Dynamics Modeling and Theoretical Study of the Two-Axis Four-Gimbal Coarse-Fine Composite UAV Electro-Optical Pod  
[PERSON]  
1 College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China; [EMAIL_ADDRESS] (C.S.); jdl123 [EMAIL_ADDRESS] (X.J.); [EMAIL_ADDRESS] (R.T.); [EMAIL_ADDRESS] (D.F)  
[PERSON]  
1 College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China; [EMAIL_ADDRESS] (C.S.); jdl123 [EMAIL_ADDRESS] (X.J.); [EMAIL_ADDRESS] (R.T.); [EMAIL_ADDRESS] (D.F)  
[PERSON]  
1 College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China; [EMAIL_ADDRESS] (C.S.); jdl123 [EMAIL_ADDRESS] (X.J.); [EMAIL_ADDRESS] (R.T.); [EMAIL_ADDRESS] (D.F)  
[PERSON]. 1 College of Intelligence Science and Technology, National University of Defense Technology, Changsha 410073, China; shensicheng1996@sina.  
A previous study [10] adopted external prestressed steel, which is applied to concrete cylinder pipes. This derivation configures the prestress of steel strands to meet the requirements of ultimate limit states, serviceability limit states, and quasi-permanent limit states, considering the tensile strength of the concrete core and the mortar coating, respectively. Another study [11] presents a simplified mathematical model for the analysis of varying compliance vibrations of a rolling bearing. The results of the parametric analysis demonstrate that, with the proper choice of the size of the internal radial clearance and external radial load, the level of the varying compliance vibrations in a rolling bearing can be theoretically reduced to zero. In the literature [12,13], an aluminum conductor steel-reinforced cable and a racing tire are modeled to study their vibrations and finite element analysis. The above modeling methods are worth being referred to. However, these methods do not study the two-axis four-gimbal electro-optical pod for use in a UAV, and there is lack of experiments on dynamics modeling of a coarse-fine composite structure platform.  
Another previous study [14] analyzed the equal-acceleration model of a two-axis four-gimbal maneuvering target. Taking the equivalent sinusoidal movement and the uniform linear movement as examples, the system was simulated. The results show that the precision of the coarse-fine composite control is higher than that of single-detector control, and the two-axis four-gimbal structure is simple and suitable for engineering implementation. Reference [15] presents the magnetic field analysis for the double layer Halbach array voice coil motor. The analytical model is built by adopting Fourier analysis and proves the feasibility of the analytic method with the equivalent structure. Reference [16] is an analysis and modeling the fast steering mirror. A detailed analysis was provided to show the proposed approach and improve disturbance suppression performance with only a slight weakening of the target tracking ability. The proposed feed-forward control was effectively verified through a series of comparative simulations and experiments. Besides, the method was applied in a real ship-based project. However, this dynamic modeling and the theoretical study of these methods are applicable to medium or large platforms and devices. It is of little significance to the design of an ultralight two-axis four-gimbal coarse-fine UAV electro-optical pod.  
In this paper, the dynamics modeling and theoretical study of the two-axis four-gimbal coarse-fine composite UAV electro-optical pod is deeply analyzed. In response to this problem, finite element analysis (FEA) and theoretical analysis of the stress and deflection of the key structural component are used to design the structure. According to the Euler rigid body dynamics model, the transmission path and motion coupling compensation matrix between two-axis four-gimbal are obtained, and suitable aerospace materials were used for analysis. Finally, the simulation verifies the correctness of the model.