We are facing a gradual altitude increase during AUTO missions on an agri drone (MTOW 27 kg) running Cube Orange+ (ArduCopter 4.4.4) with a single HERE4 (CAN, FW 1.39), where EK3_SRC1_POSZ is set to 3 (GPS). Visually, the drone climbs higher than desired but the HUD and logs do not reflect a matching altitude change. The HERE4 barometer is disabled (default CAN setting), we are not using RTK, and altitude is explicitly set to GPS source. Bootloader update was completed but did not change behavior. Any guidance on parameters, GNSS/CAN settings, or validation steps to isolate the root cause would be appreciated.
We’ve tried running the same test with Here3Plus GPS (Barometer still disabled) & it works perfectly over the course of multiple flights.
The problem persists only with the Here4 GPS module.
Just to clarify something that can often cause the behavior you’re seeing: the Here4 module does include an onboard barometer (MS5611) in addition to GNSS/IMU sensors. That barometer is the better altitude source because it’s higher resolution for vertical motion than GNSS.
If you completely disable the barometer, ArduPilot has no choice but to use GNSS altitude alone. GPS-derived altitude — even with RTK corrections — is much noisier and less accurate than barometric altitude, especially over short time scales. So seeing the vehicle slowly drift upward or diverge from the planned altitude in AUTO isn’t surprising; GPS height simply doesn’t hold as tight a vertical reference as baro does.
This hypothesis is supported by your report that the HUD and logs do not reflect a matching altitude change.
For a stable altitude estimate in AUTO/Loiter, keeping the barometer enabled (and properly mounted/masked from airflow) is recommended.
Thanks for the response.
We’ve tried running the same test with Here3Plus GPS (Barometer still disabled) & it works perfectly over the course of multiple flights.
The problem persists only with the Here4 GPS module.