Introduction: 3d Printed Gearbox for Small Dc Motors

Picture of 3d Printed Gearbox for Small Dc Motors

I have many salvaged dc motors just laying around in my garage. They
often produce too high rpm/ low torque for many application. So I decided do something about this problem. I just bought my first 3d printer (prusa i3 clone) so this was quite easy problem to fix. I only got PLA plastic available so the heat was bit a problem but if you follow this guide you can make it work too. I also made a test wheels so your next robot can move around :)

Step 1: Assembly Video

All steps are included in this video. There's some test setups in 5.40 mark.

Step 2: Technical Details and Materials

Picture of Technical Details and Materials

This gearbox has ratio of 1/16. With this 12v motor it can lift around 3,5kg (straight from the shaft.) 2 washers should place between each gear (see details in video). It reduces heat between plastic parts when 2 washers is rubbing each other. Adding lots of bearing grease between everything is essential. Depending your printer tolerances you might need drill out some holes bigger. Motor mount should be standard size.

My print settings with slicer.


  • layer 0.2
  • infill 25%
  • perimeters 3
  • bottom layer 2, top 3


  • Layer 0.3
  • infill 20%
  • perimeters 2
  • bottom layer 2, top 3

Step 3: Files

If you want know more about gears and ratios check for google "compound gears".

All comments are welcome. Thank you !


hbaker6 (author)2017-09-24

Happy to see a use for my salvaged DC motors! 2 questions though.

1. My Prusa clone (CTC) consistently prints PLA small, resulting in me having to up the scale 102%, does your printer do this and did you design it accordingly?

2. Would you ever consider sharing CAD files for some of us to tinker with it? Say to change gear ratios for different applications.

fortzero (author)hbaker62017-09-28


I don't have any problems with scaling when printing it. The Design should print fine with 100% scale option. Right now I don't have a time to convert sketch up files to CAD compatible format. Thnx for your interest.

Ahmed Mourad (author)2017-08-22

Cool project ... thnx for sharing with us ... can u tell me the weight of this gear box To calculate it's cost for me ?!

tim.detwiler.9 made it! (author)2017-04-21

I’m having trouble printing the output shaft and gear. It prints poorly at the intersection of the chamfer at the bottom of the shaft and the rest of the shaft. It breaks very easily there. I've printed it by itself and with both Cura and Slic3r with the same result. Anyone else having the same problem? Anyone have a fix?

fortzero (author)tim.detwiler.92017-04-21

I made couple changes to the shaft. Download "gearbox_shaft_v2" file and try that one. I removed some polygon lines from that problem area. Let me know if that helped.

tim.detwiler.9 (author)fortzero2017-04-21

That fixed it. Thanks

fortzero (author)tim.detwiler.92017-04-21

Good :).

fjbailey3 (author)fortzero2017-04-24

I had the same problem with the output gear shaft, although I solved it
by importing the gear into DesignSpark Mechanical and reextruding the
shaft. Also had a problem in that my motors don't have mounting screws,
so I had to fabricate a U-shaped clamp and relocate the mounting holes.
But it went together well and works fine. Noisy as heck. I've printed a
second one for a friend to assemble, it will be interesting to see how
his copy works. Thanks for a fun project!

fortzero (author)fjbailey32017-04-25

Yes it's a bit noisy :). Maybe different types of gears and tighter tolerances between gears might help to reduce sound. Can you post your result ? I really like to see your print quality and that "U clamp" you did.

fjbailey3 (author)fortzero2017-04-25

I'm more than a little embarrassed to show off my work... I haven't yet done any finishing, and probably won't on this first draft. I used ABS, and the box warped a little, causing the rods to be non-parallel and the upper gears to be a little too close together. Took a little more sanding to get it to work. To mount my motor clamp I just drilled through the box bottom, so there aren't enough threads to hold well, I just now added some hot glue to supplement. For the second unit I printed, I added an extrusion to the holes to allow 9mm of threads, so that should work better in the future (also printed with a raft... still got a little warping, but a lot less). I also glued in a terminal block on top so I can plug in a Li-ion battery - my motors seem to run from 3v to 18v, and work just fine on 4.7v. When I get back from my vacation, I want to print another box or two, this time using Polymaker's PolyPlus PLA. I haven't printed with that before, so it should be a fun experiment.

fortzero (author)fjbailey32017-04-26

Your motor mount fits nicely and integrating terminal block to the frame is good idea. ABS is a bit harder material to play with :). Thnx for sharing your progress.

SanjuhsH (author)2017-04-20

This is beautiful !!!
really liked it looked really proffesional!

whericlau (author)2017-04-14

Thanks for your nice job. What chemical did you used in the surface finishing step of the gearbox?

fortzero (author)whericlau2017-04-16

Firts I clean all surfaces with oil and dirt cleaner. Then I add 1 layer of primer, 2 layers of surface paint and 2 layers of clear laquer. Im using acrylic spray paints.

WilliamB211 (author)2017-04-14

Very good!

ttajaf68 (author)2017-04-14

good for a battery powered irrigation controller - thanks a lot !

DaveL6 (author)2017-04-13

The gearbox looks great and it's just what I need for a project I am working on. What is the electric motor you are using and where can I buy one?

fortzero (author)DaveL62017-04-14

My motor 12v version. If you have old printers, scanners.... you may find these motors inside it.

Here's couple links to ebay.

AndrewA189 (author)2017-04-13

I really enjoyed this instructable; as others have said (and you mentioned inspiration from), you're not too far away from it being a servo!

carl5blum (author)2017-04-13

Very nice job. The press fit to the motor shaft is common. In older toy trains the stress of the press fit can lead to splitting, so don't skimp on the diameter of the hub. I've added brass rings to fix split hubs with good results. Good luck and thank you for the inspiration.

Timofte Andrei (author)2017-04-09

Add a potentiometer, make some space for an ATTINY and a H bridge inside the casing and you've got yourself a servo

fortzero (author)Timofte Andrei2017-04-10

Good point. When I designed this gearbox I actually studied servos and how the gears are arranged inside it.

Cats Science Club (author)2017-04-06

This is amazing. Nice video! You have our vote.


allangee (author)2017-04-07

Did you just press fit the gear onto the motor shaft? What keeps the shaft from just spinning without the gear moving?

fortzero (author)allangee2017-04-08

yes it's press fitted. Press fit if common way to attach gear to the motor shaft (small dc motors) High friction keep it in place.

About This Instructable




Bio: Passion for making.
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