## 1 Introduction  
With the advancement of science and technology, UAVs have been widely applied in both military and civilian fields, such as communication relay, disaster monitoring, border patrol, and more [1, 2, 3, 4, 5, 6, 7], where they play a crucial role. However, in spatially constrained environments, aerial drones still need to further improve their maneuverability and adaptability. To enhance the adaptability of UAVs to diverse environments, amphibious drones capable of both ground and aerial operations have gradually become a focal point of research and application hotspot [8; 9; 10; 11; 12; 13; 14]. Complex environments such as mines, pipelines, and post-earthquake debris are characterized by unknown conditions and high risks, making manual operations extremely challenging. Consequently, reckless human entry may always lead to significant losses. UAVs [15], relying on their advantages of compact size, high agility, and suitability for navigating narrow and hazardous spaces, can be effectively deployed for tasks such as environmental reconnaissance and the transportation of small-scale rescue supplies. Currently, in the field of UAVs, some widely applied solutions to this problem include the following: [PERSON] introduced a small four-wheeled land-air amphibious UAV [16], and [PERSON] proposed a search-and-rescue rotor UAV [17]. The quad-wheeled amphibious drone proposed by [PERSON] can traverse land using its four-wheeled mechanism, and its compact design allows it to adapt well to complex environments. However, it is prone to tipping over on uneven terrain, and its electronic components lack adequate protection, rendering the drone vulnerable to damage. [PERSON]'s SR-RUAV system incorporates a low-altitude statistical image processing method for collapsed building detection, enabling the assessment of survivor presence. Despite its ability to efficiently cover large areas, such UAVs lack precision in close-range detection and cannot specifically search for people. [PERSON] proposed a caged quadrotor drone for the inspection of central HVAC ducts [18], and [19; 20; 21; 22; 23] are all recent papers on caged drones. These cage-shaped drones have provided valuable insights for this study. The infrared search and rescue methodology presented in Reference [24] has significantly informed the experimental approach in this study. But nearly all previous caged UAV designs face an unavoidable issue: their cameras and LiDAR sensors are inevitably obstructed by the cage structure. Furthermore, the single-cage structure inherently prevents the integration of ground locomotion capabilities in UAVs. Based on the above considerations, this paper proposes a novel aerial-terrestrial search-and-rescue UAV. The innovative separation cage structure endows the drone with ground mobility while ensuring a stable traversal over rugged terrain through its fullerene-inspired geometric design, effectively minimizing rollover risks. The framework primarily employs 2 mm-diameter carbon rods that exhibit diamond-level hardness, high flexibility with elastic deformation capability, and a density merely one-sixth that of steel, which achieves a simultaneous weight reduction, resulting in a final drone weight of 1.2 kg. The UAV's gross takeoff weight under full payload conditions is 2.2 kg. This separation cage structure not only significantly increases the hollow space to boost propulsive efficiency--achieving 40 min of endurance under full payload at the endurance speed of 10 m/s but also decisively addresses the critical limitation of internal camera occlusion inherent in traditional cage designs. The H-shaped quadrotor frame improves aerial stability and obstacle navigation, enabling operations in deep, narrow spaces through real-time environmental mapping via front-mounted LED arrays and a depth camera. This structural configuration also enhances payload capacity, supporting up to 1 kg while maintaining flight stability.