Serious bug in the Mavic's "Home Point Me" function - caused loss of drone!

finlayson · Sep 10, 2017

I have very clear evidence of a serious bug in the Mavic Pro’s "Home Point Me” function (initiated from the DJI GO 4 iPhone app). To summarize: When I did “Home Point Me” (on three separate occasions), the Mavic Pro set its home point not to the location of the controller, but instead to the location of the previous flight’s home point - which, in my case, was more than 7000 feet (2000m) away from the controller. Not realizing what had happened, I then did a “Return to Home’ - which caused my Mavic to fly away.

I have uploaded the flight log here: DJI Flight Log Viewer - PhantomHelp.com

The cached flight video (from my controller) is here:
I would be happy to provide additional flight data - from my controller - if necessary to help resolve/fix this bug. (Unfortunately, because my Mavic was lost, I don’t have any video or data from the Mavic itself.)

Here is a summary of key events from the flight log and/or cached controller video:

Flight time Time in cached video Event
0:02 n/a Takeoff (GPS mode); Home Point recorded at [36.608828,-121.711527]
0:56 0:00 Video starts
1:31 0:35 Follow Me mode enabled
7:07 6:11 Error: "Satellite Signal Lost. Acquire signal and retry." (This is a confusing message; I’m guessing that it refers to the loss of GPS coordinates of the *controller*, not the GPS coordinates of the Mavic (because the Mavic was seeing 18 satellites).)
7:10 6:14 Speed drops to zero; Mavic’s GPS location: [36.613579,-121.700561]
~8:40 ~7:44 I stop riding, and realize that my Mavic has stopped following me. I (and the controller) are at [36.61499,-121.69624]
9:26 8:30 Break in downlink (& cached video)
9:39 8:30 Downlink (& cached video) resumes
9:45 8:36 Break in downlink (& cached video)
11:01 8:36 Downlink (& cached video) resumes
11:15 8:50 I use “Home Point Me” to reset the home point, supposedly to the Remote Controller (i.e., my) position, which is at [36.61499,-121.69624]. But instead, the ‘home point' gets set to [36.607533,-121.724625], which was my home point of my *previous* flight - more than 1.6 miles (2.6 km) away from me! (Find My Drone also reports this as the “Aircraft Missing Coordinates”)
11:22 8:57 Without realizing what has actually happened to the home point, I do a RtH
11:49 9:24 Mavic finishes ascending, and starts moving ‘home’. In reality, it’s moving away from me, at a speed of 22 miles per hour (35 km/h)!
12:05 9:40 Confused and concerned about what’s happening, I did “Home Point Me” once again. But the home point remained unchanged; it’s still the home point of my *previous* flight; and my Mavic is still flying away from me at 22 mph!
12:17 9:52 The Mavic switches from “Go Home” mode to P-GPS mode. (I think I may have pressed the “Pause” button here; I’m not sure)
12:20 9:55 Speed drops to zero
12:29 10:04 Forward speed resumes
12:34 10:09 I get a “Weak Signal” warning
13:06 10:41 I do “Home Point Me” once again. But the home point is still wrong (but unfortunately I don’t realize this)!
13:12 10:47 I do a RtH once again (this turned out to be a fatal mistake, because I didn’t appreciate that the home point was wrong, and I’m now near the edge of transmission range)
13:15 10:50 The Mavic starts returning ‘home’ once again. But yet again, it’s moving away from me
13:21 10:56 The cached video ends
13:42 n/a I lose connectivity. The Mavic is moving away from me at 22 mph!

Comments:

There’s unquestionably a bug in “Home Point Me”. Why did it reset the ‘home point’ to a point that was far away from the controller, and why did it choose the point that happened to be the home (starting) point for my *previous* flight?

The RtH speed of around 22 mph (35 km/h) seems unusually large. There weren’t strong winds, and I was not in ‘sport mode’. This behavior appears similar to some ‘fly aways’ that have been reported by other people.

