Planetary Gear Demo

by 98jtmartin, published

Planetary Gear Demo by 98jtmartin Dec 3, 2015
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The total assembly is there to use as a reference to the original design, the gears are not aligned in the total assembly, you have to set them individually

There are 3 Planetary Gears revolving around one Sun Gear. These four gears are encased in a Ring Gear, therefore creating the Planetary Gear system. This is just a small demo that I made from scratch, mostly using AutoCAD Inventor's Design Accelerator to create the necessary gears with the correct ratios, tooth count, and center/mount distance.

This small demo can be used for engineering teachers to show how gears can interact with each other to create different ratios. It can also show what ratios can be used more for speed and which can be used more for torque/power.

Print Settings




Doesn't Matter



They can be in the same print bed, but not as the assembled file

Make sure to print 3 PLANETARY and 1 SUN gear.

I don't really see supports super necessary if you orient the parts in the right way, you wouldn't need them.


Print 3 Planet gear and 1 of the sun

You may have to either shave off a small amount on each shaft on the "Pin Structure" OR bore out the hole on each gear slightly. When printed, it tends to be a little firm to put together and rotate

The original design of this was to have 3 "Planetary Gears" and 1 "Sun Gear" as the files are named. The sun goes on the middle peg, while the planetary gears go on the outside pegs. The ring then goes on the outside of all three planetary gears, and it should encase the entire thing.

How I Designed This

I am a very active member of my robotics team (I won't go too deep in this story, its unecessary) and I come in contact with gearboxes and gears almost on every meeting we have. So I kinda thought that making a small demo of a very basic planetary gear system would be perfect as one of my entries (I'll probably come up with more later). So I sat down and started figuring out the Design Accelerator in Inventor, which took a little time, but I finally got it where I wanted it, which created this.

Project: Basic Planetary Gear Systems


This simple design can be easily taken apart and put together. Students will be expected to learn the basics of how gears work and interact with each other. They can learn about how putting different sized gears with a different tooth count can affect the ratio of input to output.


This Project would be mostly appropriate for middle school engineering/robotics students and above (usually grades 7 and up).


With the project plan that I am thinking of, the students will need to know some basic CAD skills, therefore they require a computer, access to a 3d printer, and any form of CAD software that can be converted to the 3d printer programs.


  1. Choose your favorite CAD software

  2. Come up with a usable gear ratio with gears that can be accurately printed on your 3d printer (radius and tooth size)

  3. CAD them all up, assemble to check your work (simulate interaction if necessary to check for correct meshing)

  4. Print all parts and assemble


The students should have designed and printed a basic, fully functioning planetary gear system. It should consist of, at least, 3 "planet" gears, one "sun" gear, a "ring" gear, and some way to support all four inner (planet and sun) gears at the required distance so that it will all mesh together and rotate together.

If students use the free (and easy, in my opinion) AutoCAD Inventor software, they can learn how to use the Design Accelerator to create gears that will interact with each other and work correctly. If they use this software or not, they will learn the basics of gears and how they can work together to create a basic gear ratio.

For grading, teachers can grade on:

  1. How well the students use the software (3d printer and CAD) to create the Project

  2. How well the system fits together, such as gears meshing and correct ratios

3.(Optional) Aesthetics

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This did not work for me. I scaled it down 0.9 to reduce print sessions but the sun gear was way too big. Eventually I got around it by scaling down the sun gear to 0.8 and then messed around to get a snug fit (~0.825). I would not recommend this to anyone using an anycubic kossel.

I've not long had my printer (Anet A8), so I'm still learning. This is the most complicated thing I've tried printing yet. After a few failures (bed adhesion issues mainly with PETG) I finally got a mostly decent print last night with PLA. The support piece failed (one pin didn't print, the others all came off with almost no effort), but everything else printed beautifully, possibly the cleanest print I've had yet.

But, they don't fit together. Not even close. Positioning the planet gears into a best mesh position, the sun gear is a good 3mm too wide. I can't just rescale the sun gear down as then the teeth sizes would change, so I'm going to have to redo that gear altogether. Comparing my print to the picture it seems my teeth aren't quite as well detailed, they're slightly broader.

I had the same issue, so I decided to make a fitting version. Check remixes