November 10, 2024
Description
A compact (planetary) gearbox that can be mounted on top of a Nema 17 motor to increase the torque at the cost of speed.
In this case, the ratio is 1:4.36 (the output shaft moves once every 4.36 rotations of the stepper motor).
It has been designed to replace these two large gears
which took up a lot of space and were suboptimal for my project.
The gearbox consists of a sun gear with 11 teeth and 4 planets with 13 teeth each. The outer ring has 37 teeth. Note that all teeth are prime numbers, which reduces wear on the teeth.
There are many planetary gearboxes out there like
but many have restrictive licenses that limit one's ability to use them in their own projects or are missing the parametric step files.
That is why I created my own planetary gearbox that can be used without restrictions in any project.
I primarily design my models in Shapr3D, which unfortunately does not have the ability to generate gears.
Finding a good tutorial that explains how planetary gears are made was quite difficult as well, which is why I document it here, in case someone else struggles with it too.
This site was useful for finding different combinations of teeth that work and which ratios one will get: https://planetarygenerator.mateuszdrwal.com/
The gears were generated in Fusion 360 with the Helical Gear Generator and the following settings:
The ring gear was created like described in this tutorial, but without the mentioned adjustments (I simply generated the ring gear with a backlash of -1mm and then subtracted it from a cylinder to create the internal ring gear).
The gears were then incorporated into a frame that holds them in place in Shapr3D. I went through many iterations until I ended up with the design that you see here. The current design is optimized to be as slim as possible, the gearbox ended up with a height of only 18.8mm, which is a bit taller than this model (according to the slicer it has a height of 17mm, but the screw heads are not in the lid, with them included, it would have a height of 20mm).
While designing, I thought that it would be nice to add bearings, but they don't seem to be an improvement. The option is still there in the print profile if you already have the bearings.
If you want, you can add a bit of grease between the gears to reduce friction/noise. I used the same grease that I use for the z-axis of my printer. In my case that is the "liqui moly silicone grease", but other ones like super lube or the one included with the printer should work as well. In the worst case, you would have to reprint the parts, but with only a few grams of filament that shouldn't be much of an issue.
For bearings, you might notice that the names will have a ZZ or RS at the end, like MR128ZZ or MR128RS. They are the same bearing with the same dimensions. The suffix refers to how the bearings are sealed. The ZZ ones have a metal lid that is pressed onto the bearing and will only keep out dirt. The RS ones have a rubber seal, they are not waterproof but make it harder for liquids to enter the bearing. For this project it doesn't really matter which ones you get, and like mentioned above, there is little benefit to adding bearings.
0. First start by printing all the necessary parts, you should have
If you are having problems fitting the parts together, you might have to calibrate the flow rate and pressure advance (flow dynamics) for your filament. I had some filaments that printed perfectly and others where the parts were a bit too large/small.
Note: The carrier should be printed separately from the other parts. Otherwise, the thin poles might print imperfectly.
1. Find the carrier
(1.a) If you have chosen the version with the MR128 bearing, insert it into the bottom of the carrier. You might need a bit of force to get it in.
(1.b) If you have MR63 bearings, you should insert two of the small bearings in each planet gear.
2. Add the sun gear into the middle of the carrier:
3. Place the body on the Nema 17 stepper with the carrier and sun gear in the middle, like this:
If the stepper shaft is not going into the sun gear, you need to rotate it until it goes in.
4. Add the planets to the carrier (you might have to wriggle them around a bit, to make them go in):
5. Now place the output shaft on the carrier like this:
6. Place the lid on top
7. Then add the four M3 x 20mm screws in the four holes to complete the assembly. Note that the screws should screw into the holes of the stepper motor.
The planetary gearbox output shaft has a pattern that is supposed to be like a torx bit. There is an “output receiver” in the attached step file that you can use for your own model to attach it to the gearbox.
Using a different output shaft is an option as well, that is why I included the step files.
Just keep in mind that I chose the “torx bit” design for a good reason. Before that, I used something like a six head bit for the output shaft. This worked, but when the motor applied a lot of torque (which you want to do with a gearbox) the output shaft would slip and over time the output receiver became round and failed to grab onto the shaft.
The torx bit is less likely to slip, at the cost of the stepper motor skipping steps if it can't provide enough torque, but that is desirable, especially if you want to use the stepper in combination with a driver that can detect stalls like a TMC2209.
Makerworld offers an exclusive program through which one can earn more points, at the cost of only sharing the model here.
To prevent others from posting the model on different platforms, you are required to license the project under a “Standard Digital File License”. Most of my models are Makerworld exclusive, which is why I want to give the program a try.
I only selected that it is 14-Day Exclusive. After that time period, the program ends, and I will license this project as CC0 (public domain), so you can use this in any project, sell it or do whatever you want to do with it.
You are not required to note that you used my model for your own project, but I would love to see what you used it for.
License:
CC0
luro02
