Holy S... moment.

[Davowalshy]

Was out flying a GS mission over the water today and had that horrible sinking feeling that my Phantom was also on it's way to doing some sinking as well. I had 100% battery before the flight but have had a few problems with this battery lately. I noticed previously the percentage started dropping really quickly when it hit about 50%. It was only a 3 minute mission so I thought it would be ok. It was about 400m out over the ocean and on it's way back home when the battery power just plummeted and it started to auto land. ****..... At this moment all I could think about was how much I would miss flying until I could afford another quad and was instantly heartbroken.
I noticed on the FPV that the bird was on its way down and seemed to be moving further away. I switched down to RTH and it obviously thought it didn't have the power to get home so still kept descending. I went to Atti mode and punched the altitude and hit full speed back to land while guiding it back through FPV.
Litchi was telling me there was 7% left as It screamed back into sight and I left it to auto land. I checked the battery just then on the assistant though and said it had a 65% charge.
I don't get it. This battery has only had 45 cycles, has 85% life left, has been fully discharged to reset twice, no bloating and all three cell levels are almost the same(middle one out about 20).
My other battery has been cycled more than this one and is way more stable.
What is going on guys?

 

[WetDog]

1. Flying over water with a battery that you 'have had a few problems lately' seems, well, a tad optimistic.
2. When you say the battery was '100%' was that just off the charger, or did it have 4 bars (which really means something greater than 80%)?
3. Was the battery charged up several days before flight? Could it have been in self discharge mode?

There have been a number of threads that center around the battery losing charge or not showing the true charge with predictable results.

Flight logs?

 

[Davowalshy]

1. Flying over water with a battery that you 'have had a few problems lately' seems, well, a tad optimistic.
2. When you say the battery was '100%' was that just off the charger, or did it have 4 bars (which really means something greater than 80%)?
3. Was the battery charged up several days before flight? Could it have been in self discharge mode?

There have been a number of threads that center around the battery losing charge or not showing the true charge with predictable results.

Flight logs?

Thanks for the reply
1. Yeah..you are right. Not real smart. I flew a POI with a large radius a few days ago and the discharge wasn't as dramatic.
2&3 The battery had been fully charged only about 3 days prior so I don't think it was in discharge mode. The Litchi app said it was at 97% at take off.

Tried to post the flight log but it won't upload. Not sure how to do that.

 

[yorlik]

1) I had 100% battery before the flight but have had a few problems with this battery lately. I noticed previously the percentage started dropping really quickly when it hit about 50%.

2) Litchi was telling me there was 7% left as It screamed back into sight and I left it to auto land.

3) I checked the battery just then on the assistant though and said it had a 65% charge.

Glad you saved it! Yours is a very unique situation that has never been reported by anyone else yet in the history of the phantom! Sure will be interesting to get more data to try to figure this one out!

1) 100%. In past had quick drop from 50%. So far this is normal and has happened to many!
2) Again, when the sudden drop in % charge left happens, it often drops from 60 or 50 or 40 or 30 or 20% down to 3-4-5-6-7-8% in about 5 seconds - again normal that has happened to many!
3) THIS is unique! Studying the sudden drop off issue in detail and doing lots of testing on it, and actually identifying the issue, NEVER have I seen anyone report the dropped off % charge GOING BACK UP AFTER THE FLIGHT without charging the battery! WOW!

Please give some more details on #3. It sounds like you took a computer with you and as soon as it landed you plugged into the assistant program to look t battery data? And it showed 65% charge left? Did you write this down? Did you also write down all the other data (mah left, mah capacity, cell1,2,3 voltage, output voltage?

I am intrigued with the instant 'recharge' from 7% to 65%.

 

[Davowalshy]

Hi yorlik
In reply to number three question.
If i could send you a video of the flight and the logs as it might explain it a bit better.
Im not really sure how to do this so I will go into a bit more detail as to what happened.

The Litchi app shows the time you have on the mission and the battery left obviously before the flight.

On the way back from a GS mission it just suddenly stopped over the ocean. I was watching the GS screen with the red arrow and it just stalled.

I was expecting it to finish its mission to come back and it just started to auto land in the ocean.

I saw the auto land message on the screen and also saw the battery limit on the screen plumetting at the same time.

I switched for it to come back home but it thought it was low on battery so it kept descending.

Went to Atti mode and bought it back through FPV and landed it with just 7% battery on the Litchi app showing while scaring my girlfriend on how fast it came back. It landed close to her.

I got home about half an hour later to check on the assistant if the battery was on the way out and dying.

It showed 57%.

App problem or battery problem? I dont know. But my other battery is solid as a rock so far.

Wont be using that battery again except for checking assistant.

What do you think?

 

[Davowalshy]

Im only a novice on how to intepret flight logs.

 

[Davowalshy]

It seems that the only flight videos here are on youtube only as well

 

[yorlik]

when I click on reply or type into the little reply box at the bottom of the page, being logged in of course, there are 3 buttons to choose from on bottom right: POST-REPLY, UPLOAD-A-FILE, AND MORE-OPTIONS....

if I click on UPLOAD-A-FILE, window opens letting me pick a file to upload. I just picked one as example here...

I think you should be able to so same on your computer?

 

[yorlik]

So you REALLY are saying flight app showed drop from 60 to 7% and autoland started as expected with 7%, then an hour and half later assistant showed 57%. WOW. this is a first... since the smart battery counts down % charge based on actual mah removed during use, there should be no way it should ever show anything but 7% an hour and half later....

The sudden % charge drop while flying is not uncommon, and it IS a known battery issue. what appears to happen is the smart battery firmware has a programming bug: mah is calculated VERY accurately, but in time, after use, it does drift off. So dji has this scheme where they tell us to discharge to 8% every so often. A recalibrate routine then runs. How it works is the mah & % charge count go down and down - until it appears a certain low voltage is hit - this low voltage around 8% turns on a software subroutine in the smart battery that then STOPS counting down the mah until another trigger point (I believe another lower yet voltage), and then it continues to count down to 0... You recharge and it counts the mah put back in and all is again calibrated. The problem is this subroutine runs DURING FLIGHT IF YOU RUN YOUR BATTERY TOO LOW AND HIT THIS LOW CELL VOLTAGE TRIGGER. Result is %charge number almost immediately goes down from 60-50-40-30-20% whatever it was just before the trigger to 8% to recalibrate. The error in their software is they need to NOT go to this subroutine if motors are running! Until they fix this coding error, we all have the chance to get an autoland wherever if we fly too low in %charge.

So I do not see how YOUR battery popped back up to 50 or 65% after going into this routine without a recharge. Unique issue!

 

[Davowalshy]

So you REALLY are saying flight app showed drop from 60 to 7% and autoland started as expected with 7%, then an hour and half later assistant showed 57%. WOW. this is a first... since the smart battery counts down % charge based on actual mah removed during use, there should be no way it should ever show anything but 7% an hour and half later....

The sudden % charge drop while flying is not uncommon, and it IS a known battery issue. what appears to happen is the smart battery firmware has a programming bug: mah is calculated VERY accurately, but in time, after use, it does drift off. So dji has this scheme where they tell us to discharge to 8% every so often. A recalibrate routine then runs. How it works is the mah & % charge count go down and down - until it appears a certain low voltage is hit - this low voltage around 8% turns on a software subroutine in the smart battery that then STOPS counting down the mah until another trigger point (I believe another lower yet voltage), and then it continues to count down to 0... You recharge and it counts the mah put back in and all is again calibrated. The problem is this subroutine runs DURING FLIGHT IF YOU RUN YOUR BATTERY TOO LOW AND HIT THIS LOW CELL VOLTAGE TRIGGER. Result is %charge number almost immediately goes down from 60-50-40-30-20% whatever it was just before the trigger to 8% to recalibrate. The error in their software is they need to NOT go to this subroutine if motors are running! Until they fix this coding error, we all have the chance to get an autoland wherever if we fly too low in %charge.

So I do not see how YOUR battery popped back up to 50 or 65% after going into this routine without a recharge. Unique issue!

Hi again
I tried to upload the video and the flight log but because the video is an MP4 and the log is an excel file they won't upload.
If you know how to get around this I can send.

