Compound Planetary Gear Box (37:1 or 49.3:1) NEMA 17, No Hardware.

by Gear_Down_For_What, published

Compound Planetary Gear Box (37:1 or 49.3:1) NEMA 17, No Hardware. by Gear_Down_For_What Jan 22, 2017
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I strongly believe that this is the best 3D printable gear configuration. It has very little friction and does not require hardware or bearings to run for a long time at 1000+ RPM. With some of my newer remixes of this, this type of gearbox can be mounted to a NEMA 17 Motor and with more modules and interconnecting ever other sun gear the backlash nearly disappears completely

I have made a lot of newer, better gearboxes (with some HUGE gear ratios) like this one! Check out my other "Things"

4/7/14- Video of gearbox driving knee joint on InMoov. Legs https://m.youtube.com/watch?v=Ah7cCeW9HrY
Please Check out my Youtube Video Below!

This design has two different gear ratios depending on which sun gear is driven. The large ring gears have a different teeth but the OD and notches are the same meaning you can choose which way you insert it into the capsule, this is how the gear ratio is changed, along with using different sun gears. Please note that you actually don't need the other sun gear or the mounts just to try it, but it will not work as well without it. Also, make sure you don't couple the two sun gears together, won't work that way.

These parts have all been printed and proven to fit. I ran this on with a drill at full speed for 3 minutes had the gearbox held up very well, i suspect that with a couple dabs of grease this gearbox could handle 1700 RPM input speed for hours.


You will need 3 or 4 planet gear's, those are the long double gears. 4 is best.

you will need a large carrier ring, and the small carrier ring.

For the 37:1 gear ratio setup you will need the "Drive Sun 37:1" and the "Driven Sun 37:1"

For the 49.something:1 gear ratio setup you will need the "Drive Sun 51:1" and the "Driven Sun 51:1"

if you plan to use it for anything more than demonstration you will also want to print the NEMA 17 mount and the end cap that mates with it.


The planet gears are technically dual gears. They are two gears attached together and have a different number of teeth, after some studying i realized that this means they must be assembled so that they are "relative" to each other, Theres a picture in the files to help you do this properly.

I included the Fusion 360 project files, and if you want you can modify this and stack the planetary gears to give this gearbox 4 or 8 modules for use in high torque applications, i would also suggest that you interconnect every other sun gear to do this.

Thanks for checking this thing out!

Update 3/27/17- I figured out how to calculate the gear ratios on these gearboxes, So i wrote a arduino program to spit out the best teeth combinations. I'm currently working on making one that will be a gear ratio of 1,400:1 and that is with the largest number of teeth being a 53 tooth ring gear. I will include this program with my gearboxes.

For More Cool Projects and Upgrades, Don't forget to Follow Me on Thingiverse and Subscribe to my Youtube Channel, Gear Down For What?https://www.youtube.com/c/GearDownForWhat

Assembly, Important Information and Operation!

Important Assembly instruction and Theory of Operation!

Spinning it with a cordless Drill!

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Thank you for sharing this! Great job!! I would like to down scale that model by a factor of 2.5. Would you supply me with
the dimensions of your model?

Hi, I'm trying to print and build this gearbox, but the issue I'm having is that the ring gear gaps seem to be stretched apart too far when the planet gears pass over them. This causes the turning of the sun gear to be jumpy. I printed the files using the exact wall thickness and infill settings you mention at the beginning of the accompanying youtube video. Any ideas what I could do to fix this?

how do you figure it is a harmonics gear? there is no flexible gear!

I didn't know what else to call it at the time

i understand now . thx for the clarification.

This is a cool idea! I tried the wave generator style one already, but I don't care for the idea of having to use tons of skateboard bearings to form the ellipse. This really limits the size of the system. This sort of things seems to be a lot simpler. I'll give it a shot and let you know how it goes!

Hey thanks for the kind words. I'm going to try to do another video tonight explaining assembly better

Hey So i just printed your driven 37-1 gear and its sorta tight on my 5mm shaft stepper motor with a D shaft, maybe my printers over extruding a bit... what module and helical angle did you use to design the gears? I'll just make another one if you don't want to re-upload it.

On second thought. The gear box has a little slop. For a temporary solution try scaling that gear up my .003 or .006 in the x and y direction

I honestly can't remember but it's gonna be hard to replicate cause its scaled by a factor of .4 I'll see if I can figure it out for you.

I had the same issue and I couldn't get it on the first time but now it's really loose, I'll maby add .05mm tolerance to that part. I'll try get that done tonight after I get the video uploaded.

So I sort of figure it out based on one of the gears I printed, in 1 to 1 scale your at a 8mm face width on your gears, something like a module 1.2 in for your tooth size, and something like a 20 degree helix angle. If you're interested, I've had luck printing all the way down to .6 module gears, though it probably should be done with a .3mm nozzle, that would help reduce the size of this gear box significantly. i use module 1 if size doesn't matter and .8 usually for things to still work on my system. I might try redesigning one of these to be a bit smaller for a small robotic arm i'm working on. So far the gears have come out awesome though!


Yeah I think it would be useful to downsize this gearbox i think it's bigger than it needs to be for sure!

Comments deleted.

It's designed to mount to a nema 17 stepper motor. I will test it tonight if I get my motors in the mail. I'll post pictures too

Love it.
Any chance of posting the mount for the opposite side to the stepper motor?
Final request - for anyone wishing to integrate this into a larger project, can you provide the source or alternatively the design requirements for the mounts?

I misread your first post, yes I will post the enclosure for the other side as soon as I can get fusion 360 to behave for long enough to make it fit correctly.