Two different P4P v1, two different controllers, almost the same result! The samething happened tonight that happened two nights ago. See "RTH Right Into A Tree". Tonight I was using RTH and it was landing fine, right on target when suddly it shot off to the left towards my neighbors house. I hit the RTH button and this time I was able to regain controll just in time. What the hell is going on with these two drones? I'll upload the fight data but I'm going to have to ground the rest of my DJI drones till it gets figured out. I aready lost one P4P and almost lost my other one. Now I don't feel like I can trust my Mavic Air either! This could have ended badly in so many ways.
This time I was using my plus controller last time I was using the one w/my tablet. All the firmware is up todate on both the controllers and the birds.

https://www.phantomhelp.com/logviewer/85Z65Z7S3HTW4ORIPEGA/

This can't be a coincident........ something is going very wrong with something!!!!

Looking at your flight, are you starting/taking off from the concrete driveway or footpath at the front of the house?

Geebax Posted at 2-15 18:36
Looking at your flight, are you starting/taking off from the concrete driveway or footpath at the front of the house?

from the sidewalk in front of my drive way.

I know what you are going to say about the rebar in the side walk but I've been taking off from the exact same spot since July 2017. I checked the compass today before I took off 2 batteries earlier and it only had 10% interference.  

Edward J Smith Posted at 2-15 18:40
from the sidewalk in front of my drive way.

OK, not a good move. As a rule, you should never take off from a concrete surface, as that concrete most likely contains rebar which will screw up your compass. And just as important, do not power up the aircraft on concrete either, as the compass error is created dsuring the power up procedure. Try powering up/taking off from the grass at the front of the house.

Sounds like a clear case of magnetic interference, thats exactly what can happen when the field changes.
Another thing that could happen is the GPS being blocked from a direction thus weakening the signal, the unit then thinks its at a different position and adjusts course
Im not quite sure how accurate the latter idea is to be honest, its what came to mind but the magnetic interference is normally the case, interestingly there are no errors relating in the log :/

Also note, as Geebax has said, do not take off from the sidewalk, roadway, concrete or drives due to rebar, just because youve gotten away with it in the past, does not mean its safe to do so, it just means yove been lucky

Edward J Smith Posted at 2-15 18:44
I know what you are going to say about the rebar in the side walk but I've been taking off from the exact same spot since July 2017. I checked the compass today before I took off 2 batteries earlier and it only had 10% interference.

I know what you are going to say about the rebar in the side walk but I've been taking off from the exact same spot since July 2017. I checked the compass today before I took off 2 batteries earlier and it only had 10% interference.
Looking at your flight data, it fits what Geebax suggested.
When you say you've been taking off from the exact same spot, you probably haven't.
Just an inch or two difference in your position could be all it takes to make the difference.
While you get a compass error warning if you put the compass close to a large steel object, you wouldn't see any warning of a compass error if the magnetic field of the steel isn't significantly stronger than the earth's normal magnetic field.

The problem with reinforced concrete is that you can't see what's under the drone.
It might be 8 inch mesh and the way you position the drone could put the compass far enough away from the steel that it doesn't matter.
Or the concrete might be thin and you put the drone down with the compass right above a crossing point in the mesh, or worst, it could be an overlap of two panels of steel mesh.

You can check the orientation of the paper plane icon in your map or radar display before landing to see if things are OK.
If the actual drone is pointing north and the icon also points north things are good.
If the icon points a different direction from the drone, power down and move away to a clean location and start again.

I do understand what all of you are saying.  Just as it was about to shoot off I saw on the controller the little green box and If I remember right I says Precision land correction and I thought that is weird because it is coming down right where it needs to be and then I looked back up at the drone in time to see it shoot off backwards. As far as taking off in the grass LOL there is 8-9 inches of snow but I do get and if I can muster up the courage to fly it again, that will be where I will try it from. I just don't have a lot of confidence in it anymore not knowing for sure that the compass was the problem. The last thing I want to do is total out another P4P not to mention property damage of hurting someone.

Hello and good day Edward J Smith. I am sorry for the trouble this has caused and to read what happened to your previous flight. The above suggestions and recommendations are correct. In addition kindly please try to fly your drone to a different location where there is less interference such as magnetite, parking structures, or steel reinforcements underground to see if the said issue will still persist. Please try to calibrate the compass of the said drone as well. Thank you and have a safe flight always.

Edward J Smith Posted at 2-16 07:56
I do understand what all of you are saying.  Just as it was about to shoot off I saw on the controller the little green box and If I remember right I says Precision land correction and I thought that is weird because it is coming down right where it needs to be and then I looked back up at the drone in time to see it shoot off backwards. As far as taking off in the grass LOL there is 8-9 inches of snow but I do get and if I can muster up the courage to fly it again, that will be where I will try it from. I just don't have a lot of confidence in it anymore not knowing for sure that the compass was the problem. The last thing I want to do is total out another P4P not to mention property damage of hurting someone.

Hi Edward,

Had a look at your flight too.

