## 3 Novel Rotating Motion Mechanism
### Multi-Link Rotating Mechanism
#### 3.5.3 Cycloid Reducer  
1. Universal RV reducer  
The RV reducer is a two-stage transmission mechanism [134], as shown in Figure 74. The motion of the RV reducer can be divided into two stages: at high speed, the sun gear one is connected to the drive shaft and meshes with the planetary gears 2, rigidly connected to the crankshaft 3. At low speeds, swing gear 6 is driven by the crankshaft and locked with pin gear 4 located in pin housing 5. Due to the two-stage gear pair, namely (1) sun gear and planetary gear, and (2) cycloid gear and pin gear, the crankshaft rotates around its axis while also rotating around the centerline of the RV reducer. The rotation of the crankshaft is then transmitted to output disc 8, thereby achieving a large transmission ratio. Figure 73: Variable pitch biomimetic propeller. Figure 72: Cam connecting rod planetary gear system seedling picking mechanism: 1. Left housing; 2. Planetary gears; 3. Intermediate gear; 4. Sun gear; 5. Cam; 6. Linkage mechanism; 7. Roller; 8. Seedling picking arm; 9. Proper housing; 10. Rack mounting board; 11. Input shaft. 2. New two-stage cycloidal reducer  
[PERSON] et al. [135] proposed a new design scheme for a two-stage cycloidal reducer, as shown in Figure 75. The reducer mechanism only uses one cycloidal disc per stage, and a central disc roller connects the two-stage cycloidal discs. The first-stage cycloidal disc meshes with the fixed ring gear, while the second-stage cycloidal disc meshes with the rotating ring gear. The central disc roller synchronously transmits motion, and the final output shaft rotates in the same direction as the input shaft. The number of cycloid discs in this mechanism has been reduced by half, resulting in a smaller volume. Using a two-stage cycloidal disc phase difference to counteract centrifugal vibration requires no additional balancing mechanism. 3. New single-stage precision cycloidal pinwheel reducer  
[PERSON] et al. [136] designed and developed a new type of single-stage precision cycloidal pinwheel reducer, as shown in Figure 76. Replacing the traditional fixed output pin mechanism with a rotatable output pin mechanism and introducing bearings to convert the sliding friction between the output pin and the output hole into rolling friction significantly improves transmission efficiency. The performance of three different tolerance  
Figure 74: CAD model and schematic diagram of RV reducer (1—sun gear; 2—planetary gear; 3—crankshaft; 4—pin gear; 5—needle housing; 6—cyclic gear; 7—carrier; 8—output disk). Figure 75: Structural diagram of two-stage cycloidal reducer: 1—input shaft of reducer, 2—first stage cycloidal disc, 3—shell roller of fixed ring gear of first stage, 4—central disc, 5—second stage cycloidal disc, 6—ring gear. design schemes for the reducer was verified through simulation and experimentation. The results show that under reasonable tolerance design, the new reducer can achieve high transmission accuracy, and the transmission efficiency under rated load can reach 83.39%, which is better than the traditional design. The new reducer adopts a rotatable output pin mechanism, and the output pin is connected to the flange through a needle roller bearing. When the cycloidal gear rotates, the sliding friction between the output hole and the output pin is converted into rolling friction. At the same time, the flange adopts a fan-shaped connection mechanism to improve torsional stiffness. Table 15 summarizes and compares the transmission performance of the different planetary rotation mechanisms mentioned above.