  It is well known that the conventional quadrotor is an under-actuated MIMO
system. The number of the inputs is less than the degree of freedom. One
approach in controlling this non-holonomic system is feedback linearization. In
the frequently cited (305 times) application, the yaw and the position are
selected as the controlled variables. It is reported that no singularity is
found in their delta matrix, making it possible to apply the inversion within a
wide range. However, we find the ignored singular zone within the range of
interest. The unreported singular area can cause the failure in the controller
design. This paper visualizes this uninvertible area and details the deduction
process.

Systems and Control;Systems and Control