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Newbie Needs Help with Altitude Issue

VLL

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I have about two weeks worth of flying on my new Mavic 2 Pro. Because I'm new, I'm using most flights to learn and practice flying skills, and to explore the many photo-video features and to try to become more proficient at it all. In other words, I'm not trying to do anything very fancy.

This morning I took a flight pretty much straight up over my head, and our house, just to take a look at the landscape as the rising sun broke through the trees and a thin bit of fog to the east dissipated. Although I was intending to be only about 75 ft up, I suddenly was way higher (like 170) according to my SC. As I brought the drone down, I realized it wasn't as high as the altitude reading. I don't know how much it was off when I first noticed the 170 or so reading, but when I landed, as I was within 2 or 3 feet of the ground, I had a reading of about 80 ft. After landing, I decided to go back up for a short flight just to see if the problem was still there. I took the drone up to about 70 feet, spin around in a circle while recording some video, and came back down and landed. The data that downloaded to airdata shows an actual max height of about 81ft, and a landing altitude of close to a negative 10 feet.

Any ideas on what is happening? I've found a few posts about faulty barometric readings in the drone, and I'm concerned that perhaps my new drone is already experiencing a serious problem.
 

VLL

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Ok then. Time for me to learn how to retrieve and post a log flight. I will do that, and welcome all analysis and advice. Including any assessment of user error!
 
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VLL

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A potential problem with my barometer was not what I was hoping to hear on a drone I’ve had for only two weeks . . . 😓.

Seems like the Airdata file may be helpful If anyone with the know how wants to take a look. Here is the flight that told me I was still 80 ft or so above ground as I neared my landing pad:


Then this is the flight that suggested I was - 10 ft in altitude on my second landing a few minutes later.


Not sure if these files are what are needed. If they are, do they suggest it’s time to call DJI?
 

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A potential problem with my barometer was not what I was hoping to hear on a drone I’ve had for only two weeks . . . 😓.

Seems like the Airdata file may be helpful If anyone with the know how wants to take a look. Here is the flight that told me I was still 80 ft or so above ground as I neared my landing pad:


Then this is the flight that suggested I was - 10 ft in altitude on my second landing a few minutes later.


Not sure if these files are what are needed. If they are, do they suggest it’s time to call DJI?
Looks like its saying the same, when you were landed it showed you were still 81ft. high. I would definitely contact DJI. I mean you can check the arbitrary things like making sure your firmware is up to date, although I doubt that would be the issue.
 

sar104

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A potential problem with my barometer was not what I was hoping to hear on a drone I’ve had for only two weeks . . . 😓.

Seems like the Airdata file may be helpful If anyone with the know how wants to take a look. Here is the flight that told me I was still 80 ft or so above ground as I neared my landing pad:


Then this is the flight that suggested I was - 10 ft in altitude on my second landing a few minutes later.


Not sure if these files are what are needed. If they are, do they suggest it’s time to call DJI?
I don't think this is a barometer problem - I think it's the IMU. If you can retrieve and post the mobile device DAT file ending FLY049.DAT then we can take a look at the raw sensor data.

Climb.png
 
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VLL

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sar104, in advance, can't tell you how much I appreciate this help.

If I've got the right file, it was on internal storage on my Smart Controller. I copied it to the removable sd micro card and am attaching it below. In the FWIW category, I did get an IMU error within my first few flights and recalibrated it. No further error messages. I just did a "Sensors State" check on the SC and the four IMU sensors all are in the green (with one, the ACC0, having a blue dot next to signifying it's in use while the others lack that -- all with the drone sitting on my table top).

Here's the file.
 

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sar104

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sar104, in advance, can't tell you how much I appreciate this help.

If I've got the right file, it was on internal storage on my Smart Controller. I copied it to the removable sd micro card and am attaching it below. In the FWIW category, I did get an IMU error within my first few flights and recalibrated it. No further error messages. I just did a "Sensors State" check on the SC and the four IMU sensors all are in the green (with one, the ACC0, having a blue dot next to signifying it's in use while the others lack that -- all with the drone sitting on my table top).

Here's the file.
Yes - that's the correct file, and it has data for both the flights you mentioned above. The barometric data are good, and agree closely with the GPS altitude data - both bring the aircraft back to the takeoff height. The IMU vertical velocity data are bad. In the graph below the thick dotted blue trace is the active IMU 1 height reading, and shows the offsets of + 84 ft and - 10 ft that you mentioned. It represents the vertical motion detected by the IMU accelerometers (red) slowly corrected by the absolute barometric data. Have you done an IMU calibration?

sensors.png
 

VLL

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I have not recently calibrated the IMU. I did several flights ago. I got an IMU error message of some kind as I recall, reviewed the procedure for calibrating the IMU, and went through the calibration. In looking at some of my other flights on Airdata, I may have had this problem on a smaller scale before today. Last Sunday I had a landing with a negative 3.9 altitude, and I think a few of the inflight altitudes may have been off as well on the flight.

