If we fixed an axis, then the gear train will rotate with around fixed axis and continue to drive the other axis to keep rotate.
If we fixed an axis, then the gear train will rotate with around fixed axis and continue to drive the other axis to keep rotate.
如果固定一个旋转轴不动，齿轮组就会绕著固定轴旋转而继续转动另一个旋转轴。