Smart controller displays incorrect height

[High View]

While flying the Air 2S with Smart Controller over a flat field at about 8 m, the controller indicated a height of minus 4.3 m. What should I change to get the correct height?

 

[Rich QR]

While flying the Air 2S with Smart Controller over a flat field at about 8 m, the controller indicated a height of minus 4.3 m. What should I change to get the correct height?

You could land and then take off again. That would reset the altimeter so that it would read 0 at your landing point.

For background, your altitude display shows barometric (pressure) altitude as referenced from your take-off point. It does not show height above sea level. If you are flying over ground that is at a different height than your takeoff point, the drone does not attempt to correct for this, but it continues displaying height above takeoff point (or below takeoff point, where it will indicate a negative altitude). It will reset to zero when the drone lands.

Of course air pressure changes with altitude, but it also changes with temperature, and it may change with the drone's orientation or speed, depending on the airflow over the sensor port. Full-sized fixed wing airplanes have a "static port" which is carefully located at a spot on the side of the plane, perpendicular to the airflow, so that the pressure measured at the static port will be minimally affected by changes in angle of attack or airspeed. But you can still get the plane's altimeter to show an apparent change in altitude by doing a side slip, to point the static port slightly toward or away from the airflow. Drones typically do not have a carefully calibrated static port, and the airflow over a drone may be coming from any direction. While a drone is in a GPS-stabilized hover, the speed and direction of airflow over the drone is determined by the wind.

All of the preceeding is a long-winded explanation of why you should expect the altitude indicated on the display to be somewhat inaccurate. A few feet of error is something you'll have to live with.

 

[zeusfl]

While flying the Air 2S with Smart Controller over a flat field at about 8 m, the controller indicated a height of minus 4.3 m. What should I change to get the correct height?

The aircraft sensors do not measure the current altitude location. They measure base in the take-off location.

 

[High View]

Thanks for your response. I was flying over a FLAT field when I noticed the negative numbers. I was practicing flying tighter and tighter orbits and figure 8s.

I can't think of any reason why those patterns should cause the incorrect numbers.

On the next flight, I'll check the numbers at a higher altitude. My biggest concern is that a RTH might get the wrong data.
I did notice that when I changed batteries the numbers were correct for a little while.

 

[Rich QR]

Thanks for your response. I was flying over a FLAT field when I noticed the negative numbers. I was practicing flying tighter and tighter orbits and figure 8s.

I can't think of any reason why those patterns should cause the incorrect numbers.

On the next flight, I'll check the numbers at a higher altitude. My biggest concern is that a RTH might get the wrong data.
I did notice that when I changed batteries the numbers were correct for a little while.

I used to live in South Florida, and when someone in your area says a field is flat, I believe it.

In your case, I'd guess the most likely source of error was a change in temperature of the barometric sensor. The electronics in the drone produce heat, and of course flying out in the Florida sun can make things warm up, as well.

 

[RGS2010]

While flying the Air 2S with Smart Controller over a flat field at about 8 m, the controller indicated a height of minus 4.3 m. What should I change to get the correct height?

Did you take off from a hill and go down into a valley or take off from your car roof or ???

 

[High View]

No flying on a flat field.

 

[Meta4]

Thanks for your response. I was flying over a FLAT field when I noticed the negative numbers. I was practicing flying tighter and tighter orbits and figure 8s.

I can't think of any reason why those patterns should cause the incorrect numbers.

The indicated altitude comes from a sensor that measures small changes in air pressure.
It's common and normal for the indicated altitude to change over the course of a flight by 10 or more feet.

On the next flight, I'll check the numbers at a higher altitude. My biggest concern is that a RTH might get the wrong data.
I did notice that when I changed batteries the numbers were correct for a little while.

The altitude will be reset each time the drone is powered off and on again.
There is no altitude number in the recorded home point.
There won't be any problem with RTH, as long as you have set your RTH height with a comfortable safety buffer to clear any obstacles in the vicinity.

 

[Dave Maine]

The altimeter is in the drone. It’s measurements are included in the downstream telemetry from the drone to whatever controller you are linked to and flying with. The controller does nothing but display the drone’s barometric height from the launch point.