GPS horizontal drift and disarm after arming

acpl00 · May 27, 2019, 11:44am

Dear people,

I have the PixHawk 4 mini and when I tested in both position and mission modes I do get two issues.

When I arm the drone and rest the throttle stick either the minimum or arm positions respectively. The drone arms and then after 3 seconds it disarm itself. Should it be armed after I have armed it? and then disarm if I myself disarm it?
When a mission loaded under mission mode, I get the following warning:

GPS Horizontal Pos Drift too high

I can see in the GPS status:

– GPS count 13
– GPS lock 3D GPS Lock
– HDOP 0.9
– VDOP 1.3

As you can see it in the picture below:

Any advise and help will be appreciated.

Thank you

AlexandreBorowczyk · May 28, 2019, 12:08pm

Can you share a log?

acpl00 · May 28, 2019, 12:52pm

Hi,

I have not really flown the drone, just arm it with small propellers.

this is the log

https://logs.px4.io/plot_app?log=307fecf0-a010-4bd6-8d0c-02395d247b13

Thank you

rollys · May 28, 2019, 1:52pm

Is it possible that the Land Mode Settings is checked? Just uncheck if it is and see if that resolves it.

Good luck.

acpl00 · May 29, 2019, 12:36pm

Hi,

Thank you for the answer, it was the Land mode settings.

Not it does not disarm itself.

But I still have the following issue

When I arm the drone I get the following warnings:

         - `GPS Horizontal Pos Drift too high`

         - GPS   Speed accuracy too law

             the vehicle has failed to pre-arm

             check in order to arm the vehicle

             resolve the failure

  Do you have a clue how to solve these warnings?

rollys · May 29, 2019, 1:30pm

Sorry, not quite sure what the answer is to that and will have to defer to @AlexandreBorowczyk who can hopefully decipher your log.

Good luck.

AlexandreBorowczyk · May 29, 2019, 6:31pm

The log show no GPS lock.

Can you provided another log with the problem to compare?
What is your physical setup? Where is the antenna and what is around it?

acpl00 · May 30, 2019, 5:44am

Hi Alexandre.

1
I show up two logs;

https://logs.px4.io/plot_app?log=87111951-a112-4812-9892-61b14739969a

https://logs.px4.io/plot_app?log=e8ae80c6-e404-44ce-9794-80e58e76ab67

2
The PixHawk 4 mini is on the top surface of the drone just over the center of gravity and the GPS comes with two sticks, one is 14 cm and the other one is 9 cm.

The setup is mainly like this one;
https://github.com/NVIDIA-AI-IOT/redtail/wiki/Skypad-TBS-Discovery-Setup

First, I positioned the GPS in front of the GPS at the distance of 6cm and at height of 14cm, then I changed the GPS to the lower stick which is 9cm height. And then I re calibrate the sensors again.

In a few words, the GPS on the top surface of the drone at horizontal distance from the pixhawk of 6cm and at height of 9cm.

I have tried to arm the drone again, in mission mode and manual mode but with small propellers so the drone did not fly and I still get the following issue:

When I arm the drone I get the following warnings:
```
        - `GPS Horizontal Pos Drift too high`

         - GPS   Speed accuracy too law

            the vehicle has failed to pre-arm

            check in order to arm the vehicle

            resolve the failure
```
I can see in the GPS status:

– GPS count 11
– GPS lock 3D GPS Lock
– HDOP 0.9
– VDOP 1.4

Do you have a clue how to solve these warnings?

acpl00 · May 31, 2019, 10:27am

Hi,

I have thinking that since I have a companion computer
(Jetson TX2) with USB3, that could prompt the issue, because I read

http://docs.px4.io/en/log/flight_review.html#gps-uncertainty

USB 3 is known to be an effective GPS jamming source. The **jamming
indicator** should be around or below 40. Values around 80 or higher 
are too high and the setup must be inspected.

And there is a new PX4 version V1.9 stable, which I load it and I re calibrate everything again, and I have also enabled the CAL_MAG1_EN

Then I have covered the GPS with aluminum paper as you can see it in the picture

I made some tests in mission and manual mode, with small propellers so the drone did not fly.

And, the GPS position was good and I did not get any warning.

I believe that noise from the JetsonTX2 USB3 was causing the problem.

I have another issue, maybe you could help me

I use EKF2 and I have Set

 SENS_FLOW_ROT to 270 degrees, default 
 EKF2_AID_MASK to use optical flow and GPS
 EKF2_HGT_MODE to use the range finder

The question is:

How can I check that the PX4FLOW sensor is working correctly together with the GPS ?

In other words, I guess that I shall get a position [xyz] that comes from the combination of both the GPS and the PX4FLOW , right?
So far I can see in the mavlink inspector the:

  -optical_flow_rad 
  -local_position_ned

AlexandreBorowczyk · May 31, 2019, 5:28pm

Good move on the shielding, it could very well be part of the issue.
I would switch EKF2_HGT_MODE back to default for now.

What is weird is that the PMW3901 seem to crash at startup but the optical flow msg are publish anyway and dont seem to be incorrect.