Recalculate again? If so, is there a recommended way to test the drone without too much risk of it doing something wonky?

My ongoing thanks for your help. Your expertise is invaluable.
 
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sar104

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I have not recently calibrated the IMU. I did several flights ago. I got an IMU error message of some kind as I recall, reviewed the procedure for calibrating the IMU, and went through the calibration. In looking at some of my other flights on Airdata, I may have had this problem on a smaller scale before today. Last Sunday I had a landing with a negative 3.9 altitude, and I think a few of the inflight altitudes may have been off as well on the flight.

Recalculate again? If so, is there a recommended way to test the drone without too much risk of it doing something wonky?

My ongoing thanks for your help. Your expertise is invaluable.
I would definitely do another IMU calibration. It doesn't seem like the problem is causing significant flight control issues, and so I would not be too worried about doing test flights. I recommend posting the resulting DAT file(s) after you have done that for comparison.
 
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VLL

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I will recalibrate and do some cautious flying. Will see if I can get a flight in yet today. If not, the forecast is for rainy, cool, windy weather until next Tuesday. But as soon as I can calibrate and fly, I will post the data file and welcome your analysis. Thanks much.
 
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VLL

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The recalibration was textbook. No issues. Afterwards, I managed to get a 14 minute flight in. My M2P seemed rock solid throughout -- more so than this am, really. Although winds were light for both flights, this am it seemed to be working harder to maintain position at times. Maybe my imagination, not sure. But in my flight about 45 minutes ago, I didn't have that same sense. Altitude reading on the SC seemed consistent with both my visual perceptions and what I was trying to do with the controls. Landing altitude seemed right on.

Here is the file from the flight, if Sar104 or one of the other gurus on this forum have time to take a look at it. The post-calibration flight sure seems like the problem is fixed, but I trust the data much more than my visceral sense.

Thanks!
 

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sar104

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The recalibration was textbook. No issues. Afterwards, I managed to get a 14 minute flight in. My M2P seemed rock solid throughout -- more so than this am, really. Although winds were light for both flights, this am it seemed to be working harder to maintain position at times. Maybe my imagination, not sure. But in my flight about 45 minutes ago, I didn't have that same sense. Altitude reading on the SC seemed consistent with both my visual perceptions and what I was trying to do with the controls. Landing altitude seemed right on.

Here is the file from the flight, if Sar104 or one of the other gurus on this forum have time to take a look at it. The post-calibration flight sure seems like the problem is fixed, but I trust the data much more than my visceral sense.

Thanks!
Much better - the offset was only 1.77 meters. Not perfect though - IMU 1 still looks a bit off. You might want to try another flight with more vertical.

sensors_FLY053.png
 

VLL

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Great info. I will have it ready to fly if there are any good breaks in the incoming weather front that permit a good flight. I will also take it to another area to fly, where I can get some meaningful vertical. I’m close enough to the local airport to be restricted to 50 ft here, which gives me about 80 ft if I’m flying near our 30 ft high home. Ongoing thanks, sar104.
 

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Great info. I will have it ready to fly if there are any good breaks in the incoming weather front that permit a good flight. I will also take it to another area to fly, where I can get some meaningful vertical. I’m close enough to the local airport to be restricted to 50 ft here, which gives me about 80 ft if I’m flying near our 30 ft high home. Ongoing thanks, sar104.
Be careful here. If you have LAANC authorization to fly to 50 feet near the airport, I don't think you can add the height of your house or any other structure to it, as you could if you were in Class G airspace.
 

sar104

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Be careful here. If you have LAANC authorization to fly to 50 feet near the airport, I don't think you can add the height of your house or any other structure to it, as you could if you were in Class G airspace.
That's correct, and this location is in a 50 ft LAANC grid location:

1585316511231.png
 

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All my DJI quads have a height error/drift within 10ft, so an error of 1.77m seems normal to me. In my case it drifts to lower than actual, where it reads negative when I land.
 

sar104

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All my DJI quads have a height error/drift within 10ft, so an error of 1.77m seems normal to me. In my case it drifts to lower than actual, where it reads negative when I land.
I think a consistent drift to higher pressure (lower) is likely due to the change in sensor temperature over the duration of the flight.