## 4 Results and Discussion
### Prototype Flight Experiment  
A physical prototype has been developed according to design requirements and tested via remote control for terrestrial movement and confined-space flight. All experimental validations are conducted under full payload conditions. The prototype's gross takeoff weight under full payload conditions is 2.2 kg. Figure 15a shows terrestrial locomotion experiments conducted on Nanjing Funiu Mountain. The prototype commences terrestrial locomotion tests on the ground from a stationary level position. The prototype maintains a fixed pitch angle through the differential thrust between front and rear rotors, propelling forward via rotor thrust and ground friction with its cage structure. Steering is achieved by adjusting the differential speeds of diagonal rotor pairs. The system demonstrates stable movement on rugged terrain with smooth forward and backward motion and agile steering. The prototype maintains stable ground locomotion even when tilted to a 30\({}^{\circ}\) roll angle relative to the horizontal plane. The terrestrial maneuvering mode demonstrates an enhanced stability, sustaining normal operation in outdoor environments with Beaufort Force 5 winds. Nevertheless, the walking velocity decreases significantly under such conditions, while power consumption escalates proportionally to airspeed disturbance intensity. Figure 15b documents the prototype's flight test conducted in the forest. The prototype commences flight testing from a stationary horizontal position on the ground. Like conventional quadrotor drones, this prototype achieves lift through the four rotors' thrust and maneuvers (forward/backward motion and directional turns) via differential motor speed control. The dual LED arrays flanking the front-mounted camera enable visual exploration and obstacle avoidance in dark, enclosed spaces through pure vision-based navigation. The separation cage structure demonstrates critical protective functionality: when colliding with obstacles, it safeguards rotors from damage while allowing for rapid stabilization recovery. During flight operations, the prototype can regain flight stability within one second when subjected to collisions at its endurance-optimized cruising velocity  
Figure 15: Land walking experiment (**a**); flight experiment (**b**). of 10 m/s. At the maximum demonstrated speed of 18 m/s, stability recovery requires no more than two seconds under equivalent impact conditions. Experimental results confirm the prototype's successful execution of all designed flight operations, with performance metrics aligning with predetermined specifications. The supplemental experiments entail positioning the prototype in a deliberately inverted 90-degree orientation, establishing this configuration--where the circular cross-sections of its dual cage structures remain parallel to the ground--as the predefined initial state. Under these constrained conditions, unobstructed environments enable an autonomous self-recovery to the standard operating posture, and parallel wall confinement permits the structural rotation facilitates' rolling locomotion along the constraining surfaces; however, scenarios where walls immobilize the cage assembly resulted in complete mobility failure. When the drone is in operational status and encounters a passage impassable in its default attitude, it uses a depth camera to measure the channel width. If the channel accommodates traversal in vertical flight mode, the system further verifies whether the channel floor constitutes a navigable terrain. Upon confirmation, the drone activates vertical flight mode, adjusts its attitude to the vertical orientation, reconfigures propeller orientation, and subsequently traverses the narrow passage. If the channel floor is identified as non-navigable terrain, the drone aborts the traversal and reroutes via alternative paths.