Unfortunately I wasn’t able to find my Mavic. It didn’t return to what it thought was the ‘home’ point (nor to the actual ‘home’ (i.e., starting) point of this flight). I searched along the line from its last known position to its assumed ‘home’ point (and beyond, in case it ended up overshooting this point). Unfortunately it wasn’t possible to do an exhaustive search, because the area is filled with long grass, thick chaparral, large oak trees, and 'poison oak'.

The bottom line: Do not use the “Home Point Me” function until DJI fixes this bug.

(I have also posted this report to DJI’s forum, but I’m also posting it here, in case DJI ignores or deletes it.)

EsiMavic · Sep 10, 2017

That's an issue way before I guess it was the first batch of mavic that were released. The worst thing is that when Press RTH you can't control it .

BTW did you switch the sportmode back and forth to regain control?

BerndM · Sep 10, 2017

Sorry to hear about your loss. That really sucks. it sure looks like the MP was having some serious issues towards the end as shown on the video. I wonder if the MP got totally confused when it was not able to see you in most of the video because the camera was pointing straight down giving it the smallest point of view. Maybe if the camera had been set at a 45 degree angle it would have kept you in view and locked on to you better.
I hope DJI can offer some help with this.

finlayson · Sep 10, 2017

EsiMavic said:
That's an issue way before I guess it was the first batch of mavic that were released.

FYI, my Mavic was quite new - bought in July 2017.

EsiMavic said:
BTW did you switch the sportmode back and forth to regain control?

No, I never entered 'sport mode' (which makes the 22 miles-per-hour 'RtH' speed strange).

If I'd had a better appreciation that 'Home Point Me' had failed, then I would have been able to recover my drone. But because I was near the edge of transmission range, and because my drone was moving away from me so quickly, it flew out of range before I could come to my senses :-(

finlayson · Sep 10, 2017

BerndM said:
I wonder if the MP got totally confused when it was not able to see you in most of the video because the camera was pointing straight down giving it the smallest point of view. Maybe if the camera had been set at a 45 degree angle it would have kept you in view and locked on to you better.

No - I was in "Follow Me" mode - not "Active Track". The Mavic didn't need to keep me in view; it just needed to keep hearing from my controller.

BuzzyOne · Sep 10, 2017

Can you post the complete flight log? That would be more telling.

Not sure if you want to go over what you could have done to save it or not, but there were several things you could/should have done.

Sorry for the loss.

BigDuke6ixx · Sep 10, 2017

Did it ask you to check the Home Point Me on the map? When it became obvious it was flying away why didn't you hit pause and try and get LOS?

finlayson · Sep 10, 2017

BuzzyOne said:
Can you post the complete flight log? That would be more telling.

My post contained a link to a "phantomhelp.com" log. Was that not sufficient?

BuzzyOne said:
Not sure if you want to go over what you could have done to save it or not, but there were several things you could/should have done.

Definitely. "Hindsight is 20-20"

finlayson · Sep 10, 2017

BigDuke6ixx said:
When it became obvious it was flying away why didn't you hit pause and try and get LOS?

"Hindsight is 20-20"

:-( It was so near the edge of transmission range, and flew away so quickly, I lost transmission before I could come to my senses...

BuzzyOne · Sep 10, 2017

Sorry, missed the link.

After a quick look:

The RTH Lat/Long was correct at start up and take off. The Home Point was recorded correctly. While you were riding and the MP was following you in Follow Mode, your RC lost GPS lock and you got the warning. (This was mistake one, should have stopped). When you then tried to set the Home Point to the RC it didn't have GPS lock and set RTH to the incorrect coordinates (this may be the FW bug). When it started to fly away and you noticed it was trying to go to the wrong Home Point, you should have hit pause and flew it back manually by using the arrow on the radar. It wasn't all that far away from you, just rotate the MP until the arrow points to the middle and give it forward stick. After that trying to reset the Home Point didn't work due to the GPS lock error.

Last ditch you should have just landed in a clear spot and use the find my drone feature.

