Comprehensive System Identification of Ducted Fan UAVs - Cal Poly

A 0th/2nd order transfer function is included in the identification to take intoaccount the actuator dynamics. The form of this transfer function is as follows:ωn 2TF =s 2 + 2ζω n+ ωn 2The values of the damping and natural frequency of the actuator used wereobtained from bench tests of the actuator dynamics presented in section 3.3 for theAirtronics 94091 servo actuator running at nominally 5 volts. The natural frequency forthis case is 28.2 rad/sec and the damping ratio is 0.52.The DERIVID utility was used to identify the elements of the state-space model.The stability derivative results are shown Table 3.8.Table 3.8 – MAV Identified Stability DerivativesCOUP02Derivativ e Param Value CR Bound C.R. (%) Insens.(%)X u -0.1090 0.04395 40.33 10.92M u 0.5014 0.03412 6.805 2.729M q 0.000 + ...... ...... ......M p 0.000 + ...... ...... ......Y v -0.1090 * ...... ...... ......L q 0.000 + ...... ...... ......L v -0.5014 * ...... ...... ......L p 0.000 + ...... ...... ......I pr op 0.000 + ...... ...... ......+ Eliminated during model structure determinationy Fixed value in model* Fixed derivativ e tied to a free derivativ eY v = 1.000E+00* X u ( COUP02 )L v =-1.000E+00* M u ( COUP02 )The value of the rotating inertia (I prop ) was insensitive in the identification andwas dropped from the list of active elements. This is because there was no goodcoherence in the off-axis roll and pitch rate responses, which result for the gyroscopic- 39 -