This particular 3D-printed transmission is a four-speed, and it includes a reverse gear. You can see that almost the entirety of the machine is 3D-printed in PLA plastic, besides things like springs, shafts, and belts. And thanks to the fact that there’s no case around it, we can see exactly how it works.
The barrel cam is basically just a mechanical program for how the shift forks—the part that carries around the dog clutches—are going to move. The shift selector rotates the cam a few degrees, which in turn pushes each fork in a different position, engaging the selected gearset via a dog clutch. One position will deselect first and simultaneously select second, the next deselects second and selects third, etc.
This sort of shift selection system is typically used on racing cars, as you can just push the shifter forwards or backward to quickly and mindlessly go up and down gears. A regular H-pattern shifter is more conventional when using a dog clutch on heavy trucks, however, as it allows for “double-clutching,” a method that makes shifting with such a system less jarring—the dog clutches smashing into each other is not pleasant.
But this model doesn’t have that issue due to its slow running speed, and it’s just a plastic model. The creator of this transmission has also made an F1-style paddle-shifted gearbox, which is a bit more complex. It just goes to show you what you can do with some CAD skills and a little imagination.
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