IMU Mounting Orientation Settings
Any AutoQuad board can be mounted facing whichever direction you want (rotation). Also, any AQ that is based on a DIMU (M4 or AQ6 with add-on) can be flipped 180 degrees around the pith or roll axis so that it can be mounted upside down. This is especially handy for M4 where you might need to flip it upside down to give better access to the expansion headers.
Between the two options, you have complete freedom to mount your DIMU based AQ board anyway you will want. You can find the settings in the “Misc. Settings” tab in QGC.
Flight direction (IMU rotation)
The first image will show the default flight direction (IMU Rotation = 0), but the parameter IMU_ROT allows for any angle in degrees. The second picture will need an IMU Rotation of -45, for example.
Here is the M4 rotated -45 degrees:
Flip setting (which way is up)
This setting is only available with a DIMU-equipped board. The flip function is controlled by a single parameter:
#define DEFAULT_IMU_FLIP 0 // flip DIMU: 0 == none, 1 == around Y (roll) axis, 2 == around X (pitch) axis
The comment says it really, but lets make an example with an M4:
Default orientation for M4 is a plus configuration with the MCU side up and Arm1 pointing forward.
If you flip around the Y (roll) axis, you then set IMU_FLIP = 1, write to flash, restart and flip the board 180 degrees on the roll axis. Notice that Arm1 is still pointing forward after a roll axis flip.
Rotation and flip
Now let’s put the two examples together. Say you want to mount an M4 upside-down and in an X configuration. You then enter a value of -45 degrees into the IMU Rotation field and specify the Y axis for DIMU Flip setting (IMU_FLIP = 1). Save the parameters, restart, and now the IMU will be rotated to bring M1 to the forward left position.