This project started out as an experiment. The idea was that standard flight controllers should be able to control non-planar shaped quadrotors as long as the control board is mounted near the center of gravity. I decided to try the idea out. The project addresses the symmteric / non-symmetric forms of non-planar motor layouts.

Basic Theory

Quadrotors control their attitude using the thrust generated from each rotor on the arms. The torque which control the attitude is generated by the thrust difference of the motors. Moving the motor location in the z axis does not change the moment arm which results in the same amount of torque generated from the thrust.

What does change, however is the moment of inertia. If the quadrotor is symmetric, the non-diagonal terms of the inertia tensor would be zero, thus from the equation of motion below, there will be coupling of body angular rates. In case of a non-symmetric configuration, the non-diagonal terms will have nonzero values.

The image below shows an example of symmetic quadrotor and a non-symmetic quadrotor examples. As the quadrotor stays near hover, the effect of non-symmetry will be small but in high body angular rates, the quadrotor will show strange control characteristics.

Dihedral attachment of rotors on ordinary quadrotors may enhance stability. However, if the arms are attached in a different plane with the center of gravity, such configurations may make the system less stable or unstable.