Phantom 3 took a surprise swim. Looking for advice.

mostly_tacos · Jul 29, 2020

Relatively new pilot, here. Took my Phantom 3 Pro out on a family camping trip this weekend. Had several successful short flights. Thought I'd get one more in before we started breaking down camp, and ~12 seconds into the flight over the quiet lake, it fell from the sky. I did not hit CSC.

Flight log is here.

Thanks to the help of a kind stranger who offered to take me out on his rowboat, I was able to dive down and pull it out of ~12-14' of cold, clear water. I pulled the battery as soon as I got back in the boat.

After drying out, and with a fairly fresh battery, the drone status lights indicated it wasn't paired with a controller. I re-paired, and things seem pretty good, all things considered. It flew for a few moments, and I had a shaky, pixelated and color-shifted image from the camera. After a couple moments of hovering, it fell from the sky again. Nothing stands out in the flight log except for some significant cell deviation in the battery.

I inspected it, found condensation in the camera lens, which explains the image issues. I suspect I'll be able to dry it out with some desiccant. Regardless, I thought I'd try another short and low flight. It took off, hovered for a couple seconds, I could perform all maneuvering functions. I had no image, but that was to be expected given the condensation. I tested an RTH landing and it landed fine. Same regarding the flight log; no warnings or notes apart from being proximate to an unpaved airport and the RTH initiation.

I'm not inclined to post the two test flight logs because they're at my home, but if there's something I can look for, I'd love to.

Here are my questions:

Is this thing safe to fly at all?
If yes, and drying the camera out doesn't restore image tx, would replacing the camera do so? Is the image transmitted from elsewhere?
If it's not safe to fly, are there usable parts that would be worth reselling?

Any helpful advice is appreciated.

lannes · Jul 29, 2020

Fresh water can still cause corrosion because of the suspended contaminants in it.
If it had recently hit the water, I'd open up the drone and spray/ dunk it with distilled water. Then I'd brush and spray it all over with iso propyl alcohol (99% pure so there is no oily residue) and scrub with a tooth brush any visible signs of corrosion on the circuit boards and connectors. Then you need to let it dry for a couple of week with some desiccant in a container.

Given it's been a while, I'd stilll give it a scrub with alcohol when you replace the camera

Steve7777 · Jul 29, 2020

Hope you get it sorted out. Difficult to say whether the drone will recover completely - I would predict not without some possibly costly TLC, but only time will tell...

As regards the cause of the crash, you took off with a battery which wasn't fully charged and in that situation it's well known here that what is being indicated as percentage battery remaining is often not accurate. This is borne out by the respective voltages of all your cells at take-off and subsequently...

At 12 secs you were accelerating up and forwards and thus straining the battery quite hard, causing the cell voltages to dip even lower and, in effect, after being badly overstretched, all battery power shut down.

It's always tempting, when you see a little bit of power apparently left in the battery after a previous flight, to take off again just for a 'quick 30 second run'.

Of course, the best advice is 'Please don't!'....

Andy9 · Jul 29, 2020

How long did you dry the drone after took it out of the water ?
How old was the battery?
What did you do with that battery? Once the battery in the water it is mostly a garbage. I would never use it again.
And it is much more useful that you from time to time during the flight check the voltage the battery provides not just the percentage. Particular if you not take off with 100%.

mostly_tacos · Jul 29, 2020

lannes said:
Given it's been a while, I'd stilll give it a scrub with alcohol when you replace the camera

Thanks, good advice re: cleaning off. Does the camera and gimbal board handle transmission of images? What concerns me is that I was getting "image transmission strength low" and not good transmission strength and a distorted or black image.

@[B]Steve7777[/B] I likely underestimated how bad shape this battery was in. However, on my first flight after returning home, something similar happened with a different, >70% charged battery.

@Andy9 Good advice. Yes, that battery is trash.

REL · Jul 29, 2020

Sorry to see this happen to you. I've read investigations of many crashes and fly-aways while stuck at home these last 3 months. Again and again I see unexpected issues when a flight is attempted with a battery not fully charged. What it reminds us is no matter how safe it seems .....just NEVER take off with a partially charged battery ..... even on a short test flight. Doing so just opens up a pandora box of potential problems that would not otherwise come into play. The LiPos we are using on P3's are 3-4 years old now ..... so we need to plan accordingly (for their decline from new) if we continue to use them.
Again, not trying to be condescending to you..... just offering advice to others who might try to do the same thing .... and save them some grief.

mostly_tacos · Jul 29, 2020

@REL no hard feelings at all, quite the opposite. Thanks for your insight. Lesson learned, and I’m thankful that it ends with just a wet quad, a quick swim, and a good story.

