  A mini scale helicopter exhibits not only increased sensitivity to control
inputs and disturbances, but also higher bandwidth of its dynamics. These
properties make model helicopters, as a flying robot, more difficult to
control. The dynamics model accuracy will determine the performance of the
designed controller. It is attractive in this regards to have a controller that
can accommodate the unmodeled dynamics or parameter changes and perform well in
such situations. Coefficient Diagram Method (CDM) is chosen as the candidate to
synthesize such a controller due to its simplicity and convenience in
demonstrating integrated performance measures including equivalent time
constant, stability indices and robustness. In this study, CDM is implemented
for a design of multivariable controller for a small scale helicopter during
hover and cruise flight. In the synthesis of MIMO CDM, good design common sense
based on hands-on experience is necessary. The low level controller algorithm
is designed as part of hybrid supervisory control architecture to be
implemented on an onboard computer system. Its feasibility and performance are
evaluated based on its robustness, desired time domain system responses and
compliance to hard-real time requirements.
