When I use Ardupilot ALTHOLD, the altitude goes up and down a lot and it is not stable. The FC is MATEK F405STD.
That’s usually just some tuning required, as the copter might be too unstable to hover long enough at one altitude for the hover throttle to learn.
If the copter is over-powered, the hover throttle value will only go so low without you manually setting it.
You can check in a log for CTUN.ThO (throttle out) and average that value over a period of flight with the most stable altitude, then set that value in MOT_THST_HOVER
You may need to adjust that hover thrust value over time to get it just right, and the copter should hover OK at mid-throttle stick.
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Thanks. I’ll try that. I noticed something else when I looked at the data: the BARO value is quite strange. Sometimes it goes negative in the air. This is not the case with airplanes with FC inside the fuselage. Could this be the effect of the wind? Could this also be the reason why I can’t hold ALT? I’m thinking of covering the bmp280 with a soft sponge.
The sponge or foam over the baro is a good idea. Matek does that on the boards with two levels like the F405-VTOL and the H743-Wlite.
The other thing you can do is the Windspeed Estimation and Baro compensation. You’ll have to do the calculations manually because you can’t run the calibration script on an F405, but it will help a lot too.
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