I have a custom designed x4 multicopter frame which is very similar to 3DR solo. The hand drawing is attached, sorry my bad drawings. The drone overall is nearly 6.5 kgs, and i use MN4014-9 400KV motors with 16" propellers.
For some tuning and stability tests, we observe the multicopter has unstable behaviours in HOLD or POSCTRL mode using INAV estimators. It climbs and can not hold altitude. We are digging the rates and attitudes PID gains to have more stable HOLD and position control before flying a mission autonomously. Should we use quad_x mixer in the attached drawing? Also any suggestions about PID tuning looking at drawing? I also have flight logs in HOLD and POSCTRL mode. We observe also not stabilizing the altitude hen it is in HOLD or POSCTRL mode after we manually takeoff.