How to keep a drone upright

using accelerometers always try to keep them at 0 except if you press a button then the desired pitch changes.

https://www.reddit.com/r/diydrones/comments/1cm8ykx/how_is_stable_flight_possible/

https://github.com/lobodol/drone-flight-controller https://github.com/liourej/CodeDroneDIY https://electronoobs.com/eng_robotica_tut9_2_2.php

https://www.youtube.com/watch?v=4vpgjjYizVU