BuzzyOne · Sep 10, 2017

veDtdvCGL$Db.hxd said:
Not a Mavic bug, it's the last used position served by the OS of the phone/tablet while it searches for satellites. In case of "Return to me", Mavic completely relies on GPS coords served by the phone OS. Everyone observed the maps showing old location on load, then after some time it correctly shows current location. Load the maps app and ensure it locks sats and shows correct position BEFORE even lauching DJI app, let alone telling it to "return to me".

User error.

Did you look at the logs? The MP had the correct coordinates at launch and the Home Point was accurate.

The MP should never update your current location with an previously recorded home point and make you think you recorded your current location correctly. That is the bug. Why would anyone need that?

Mavic 57 · Sep 10, 2017

RTH press pause on remote or toggle sport switch.

FlyGuy8675309 · Sep 10, 2017

Sorry for your loss. Lesson learned: don't trust autonomous functions.

Kilrah · Sep 10, 2017

This has been known to happen if you don't fully close the app between flights AND the phone doesn't have correct GPS reception at the time of setting HP to controller.

Oingo Boingo · Sep 10, 2017

I suspect by reading your post you're new to flying drones. My advice to u would have been work on a preflight check system before taking off. If u did a good preflight check you would have e realised that it's a SAFE idea to go to ur map and update device home point and drone homepoint prior to take off.

mightyarrow · Sep 10, 2017

Oingo Boingo said:
I suspect by reading your post you're new to flying drones. My advice to u would have been work on a preflight check system before taking off. If u did a good preflight check you would have e realised that it's a SAFE idea to go to ur map and update device home point and drone homepoint prior to take off.

And I suspect by reading your post that you're new to reading and/or forums. Comments like these are what happens when you fail to read the rest of the thread, especially flight log analysis.

I look forward to your next gem.

finlayson · Sep 10, 2017

BuzzyOne said:
The RTH Lat/Long was correct at start up and take off. The Home Point was recorded correctly. While you were riding and the MP was following you in Follow Mode, your RC lost GPS lock and you got the warning. (This was mistake one, should have stopped).

Agreed. However, I didn't see that warning when it occurred, because I wasn't looking at my controller then (it was strapped to my backpack, and I was riding my mountain bike).

BuzzyOne said:
When you then tried to set the Home Point to the RC it didn't have GPS lock and set RTH to the incorrect coordinates (this may be the FW bug).

Note that both the Mavic and the RC had GPS reception at the time(s) that I set "Home Point Me". In a separate posting (on this thread), I'll show screenshots from my DJI GO 4's 'Flight Record' - just before and just after I do "Home Point Me". They show that the DJI GO 4 app knew my phone/RC's correct GPS location, but set the 'home point' to a completely different place.

finlayson · Sep 10, 2017

A few people have suggested that (at least part of) the problem was that my iPhone (and thus the DJI GO 4 app) did not know its GPS location at the time(s) that I did "Home Point Me". However, the DJI GOP 4's 'flight record' shows that that's not the case.

Here is a screenshot of the 'flight record' 1 second before I did "Home Point Me":

Flight Record 1 second before Home-Point-Me

finlayson
Sep 10, 2017

And here is a screenshot of the 'flight record' 1 second after I did "Home Point Me":

Flight Record 1 second after Home-Point-Me

finlayson
Sep 10, 2017

You can see that my RC's location is known (the blue dot), but that the 'home point' has been set to the completely wrong location (which happened to be the home point from my previous flight).

I don't see how this can be anything other than a bug...

finlayson · Sep 10, 2017

Oingo Boingo said:
I suspect by reading your post you're new to flying drones.

Nope. I'd been flying a Phantom 2 Vision+ for more than 2 years, and this Mavic for more than a month.

However, the P2V+ didn't have the "Home Point Me" function, and I'd never tried it on the Mavic until this flight. My mistake was assuming that what should be a simple piece of functionality (tell the Mavic where the phone/RC is located, and set the 'home point' to that location) would work properly