Hi Josh, Max did a good job with his answer here too but I may be able to offer a simple explanation.
The most force is availible to controll roll, pitch and yaw when throttle is at 50%. That measn half the motors can be at maximum and half at minimum to control one of the rotational axis.
Because we proritise yaw over thrust an over loaded quad that is hovering at 60% will loose some altitude when we use 100% yaw output. Without ATC_THR_MIX parameters a quad that is occilating or using 100% yaw for example, a quad that hovers at 25% throttle would climb. Both of these are caused by the fact that if roll, pitch or yaw goes to 100% output then by definition the thrust is 50%.
We use the ATC_THR_MIX parameters to define how and when we prioritise thrust over roll, pitch and yaw. And how much.
ATC_THR_MIX_MIN is for landing
ATC_THR_MIX_MAX is for normal flight
ATC_THR_MIX_MAN is for manual flight
These are the main cases to consider:
- Landing - we want throttle to be able to be reduced during landing to a point the aircraft can settle flat on a surface that isn’t level.
- Occilation- An aircraft that is over tuned and is occilating we want to have enough control athortiy to reduce the average thrust below hover throttle. Before we did this an occilation on a power quad could cause an uncontrolled climb (and it did).
- Breaking - During breaking the thrust is reduced, sometimes to zero. We want to have a compromise between attitude control and height control.
We found that we needed a seperate landing setting to dynamic flight setting because some aircraft would flip during a breaking manuver using ATC_THR_MIX_MIN. So we only go to ATC_THR_MIX_MIN when the aircraft may be landing. We basicly check that the aircraft is decending and not making any aggressive manuvers.