Planetary Gear




Introduction: Planetary Gear

 Intro – planetary gears also refer as epicyclic gearing consisting three elements sun gear, planet gear and ring gear. Sun gear is located at the center that transmits torque to planet gears orbiting around the sun gear. Both systems are located inside the ring gear. In the toothed formation sun and planet gears are externally mesh and ring gear internally meshes. (See Fig. 01)Fig. 01
Planetary gear is found in many variation and arrangements to meet a broad range of speed-ratio in the deign requirements. Planetary gear system is use in varies applications such as, clocks, lunar calendar, car mirror, toys, gearhead motor, turbine engine and many more.
For detail understanding on the planetary gear: Planetary Gear Design
Planetary gear system will no assemble unless the number of teeth in each gear is selected properly.
Planetary spur gear drive ratio 5:1 means the sun gear must make 5 revolutions for each revolution of the output carrier.
Desired number of teeth in the sun gear is 24.
Design requirements:
Ratio   = 5:1
Sun gear  = 24
Module = 1
Since, I am working in the metric unit every dimension will be in mm. Selecting gears in metric unit the gear tooth profile of the spur gear will be in Module.  
M = Module
N = Number of teeth
Nr = Number of teeth on the ring gear
Pd= Pitch Diameter
R = Ratio
PDs=N/M=24/1=24mm  Eq. 01
Pitch diameter of the sun gear is 24.
Calculate the number if teeth required in the ring gear for the ratio 5:1.
R=1+Nr/Pd       Eq. 02
Solve for Nr
Nr=Pd (R-1)=24(5-1)=24(4)=96 teeth

Pitch diameter of the ring gear with 96 teeth and 1 module is.
Pd=Nr/M    Eq. 03  Pd=96/1=96mm
Pitch diameter of the planet gears must be found from.
Number of teeth in the planet gears may now be found from.
PDp=N/M Eq. 04  36mm=N/1  36mm (1)=N  N =36 teeth
R=1+Nr/P_D =1+96/24=1+4=5
The ratio is 5:1, as design was required.

Teacher Notes

Teachers! Did you use this instructable in your classroom?
Add a Teacher Note to share how you incorporated it into your lesson.

Step 1: Conceptual Phase

Conceptual Phase
Compute simple calculation for the center distance or mounting distance.
Ring gear = 96 teeth
Planet gear = 36 teeth
Sun gear = 24 teeth

Step 2: Components Selection

Sun Gear - A 1Z 2MYZ1002408

Step 3: Planet Gears

Planet Gears 3 x Planet Gear - A 1P 2MYH10036

Step 4: Ring Gear

Ring Gear - 1 x Ring Gear - A 1C10MYK10096

Step 5: Assembly

- Gear assembly 

Step 6: CAD Model

Using CAD software assemble planetary gear system for the prototype.

Step 7: Prototype

Step 8: Return of the Planetary Gear

Sound from the deep space. Please disregard the motor sound.

Bikes and Wheels Contest

Participated in the
Bikes and Wheels Contest

Be the First to Share


    • Tiny Speed Challenge

      Tiny Speed Challenge
    • Woodworking Contest

      Woodworking Contest
    • Trash to Treasure Contest

      Trash to Treasure Contest

    10 Discussions


    Question 1 year ago on Step 1

    in a sun and planet type epicyclic gear system, the PCD of the internal ring gear must be as close as possible to 220mm. the module of all gear teeth must be 4mm. when the ring gear is fixed, the arm that carries three planet gears should make one revolution for every five of the sun gear . Determine the number of teeth on all the gears and the exact PCD of the annulus. if an output torque of 12Nm is applied to the sun gear , what must tye holding torque be at tge annulus? Please help me ans this?


    Question 1 year ago on Step 6

    Hello, We have made planetary gears but we faced problem for hardening. we canot get perdect accuracy.

    please suggest me complete proceduee for that. my id is


    4 years ago


    i'm interesting in building a planetary gear for this motor : with a radio of at around 5:1,

    there are a few issues i see, the first ,is that motor's shaft is 12mm with a keyway , i see sun's bore is 8mm, is it possible to get a sun gear with bigger bore

    the 2nd issue of mounting, i see no mounting holes on the ring gear, but i see some on yours, did you make them? does this mean i would have to re-make the holes each time i get replacement gear? btw the ring gears seem to be out of stock..


    4 years ago

    can any one guide me how to make pitch circle dia


    6 years ago on Introduction

    hanks, plastic gears are standard off-the-shelf and they are machined from Cast Nylon Blanks (strong). ,


    6 years ago on Introduction

    hi love all this can i ask how hard the plastic is and are you able to make custom gears and cogs ?


    Reply 6 years ago on Introduction

    Thanks, plastic gears are standard off-the-shelf and they are machined from Cast Nylon Blanks (strong). ,


    6 years ago on Introduction

    Thanks, i got these gears from stock drive products SDP A 1C10MYK10096, SDP A 1Z 2MYZ1002408, SDP A 1P 2MYH10036


    6 years ago on Introduction

    Very cool.
    Where did you get the gears?