Testing 3D prints to their limits. This gearbox is 95% 3D-printed and is capable of pulling a Ford Focus forward!
This gearbox was completely designed by us and consists of 95% 3D-printed parts. Apart from a few steel shafts and some nuts and bolts, all gears and the housing are entirely 3D-printed.
The 3D printing technique used is FDM (Fused Deposition Modeling), where a plastic filament is melted and stacked layer by layer to create a 3D object.
The material used for this prototype is PLA. This has a relatively low tensile strength compared to other higher-performance materials such as Nylon, Polycarbonate, ABS, etc. Despite the lower strength of the material, we were able to achieve a torque of 132kg*cm (~13 Nm), and the limiting factor was not the material itself, but the torque of the 36V DC motor (despite the reduction of 162:1).
We were able to achieve this relatively high torque through several specific design choices. For example, this gearbox does not use spur gears but teeth that are angled at 30° (double helical gears or herringbone gears). This angle ensures that forces are gradually transferred from one tooth to the next. This also means that the gears produce less noise. Furthermore, a relatively high gear module (ratio between tooth size and gear diameter) was chosen. These coarser teeth can be printed with more perimeters (walls), which also results in stronger gears.
In the video below, you can watch the full project.