YouTuber Robert Murray-Smith has further developed a mechanism based on the principle of the hypocycloid – a classic gear approach in which a gear wheel rolls in a larger ring gear. A special feature of the project is that the entire design is 3D printable and freely available on the Thingiverse platform.
The implementation uses a special geometry known as the Tusi pair. If the inner gear wheel is exactly half the size of the outer one, a point on the inner wheel describes a straight line as it rolls. This principle can be used to generate a linear motion from a rotary motion – for example to drive a piston. This is precisely the basis of the model presented.
Murray-Smith took the basic design of his original hypocycloidal motor and added an additional component: an adjustable sprocket system with a worm shaft. This modification makes it possible to vary the angle between the drive spin and the guide, which changes the effective stroke. The mechanism allows infinitely variable adjustment of the stroke width – a concept reminiscent of the way a continuously variable transmission (CVT) works.
Guidance is provided by a combination of slides and guide rods. Depending on the alignment of the components, the drive pin moves either exclusively linear, combined linear-rotating or not at all. This allows the mechanism to be adapted so that it generates different movement profiles.
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