The Twin Rotor MIMO System (TRMS) behaviour resembles that of a helicopter. From the control point of view it illustrates a high order nonlinear system with significant cross-couplings. A mathematical model design of TRMS needs knowledge of aero dynamical physical laws. The TRMS system has been designed to operate with a PC-based digital controller that communicates with the position, speed sensors and motors by a dedicated I/O. The I/O board is controlled by the real-time software which operates in the MATLAB / Simulink RTW/RTWT environment.
The TRMS consists of a beam pivoted on its base so that it can rotate freely both in the horizontal and vertical planes. At both ends of the beam there are rotors driven by DC motors. A counterbalance arm with a weight at its end is fixed to the beam at the pivot. The state of the beam is described by four process variables: horizontal and vertical angles measured by encoders fitted at the pivot, and two corresponding angular velocities.
Two additional state variables are the angular velocities of the rotors, measured by speed sensors coupled with the driving DC motors. In a real helicopter the aerodynamic force is controlled by changing the angle of attack. In the TRMS the angle of attack is fixed. The aerodynamic force is controlled by varying the speed of rotors. Significant cross-couplings are observed between actions of the rotors. Each rotor influences both position angles. A design of stabilising controllers for TRMS is based on decoupling.