轉動軸的尾端有一個小齒輪，這個小齒輪只有半邊有齒輪，當轉動時，小齒輪利用齒輪部位來推動物體的上下運動。

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There is a pinion with only half tooth in the end of rotary axis. When it is rotated, the pinion uses its tooth to drive objects up and down.