4:1 Planetary Gear System

This model is a small planetary gear system with a ratio of 4:1 per stage. There are as many stages as desired. The open enclosure allows visibility of the gears and it requires no hardware.

The gears are designed with a circular pitch of 2.5mm and have slightly beveled tips to avoid the need for cleaning excess material from the initial layers. The OpenSCAD model is not parametric; there are only parameters for:

• clearance (set to 0.2)
• backlash (set to 0.1)
• pressure angle (set to 22.5)
• tolerances between nuts and bolts (set to 0.4)
• length of bolts

Any other changes will not work. To use OpenSCAD, you will need the following libraries:

• Public Domain Involute Parameterized Gears (LeemonBaird) - link
• Poor Man's OpenSCAD Screw Library - link
• Knurled Surface Finishing Library - link

The libraries are included in the ZIP file along with STL files for every single part and build plates for complete sets from 1 to 4 stages, as well as upgrade kits from 1 stage to 2, 3, or 4 stages.

Print Setup: I used a Makerbot Replicator with a 0.4mm nozzle, ReplicatorG - 0034, and Skeinforge 47. The gears did not print well with the standard profile, particularly the threads, which tend to print slowly with a thicker appearance. It is crucial to set the layer height to 0.25mm, or the planets may struggle to spin. Infill should not be below 60%, or the bolts will break easily. If you do not clean the sides of the teeth, the fit will be tight but usable. If cleaned, they might be too loose. Be very careful with the bolts; do not tighten the nuts too much.