Wrong AGL reported with 2.04.2500?

[Xitor]

Had a weird, first time event yesterday, I took off, got some shots, then lowered down and moved laterally to get some more shots, but for some crazy reason it was reporting like -12 feet AGL. However, I was on flat ground, maybe 8 feet above the true takeoff AGL. Anyone seen this before? IMU didn't report that it needed recalibration but will before next flight. I updated the aircraft firmware the day before. I guess its possible I had a barometric pressure change, but was only up for about 8 minutes. TBH though, I pay more attention to the altitude when in the air then close to the ground and of course flying visually.

 

[Meta4]

Had a weird, first time event yesterday, I took off, got some shots, then lowered down and moved laterally to get some more shots, but for some crazy reason it was reporting like -12 feet AGL. However, I was on flat ground, maybe 8 feet above the true takeoff AGL. Anyone seen this before? IMU didn't report that it needed recalibration but will before next flight. I updated the aircraft firmware the day before. I guess its possible I had a barometric pressure change, but was only up for about 8 minutes. TBH though, I pay more attention to the altitude when in the air then close to the ground and of course flying visually.

Because the height is calculated with a barometric sensor, it's common to see differences of 10 feet or more between launching and landing.

 

[FLDave]

Reference is always ATL (above takeoff level) not AGL (above ground level). The reference change may not be precise and it would go level when you fly downhill.

 

[old man mavic]

@Xitor the telemetry coming from the drone ,and shown on the device screen ,is more of a fun factor ,rather than really accurate figures, and it should be viewed as such, as @Meta4 mentioned ,those readings can be out by a long way,and should not be relied upon when flying the drone.

 

[Xitor]

Reference is always ATL (above takeoff level) not AGL (above ground level). The reference change may not be precise and it would go level when you fly downhill.

Thanks, and that was my understanding as well and why I mentioned I was flying on flat ground (AKA did not fly down a hill). Just have never seen, or at least noticed such a discrepancy. Even when landing at the take off location it showed me -14 feet (rough estimate, don't recall exactly). This much of a difference, and never seeing it before worried me that there was either a drone or firmware issue. I'm updating everything and will do a few test flights. If I don't see it again I'll write it off. Checking barometer yesterday, it was climbing at the time of my flight and the 14 ft change would have been a climb of about .014 or from 29.62 to 29.634 - not likely for a 22 minute flight, weather reports barometer was rising about .01 per hour.

 

[Meta4]

Even when landing at the take off location it showed me -14 feet (rough estimate, don't recall exactly).

That could be completely normal.

This much of a difference, and never seeing it before worried me that there was either a drone or firmware issue. I'm updating everything and will do a few test flights.

Updating firmware won't do anything to make the barometric sensor less subject to variability.
You could go back through your flight logs to see what the variation was between launch and landing heights (as long as the landing was at the same place and launching) to see if 14 feet was a one-off or something else.
If you have big differences, the only thing you can do to possibly improve it, is to recalibrate the IMU.

 

[TwoSticks]

I agree on the lack of accuracy. The main issue with the variability is that we are expected to use it as our reference for elevation. If our logs show we ignored the height, just assuming it was off by some amount, then what do we have as a way to report we followed the rules. It can be aggravating at times. I have landed several times in the takeoff spot with a negative number on the display or a number higher than takeoff. No issue if you’re not getting close to the ceiling.

 

[SkyeHigh]

I agree on the lack of accuracy. The main issue with the variability is that we are expected to use it as our reference for elevation. If our logs show we ignored the height, just assuming it was off by some amount, then what do we have as a way to report we followed the rules. It can be aggravating at times. I have landed several times in the takeoff spot with a negative number on the display or a number higher than takeoff. No issue if you’re not getting close to the ceiling.

It would be very unusual for the barometric sensor to be faulty but not impossible. Although every barometric sensor is individually calibrated during manufacture it is down to the drone’s onboard processing to convert the pressure being sensed to an above ground level height.

You should expect consistency between similar flights taken around the same time at the same location as air pressure changes are very slow. So the logs will be able to show if the variation in height is consistent as @Meta4 suggests to investigate.

As far as regulations are concerned, the drone is a consumer product and not expected to be 100% accurate but close enough to ensure it doesn’t error significantly and encroach the 500ft flight level.

 

[Meta4]

The main issue with the variability is that we are expected to use it as our reference for elevation. If our logs show we ignored the height, just assuming it was off by some amount, then what do we have as a way to report we followed the rules

The error is usually going to be about 10 feet or less.
That's not enough to worry about, particularly when the ground level between your launch point and what's below your drone can often vary by significantly more.
The rules aren't about the drone's height relative to the launch point anyway.

 

[SkyeHigh]

The rules aren't about the drone's height relative to the launch point anyway.

Absolutely and a point often incorrectly stated by many on this forum, and others.

As an example, if you were to take-off/launch at the base of a 400’ hill and flew to the top of the hill you would be 400’ above launch point but you can still climb further to a point 400’ above the top of the hill and only be 400’ above ground level. However at that point you would be 800’ above launch point.

The only thing relative to the ‘launch point’ is your RTH location and the start point for any horizontal distance measured.

 

[Drone alone.]

Had a weird, first time event yesterday, I took off, got some shots, then lowered down and moved laterally to get some more shots, but for some crazy reason it was reporting like -12 feet AGL. However, I was on flat ground, maybe 8 feet above the true takeoff AGL. Anyone seen this before? IMU didn't report that it needed recalibration but will before next flight. I updated the aircraft firmware the day before. I guess its possible I had a barometric pressure change, but was only up for about 8 minutes. TBH though, I pay more attention to the altitude when in the air then close to the ground and of course flying visually.

I also have had a strange situation with my Air 2s. I purchased the new Dji rc with screen and paired it with my Air2s did a firmware update as advised. The drone lifted off as normal but after ascending to a reasonable height it would only move forward very slowly and also The aircraft would not turn left or right. Was no point continuing so I flew the drone backwards to my launching pad which was flat on the ground and descended but it got to about 1/2 a metre above the pad and then a warning came up that it had reached minimum altitude and could not land. I stood there with the drone hovering for some minutes while I was thinking how to get this thing back on the ground. I didn't want to try and snatch the aircraft or do a prop shutdown without incurring damage to myself or the drone. In desperation I hit the RTH button and it did then land and shutdown. Now I have lost confidence in both the firmware update and the linking to the new rc. Previously I flew the drone with the supplied rcn1 in the kit and it always performed flawlessly. Any ideas what may have caused this?? I will do both a compass swing and an imu recalibration but at present it's too windy to fly anyway. Thanks in anticipation.

 

[Meta4]

I will do both a compass swing and an imu recalibration but at present it's too windy to fly anyway. Thanks in anticipation.

The issues you describe have nothing to do with the compass or IMU.
Reaclibrating them won't do a thing to address the issues.

 

[SkyeHigh]

“The drone lifted off as normal but after ascending to a reasonable height it would only move forward very slowly and also The aircraft would not turn left or right. Was no point continuing so I flew the drone backwards to my launching pad which was flat on the ground and descended but it got to about 1/2 a metre above the pad and then a warning came up that it had reached minimum altitude and could not land.”


If you upload your flight log as follows, one of our experienced pilots should be able to identify what was happening:

DJI Flight Log Viewer | Phantom Help

• Post your flight data to get help
• Go to DJI Flight Log Viewer | Phantom Help
• Follow the instructions there to upload your flight record from your phone or tablet.
• That will give you a detailed report on the flight data.
• Come back and post a link to the report it provides.

DJI Flight Log Viewer - PhantomHelp.com

 

[Drone alone.]

The issues you describe have nothing to do with the compass or IMU.
Reaclibrating them won't do a thing to address the issues.

Thanks Meta4 for your response.

 

[Drone alone.]

“The drone lifted off as normal but after ascending to a reasonable height it would only move forward very slowly and also The aircraft would not turn left or right. Was no point continuing so I flew the drone backwards to my launching pad which was flat on the ground and descended but it got to about 1/2 a metre above the pad and then a warning came up that it had reached minimum altitude and could not land.”


If you upload your flight log as follows, one of our experienced pilots should be able to identify what was happening:

DJI Flight Log Viewer | Phantom Help

• Post your flight data to get help
• Go to DJI Flight Log Viewer | Phantom Help
• Follow the instructions there to upload your flight record from your phone or tablet.
• That will give you a detailed report on the flight data.
• Come back and post a link to the report it provides.

DJI Flight Log Viewer - PhantomHelp.com

Will try that, thanks.

 

[PAW]

Will try that, thanks.

Ensure that in your Fly App SAFETY/DISABLE SIDEWAYS FLIGHT is turned off. That may be your side-to-side movement issue, don't have a clue about your forward speed issue.

 

[Drone alone.]

Sideways movement is enabled as it was when I attempted to fly the drone after linking new rc and updating to latest firmware. Thanks for your comment mate.

 

[smashse]

Maybe the homepoint updated after takeoff? Ive had this happen before, where I turned on, lifted off, and then it updated home point after I was 10' in the air and reported as 0'. Not normal, but maybe this had something to do with it?

 

[Meta4]

Maybe the homepoint updated after takeoff? Ive had this happen before, where I turned on, lifted off, and then it updated home point after I was 10' in the air and reported as 0'. Not normal, but maybe this had something to do with it?

Updating the hiomepoint makes no difference to the zero altitude which is set when the drone powers up.
Homepoints have no altitude associated with them.

 

[Xitor]

I also have had a strange situation with my Air 2s. I purchased the new Dji rc with screen and paired it with my Air2s did a firmware update as advised. The drone lifted off as normal but after ascending to a reasonable height it would only move forward very slowly and also The aircraft would not turn left or right. Was no point continuing so I flew the drone backwards to my launching pad which was flat on the ground and descended but it got to about 1/2 a metre above the pad and then a warning came up that it had reached minimum altitude and could not land. I stood there with the drone hovering for some minutes while I was thinking how to get this thing back on the ground. I didn't want to try and snatch the aircraft or do a prop shutdown without incurring damage to myself or the drone. In desperation I hit the RTH button and it did then land and shutdown. Now I have lost confidence in both the firmware update and the linking to the new rc. Previously I flew the drone with the supplied rcn1 in the kit and it always performed flawlessly. Any ideas what may have caused this?? I will do both a compass swing and an imu recalibration but at present it's too windy to fly anyway. Thanks in anticipation.

Funny you mention this, because I had the same experience on my flight an attributed it to signal interference. Not likely now though if we both had the same issue.