook.

 

[Deleted member 94047]

@JohnChap, @new2mavic is spot on with the above post; it was one of the battery cells going flat out that led to the AC dropping like a stone. You were lucky it was near and low, imagine if this had occurred with the AC a mile out and 400ft up. If I were you, I would keep a closer eye on this particular battery in the future and wouldn't trust it fully until I have done a few more flights with it in a safe environment. Also, @msinger has an excellent thread (linked below) about how to monitor battery voltage - you will greatly benefit from reading it.

HOW TO: Monitor battery voltage to watch for signs of failure

It's important to monitor the battery voltage in each cell of the DJI smart battery. Be aware of the following: 1) Monitor the battery to ensure all cells maintain a similar voltage. 2) Do not allow any of the battery cells to drop below 3.3V. 3) Consider landing your Mavic when (or before) the...

mavicpilots.com

 

[JohnChap]

Many thanks for that link Doppler. I have now amended the display to show the voltage. One would think the software would issue a warning if the voltage dropped to a critical level.

 

[Deleted member 94047]

One would think the software would issue a warning if the voltage dropped to a critical level.

I uploaded your txt log to AirData to see if there were any such warnings, and it appears that GO4 did warn you twice about the issue (see below). I think you may have missed them, it is easy to do so. The first warning happened a full minute before the AC crashed at 18m 20.9s; if you had caught it, you would have had enough time to land the AC considering it was only 21m high and 65m away at the time.

 

[JohnChap]

Oh yes. And indeed I hadn't noticed it, as the drone was close to me and I was flying it visually without looking at my screen. I will have to be more attentive in future. Thanks for the info.

 

[slup]

Oh yes. And indeed I hadn't noticed it. I will have to be more attentive in future. Thanks for the info.

@JohnChap ...Even more important is to monitor the battery degradation over time & multiple flights ... this to take it off duty well before you have a disastrous voltage drop in mid air. I recommend that you sign up for a free account on AirData.com ... there you can study the batteries & the trends spanning over all the flight logs you have stored there. The upload of logs to AirData is automated with the only action from you to sync the flight logs in the GO4 app to DJI servers after each flight.

This is from one of my worst batteries, graphs compiled from hundreds of flights ... have it under observation & don't use it in colder weather.





Battery status from one of the flights that generated the last purple bar in the end above (major deviation)



If we look at your flight were one battery cell died in the similar way as above from my battery ...

 

[JohnChap]

@JohnChap ...Even more important is to monitor the battery degradation over time & multiple flights ... this to take it off duty well before you have a disastrous voltage drop in mid air. I recommend that you sign up for a free account on AirData.com ... there you can study the batteries & the trends spanning over all the flight logs you have stored there. The upload of logs to AirData is automated with the only action from you to sync the flight logs in the GO4 app to DJI servers after each flight.

This is from one of my worst batteries, graphs compiled from hundreds of flights ... have it under observation & don't use it in colder weather.

View attachment 91679

View attachment 91680

Battery status from one of the flights that generated the last purple bar in the end above (major deviation)

View attachment 91681

If we look at your flight were one battery cell died in the similar way as above from my battery ...

View attachment 91682

Thanks, I have signed up to AirData. My slight problem is that I have three batteries which I cycle through the drone during each flying session, so trends might be a bit difficult to establish. Anyway, thanks very much for showing me the capability of AirData.

 

[slup]

Have four batteries myself ... but my mistake not thinking of that battery management comes with a paid subscription, have below compiled those extras coming in from their "Gold" alternative that make it worth the cost ... a bit like an insurance.