Navigation modes
Navigation system can function in several modes: ALTHOLD, POSHOLD_2D, POSHOLD_3D, RTH, RTH_2D, WP. These modes are exposed to pilot as different flight modes or their combination: POSHOLD, ALTHOLD, RTH, WP. Lets have a look at each mode of operation in detail.
Roll, pitch and yaw inputs do not have any special meaning, their behaviour is determined by Cleanflight flight modes. Throttle input indicate climb or sink at a predetermined maximum rate.
Activated by ALTHOLD flight mode.
This mode is called 2D because only X and Y local coordinates are stabilised. Pitch and roll inputs control either lean angles or velocities in forward-right direction. Altitude (Z coordinate) is not stabilised.
Activated by POSHOLD flight mode.
This mode is a combination of ALTHOLD and POSHOLD_2D modes. When sticks are centered, copter will maintain position and altitude.
Activated by POSHOLD+ALTHOLD flight modes.
RTH and RTH_2D both will attempt to bring copter to launch position. Launch position is defined as a point where aircraft was ARMed. The only difference is that in RTH_2D mode machine will not maintain or control altitude. Throttle input goes straight to motors. Pilot can not manually choose between RTH and RTH_2D modes, firmware choose RTH or RTH_2D based on what sensors are available. RTH requires a position sensor and altitude sensor, while RTH_2D requires only position sensor
Activated by RTH flight mode.
This is a work in progress mode.
This flight mode affects on yaw axis and can be enabled together with any other flight mode. It helps to maintain current heading without pilots input and magnetometer's support. When yaw stick is neutral position, Heading Lock tries to keep total amount on rotation on yaw at zero. When pilot moves yaw stick, Heading Lock is not used. It is a equivalent of TauLabs Axis Lock mode
A diagram to indicate flight modes relation to navigation modes and illustrate sensor requirements:
