## 2 Design and Fabrication
### Quick-Release Mechanism  
As depicted in Figure 3b, to facilitate rapid verification and design iterations, the components of the quick-release mechanism were manufactured using 3D printing with nylon and metal materials. Lubricant was applied between the transmission parts to reduce frictional losses. The mechanism is driven by a DC-geared motor, which controls the deployment and rapid retraction of the landing gear by winding and quickly releasing a cable. The total weight of the mechanism is 108.5 g. To provide a clearer depiction of the motion sequence, states, and transitions of each component, we have constructed an operational cycle diagram of the quick-release mechanism, as shown in Figure 3\(f\). For simplicity, the displacement curves of reciprocating linear motion components are represented by straight lines. The operational principle of the entire mechanism is detailed in conjunction with Figures 3 and 4. (1) Landing Gear Open: Bevel gear A is connected to the output shaft of the DC-geared motor and rotates forward when driven by the motor. As bevel gear A drives bevel gear B in rotation, the spur gear on bevel gear A simultaneously drives the gear clutch shaft to produce a positive displacement. As in Figure 3e, the long shaft of the gear clutch shaft gradually withdraws from the square shaft while the rubber band is stretched. At this point, under the action of the compression spring, the meshing gear moves forward along the groove on the square shaft and gradually meshes with the end face of spiral gear B.  
Bevel gear B rotates synchronously with spiral gear A. During this process, the end face ratchet with dual-layer teeth (DFR) remains engaged with the dual-layer ratchet teeth on spiral gear A under the action of the wave spring, rotating in sync with the inner ratchet teeth. The pawl, engaging the circumferentially spaced partial teeth on the DFR through its tail teeth, rotates and makes contact with the ratchet under the pressure of the spring leaf. As shown in the schematic of Figure 3d, the DFR continues to rotate and gradually disengages from the pawl, while its side-mounted guide shaft progressively engages with the guide groove. Figure 4: The sequence of operations for the components. Under the influence of the guide groove, the DFR experiences a reverse displacement and compresses the wave spring while rotating. When the guide shaft reaches the limit position of the guide groove, the DFR is in a semi-engaged state with the outer ratchet teeth of spiral gear A. During subsequent rotations of spiral gear A, it intermittently pushes the DFR, causing the DFR to undergo reciprocating linear displacement due to the combined effects of the guide groove and the wave spring. After the meshing gear engages with spiral gear B, the rotation of the meshing gear drives the cable drum, which is fixedly attached to the square shaft. The cable, secured to the landing gear cable bracket, gradually winds onto the cable drum, causing the dual-function landing gear to open progressively to its maximum angle. Subsequently, the DC-geared motor halts, and the cable drum is locked by the ratchet and pawl mechanism. (2) Landing Gear Closed: The DC-geared motor reverses its rotation, driving bevel gear A to rotate in the opposite direction. Under the tension of the rubber band, the gear clutch shaft meshes with bevel gear A, causing reverse displacement and gradually inserting into the square shaft. At this point, the meshing gear, influenced by the thrust exerted by the gear clutch shaft of the rack on the short shaft, gradually disengages from spiral gear B, further compressing the compression spring. Simultaneously, the DFR, using its outer ratchet teeth, rotates synchronously with spiral gear A and gradually exits the guide groove. The DFR then fully engages with those of spiral gear A under the force of the wave spring. As the DFR continues to rotate, its circumferential partial teeth engage with the teeth at the tail of the pawl, which, resisting the force of the spring leaf, disengages from the ratchet.