Planetary Gear Box

Project Description -

My first time 3d modelling gears in CAD :) making a planetary gearbox since that seems like the thing most people do to learn about modelling gears in CAD as a beginner!!! Also made a housing for it allowing people to connect motors without having the risk of well getting their fingers in the way of the gears lol.

What it is - 

This is a custom single stage 3planet planetary gearbox with a fixed internal gear ring, rotating sun gear input and output shafts and ofc the 3 planet gears.

The gears are made with the following parameters -

20 teeth sun gear

all three planet gears have 22 teeth

the internal ring gear has 64teeth

the sun gear has an input shaft and an output shaft

Input and Output Shafts

btw u will need to attatch the input and output shafts yourselves since otherwise to print them with the gears themeselves would take a lot of supports hence u will need to slide the input gear into the sun gear and glue it and then also super glue the output shaft to the carrier.

So the way this works is there is an input shaft which the user would need to connect a gear to. now the reason i did not model a gear onto it myself is so cause every motor is different and every pinnion for the motor is different so i wanted the person using it to add the gear onto the input which most suits their motor and pinion combo. The input shaft is 8mm in diameter.

The output works normally it is an output shaft that has a small chamfer at the top for aesthetic purposes. The output shaft is also 8mm in diameter.

About the gears

The planetary stage has a 4:2:1 reduction when the outer ring gear  is fixed and the sun gear is used as the input hence the input shaft is connected to it (ofc)  and the carrier is used as the output.

How it Works

The sun gear in the center is connected to the input shaft. The three planet gears mesh simultaneously with both the sun gear and the internal ring gear.

The output shaft is connected to the center of the carrier

When the sun gear rotates:

1. The sun gear drives the three planet gears.

2. The planet gears rotate around their own axes.

3. The planet gears also travel around the sun gear.

4. This movement rotates the carrier.

5. The carrier transfers the reduced-speed rotation to the output shaft.

All the gears have module=2

Assembly Instructions -

So assembling this is pretty simple but there are a few things you will need to do yourself since I didnt want to make the prints super support heavy :)

1. Print everything

First print all the parts seperately. You will need the sun gear, all 3 planet gears, the internal ring gear, carrier, housing parts and the input and output shafts.

I recomend printing the gears with a smaller layer height if your printer can handle it since the teeth need to come out clean.

2. Attach the input shaft

The input shaft needs to be attatched to the sun gear.

Slide the input shaft into the center of the sun gear and make sure it is properly aliged. Once you are happy with the position use some super glue to secure it in place.

The input shaft is 8mm in diameter.

I made the shaft seperate because printing it already attached to the gear would require alot more supports.

3. Put in the planet gears

Put the 3 planet gears around the sun gear.

Each planet gear should mesh with the sun gear and the internal ring gear at the same time. Make sure all 3 planets are sitting in the correct positions before putting the carrier on top.

They should be able to rotate freely.

4. Attach the carrier

Once the planets are in place put the carrier over them.

The carrier holds all three planet gears in place while still allowing them to rotate around the sun gear.

Make sure the center of the carrier is lined up with the center of the sun gear.

5. Attach the output shaft

The output shaft needs to be glued onto the center of the carrier.

Put the shaft into the center of the carrier and check that it is straight before adding super glue. Let the glue fully dry before testing the gearbox.

The output shaft is 8mm in diameter and has a small chamfer on the top.

6. Put the ring gear around everything

Now put the internal ring gear around the 3 planet gears.

The teeth of the ring gear should mesh with all 3 planet gears.

Make sure the ring gear is sitting properly and is not touching anything that is supposed to move.

7. Put everything into the housing

Place the whole planetary assembly inside the lower housing.

The internal ring gear should be fixed to the housing so that it doesnt rotate with the other gears.

Then put the top housing on and make sure the output shaft comes through the center hole.

8. Add your motor gear

For the motor you will need to make or use a pinnion that matches your motor and the input shaft.

The input shaft is intentionally left without a motor gear because different motors will have different shafts and different pinions.

Attach your motor gear to the input shaft and make sure it is secure before powering anything.

9. Test it

Before putting a motor on it I would recomend turning the input shaft by hand first.

Check that:

1. The sun gear turns

2. All 3 planet gears rotate

3. The planets move around the sun

4. The carrier rotates

5. The output shaft rotates with the carrier

6. The ring gear stays fixed

If everything moves smoothly then you should be good to go!

All the gears have module = 2 and a 20° pressure angle.