When I first started with Multiwii, I was completely lost with all the flight mode names in the GUI. I can roughly figure out or guess some of them, and what they do, but I wasn’t 100% sure. So this post is going to discuss what each mode means and what they do.
You might find you have fewer flight modes in your Multiwii interface, you can enable them in your config.h file. But as long as you don’t need them you should keep the options minimal. I will discuss the few that we use most often here.
These flight modes are defined and can be assigned to transmitter AUX switches in the MultiWiiConf GUI.
Arm (Acro Mode)
This flight mode indicates whether your airplane is armed or not for flying.
If nothing else but this is enabled, you are automatically using the acro mode (acrobatic mode), which only needs the gyro sensor. The angle of your RC transmitter translates to how fast the copter rotates around that axes, it will not level when you let go of the sticks, and it will continue to move.
To make it stops when you let go of the sticks, you need to enable the accelerometer in self-level mode (angle or Horizon modes) which I will discuss in a minute.
The acro mode allows acrobatic flights e.g. you can do flips. You also usually need to adjust your PID values first in this mode before using other modes.
Angle (Self Level Mode)
I think this mode is known as stable or self level mode. It uses theaccelerometer (ACC) and the gyroscope to keep the multicopter self-level when there is no control input. To fly well under this mode, you need your accelerometer calibrated, and trimmed first.
However I would say ANGLE mode is obsolete. HORIZON mode is preferable in most cases.
In fact it is a mixture between ACRO and ANGLE combining the stabilizing effect in case of calm RC transmitter sticks are available and acrobatics e.g. flips in case of busy RC stick.
HORIZON MODE= ANGLE MODE mode when PITCH/ROLL sticks are centered
The barometer is used in this mode for keeping the plane at certain height unless there is no other command from Pilot.
BARO MODE needs: gyro + acc + baro (acc is needed to estimate the Z acceleration in this mode)
The magnetometer or compass is used in this mode. It is also a prerequisite for the HEADFREE mode.
When Mag Mode is enabled, if there is no yaw input, the copter will point forever to the same direction. MAG can be activated in all flight stabilization methods. Without this mode, you will still have a light deviation (drifting around the Z axis due to the imperfection of the gyro).
MAG MODE needs: gyro + acc + mag sensors (acc is needed also because it is used in heading angle determination)
This mode uses compass and GPS for the purpose of returning home to the starting point. Stabilization is done in accordance to the flight mode (ANGLE, HORIZON, or ACRO). The GPS altitude is not very accurate and therefore not usable for holding the height (usually the job for the sonar or baro sensor). GPS mode does not rely on baro sensor.
GPS POS HOLD of GPS HOME is generally used in coordination with ATL HOLD, but this is not mandatory.
You can imagine a GPS POS HOLD navigation inside a column. You can activate ALT HOLD and the GPS mode will use the same altitude.
Both GPS HOME, GPS HOLD can be activated in ANGLE or HORIZON mode
Hold current position using GPS and baro (if available).
It is not impacting the flight mode (ANGLE, HORITON or ACRO) only holding the orientation (yaw) of the copter and will always move in the same 2D direction for the same (roll-pitch) stick movement. In another word, HEADFREE holds the pilots 2D perspective as reference, MAG does not, both give a drift free tail.
HEADFREE can be activated with MAG mode.
It allows you to set a new yaw origin for HEADFREE mode.
Main flight modes, only one of the following can be active at any time:
- is the default mode when HORIZON or ANGLE are not activated.
- Uses: gyro only.
- stable mode if the 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.
- 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:
- 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.
- Heading lock mode. Can be activated in all flight stabilization methods.
- The multi 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)
- 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.
- 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.
- 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 never used in a control loop (only for display).
- 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.
- Hold current position using GPS and baro (if available).
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.