Andy9 · Jul 30, 2020

Completely agree that taking off should be done with fully charged battery.
But - there is always 'but' - when I thrust the battery if it is relatively new and can fly with it to 30% over 20 min, it would be no risk, if I start again within the same day when this battery has over 70% energy left. Of course as I said, I'm checking the voltage during that flight but I make it to 30% or even less with no issues. And it is wise if that second flight is not very far away.
Important is that you are aware that the battery was not fully charged at second take off and act accordingly.

mostly_tacos · Jul 31, 2020

Good to know, and good advice, @Andy9. Thanks again.

Russ43Phantom · Aug 1, 2020

I have flown over water for over five years. Yesterday I had my first close call. Click BLUE Vimeo link:

mostly_tacos · Aug 1, 2020

That’s a somewhat scary video. Did you get any info about what happened from the flight log?

Russ43Phantom · Aug 1, 2020

I have never had a drone malfunction. In this case it was human error. The video was an opportunity to practice both horizontal and vertical sweeps with the camera. When I nearly when into the water, I was focused on rotating my lens up while lowering my drone to the lake surface. This had to be carefully synchronized so that the video subject, the two boys on the boas, remained centered vertically on the screen. That's two operations with the left hand. It took concentration, so I didn't notice I was nearly in the water until the last minute. Fortunately, my reflexes from many hours of flying helped me make a rapid and correct movement on the left control stick to rapidly climb.

Andy9 · Aug 1, 2020

Stunning video. Definitely the pilot error. As you said - doing something else with your left hand with your finger on the stick it needs only a minimal force to make the drone slowly descend without noticing it. Your attention was focused on the picture of those people in the water.
It happened many times to me as well. Drone became descending very slowly and luckily I saw it. Looking just onto the screen I probably noticed that too late. And exactly the same happened to you in your video. As we can see a Phantom can make nice underwater pictures or videos. Just not drown it completely - only the camera. LOL

Fly Dawg · Aug 2, 2020

Simply for the sake of stating the obvious, ~3V is the battery cell shutdown point. If you note in the graph below at ~13.9 seconds, Cell#1 was the last remaining cell above 3V. Once that cell dropped below the shutoff point the battery completely shutdown ~2 seconds later. That is the cause of the incident. This is why you should never takeoff on a less than fully charged battery. Not only the charge itself, but the process rebalances the cells.

mostly_tacos · Aug 2, 2020

@Fly Dawg That’s fantastic info. Do you happen to know the shutdown point for Mavics Mini, as well?

Andy9 · Aug 3, 2020

Interesting graph but drones do not fly out of the water if the battery is shut down! Even if voltage was really low it must had the power to do that.

Oso · Aug 3, 2020

Andy9 said:
Interesting graph but drones do not fly out of the water if the battery is shut down! Even if voltage was really low it must had the power to do that.

It seems to me that @Fly Dawg graphed data from the flight log in post 1 from the owner of the drone which sank. He retrieved it by diving down ~12-14 feet and not by flying it out of the water.

Julez · Aug 7, 2020

Does anyone know why DJI allows batteries to shut down while still in the air- I can see the battery protection requirement, but from a safety point of view wouldn't it be better to allow the battery to give its last few volts if the drone is above a set height ( a couple of feet?) to prevent a crash.

mostly_tacos · Aug 7, 2020

I believe that's the behavior if you have balanced cells. In my case (Hi! I'm OP with the unintentional submarine!) my cells weren't balanced, and I took off at ~30%, so the inbuilt intelligence to prevent this event didn't have a change to kick in before the remaining cell above 3v dropped below 3v.

And I think 3v is required to keep the blades spinning. Not an intelligence shut off, but a "lack of energy makes circuitboards go dark" kind of thing. To put it in MMA terms, the drone didn't submit, it was KO'd.

Steve7777 · Aug 7, 2020

mostly_tacos said:
I believe that's the behavior if you have balanced cells. In my case (Hi! I'm OP with the unintentional submarine!) my cells weren't balanced, and I took off at ~30%, so the inbuilt intelligence to prevent this event didn't have a change to kick in before the remaining cell above 3v dropped below 3v.

And I think 3v is required to keep the blades spinning. Not an intelligence shut off, but a "lack of energy makes circuitboards go dark" kind of thing. To put it in MMA terms, the drone didn't submit, it was KO'd.

Your cells were probably balanced - (you can see that there was very little displayed voltage deviation between cells during the flight), but the lack of recent charge to 100% and the incorrect displayed overall percentage of charge gave you an 'inappropriate feeling of drone battery well-being', if I can put it that way...

If a lipo battery goes much below 3v on one or more cells, then it's most likely (but not always) a write-off thereafter. I've recovered some 'normal' lipos that have suffered that way, but I've lost a few as well... Below 3v there is not much useful and usable power left.