A while back I remember seeing a listing on Facebook Marketplace for some sort of "crawler" style remote control car that the person had built using an ammo box and disproportionately sized wheels. I really liked the rugged aesthetic of their creation and wanted to build something similar, but I always struggled with choosing where to start. One weekend in May 2025 I decided to take a dive and start designing an RC car based on some parts I already had and that could be easily 3D-Printable, despite very limited knowledge of drivetrain design. Because of my unfamiliarity, my first iteration used a direct-drive belt and pulley system to drive the rear wheels, which worked but had some room for improvement.

Project Inspiration

After my first iteration, I discovered some minor issues. The main issues came from the belt drive system that I designed. I decided to 3D print the belt itself out of TPU in order to be able to tune the length and easily replace it if need be. However, the direct drive system meant that heavy braking would shred both the belt and pulley.

The Process

Additionally, the tension of the belt put enough stress on the motor that it snapped the motor mount. To solve this, I strengthened the motor mount. Although, the main issue with the belt getting chewed up still remained. I began working on a gear system to change the way that the rear wheels were driven, but in the meantime I continued to reprint and replace belts or pulleys as they got shredded. Although it wasn't ideal, part of the purpose of my designing it to be 3D printed was to allow for easy repair and replacement of broken parts.

While redesigning the drive mechanism, my plan was to make a shifting mechanism that would allow for me to use the existing gear ratio as a "low" gear, and then use a shift fork to shift into a higher gear to give a higher top speed. As I previously mentioned, I have very little experience with designing drivetrains or gearboxes. the first iteration consisted of a two stage planetary gearbox, where a shift fork actuates the second ring gear back and forth to lock the pins on the ring into slots on either side. In "low" gear the ring is fixed and behaves like a regular planetary gearbox stage. When it is shifted into "high" gear, it is moved and locked in place with the second stage's sun gear, so that the second stage is locked and rotates at the speed of its input (the stage 1 planet carrier).

Overall, I'm happy with the way that the car turned out. The low/high gear shifting mechanism did not work as planned, but the belt drive gets the car going much faster than I expected. As long as you are careful about not braking to aggressively, it is really fun to drive around. Plus, the 3D printed tires have just enough traction to give the car good speed while still being slippery enough to let you drift if you steer it correctly.

The Result