  With the introduction of the laterally bounded forces, the tilt-rotor gains
more flexibility in the controller design. Typical feedback linearization
methods utilize all the inputs in controlling this vehicle; the magnitudes as
well as the directions of the thrusts are maneuvered simultaneously based on a
unified control rule. Although several promising results indicate that these
controllers may track the desired complicated trajectories, the tilting angles
are required to change relatively fast or in large scale during the flight,
which turns to be a challenge in application. The recent gait plan for a
tilt-rotor may solve this problem; the tilting angles are fixed or vary in a
predetermined pattern without being maneuvered by the control algorithm.
Carefully avoiding the singular decoupling matrix, several attitudes can be
tracked without changing the tilting angles frequently. While the position was
not directly regulated in that research, which left the position-tracking still
an open question. In this research, we elucidate the coupling relationship
between the position and the attitude. Based on this, we design the
position-tracking controller, adopting feedback linearization. A cat-trot gait
is further designed for a tilt-rotor to track the reference; three types of
references are designed for our tracking experiments: setpoint, uniform
rectilinear motion, and uniform circular motion. The significant improvement
with less steady state error is witnessed after equipping with our modified
attitude-position decoupler. It is also found that the frequency of the
cat-trot gait highly influenced the steady state error.
