British developer Robert Murray-Smith has adapted a historic gear design from 1786 for 3D printing. James White‘s system, known as the “perpetual wedge”, enables extreme gear reductions in a compact design.
The original design is based on two gears with a slightly different number of teeth – 100 and 99. Thanks to an eccentric arrangement and a guide roller, the upper gear wheel only moves one tooth further per revolution. This results in a reduction ratio of 100:1 and a corresponding increase in torque.
Murray-Smith has optimized this principle for modern manufacturing methods. His version uses two ring gears with a similar tooth difference. The load is distributed over three evenly arranged planetary gears. This design enables a particularly flat “pancake” construction with a central drive and output shaft.
The importance of such gearboxes is demonstrated by the interaction between motors and applications. While combustion engines and electric motors operate efficiently in the range of 1,500 to 25,000 revolutions per minute, most applications require significantly lower speeds.
The 3D-printed model clearly demonstrates how the system works. Murray-Smith has designed the components so that they can be produced using standard 3D printers. The STL files are available free of charge on Thingiverse. Assembly is carried out using a few connecting elements such as clips and pins.
The replica is suitable both as a teaching aid and as a basis for your own projects. The design can be scaled and modified depending on the application.
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