tl;dr: A 15-year-old built a 3D-printed cycloidal gearbox driven by a NEMA 17 stepper motor, along with a Python script for Fusion 360 that parametrically generates the geometry. The third iteration achieves a 1:9 reduction, 1.3 N·m output torque (up from the motor's 0.21 N·m), and 66% efficiency in a 90mm PLA housing. Planned improvements include swapping housing pins for MR128 bearings and output pins for metal-covered M2 screws to reduce friction and boost torque.