In the 1960s, engineer Donald Wilkes developed the so-called “Rite” – a mechanical system that impresses with its simplicity and efficiency. This system uses a metal strip bent into an S-shape and guided between two rollers. By moving the rollers, the belt is brought into an S-shape, whereby the rollers prevent the belt from crossing over. A special feature of the system is the ability to vary the roller size to achieve speed changes, which makes it interesting for applications such as valves, thermostats or shock absorbers.
YouTuber Robert Murray-Smith has taken this principle and developed it further. He discovered that the Rite system works in a similar way to a planetary gear. By using 3D printing technology, he was able to replicate and modify the system. Robert Murray-Smith has developed a model that comprises three large outer rollers, three smaller inner rollers, a central drive wheel and a flexible belt made of thermoplastic polyurethane (TPU). He bends the belt into a trochoid. The smaller rollers grip the inside of the belt, while the larger rollers guide it on the outside. By turning the central drive wheel, the rollers move in a similar way to a planetary gearbox.
One advantage of this system is its tolerance of inaccuracies. As long as the inner rollers do not go beyond the center of the outer rollers, the system adjusts itself and remains functional. It also requires no lubrication and transmits torque efficiently. However, the flexible belt is subject to continuous flexing, which can lead to material fatigue in the long term. However, tests have shown that such belts can withstand up to one million cycles. This corresponds to a service life of several hundred years with daily use.
Murray-Smith has made his 3D models available free of charge on the Thingiverse platform so that interested parties can build and experiment with the system themselves. In one of his videos, he demonstrates in detail how the modified Rite system is constructed and how it works.
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