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The Multiwii flight controller can be used in several different modes, depending on the sensors that are present. The table below shows the the modes and the sensors that are used:

Mode Gyroscope Accelerometer Barometer Sonar Compass (mag) GPS Optical Flow Sensor
Acro / Gyro only X
Stable / Level / Acc / Angle X X
Horizon X X
HeadFree (CareFree) X X X X o
Altitude Hold X X X
GPS Return to Home X X o X X
GPS Waypoint X X o X X
GPS Position Hold X X o X X
Failsafe X

X = Required Hardware/Mode, o = Recommended Hardware/Mode

  • Acro Mode, Stable Mode and Horizon Mode are exclusive.
  • HeadFree (CareFree), altitude hold and GPS mode all work simultaneously.
  • GPS functions all require Level Mode / Mag / GPS however Altitude hold is also advisable hence a Baro is recommended.

FIXME: outdated:

  • Features not implemented or only partially in 2.2:
    • Sonar based Altitude hold, sonar based beeper and landing lights work.
    • Optical Flow Sensor based Position Hold / Nav is not implemented, pending some code submissions by some nice volunteer.
    • GPS Waypoints have a very simple single waypoint mode in 2.2, currently being worked on for 2.3 (as of 5 June 2013)

NB: This is a work in progress, please check in the forums or IRC channel if you are unsure.

MultiWii (V2.2 & newer) Flight Modes

  • A number of flight modes are defined and can be assigned to transmitter AUX switches in the MultiWiiConf GUI.

Motor Control

  • ARM - Arms motors, can be used as an alternative to the transmitter stick command.

Main flight modes, only one of the following can be active at any time

  • ACRO - is the default mode when HORIZON or ANGLE are not activated.
    • Uses: gyro only.
  • ANGLE - stable mode if the Pitch, Roll, Yaw and Level PID values are correctly adjusted and the gyro and the accelerometers have been calibrated and trimmed.
    • According to MultiWii developers ANGLE MODE is virtually obsolete, HORIZON MODE is preferable in most cases.
    • Uses: gyro and accelerometers.
  • HORIZON - A mixture between ACRO and ANGLE modes. Combining the stabilising effect with calm rc sticks and acrobatics with busy rc sticks.
    • ANGLE MODE mode when PITCH/ROLL sticks are centered. ACRO MODE mode when full PITCH or ROLL sticks are applied, allowing flips.
    • Uses: gyro and accelerometers.

Additional flight modes that can be activated in combination with main flight modes and each other

  • BARO - The barometer only is used, for the purpose of keeping a certain height. While there is an no other command from rc sticks.
    • Needs: gyro + acc + baro (acc is needed to estimate the Z acceleration in this mode)
    • You can activate BARO (ALT HOLD) and the GPS modes will use the same altitude.
  • MAG - Heading lock mode. Can be activated in all flight stabilization methods.
    • The multirotor will continue to point in the same direction until there is a yaw input. Without this mode, you will still have a light deviation (like a tail gyro in heli).
    • compared to no MAG offers a drift free tail, just like the difference between heading hold and conventional helicopter gyros.
    • Needs: gyro + acc + mag sensors (acc is needed also because it is used in heading angle determination)
  • HEADFREE - Does not impact the flight mode (ANGLE/HORIZON/ACRO). It only holds the orientation (yaw) of the multi and will always move in the same 2D direction for the same ROLL/PITCH stick movement.
    • Can be activated with MAG mode
    • Holds the pilots 2D perspective as reference, MAG does not, both give a drift free tail.
  • HEADADJ - Sets a new yaw origin for HEADFREE mode.

GPS Modes

  • can be activated in ANGLE or HORIZON flight modes.
  • will be ignored if there is no GPS lock at time of arming. It is advisable to uncomment #define ONLY_ALLOW_ARM_WITH_GPS_3DFIX in config.h if you want to use GPS modes.
  • are generally used along with ALT HOLD, but this is not mandatory.
  • The mag sensor is mandatory for GPS control, but MAG mode is not.
  • Activation of MAG MODE has no effect in GPS MODE.
  • GPS altitude is low quality and never used in a control loop.
  • GPS HOME - Uses compass and GPS for the purpose of returning home to the starting point.
    • Stabilisation is done in accordance with the flight mode (ANGLE/HORIZON). The GPS altitude is not very accurate and therefore not usable for holding the height.
  • GPS HOLD - Hold current position using GPS and baro (if available).
  • GPS HOLD/HOME works only if there are more than 5 satellites seen, and ARM must be ON to see the mode displayed in GUI

Additional information

PITCH/ROLL rate is used in ACRO and HORIZON modes. You will see the effect of PITCH/ROLL rate in HORIZON MODE if you try to make a flip.

If using ACRO+MAG or ACRO+BARO the acc sensor is only used for sensor fusion, and does not contribute to roll or pitch stabilization. In these cases, acc sensors are used indirectly for MAG & BARO, not to compensate PITCH/ROLL inclination.

If you exceed the 25deg PITCH/ROLL limit, the heading won't be used anymore to correct the orientation, but the yaw gyro will still maintain the heading. It's not a problem if this situation is short (eg. for a flip or looping).

The mag orientation is not accurate if the tilt is too high, MAG MODE correction is deactivated after 25deg inclination.