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Why does the telemetry altitude steadily increase when the copter is just sitting in a room?

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Hi,

I noticed that the altitude shown on the ST16S is steadily rising when the drone is just sitting here on the ground doing nothing.

I thought that it's because of the rising temperature inside the enclosure (rising temperature=lower pressure), but there are two problems with this hypothesis. 1) the pressure should be equalized with the outside pressure because the drone's body has vents and 2) I thought that barometric altimeters factor in the temperature when they are calculating the altitude.

Can someone shed some light on this topic?
 

WTFDproject

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I did a search on the word "altimeter" just on this forum. I got 10 pages of results, most of them pretty much saying "don't worry, it's normal". You might want to read a few to compare with what you are seeing.
 
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May be it is because GPS accuracy is getting better over time(drone gps can see more satellites being in the air) and you get a more accurate altitude with it.
 

Steve Carr

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May be it is because GPS accuracy is getting better over time(drone gps can see more satellites being in the air) and you get a more accurate altitude with it.
The GPS is not used to determine altitude. It is derived from a combination of the barometric sensor and the accelerometers.
 
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If you mean for a drone, may be but GPS in general should be able to provide coarse altitude without a barometric sensor.

Global Positioning System (GPS) receivers can also determine altitude by trilateration with four or more satellites.
Altimeter - Wikipedia


But, it seems I have answered a wrong question. For some reason I thought we were talking about a drone hovering outside while it was about a drone on a ground and indoor. My bad anyway.
 
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@WTFDproject I know it's normal :) I saw this in many Yuneecs (all were flying fine). My question is not a troubleshooting one. My question comes from technical curiosity :). I would just like to know why.

@Steve Carr interesting, because PX4 logs show graphs for barometer altitude, GPS altitude and fused altitude estimation. Flight Review

@Wingman - I don't think so, because the discrepancy between real altitude (steady 0m AGL) and telemetry altitude (steadily rising) is increasing with time.

I made a test yesterday with H520. Altitude rose to about 8 meters quite fast, then was increasing slower and slower, after about 40 minutes it was 15 meters.
 
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Steve Carr

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Perhaps the calculation has changed with the H520 and H Plus regarding the use of GPS altitude. Does the altitude change a similar amount when the aircraft is outside?

The altitude drift is common on startup and I presume it is related to temp changes in the baro sensor. It resets to zero when the motors start. I would expect the baro sensor and GPS alt calculation to be somewhat rough and the accelerometer calc to be more accurate for small changes. You can see that by simply raising the aircraft a few feet by hand.
 
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arruntus

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Perhaps the calculation has changed with the H520 and H Plus regarding the use of GPS altitude. Does the altitude change a similar amount when the aircraft is outside?

The altitude drift is common on startup and I presume it is related to temp changes in the baro sensor. It resets to zero when the motors start. I would expect the baro sensor and GPS alt calculation to be somewhat rough and the accelerometer calc to be more accurate for small changes. You can see that by simply raising the aircraft a few feet by hand.
Temperature creates small pressure changes but especially pressure changes in small rooms. Opening or closing a door or window with negative pressure from another point quickly increases the pressure in the room and therefore affects the altitude, in the same way it happens the other way around. Let's remember that in a drone, the altitude is relative to the takeoff point in an open zone, where the pressure changes that we have commented in closed places, do not take place, they generally take place by the wind, the density of the air and those caused by temperature changes. An algorithm is in charge of eliminating them so that they are not reflected in the height. That's why we have a thermometer in our drone. Normally it figures as temperature of the electronics.
 

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