| 摘要 |
The structure has a wheel base including a set of troughs at a bottom. A driven gear (36) includes an axial hole and a fan-shaped unit at one side of the driven gear, and a set of checking units is provided to the peripheral edge of the fan-shaped unit to insert into the troughs. An active gear (42) is made and integrated to an outer side of a pivoting holder when the active gear meshes with the driven gear.
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