IMU & Compass Warnings

[cneedelman]

I was recently flying on the beach. P4P DJI 4.1.18, AC 1.04.0602, Remote 1.04.01.00....and got these warnings. I’m most concerned about the IMU & Compass, also the fact that I lost Satellite signal for about 6 seconds. I took off from my backpack sitting on the beach. On a previous flight a week before, I was getting a compass error, so I moved the P4 to a different spot, off of the concrete to take off. So after the compass error on this flight, I landed and calibrated the compass, that seemed to work. Any thoughts on what may have caused this?

 

[Fly Dawg]

On a previous flight a week before, I was getting a compass error, so I moved the P4 to a different spot, off of the concrete to take off. So after the compass error on this flight, I landed and calibrated the compass, that seemed to work. Any thoughts on what may have caused this?

If you calibrated the compass on the previous flight, there is a possibility of re-bar within the concrete which is a bad spot to calibrate. Compass calibration is rarely needed. The IMU error as noted above is a heading exception, which is related to the compass calibration. If you wish to look further in to this, upload your flight log from your device of this latest flight to the link below and place a link to that back here if you wish others to chime in. You may also need the .dat file from the AC, but try the device file first. Instructions are on the link.

DJI Flight Log Viewer

 

[cneedelman]

If you calibrated the compass on the previous flight, there is a possibility of re-bar within the concrete which is a bad spot to calibrate. Compass calibration is rarely needed. The IMU error as noted above is a heading exception, which is related to the compass calibration. If you wish to look further in to this, upload your flight log from your device of this latest flight to the link below and place a link to that back here if you wish others to chime in. You may also need the .dat file from the AC, but try the device file first. Instructions are on the link.

DJI Flight Log Viewer

Thanks, I’m not sure I’ll get to the flight log today, too much holiday prep, but maybe tomorrow morning. Thanks in advance for your help!

 

[cneedelman]

I made 4 flights that evening, It's difficult to tell which is is the right one. These 2 links are the largest files, the flight in question was the longest.

Dropbox - DJIFlightRecord_2018-05-24_[19-49-44].txt

Dropbox - DJIFlightRecord_2018-05-24_[20-05-55].txt

 

[Fly Dawg]

You should have uploaded to the link provided. Its much easier for us to look at that way. But, will take a look. This might take longer.

 

[Fly Dawg]

There are no compass nor IMU warnings in either of these two flights. They are normal. The only message was: "warnings:Remote Controller Right Dial Locked. Lightly press it to adjust." That is it. Are you certain these are the correct files?

 

[cneedelman]

There are no compass nor IMU warnings in either of these two flights. They are normal. The only message was: "warnings:Remote Controller Right Dial Locked. Lightly press it to adjust." That is it. Are you certain these are the correct files?

There are 4 files from that date, is there any way for me to match it to the screen shot in my post. Otherwise I’ll just upload the other 2 to the link. Thanks again

 

[Fly Dawg]

Possibly, look for a file as close to the date and time from the screen shot.

 

[cneedelman]

Possibly, look for a file as close to the date and time from the screen shot.
View attachment 99357

Fly Dawg, I believe I uploaded the correct file, there are some yaw errors early on, then at about 10 min in all the other errors begin, I didn't see a loss of satellite count although in the screen shot you can see 17 sats but 0 signal. After uploading the file, I could then see a Google Earth still of the location and all of the data, but there is nothing there that tells me which file I've uploaded

 

[cneedelman]

Sorry it wasn't completely clear to me how this works, Here's the link
DJI Flight Log Viewer - PhantomHelp.com

 

[Meta4]

and got these warnings. I’m most concerned about the IMU & Compass, also the fact that I lost Satellite signal for about 6 seconds. I took off from my backpack sitting on the beach. On a previous flight a week before, I was getting a compass error, so I moved the P4 to a different spot, off of the concrete to take off. So after the compass error on this flight, I landed and calibrated the compass, that seemed to work. Any thoughts on what may have caused this?

You had a Yaw Error showing from 0:36.2 till 1:05.3.
A Yaw error is related to a compass error and usually is caused by launching from an area of magnetic interference such as on a steel or reinforced concrete surface.
I would not expect this from launching from a backpack on the beach unless you had a substantial steel item in the part of the backpack you rested the Phantom on to launch.
There's no sign of your Phantom losing GPS during this flight, but the yaw error caused the condition that the IMU message is warning you about.
It's the IMU warning that it's detected a problem with the compass sensor not matching what the GPS is telling it.
It's surprising that the Phantom stayed in P-GPS mode.
A yaw error usually forces the Phantom into Atti mode.
The weak GPS message at 0:43 sounds like the Phantom was in atti mode though.

The compass/yaw problems returned when your Phantom came back after 10:11.7 until the end of the flight.
The Phantom is reporting crazy speeds that aren't possibly correct.

