Planetary Gearboxes

Chain & Drives supply and service the full range of Planetary Gearboxes & accessories.

This series of reduction gears is Reggiana Riduttori’s basic line with a wide range of output ratios and torques. They can have output supports with a male shaft or a female one with internal grooving and input bevel gear pair. The countless modular possibilities allow just as many solutions on machines in the different industrial sectors.

CDA Gearboxes

What Is Planetary Gearbox?

A planetary gearbox is a mechanical device consisting of sun gear, the planet gears, the planet gears' carrier, and the ring gear. Sun gear located at the centre that transmits torque to planet gears orbiting around the sun gear. Planet and the sun gear are located inside the ring gear.

Planetary Gearsets & Gear Ratios

Any planetary gearset has three main components:

  • The sun gear
  • The planet gears and the planet gears' carrier
  • The ring gear

Each of these three components can be the input, the output or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gearset. Let's take a look at a single planetary gearset.

One of the planetary gearsets from our transmission has a ring gear with 72 teeth and a sun gear with 30 teeth. We can get lots of different gear ratios out of this gearset.





Gear Ratio


Sun (S)

Planet Carrier (C)     

Ring (R)

1 + R/S



Planet Carrier(C)      

Ring (R)

Sun (S)

1 / (1+ S/R)            



Sun (S)

Ring (R)

Planet Carrier (C)      



Also, locking any two of the three components together will lock up the whole device at a 1:1 gear reduction. Notice that the first gear ratio listed above is a reduction -- the output speed is slower than the input speed. The second is an overdrive -- the output speed is faster than the input speed. The last is a reduction again, but the output direction is reversed. There are several other ratios that can be gotten out of this planetary gear set, but these are the ones that are relevant to our automatic transmission.



Planetary Gearbox

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