 

[yorlik]

I onlly received the cs file via email. Reason it will not upload with that upload button is it is .csv (and prob .mp4) are not allowed via it.

So it needs to be uploaded to some server to hold it that gives a link for others to download it - like dropbox.com or box.com.

I stuck it on my box.com and here is link for anyone to get it:

Box | Simple Online Collaboration: Online File Storage, FTP Replacement, Team Workspaces

Boy you sure boggied home fast! 42mph all the way! Cool! 4.6min flight per the log... loaded your csv into free plotter:

Quick look seems the battery % charge went down linearly with time and batt output voltage... like a bad battery with little capacity left... can you copy a screen shot of your assistant and post it ( if you copy to clipboard, then come to a post here and hit paste, it will come in just like my pix above).

 

[yorlik]

interesting plots of your data:

S your batt was fine and went from 100% down to 82% (battery @ 11.033v) in 2.7 min

Then dropped to the MAGIC 8% level (battery @ 10.780v) in the typical quick drop off - in your case 22 seconds!

Once it hit the magic 8%, it was recalibrated, and thus started counting down normally again down to end of flight at 5% in your remaining flight time when you turned it off.

SO, this is yet another example of the dji smart battery firmware code error. As most other sudden charge drop offs, you flew fine for almost 3 minutes, then in 22 sec the % charge dropped to cause autoland.

Why?

Firmware code error: dji appears to start a recalibrate routine ANY TIME BATT VOLT REACHES 11.03v. REGARDLESS OF IN FLIGHT OR NOT. THAT IS THE ERROR IN THEIR CODE!!!!!!!!!!!!

THEY NEED TO **NOT** RUN THE RECALIBRATE ROUTINE IF MOTORS ARE RUNNING BUT INSTEAD ISSUE AN EMERGENCY ALERT TO LAND NOW AND then not allow that battery to fly again until a recalibrate is run - OFF LINE.

Yours is the highest % charge I have seen yet that went into the recalibrate routine! 80%. Wow.

If I plotted better, I would have put the voltage on the other side of the chart so it was full scale too; then it could be seen that the voltage did NOT droop the equivalent amoutn during this re-calibrate: I could not delete the first chart but added the other above it showing the battery voltage. Realize the knee of the curve on our lipo batteries is about 3.3v, so when the batt voltage goes below 3.3*3=10v, THEN it will REALLY drop and drop fast. Until then, it is capable of outputing the same power for the same time. So this sudden recalibrate is bullsh1t during flight - you would have had plenty of time to bring it back if an emergency message flashed instead of autoland. Interpolating your voltage curve out to the right at the same drop angle, it would have flown another 3 minutes or so before you hit that point.

I still have no clue why later it showed 65% left; seems somehow the recalibrate info shown above was thrown out or something. Never heard of that one.

Glad you got it back before the autoland in the water - you must have nerves of steel to see it begin autoland way out there over the water and have the wherewithal to calmly switch to ATTI and bring it back!!!!!!



.

 

[yorlik]

In case you crash due to this battery, arm yourself with the info on this thread:

DJI Forum|The head-scratcher's battery tests and thoughts.

It seems dji has finally maybe taken their heads out of the sand and looked at my data.

Reward dji? $ 50,000.00 will do.... Send express so I get it before Christmas.

 

[Davowalshy]

In case you crash due to this battery, arm yourself with the info on this thread:

DJI Forum|The head-scratcher's battery tests and thoughts.

It seems dji has finally maybe taken their heads out of the sand and looked at my data.

Reward dji? $ 50,000.00 will do.... Send express so I get it before Christmas.

Hi again

Here's a screenshot of the battery. I sent a copy of the video via Google Drive. It took a while to upload it.
Wow what an amazing analysis. If I do dare to use that battery again I will do a screen record of the Litchi app while flying and keeping the quad low and close.
Well I don't know about "nerves of steel" and "calmly". There were a few colourful expletives being thrown around at that stage. I went through a second of total dismay into a "what can I do about this?" mode. Luckily I use the FPV in a lot in my flights to navigate and return home so I guess that practice paid off.
So that poses the question.
Is my battery destined for the bin or can I save it?