The exact cause is puzzling but is compass related.
Compass errors are not a condition that needs fixing and calibrating does not "fix" them.
A compass error is a working compass warning you of a problem that it has detected and moving the Phantom away from the problem is the correct action.

I would want to re-calibrate the compass somewhere else in a clean location and
be cautious flying with this Phantom until it has flown a satisfactory flight somewhere away from the problem flight to make sure that the problem is not in the Phantom

 

[Oso]

So after the compass error on this flight, I landed and calibrated the compass..

This to me is the most serious thing that you stated about the experience. You should not have calibrated in that area.

I agree with Meta. If it were me I would not fly this Phantom until I did a proper compass calibration in a magnetically clean area.
If you don't mind, please let us know how it goes.
Cheers!

 

[Fly Dawg]

Fly Dawg, I believe I uploaded the correct file

The first 2 files you uploaded were the same date but different times, with no errors noted. The last one appears to be the correct file. The same comments apply that were made earlier and in subsequent posts.

 

[cneedelman]

I just did a compass calibration, and to my surprise that seemed to fix the radar heading that was intermittently not matching the AC heading. The North point on radar was also wrong and now is indicating North. I hope this is not a coincidence, using the radar to tell which way the AC is facing when it’s a small dot in the sky is useful to me.

 

[Fly Dawg]

that seemed to fix the radar heading that was intermittently not matching the AC heading. The North point on radar was also wrong and now is indicating North

No its not coincidence. That little indicator is always part of pre-flight checks to insure the compass is calibrated properly.

 

[cneedelman]

No its not coincidence. That little indicator is always part of pre-flight checks to insure the compass is calibrated properly.

Fly Dawg, thanks so much for the help. I must have been flying for quite some time with an improper compass calibration, although I never got a warning until now. The radar was always 90 degrees out. I flew today and everything was perfect. I did lose the AC in the sky and navigated back using the radar screen. Thanks again!

 

[Fly Dawg]

I must have been flying for quite some time with an improper compass calibration, although I never got a warning until now.

Good thing you got it sorted out. Many times it's the little things that cause huge issues. The compass is a biggie. Happy Flying!

 

[sar104]

Fly Dawg, thanks so much for the help. I must have been flying for quite some time with an improper compass calibration, although I never got a warning until now. The radar was always 90 degrees out. I flew today and everything was perfect. I did lose the AC in the sky and navigated back using the radar screen. Thanks again!

I guess I'm unconvinced about the diagnosis here. The aircraft initialized on a heading of 38° but when the first video recording started at 20 s, still with a yaw value of 38°, the gimbal was clearly pointing at around -2°.

Additionally, the initial motion of the aircraft, until 33 s, was only under right aileron input, and the GPS track indicates, as expected, movement due east. The IMU velocity data indicate movement on a track of around 120 - 130°, consistent with the incorrect yaw value.

The first yaw error occurred at 36 seconds. My initial hypothesis would be that the yaw value was initialized 40° off due to interference from something in the backpack. We would need to see the the DAT file from the aircraft or the mobile device to confirm that, however.

 

[BudWalker]

I guess I'm unconvinced about the diagnosis here. The aircraft initialized on a heading of 38° but when the first video recording started at 20 s, still with a yaw value of 38°, the gimbal was clearly pointing at around -2°.

View attachment 99454

Additionally, the initial motion of the aircraft, until 33 s, was only under right aileron input, and the GPS track indicates, as expected, movement due east. The IMU velocity data indicate movement on a track of around 120 - 130°, consistent with the incorrect yaw value.

View attachment 99456

The first yaw error occurred at 36 seconds. My initial hypothesis would be that the yaw value was initialized 40° off due to interference from something in the backpack. We would need to see the the DAT file from the aircraft or the mobile device to confirm that, however.

I'm also unconvinced without even looking at the data. It's been a while since an incident was attributed to a flawed compass calibration. Likewise a flawed calibration that was caused by a particular location. These things just never happen.

I'm guessing it was a rivet, zipper, buckle, etc. Doesn't have to be large since the P4 compass is in the leg.

.....I must have been flying for quite some time with an improper compass calibration, although I never got a warning until now. .......

This. The obvious explanation is that there was no improper compass calibration.

....That little indicator is always part of pre-flight checks to insure the compass is calibrated properly.

This is to check that the Yaw value is correct. Has nothing to do with checking the compass calibration.

 

[Fly Dawg]

This is to check that the Yaw value is correct. Has nothing to do with checking the compass calibration.

I agree with the yaw value, however, when this icon is obviously off visually from the directional heading of the aircraft, there is obviously an issue. My wording should have said "an indicator of needed calibration" rather than "assurance". But for the average flyer, other than a "calibration needed" warning, this is the only way to determine if the compass direction is at the very least approximately correct. As the OP stated, the "indicator" was always 90 degrees off. My statement was merely to say that this is something that should be verified pre-flight each time. There still could be future errors after takeoff, but this should be verified prior to that.