Lost Control at 44' and Crashed

[gregklau]

I was flying my drone a couple of days ago when the program alerted me that my battery was getting low. I started bringing the bird back and was dropping it's altitude when I suddenly had no control and the bird started falling from about 44' altitude and was jerking side to side. It landed on it's top. I flew it once more afterwards and confirmed that everything was OK. Thankfully no damage. I was getting Strong Interference Detected warnings, but I've always flown it with those warnings at home without this happening. When I flew it after the accident to see if it was OK, I had absolutely no Strong Interference warnings. I've uploaded the log and was wondering if anyone can tell me what happened.

https://www.phantomhelp.com/LogViewer/PVKFMOS1K6D5KDCS631K/#


Thanks for any help - I'd like to get to the bottom of this before I take another extended flight.

 

[RodPad]

Welcome to the Forum!

Does this log look like your flight?

At the very end it shows your under 2' but 140' away and at 28% battery.

Is your battery low warning set at 30%?

Rod

 

[gregklau]

Welcome to the Forum!

Does this log look like your flight?

At the very end it shows your under 2' but 140' away and at 28% battery.

Is your battery low warning set at 30%?

Rod

Yes, the log I posted looks like my flight. It was just around my home with my max altitude set to 80m and max distance set to 90m. The low battery warning is set at 30%. It fell from about 40 feet and ended up upside down, maybe why the last posting only shows 1.3 feet?

 

[RodPad]

15m 49 secs :39.4'
15m 44 secs : 2.3'

Yeah I guess so
37' drop in 5 secs.

Must have knocked the battery out?

You should still had control until critical battery.

There is no battery warning in the log.

If you play back your flight on your mobile do you have a battery warning?

See if somebody else chimes in, something is missing.

Rod

 

[gregklau]

15m 49 secs :39.4'
15m 44 secs : 2.3'

Yeah I guess so
37' drop in 5 secs.

Must have knocked the battery out?

You should still had control until critical battery.

There is no battery warning in the log.

If you play back your flight on your mobile do you have a battery warning?

See if somebody else chimes in, something is missing.

Rod

No critical warning. Was dropping altitude and returning back because the battery was at 30%.

 

[sar104]

This actually looks like VRS, which is unusual on a P3. If you look at the graph below, from 915 s to 935 s it was descending under close to full down throttle. At 935 s the throttle was centered but the descent rate increased and significant pitch and roll oscillations began that are consistent with VRS. Battery voltage was within spec for flight at that time.

The DAT file would show what the FC was requesting and what the motors were delivering, and probably provide a more definitive explanation.

 

[gregklau]

This actually looks like VRS, which is unusual on a P3. If you look at the graph below, from 915 s to 935 s it was descending under close to full down throttle. At 935 s the throttle was centered but the descent rate increased and significant pitch and roll oscillations began that are consistent with VRS. Battery voltage was within spec for flight at that time.

The DAT file would show what the FC was requesting and what the motors were delivering, and probably provide a more definitive explanation.

View attachment 88219

Where would I get the DAT file? Is it in the program?

 

[sar104]

Where would I get the DAT file? Is it in the program?

It's on the aircraft.

How to retrieve a .DAT

 

[Just Mark]

QUESTION: How is it that the 107 certificate test didn't have anything on VRS? I never would have heard of it if I hadn't browsed into this thread.

 

[sar104]

QUESTION: How is it that the 107 certificate test didn't have anything on VRS? I never would have heard of it if I hadn't browsed into this thread.

It was common back with the P2 and earlier, before some design changes were made in motor angles and firmware limits were placed on descent speed. It seems very rare now on any platform.

 

[Just Mark]

It was common back with the P2 and earlier, before some design changes were made in motor angles and firmware limits were placed on descent speed. It seems very rare now on any platform.

Thank you! I am assuming that the automatic RTH functions will descend the craft slow enough that it SHOULD avoid VRS, right? Or is that just wishful thinking on my part?

 

[sar104]

Thank you! I am assuming that the automatic RTH functions will descend the craft slow enough that it SHOULD avoid VRS, right? Or is that just wishful thinking on my part?

That, plus divergent motor angles, has made it very rare. Even without using RTH, descent rate is limited to prevent its occurrence.

 

[Just Mark]

That, plus divergent motor angles, has made it very rare. Even without using RTH, descent rate is limited to prevent its occurrence.

Thanks for the reassurance.

 

[gregklau]

I have the DAT file, how do I go about uploading it? Getting an error on the DJI Flight Log Viewer page and won't upload.

 

[sar104]

I have the DAT file, how do I go about uploading it? Getting an error on the DJI Flight Log Viewer page and won't upload.

If you want to look at it yourself you will need to install and use DatCon from the link that I posted earlier since the online viewers such as PhantomHelp or AirData will not read DAT files. Alternatively, if you make it available via Dropbox (it's probably too large just to post on this site) then there are several of us who can take a look at it to see what happened.

 

[msinger]

@gregklau, were you flying with 3rd party props?

 

[gregklau]

@gregklau, were you flying with 3rd party props?

Yes, I had 3rd party props. Could this be the problem?

Here's a link to my DAT file

Dropbox - FLY087.DAT

Thanks

 

[msinger]

Yes, I had 3rd party props. Could this be the problem?

Yes. Make sure you only use OEM DJI props. VRS and/or erratic flight won't be an issue then.

 

[RodPad]

OMG

Search Results for Query: after market props | DJI Phantom Drone Forum

@msinger


Rod

 

[sar104]

Yes, I had 3rd party props. Could this be the problem?

Here's a link to my DAT file

Dropbox - FLY087.DAT

Thanks

Those data clearly show unstable oscillations that the FC was trying to correct. In the case of the P3S, which does not record motor speed, it's most easily visualized by comparing pitch and roll with motor command. Since the motor command typically precedes actual motor speed by about 0.15 seconds, I've shifted the motor command data to the right by that amount, so that it approximates motor speed.

The worst oscillations were on a front right / left back axis, and so the first graph shows the pitch and roll (positive backwards pitch and right roll) together with the difference between the front left motor and the right rear motor that were working hardest to correct the oscillations.

That's a little tricky to visualize, so the next graph shows pitch vs. front - back motor difference. Here it is clear that the FC is struggling to damp the oscillations that are out of phase with the motor corrections.

The same is visible looking at roll vs. left - right motor difference.

The fact that you were using non-DJI props complicates things, and I don't know a good way to distinguish instabilities due to the props from VRS. Perhaps someone else can suggest something.

Either way - it appears to me that it crashed due to increasingly unstable pitch and roll excursions rather than due to low battery since, as the graph below shows, the battery voltage and current held up just fine.