Drone lost - need help

[Jackcutrone]

I really hoped I would never have to post here. I flew my Mavic Pro today. Everything seemed fine as I took off. I had 13 satellites. The wind was not strong. I was using a trackimo device just in case. Well, in case happened and I cannot find it with the trackimo but that is a story for another time. I flew about 2200 feet. The signal was strong. By that time I had 16 satellites. After about 4 minutes, I got a warning of a weak signal on the DJI app. I stopped control inputs thinking it was a momentary blip. The signal did not come back and instead I got a disconnect on the DJI app. Usually when that happens it is because of me knocking the plug out of my ipad. This time, however, the DJI controller also showed disconnected and that it was trying to reconnect. I waited around but it never reconnected. I waited longer still trying to reconnect which it never did. I hung around for a about ten minutes waiting for the drone to return home, which I what I think it is supposed to do if it loses signal from the RC. However it never came back. I was flying over a forest preserve and could see on the trackimo app where it had stopped moving and therefore where it should be. I tried to find it using trackimo on my iPhone but the closer I got to the trackimo location which was 42.454442, -88.022637 I noted that while trackimo was showing the drone's location, the location it showed for me was not accurate. Therefore I could not use it to get close. SO all I have to show for it is scratches all over my legs from the brush and wet shoes from wading through a creek. So anyway, long story, but can anyone tell me what happened?
I uploaded the flight log - is it at: DJI Flight Log Viewer - PhantomHelp.com.

I saw a similar thread and the replies indicated that a likely scenario was that the battery came out. I know the battery solidly clicked in before the flight and sine the last transmission from the drone showing the weak signal also showed strong batteries so I don’t think it came out. If the battery was loose I would assume it would be an abrupt signal loss entirely and I wouldn’t have gotten the weak signal warning.

Any help would be greatly appreciated and if I made some bonehead error, feel free to tell me that.

 

[Simmo]

@sar104

 

[razoraerial]

@sar104

Lol. True dat.

 

[sar104]

Unfortunately that looks like a sudden shutdown or loss of power. The link ends after an abrupt centering of the elevator, from full forwards to stop. That maneuver has caused batteries to disconnect on many occasions, so that's perhaps the most likely possibility.



If that happened, then the resulting descent trajectory can be estimated given the last recorded position and velocity together with the computed wind field:





Did you look in the trees?

The Trackimo location doesn't look far off to me:

 

[Jackcutrone]

SArR. Thanks for the help. But I didn’t Center the sticks until after I got the weak signal warning. And I fly rc planes and heli’s and almost never move sticks abruptly. But I must have if that's what the data shows.

Am going back out to look again tomorrow and if I find it will let you know if I knocked the battery out. Thanks again

 

[Meta4]

I tried to find it using trackimo on my iPhone but the closer I got to the trackimo location which was 42.454442, -88.022637
I noted that while trackimo was showing the drone's location, the location it showed for me was not accurate.
Therefore I could not use it to get close. SO all I have to show for it is scratches all over my legs from the brush and wet shoes from wading through a creek.

If you were under tree cover, it's likely that the phone GPS is not getting a good signal from enough satellites for accuracy.
Depending on how dense the canopy is, you might have better results with a good Garmin handheld GPS unit.

 

[Jackcutrone]

SAR104 and Meta4 -

The GPS issue is only part of what puzzles me about this. When I first went into the underbrush using my iPhone 7 to pull up the Trackimo app, that's when it was not showing me the correct location for where I was with the phone. And it was only underbrush, there was no tree canopy. So there shouldn't have been anything to interfere with its determining my actual location. I did know where the last signal from Trackimo was so I had a pretty good idea of the area where the drone would be but it was weird. The Trackimo app would show where I was approximately but when I moved in one direction, the dot showing my location wouldn't move with me. It would move but in a variety of directions. Thus, as I tried to get through the underbrush, it was really taking me in a circle around the last signal location for the Trackimo device. Which is another story and makes me think the drone did indeed crash at some point because I am no longer getting signals for it on the Trackimo app.

I went out again thinking I had the problem solved. I took my iPad out and opened Google maps and typed in the latitude and longitude of the last Trackimo signal and then asked for directions from where I was to the trackimo. But when I looked at the screen on the iPad, it had my location about 250 away from where I really was. And even after I started walking a trail toward the drone, Google maps didn't move the supposed location of the iPad. I was using a Verizon device as a mobile hotspot.

