Resonant frequency calculation and test for damper of two axes four-gimbal EO pod

The selection of the dampers for two axes four-gimbal electro-optical (EO) pod is investigated according to vibration theory. A frequency scanning vibration test was carried out for a helicopter pod whose inner gimbal was connected with the outer gimbal by rigid link. The resonant frequency and amplification factors were measured and the amplification curves were drawn. Using the amplification curves, the stiffness of the rigid link between the inner and outer gimbals of the pod in three direction was calculated. With the stiffness value of the damper, using cascade spring connection calculation method, the three direction rigidity and resonant frequency of the pod were calculated again with damper installed. The pod was tested again and the results indicate that the resonance frequency and amplification factor meet the requirement. It is concluded that three factors shall be considered for the selection of dampers, its amplification range shall be within the servo bandwidth, system resonant frequency shall avoid external disturbance frequency, and amplification factor shall be minimized.