The exhibit you are currently experiencing is called 'Rolling Out of a Straight Line'. Inside the acrylic transparent cover on the circular exhibition stand, there are two interlocking circular gears, one large and one small, with a straight track in the middle. Pressing the start button, you can see the small circle making internal cutting movements around the large circle, and the small monkey fixed on the small circle making linear reciprocating movements along the track. This is because the exhibits mainly use the principle of hypocycloid, which means that the diameter of a small circle is equal to half of the diameter of a large circle. Only the motion trajectory of any point on the edge of a small circle that meets this condition will be a straight line passing through the center of a large circle, and its length is the diameter of the large circle. The little monkey in the exhibit travels back and forth on the diameter of a large circle according to this pattern. The epitrochoid is also widely used in people's lives, such as in mechanical processing, where the reciprocating linear movement of the blade on the planer also utilizes this characteristic of the epitrochoid.https://zoomkingzg.com/