Configuration for the quadcopter with a significantly offset center of mass

#1

We have an experimental “H”-type quadcopter. The flight controller is mounted at the geometric center of the craft. The battery, however, is mounted at the “tail”, so that the center of mass is, say, halfway towards the back from the geometric center. The motors / props at the back of the craft are the same as the ones on the front. We understand that it might be optimal to actually use different setups for front and back rotors.

What are the considerations here from the point of view of setting up the firmware?
I was considering two things:

  1. setting up a custom mixer
  2. setting EKF2_IMU_POS_{X,Y,Z} to the offset of the FC relative to the center of mass

As for the mixer I am a bit lost, since it seems, that there’s no way to account for the difference in moment arms for front and back rotors.

Any considerations for setting up PX4 for such a vehicle?

#2

Have a look at this https://github.com/PX4/Firmware/pull/8063
I’m not sure if there is documentation, you might want to do a quick search.
But essentially you can define your geometry in a toml file which then computes your mixer matrix.

#3
#4

And for the procedure personally I would suggest the following:

  1. Figure out where your CG is in the horizontal plane
  2. Add the numbers to the toml file and create a mixer from it (not docs yet but use the above links)
  3. Specify the offset of the IMU to the CG using the ekf offset parameters