Stackable Nema 17 Gearbox

This is a stackable gearbox for Nema 17 stepper motors that I built for use in various robotics projects. Each stage adds a 4:1 gear reduction. I tried to keep the number of non-printed parts to a minimum while maintaining reliability and performance. 

Each stage uses two bearings to hold the planet carrier in place to reduce friction and vibration. Each stage is mounted with two screws in opposite corners with two threaded inserts in the other corners for mounting the next stage. This pattern allows the gearbox to be stackable while maintaining the Nema 17 form factor.

I provided two output shafts. One has a simple four hole mounting pattern. The other has a keyed output with a single threaded insert in the center. The keyed output can be simpler to use and is more reminiscent of added a servo horn on a hobby servo. You also may have noticed that the cap does not have any threaded inserts for mounting the motor. In stead of increasing the height of the cap to provide room for the threaded insert, I recommend simply removing the cap and mounting the end of the gearbox directly to your project.

Non-Printed Parts (per stage):

1. 2x M3x12mm screws (amazon*)

2. 2x M3 (6mm L x 5mm OD) threaded inserts (amazon*)

3. 2x 30x37x4mm ball bearings (amazon*)

* Affiliate links support my work by helping me earn a small commission at no cost to you.

Printing:

Recommended settings:

• Layer Height: .2mm

• Infill: 15%

• Supports: No

Assembly:

1. Place the Sun Gear on the motor's output shaft.

2. Place Spacer over mounting holes. (open side up)

3. Insert one bearing into the top of the Spacer.

4. Press the Carrier in to the bearing.

5. Place the Ring Gear around the Carrier. Align mounting holes.

6. Screw the Ring Gear in place using two screws.

7. Add the Planet Gears to the Carrier posts.

8. Place an output shaft on top of the Carrier.

   1. If adding another stage, use Stage Output.

   2. else, use one of the other output shafts.

9. Place a bearing around the output shaft.

10. If adding another stage, repeat steps 2-9.

11. Place the Cap on top of the bearing and output shaft.

12. Screw the Cap down using two screws.

Modding:

I support anyone who wants to modify this design and create their own remixes. To make things easier, I provide the onshape document.