MultiWii 2.2 Flight Modes Explained

[iWolf51]

As a multirotor noob I';ve found theres a great deal to learn if you want to use and tune the MultiWii firmware.
Theres certainly a lot of information to be had, but it can be very time consuming finding and wading through many pages of forum posts to get the answers you want.

The following is the best description I';ve been able to put together that explains MultiWii 2.2 flight modes and the sensors required for them to work.
I hope it helps others to understand the available flight control options and how you can use them.

It combines information from the following topics on the multiWii website.
MultiWii flightmodes table: http://www.multiwii.com/wiki/index.php?title=Flightmodes
MultiWii flightmode names: http://www.multiwii.com/forum/viewtopic.php?f=16&t=3011&hilit=flight+mode+names

MultiWii V2.2 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 controls.

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 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 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)

. 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:
   - 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).

. 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).


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.

[philtrum]

Nicely written, thank you

[JT]

. 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.

Headfree doesn';t hold the yaw position or the orientation, the multicopter is still free to yaw about to its hearts content. What it does do is as you have said, hold the pilots 2d perspective, that is to say regardless of the orientation of the multirotor left stick will move it to YOUR left, right YOUR right etc, as long as you are facing the same way as the craft when it was armed.  Headadj sets up a new reference for the headfree.

[barneyg]

Also for clarity ... Angle/Horizon and Mag mode MUST be enabled for GPS hold and GPS home to work

[iWolf51]

Thanks for the feedback chaps.

Being new to multicopters and MultiWii 2.2 I haven';t personally tested all the flight modes yet.

However, the operation of the features listed in the OP is lifted from the MultiWii forum and the explanations there were given
by a senior member in a lengthy and detailed discussion on the subject. (see the linked topics).

I';ll be testing more of the multiWii modes in a week or so, when I get my quad back in the air.
I should then be able to confirm whether the information on their forum is correct or not.

[Hands0n]

I know that this is a very old topic - but seeing as I am working on Baseflight today and got wondering about flight modes I found this topic and also updated MultiWii wiki page (see below) that gives good explanations of the various modes.  Some little more clarification required in places, but this is good.

Applicable to Baseflight and Cleanflight - both derivatives of MultiWii of course, these mode descriptions apply to the two flight OS.

MultiWii Wiki Flight Modes page: http://www.multiwii.com/wiki/?title=Flightmodes