The moment your P4 start to correct the landing for a "Precision Landing__Correcting Landing Position" it needed some light to perform well.

Ambient light too low, few times (6x) an error like this
- Exit Forward.Backward Sensing system__Ambient Light is too weak.
- Forward Obstacle Sensing is not functioning.__Ambient Light is too weak.

So why did your P4 moved away, i think because of the low light setting.

Your yaw signals are in sync the whole flight, so that rules out for 98% a compass error, plus it does not often happens after a flight of 18 minutes.

So try again with better light conditions, think you will find out that there is no problem.

cheers
JJB

JJB* Posted at 2-16 13:20
Hi Edward,

Had a look at your flight too.

Yes, that was going to be a secondary issue I was going to point out, low light level making it difficult for the aircraft to land using precision landing.

Geebax Posted at 2-16 13:29
Yes, that was going to be a secondary issue I was going to point out, low light level making it difficult for the aircraft to land using precision landing.

Hi Geebax,

Thanks for your reaction.
It is good to see in the chart, and after cancel the landing the move away speed back to zero again.
So another 'fact' for not having a compass/yaw related problem/fly away.

VPS height at precision lannding not yet active due to low light.

cheers
JJB

So just so I understand, because of low light the VPS couldn't tell where the home point was so it decided to just shoot of to anywhere? I kind of get the VPS not having enough light to work but why would it think it was that far a way from the home point that it would shoot off t\like that. It did it to both of my P4Ps at almost the same height and the same time of night (it was dark on both flights)t. 30 mins after sunset. In fact that was what I was shooting.

So the answer to a safer landing using RTH in low light is not to use the precision landing?

JJB* Posted at 2-17 00:52
Hi Geebax,

Thanks for your reaction.

Could you have a look at this one too please?

https://www.phantomhelp.com/logviewer/81QS5UYD3CKH4JJ4P97W/

Edward J Smith Posted at 2-17 14:18
So just so I understand, because of low light the VPS couldn't tell where the home point was so it decided to just shoot of to anywhere? I kind of get the VPS not having enough light to work but why would it think it was that far a way from the home point that it would shoot off t\like that. It did it to both of my P4Ps at almost the same height and the same time of night (it was dark on both flights)t. 30 mins after sunset. In fact that was what I was shooting.

Hard to say what was hapenning here. If the downward vision system cannot identify the area below it as the landing site, then it may go looking elsewhere, but who knows?

Edward J Smith Posted at 2-17 14:42
Could you have a look at this one too please?

https://www.phantomhelp.com/logviewer/81QS5UYD3CKH4JJ4P97W/

Hi Edward,

It has to do with low light setting i guess.

During autolanding (wich performed well from 108 meters to 14.6 meters) at 14.6 meters your P4 drifted away. But after cancel the autoland speed back to zero, so P4 back into a stabilized GPS hover.
After that see lot of RC input, and 2 seonds it crashed into something.
VPS height starts to indicate at 4.1 meter, wich is bit late but explained by low light setting.

Again in my opinion no compass error, cancelation of autolandingand P4 stabilized, this will not happen with a compass/yaw error.

But i can be wrong ofcourse, but i would suggest to test your craft in daylight setting.

cheers
JJB

From what I understand the VPS only works from around 15' ish (4.5 meters)  to 0. Well if I don't check the precision landing box on the auto take off will that stop the problem?  I think I will just manually land and hold my breath and cross my fingers.  It really did shake my confidence in my drones!!

Thanks everyone for their help

Edward J Smith Posted at 2-18 12:55
From what I understand the VPS only works from around 15' ish (4.5 meters)  to 0. Well if I don't check the precision landing box on the auto take off will that stop the problem?  I think I will just manually land and hold my breath and cross my fingers.  It really did shake my confidence in my drones!!

Thanks everyone for their help

i read in the specs up to 10 meters for VPS height and up to 30 for vision wich is used (afaik) for landing positioning.

JJB* Posted at 2-19 03:03
i read in the specs up to 10 meters for VPS height and up to 30 for vision wich is used (afaik) for landing positioning.

You ae correct .

I took my Mavic Air out last night to video the sunset but I used the RTH till it got over head then cancelled it and brought it home manually. Baby steps I guess. Besides I still have DJI care on the Air. LOL It's like losing a dog, guess it will just take time to bring my confidence back.

Again thanks for the help in understanding what went wrong now I know how not to land.

I just noticed that the phantom icon is missing under everyone's avatar  hmmm

Edward J Smith Posted at 2-19 15:03
I just noticed that the phantom icon is missing under everyone's avatar  hmmm

It is there on mine and yours.

It's not a good idea to take off from concrete reinforced surfaces, we hear that quite often. Oddly enough, Ken Heron, a popular Youtube drone pilot and instructor, does that quite regularly, taking off from ridges and other structures with seemingly not a worry about compass errors. Meanwhile, if I'm within 15' of my aluminum boat I get a compass error and cannot even start the motors. Go figure.