3D Printed Planetary Gear for a Stepper Motor
- Source with great explanation of planetary gears - 
- In this example, bearings should be added to planet gears to make the output shaft not wear out
- Thus, this is not a turnkey solution for practical applications. Design must be modified.
- This design appears to be completely stackable. 4x per stage gets you good geardown. Successive stages should be enlarged to handle higher torque.
- This is good for a geared down extruder for 3 mm filament.
- This may be applicable to vehicle geardown with rubber-on-plastic drive for heavy duty applications up to 1000 lb drive for solar slow traction vehicles
- add bearings to planet gears
- add a cover with bearing. Planet gears serve as second bearing support point, but a double bearing in cover would release pressure from plastic gears. Because of short profile, we can add double bearing in cover to get lifetime >>1000 hours for extruder geardown applications
- Use hobbed bolt as the integrated shaft
Straight Gear Version
- This one has bearings, so it appears to be usable as is. No herringbone gears, though. - 
- May need to increase cover plate and double up shaft bearing to address radial thrust in filament drive application.
- Easy fix, outside of getting bolt lengths correct.
- Disadvantage - there will.be wear as axial thrust is not addressed without herringbone design.
- Note that herringbone gears eliminate the need for a thrust bearing. That is a great point of size.plification when using planetary gears.
- "Here is a design for a low-profile (18mm) stackable gearbox that fits onto a standard NEMA 17 stepper motor. The gearing ratio of 4:1 allows for increased torque and positional accuracy from the motor. Herringbone gears are used to provide smooth power transmission from the stepper motor while eliminating the need for thrust bearings. A flat rotating output platform is also provided to allow for easy mounting of attachments. More details along with a step-by-step guide to designing gears for 3D printing in Autodesk Inventor is provided below."