Try

setting EKF2_HGT_MODE to default
then if there is still a problem
set EKF2_AID_MASK to default
the if there is still a problem
disconnect the optical flow

acpl00 · June 3, 2019, 7:20am

Hi Alexandre.

The 3 points you have mentioned are exactly to solve what issue?

Because I have two issues.

1.- About:
GPS Horizontal Pos Drift too high

GPS Speed accuracy too law
2.- About how can I check that the optical flow is fusing the data with the GPS to have a good estimator.

Thank you.

AlexandreBorowczyk · June 3, 2019, 11:26am

Right now I would say the priority is to figure out what is happening with the GPS.
For the optical flow, if it is safe and you have enough space, fly inside on position mode and if the mode is available the optical flow works. If you can’t fly inside, when on position mode the drone horizontal drift show be almost inexistant.

acpl00 · June 3, 2019, 11:41am

Well,

I have implemented the 3 steps you suggested, then I have armed the drone.

All the times I armed the drone, lets say 10 times, I got like 3 warning GPS messages, one had to do with the GPS accuracy to law and the other one had to do with GPS Horizontal or vertical (do not remember) Pos Drift too high and one with compass Compass Sensors inconsistent But the drone was armed anyway.

The question is that if I armed the drone with proper propellers, that would affect the drone flight. What do you think?
My idea to use PX4FLOW is to fuse it with GPS in outdoor flight. I do not fly indoors. Does it worth to use sensor flow?

AlexandreBorowczyk · June 3, 2019, 11:52am

Please share the log, it’s will help alot

acpl00 · June 3, 2019, 1:38pm

I do not quite remember which one belong to the warnings,

Even though I have armed the drone many times I just found like two .ulg files in the log Download tab , which I share the link here.

It is worth to mentioned that I did not fly the drone I just armed it in mission plan mode with small propellers. So, the drone was armed.

When I was downloading one .ulg file I got many times the following message

Mag 0 fail: TIMEOUT!!
Mag 1 fail: TIMEOUT!

https://logs.px4.io/plot_app?log=40286953-2bd5-4039-8a4b-f5c988dbc223

I am planning to fly the drone in position mode, then I can send you a log.

I am not there to fly the drone in mission mode.

What can be wrong?

AlexandreBorowczyk · June 3, 2019, 2:05pm

There is alot going on in this log!!! (Lost RC link, jammed GPS, problems with MAG)

Can you provide a log for the following flight:

Setup:

Set RC remote such as drone will be in manual or stabilized mode and don’t switch after
Set the drone at take location and dont move it afterward

Turn on the remote
Power on drone
— wait 5 min —
press and hold safety switch
— wait 1 min —
Arm drone
— wait 1 min —
Takeoff and hover at a altitude of ~5m
– wait 2 min —
Land
– wait 2 min –
Disarm
Power off drone
power off remote

acpl00 · June 4, 2019, 10:14am

Hi Alexandre.

Here you have two logs, during the downloading of the .ulg file to my computer, I got the following warnings.

Mag 0 fail: TIMEOUT!!
Mag 1 fail: TIMEOUT!

I guess the following log is just a test to take the drone off in manual mode.
https://logs.px4.io/plot_app?log=ee0dd1b7-e846-4701-ad3a-06275aac480f

And, I think the following log is the one which steps you suggested. we tried to hoover the drone, however was a bit difficult in manual mode.
https://logs.px4.io/plot_app?log=38b4e726-a80e-49b7-bae1-4912eab258a6

I have noticed that when the drone was armed I got the message

GPS Horizontal or vertical (do not remember) Pos Drift too high
Also noted that every time we had to take the drone off with the RC, the RC had be trimmed, is this normal?? Otherwise, the drone would just has turned upside down.
Under this condition, do you think would be safe if I try the drone in mission planner mode?
Concerning the sensor flow.
My idea to use PX4FLOW is to fuse it with GPS in outdoor flight to have a better pose estimate position. I do not fly the drone indoors. Is it worth to use sensor flow?
Also noticed that in the open 3D view tab, the drone is placed in front of Africa on the sea, that’s weird.

Thank you.

acpl00 · June 7, 2019, 12:44pm

Hi Alexandre,

I have flied the drone in mission plan mode.

I share a log.

https://logs.px4.io/plot_app?log=28f6ad9e-13e2-496d-83fa-c79949e3a164

How do you see it?

AlexandreBorowczyk · June 10, 2019, 9:54pm

Hi,

Sorry I was away for the last week.
I took a quick look at “38b4e726-a80e-49b7-bae1-4912eab258a6”, weirdly it looks pretty normal.
I will need to dig abit in the mavlink msg directly to see more.

Do you have another GPS unit? I would like to rule out a H/W issues.

acpl00 · June 11, 2019, 6:26am

Hi Alexandre,

Thank you for your replay.

well, if it looks normal to you, probably it has to do with the version 1.9.0 stable.

How can you dig into mavlink msg??

I do not have a GPS for the PixHawk 4 mini