Today, we will discuss harmonic drives. Did you play with toys like this when you were young, where a small gear rotates inside a larger one? Did you notice that the holes on the small gear also rotate in the same direction, just at a slower speed? This principle is precisely what makes a speed reducer possible. Here you can see the large and small gears of a harmonic drive. The small gear is positioned right in the center of the large gear and can rotate. However, it may appear that the two gears are not engaged, so how do they achieve a reduction ratio? Don't worry—the small gear is actually flexible. By deforming it through compression, it can engage with the large gear. As you can see, it works like this. When assembled properly, you can observe two bearings compressing the small gear. Turning the crank achieves the desired speed reduction. Harmonic drives are characterized by high reduction ratios and high precision, making them particularly suitable for advanced industrial robots.