⚙️ Project: 3D Printed Cycloidal Gearbox

Created by a 15-year-old aspiring engineer

This project focuses on the creation of a cycloidal gearbox—a mechanical system designed to efficiently convert high-speed rotation into high-torque output.

🛠️ The Evolution of the Design

The development of this gearbox happened in three distinct stages, moving from a proof-of-concept to a fully functional mechanical drive.

Iteration History

Version 1: A manual, hand-operated prototype. Its primary purpose was to verify that the custom Python generator was producing accurate geometry.
~~Version 2~~: An attempt at a "micro" version with a 1:9 ratio. The goal was to match the footprint of a NEMA 17 motor. However, because 3D printing lacks the extreme precision required for such small tolerances, this version was unsuccessful.
Version 3: The first fully operational version powered by a NEMA 17. By increasing the overall footprint, the design allowed for more forgiving tolerances, resulting in a stable, working gearbox.

💻 The Python Generator

To create the complex curves of the cycloidal disk, I developed a Python script inspired by a Building a Cycloidal Drive with SOLIDWORKS guide.

The Mathematics

The geometry is defined by the following parametric equations:

$x = R \cos(t) - E \cos(N t) - r \cos(t + \psi)$ $y = R \sin(t) - E \sin(N t) - r \sin(t + \psi)$

Where the angle $\psi$ is calculated as: $\psi = \text{atan2}\left(\sin((1 - N) t), \frac{R}{E \cdot N} - \cos((1 - N) t)\right)$

Key Note: The resulting reduction ratio is $1 : (N - 1)$ , with the rotor spinning in the opposite direction of the input shaft.

Setup & Execution

To use the generator, follow these steps:

Clone the repository from GitHub.
Open Fusion 360.
Navigate to Scripts and Add-Ins using the shortcut Shift + S.

# Example: Cloning the project
git clone https://github.com/tom-ilan/cycloidal_gearbox.git

Configurable Parameters

Parameter	Symbol	Description
Pins	$N$	Number of outer pins (Rotor lobes = $N-1$ ).
Pitch Radius	$R$	Determines the outer housing size (must be checked against $r_{\text{max}}$ to avoid undercutting).
Profile Offset	-	Sets the angular step and clearance (use a positive value for 3D printing gaps).
Bolt Radius	-	Defines the placement of output pins and rotor holes ( $r_{\text{pin}} + E$ ).

🚀 Deep Dive: Version 3

The files for this specific iteration are located in cad_models/version_3.

Technical Specifications

Metric	Detail
Gear Ratio	1:9 ( $N=10$ pins, 9 lobes)
Outer Diameter	90 mm (9.0 cm)
Motor	NEMA 17 Stepper (`42bygh40-A24dh`)
Material	PLA
Hardware	4× M3 $\times$ 8 screws, 2× 6704 Bearings
Tolerance Offset	`+0.15 mm`
Output Torque	$1.3\text{ N}\cdot\text{m} \pm 0.007\text{ N}\cdot\text{m}$
Input Torque	$0.21\text{ N}\cdot\text{m} \pm 0.007\text{ N}\cdot\text{m}$
Efficiency	$66\% \pm 0.22\%$

📈 Potential Improvements

To further optimize the system, the following upgrades are planned:

Reduce Friction: Swap the static housing pins for MR128 bearings to boost efficiency.
Increase Rigidity: Replace the 3D printed output pins with M2 screws and metal caps to handle higher torque loads.