Ardupilot - Middle Throttle Stick.

Credit to this instruction

https://discuss.ardupilot.org/t/pilot-thr-behaviour-parameter-use/53103

If you have a center sprung throttle stick, you want PILOT_THR_BHV set for a value of 7. Also set MOT_HOVER_LEARN to a value of 2, for learn and save. Your hover throttle will be set automatically while hovering.

And this will only work for Alt Hold and Loiter Flight Mode.