Sorry for bring this up again but what is the exact difference between ATC_THR_MIX_MAN vs ATC_THR_MIX_MAX?
I have on my 7inch ATC_THR_MIX_MAN,4 and ATC_THR_MIX_MAX,0.5 since years and it is flying great in Acro and Auto.
I am working on a heavy Y6 copter and while descending it gets instable. In 9.6 Performance evaluation flight of the Methodic Configurator they suggest to set ATC_THR_MIX_MAX,0.9. With ATC_THR_MIX_MAX,1.1 I can descent in ALTHOLD full stick and it stays stable.
Is it therefore correct that ATC_THR_MIX_MAN is for Acro and Stabilize and ATC_THR_MIX_MAX for ALTHOLD, LOITER, AUTO?
First, ATC_THR_MIX_MIN is the value used when landing. This also applies to manual throttle mode (Acro and Stabilize) when the throttle stick is around the minimum - unless you configured the so called “air mode” (see ACRO_OPTIONS, RCx_OPTION = 84, and arming options 153 vs 154). The concept of air mode is a bit challenging, and I would need to refresh my codebase knowledge before properly commenting on that.
Otherwise, manual modes use ATC_THR_MIX_MAN and managed modes use a linear interpolation between ATC_THR_MIX_MAX and ATC_THR_MIX_MIN depending on various aspects of the flight.
And one more: setting any of these, including the _MIN, to above 1 does not ultimately prevent descending. If there are no problems with attitude holding, throttle can go down to whatever desired. But if/when the control authority is not enough to command outputs to hold attitude, higher mixer values would allow throttle to increase above what you command.
In other words, in rapid descent with a commanded zero throttle, there is a direct conflict between maintaining the commanded throttle and maintaining the commanded attitude. In different flight modes, the desired trade-offs are different:
In Acro, you may find yourself in such a situation e.g. when diving: you want to fall, but you still want perfect attitude control, which results in some propellers running hotter than others, which means you do not descend as fast as a brick of the same mass and shape. Theoretically, given particular attitude, mass, area and wind speeds, with ATC_THR_MIX_MAN = 4 the machine can go up with minimum throttle - but since the pilot is actively engaged when flying in Acro, they can always find a way out of that.
In managed modes when landing, you usually have the maximum descent speed configured. The machine will try to follow that as well as it can do, and if the control authority is too weak, the machine may start wobbling. For example, one may aim at optimizing for the maximum descent speed, while keeping maximum attitude deviations below X degrees under 99% of possible environmental conditions - which one would do by carefully configuring the landing speed and MIX_MIN.