Then I thought it probably didn't have the GPS chip that the iPhone has so if I switched to the GPS enabled iPhone, it should show my real location. Well, so I thought, When I started using my iPhone as the personal hotspot for the iPad, it still showed the location as it had when I was using the mobile hot spot. At the start, it was about 250 feet east of where I was and as I walked the trail, that dot did not move on the iPad screen no matter how far I got away from that location. It's weird, the spot shows accurately on the iPhone but it is not accurate on the iPad which should be getting location information from the iPhone. TheiPad is an iPad 4 that is only a few months old. I am absolutely flummoxed.

I thought technology would take me right to the last broadcast location for the drone but it isn't working that way. I will go out again tomorrow. The brush is really bad and it makes it hard to get to the spot where the drone probably went into the trees. And it is hard just trying by looking at the trees and trying to relate that to what shows in Trackimo or on Google maps as the location of the drone. Things look a lot different from the ground looking up at the trees instead of being over the trees as shown in Google maps.

I may try to get a friend with a commercial drone to fly to the spot indicated by trackimo and then just home in on his drone, but that would be for another day.

Anyway, I am long-winded. Let me know if you have any thoughts.

Thanks,
Jack

 

[Meta4]

The GPS issue is only part of what puzzles me about this. When I first went into the underbrush using my iPhone 7 to pull up the Trackimo app, that's when it was not showing me the correct location for where I was with the phone. And it was only underbrush, there was no tree canopy. So there shouldn't have been anything to interfere with its determining my actual location.

Have you checked that the phone will give you an accurate location anywhere?
It would be good to confirm this and eliminate one possible issue.
It would be good to try without wifi or cell data which the iPhone also uses to approximate a location, which can cause confusion.

I went out again thinking I had the problem solved. I took my iPad out and opened Google maps and typed in the latitude and longitude of the last Trackimo signal and then asked for directions from where I was to the trackimo. But when I looked at the screen on the iPad, it had my location about 250 away from where I really was. And even after I started walking a trail toward the drone, Google maps didn't move the supposed location of the iPad. I was using a Verizon device as a mobile hotspot.
... It's weird, the spot shows accurately on the iPhone but it is not accurate on the iPad which should be getting location information from the iPhone.

That's not surprising.
Wifi hotspotting shares an internet connection but not location data.

 

[DanMan32]

Location services do use other sources when GPS is turned off or unavailable. Cell tower triangulation is one of them. Wi-Fi public hotspots might also provide location. Of course accuracy is limited though.

 

[DanMan32]

By the way, I googled GPS foe iPad from iPhone. The answer was Airlocation app.

Older iPad/iPhone products may have had that feature natively.
It wouldn't surprise me that Apple would provide more than just networking over tethering for their own products.

 

[Meta4]

By the way, I googled GPS for iPad from iPhone. The answer was Airlocation app.

It wouldn't surprise me that Apple would provide more than just networking over tethering for their own products.

If they did, there would have been no reason for anyone to write that app.

 

[sar104]

SArR. Thanks for the help. But I didn’t Center the sticks until after I got the weak signal warning. And I fly rc planes and heli’s and almost never move sticks abruptly. But I must have if that's what the data shows.

Am going back out to look again tomorrow and if I find it will let you know if I knocked the battery out. Thanks again

I'm not sure about that. I've seen at least a couple of cases where the last recorded stick inputs showed similar sudden centering but the pilot didn't recall doing that. I don't have a credible alternative hypothesis though. The last time I saw this, which was quite recently, the DAT file terminated before the txt file. It might be interesting to take a look at the DAT file for this flight (FLY131.DAT).

 

[sar104]

Have you checked that the phone will give you an accurate location anywhere?
It would be good to confirm this and eliminate one possible issue.
It would be good to try without wifi or cell data which the iPhone also uses to approximate a location, which can cause confusion.

That's not surprising.
Wifi hotspotting shares an internet connection but not location data.

And if it's an iPad without a cellular radio, it may not even have a GPS receiver, and will be doing location by wifi signal pattern.

 

[Jackcutrone]

I think I have the location close enough thanks to you guys. We had heavy rain last night so I’m not going to look today. Will try tomorrow.

I trust it will be on the ground rather than in a tree. I calculated the terminal velocity from 385 feet of about 120 mph ignoring wind resistance. So I am pretty sure it didn’t catch in a tree at that speed. Probably broke apart when it hit a tree branch. So the ground pattern for parts of the drone should be pretty large.

