## 2 Structural Design
### Main Structural Design
#### 2.2.1 Design of the Separation Cage Structure  
As documented in [25], radar and photoelectric sensors are subject to environmental interference. Concurrently, traditional integrated caged drones experience sensor performance issues during ground locomotion due to disturbances generated by their rotating protective cages. Therefore, the proposed separation cage structure effectively addresses the problem of sensor occlusion encountered in traditional monolithic cage designs. By sep  
Figure 1: Three-dimensional image of the proposed UAV structure. arating the two cage modules, the design ensures that sensors such as cameras and LiDAR remain unobstructed during ground operation, thereby improving measurement accuracy. Furthermore, this design enables the UAV to achieve stable terrestrial locomotion even under adverse environmental conditions, such as high winds. In this mode, the UAV can operate for extended periods and pass through narrow apertures more easily, thereby efficiently transporting emergency supplies and executing search-and-rescue missions. The separation cage structure provides robust protection for the UAV's critical components, particularly the motors and propellers, while also preventing potential environmental hazards caused by rotor operation. This design significantly improves the safety of the UAV, effectively protecting people in densely populated areas from being injured by high-speed rotating propellers. As shown in Figure 3, this is a single-cage structure. Each single-cage structural module adopts a design based on the molecular geometry of fullerene, characterized by a pentagon surrounded by five hexagons on both sides. Compared to the conventional radial circular cage structure, this design is more stable and robust, reducing the risk of tipping over on uneven terrain. The main frame consists of 2 mm carbon rods connected by nylon joints. This construction reduces the weight of the body while increasing the hollow area, minimizing the motor thrust reduction caused by the cage structure. Consequently, motor efficiency is maximized, significantly extending flight duration. Additionally, the hollow design of the cage structure cushions impact forces during operation. Figure 3: A single isolated cage structure. Figure 2: Overall structure diagram of the UAV. As shown in Figure 4, this is the structure diagram of the fullerene. The fullerene-inspired structure can be derived from a regular icosahedron by truncating all twelve vertices where the truncation ratio \(\lambda\) is defined as follows:  
\[\lambda=\ \frac{\text{Truncated edge length}}{\text{Original edge length}} \tag{1}\]  
The \(\lambda\) parameter of the regular icosahedron significantly influences the global stress distribution in the fullerene-inspired structure, warranting a focused analysis [26]. This structure can be regarded as a rigid frame structure, and the maximum equivalent stress is calculated by the stiffness matrix. Each node in the spatial frame element possesses six degrees of freedom (\(u_{x}\), \(u_{y}\), \(u_{z}\), \(\theta_{x}\), \(\theta_{y}\), and \(\theta_{z}\)), while the fullerene-like structure has 60 nodes, making the overall stiffness matrix **K** a 360 \(\times\) 360 matrix [27]. A global coordinate system (\(x\), \(y\), and \(z\)) and local coordinate system (\(\overline{x}\), \(\overline{y}\), and \(\overline{z}\)) are established, where \(\overline{x}\) aligns with the rod axis, and \(\overline{y}\) and \(\overline{z}\) are orthogonal to \(\overline{x}\). The elemental stiffness matrix for rod elements is expressed as follows:  
\[\overline{k}_{ij}=\ \begin{bmatrix}\overline{k}_{11}^{ij}&\overline{k}_{12}^{ ij}\\ \overline{k}_{21}^{ij}&\overline{k}_{22}^{ij}\end{bmatrix} _{12\times 12} \tag{2}\]  
The coordinate transformation matrix facilitates the conversion of elemental stiffness matrices from local to global coordinate systems:  
\[K_{ij}=\ R_{ij}^{T}K_{ij}R_{ij}=\ \begin{bmatrix}k_{11}^{ij}&k_{12}^{ij}\\ k_{21}^{ij}&k_{22}^{ij}\end{bmatrix}