DJI Go 4 reporting incorrect altitude readings causing shaky landings?

[smokinsound]

Today, I had several flights where I maintained low altitude for most of the flight's duration. I was on flat ground with no slope or change in altitude, taking off and landing from the same place. I noticed about 3 minutes into the flight, after flying around about 3-4' AGL, the altimeter on the DJI Go4 app (latest firmware/software available for P4P+) was telling me the bird was 15' off of the ground, when in fact it was absolutely no more than 3' off of the ground. It seemed like I was also getting some false positive readings from the downward and/or forward obstacle avoidance sensors. More importantly, I noticed that the P4P shutters and shakes violently when landing and the altimeter is giving a reading of 6-8" AGL when in fact the drone is already on the ground. I know that the shuttering/shaking problem is being discussed in the P4P+ firmware thread, but has anyone else experienced any of these symptoms, or come up with a fix? The compass and IMU were calibrated not long ago. I suppose I can re-calibrate, but all of the interference values are extremely low, and show no indication of needing a calibration. I wanted to make sure this wasn't a bigger issue that needed a fix from DJI before I jumped in the rabbit hole looking for problems on my end. In summary...

1. P4P is giving a bad altimeter reading when flown consistently 2-5' AGL. (Usually off by 10-15')
2. Low AGL flying seems to trigger obstacle avoidance (and bad altimeter reading) even when the area is free and clear.
3. Incorrect altimeter values seem to have negative effect on landing operation, causing violent shutter/shaking until motors are completely shut down.

Sidenote, after low AGL flying I took it up to about 200ft AGL (at least 100' above any land obstacles) and would get occasional obstacle avoidance alerts. Very sunny day today, and wondering if it could have been sun glare causing the alerts... is this a known issue?

Attached is a screenshot from my P4P+ controller while hovering above the takeoff position. DJI Go 4 app indicates that I'm about 30' AGL. The second photo is a shot from my cell phone while it was hovering in the same spot, showing that the height is no where near 30ft AGL, but in fact about 2' off of the ground.

 

[Meta4]

I noticed about 3 minutes into the flight, after flying around about 3-4' AGL, the altimeter on the DJI Go4 app (latest firmware/software available for P4P+) was telling me the bird was 15' off of the ground, when in fact it was absolutely no more than 3' off of the ground. It seemed like I was also getting some false positive readings from the downward and/or forward obstacle avoidance sensors. More importantly, I noticed that the P4P shutters and shakes violently when landing and the altimeter is giving a reading of 6-8" AGL when in fact the drone is already on the ground.

Sidenote, after low AGL flying I took it up to about 200ft AGL (at least 100' above any land obstacles) and would get occasional obstacle avoidance alerts. Very sunny day today, and wondering if it could have been sun glare causing the alerts... is this a known issue?

The altitude calculation comes from the air pressure measured by the barometer in the IMU.
Changing temperature causes changes in air pressure and can affect altitude readings.
You've already recalibrated the IMU so that's probably taken care of.
If you are flying in cold conditions better precision might be achieved by allowing the Phantom to warm up a little before liftoff.

The altitude reading shouldn't affect landing as the Phantom just comes down until it feels the ground beneath its feet and ignores altitude.

 

[smokinsound]

The altitude calculation comes from the air pressure measured by the barometer in the IMU.
Changing temperature causes changes in air pressure and can affect altitude readings.
You've already recalibrated the IMU so that's probably taken care of.
If you are flying in cold conditions better precision might be achieved by allowing the Phantom to warm up a little before liftoff.

The altitude reading shouldn't affect landing as the Phantom just comes down until it feels the ground beneath its feet and ignores altitude.

Thanks for the heads up! Not sure what it could have been. It was almost 80F today, and this screencap was during my second battery of flytime. I'm concerned about the altitude readings because I'm headed to a shoot next week in a very hilly area. I wish the P4P+ inspired more confidence to fly. A firmware update can't come soon enough.

 

[Doctorcobani]

You did the sensors calibration in DJI Assistance?

Enviado desde mi Nexus 6P mediante Tapatalk

 

[smokinsound]

You did the sensors calibration in DJI Assistance?

Enviado desde mi Nexus 6P mediante Tapatalk

Yes, performed the on-screen sensor calibration twice. This is the first time I've noticed this altitude discrepancy after 11 hours of flight time.

 

[GMack]

I've seen the altitude errors more times than I care to with my P4. Don't know what's up with it. Mine often lands showing -40 feet and often flies around at -6 feet. Takeoff is zero feet on GO.

I tried Autopilot last week and outgoing flights were okay at 30 feet, but coming back the drone was maybe 45 feet high while the Autopilot screen was still showing 30 feet. Autopilot now has some means of tightening up the altitude and distance and by default it was 16 feet so that might account for the error. If the DGI GO app has the same 16 foot tolerance by default or more, who knows? I did set the Autopilot tolerance to the minimum of 3 feet but I haven't repeated that flight pattern yet to see if it is correct on both coming and going.

For now, I set my safety buffer to about 50 feet to clear anything I think it could hit. Just do not trust the GO screen info and what the bird is really doing.

 

[photoskyview]

Maybe this can affect.

 

[Meta4]

View attachment 76307 Maybe this can affect.

No chance. Altitude readings are from air pressure and not affected by anything electromagnetic.
The k-index is mostly hype and nothing you need to be concerned about when you are flying.

Sent from my SM-G900I using PhantomPilots mobile app