I just hope I find enough pieces to get DJI refresh to replace although I think. I have a strong argument for replacement even if I don’t find it. Should not have been a weak signal in the first place Oddly enough Airdata shows 100% signal strength at the same time as the weak signal warning. I am pretty sure I just would have let go of the sticks when I got the warning so I have a hard time thinking the battery came out from a stop from 20 mph. But SAR104 has much more knowledge than I do I will accept what he says.

If it hit the trees at 120 mph no wonder the TRACKIMO quit reporting location.

 

[Meta4]

I calculated the terminal velocity from 385 feet of about 120 mph ignoring wind resistance.

The drone has a lot more wind resistance than you imagine.
Terminal velocity in free fall would have been less than 40 mph.

 

[Jackcutrone]

Ouch. Maybe it did catch in a tree. If it did I’m probably toast with dji refresh

 

[sar104]

I think I have the location close enough thanks to you guys. We had heavy rain last night so I’m not going to look today. Will try tomorrow.

I trust it will be on the ground rather than in a tree. I calculated the terminal velocity from 385 feet of about 120 mph ignoring wind resistance. So I am pretty sure it didn’t catch in a tree at that speed. Probably broke apart when it hit a tree branch. So the ground pattern for parts of the drone should be pretty large.

I just hope I find enough pieces to get DJI refresh to replace although I think. I have a strong argument for replacement even if I don’t find it. Should not have been a weak signal in the first place Oddly enough Airdata shows 100% signal strength at the same time as the weak signal warning. I am pretty sure I just would have let go of the sticks when I got the warning so I have a hard time thinking the battery came out from a stop from 20 mph. But SAR104 has much more knowledge than I do I will accept what he says.

If it hit the trees at 120 mph no wonder the TRACKIMO quit reporting location.

@Meta4 is correct - you cannot ignore drag and get anywhere close to the right impact speed. And if you ignore drag there is no "terminal velocity" - it just keeps accelerating. Anyway, the calculated velocity-time curves for this event look like this:



At ground level, indicated by the markers and labels, and including the horizontal velocity components, it should have been moving at 18 m/s (40 mph). As you can see, the vertical velocity curve has leveled out, showing that it is at terminal velocity.

 

[Jackcutrone]

Well, actually 40 mph may have been enough to cause it to break apart rather than get stuck in a tree. AM going to go back out to look tomorrow. Will post the results and hopefully photos of what a drone looks like when it crashes at 40 mph.

 

[Skywatcher2001]

Unfortunately that looks like a sudden shutdown or loss of power. The link ends after an abrupt centering of the elevator, from full forwards to stop. That maneuver has caused batteries to disconnect on many occasions, so that's perhaps the most likely possibility.

View attachment 81604

If that happened, then the resulting descent trajectory can be estimated given the last recorded position and velocity together with the computed wind field:

View attachment 81606

View attachment 81605

Did you look in the trees?

The Trackimo location doesn't look far off to me:

View attachment 81607

Sar104 . . . I cannot cuss but you are off the (blankity blank) chain!! Dude you are a freaking genius! Is this public software (trackimo) you use? I would love to learn to read telemetry and logs like this. Recommendations/classes? Oh, sorry Jackcutrone, losing a drone hurts the entire community. I didn't mean to be insensitive. We do feel for you. If this guy can't find it for you (sar104) it ain't getting found.

 

[sar104]

Sar104 . . . I cannot cuss but you are off the (blankity blank) chain!! Dude you are a freaking genius! Is this public software (trackimo) you use? I would love to learn to read telemetry and logs like this. Recommendations/classes? Oh, sorry Jackcutrone, losing a drone hurts the entire community. I didn't mean to be insensitive. We do feel for you. If this guy can't find it for you (sar104) it ain't getting found.

Thanks, although as I've mentioned before - stuff that you are unfamiliar with always tends to look cleverer than it really is.

Trackimo isn't software - it's a small cellular-enabled device that reports position at pre-determined intervals to a server. I got a couple of them to test, and I found them almost entirely worthless - even if they are actually able to connect to the cellular network, which seems to be rarely, they mostly report positions with tens, if not hundreds of meters error.

The numerical simulations above were done in a scientific analysis software package (Igor Pro), taking the initial conditions (aircraft position, velocity and wind velocity) from the end of the flight log and predicting forwards using the drag-limited equations of motion. The resulting position data are written to a 3-D KML file and plotted on Google Earth.