3 min readApr 18, 2022

Planetary Gearbox is the Gearbox in which Input and Output Shaft are aligned in Inline Structure. Planetary Gearbox are Generally used to slow down motors and increase Torque. Planetary Gearbox consists of 3 main parts a Sun Gear, Satellite Gear and two or more planet Gears. The sun gear is driven and thus move the planet gears locked in the planet carrier and form the output shaft and the satellite Gears have fixed position. This system looks similar to Planetary Solar System.

While considering the selection of Primary Gearbox the Torque, backlash and Ratio must be correct but after that corrosion resistance, noise level should also be checked. After all this factors the main aim while selecting the Gearbox should be Precision hence SMD Provider High Precision Planetary Gearboxes with various factors keeping in mind such as Price, Stock Availability, Service, Delivery time etc.

Planetary Gearset


Sun Gear- “sun” gear is in the middle of the planetary gearbox –also introduced as a central gear. This is always the input part.

Planet Gear- There are two or more “planet” gears or outer gears around the outside of sun gear

Ring Gear- Also known as an internal gear, the ring gear is the component that combines the formation surrounding the planet parts

Carrier- The planet gears are joined by a carrier which in turn is attached to the output shaft.

Input Shaft- It is the shaft which is connected to sun gear which can be found solid shaft as well as hollow.

Output Shaft- It is the shaft which is connected to carrier gear. Similar to input shat it can also be found solid shaft as well as hollow.

Input shaft cover- It is the part which cover the input side of the gearbox

Output Shaft Cover- It is the part which cover the output side of the gearbox

  • Bearing- Deep Groove Ball Bearings are used on input and output shafts for handling loads and smooth rotational transmission


The Design and the features of SMD Planetary Gearbox allows it to be used in various Applications such as Aerospace, Agriculture, Conveyors, Robotics, Pumps, Medical Applications etc.



Number of Teeth :

S + 2P = R

S- No. of Teeth on Sun Gear, P — No. of Teeth on Planet Gear, R — No. of Teeth on Ring Gear.

To check if the Planetary Gears taken are possible or not, use below formulae. If the answer is a integer then the no. of planetary gears taken is correct.

R-S/N = ?

Where n = No. of Planet Gears.

Formula to Calculate the overall Ratio for Planetary Gearset. =

Where Wr, Ws,Wp and Wc is the angular velocity of Ring, Sun, Planet and Carrier accordingly and Nr, Ns and Np is the number of teeth for ring, Sun and Planet.


SMD Planetary Gearbox has a huge demand in Indian as well as overseas Market as they provide less Backlash than most of its Competitor. This gearbox is available in 2 Models i.e. Planetary Gearbox with Shaft Output( SNP Series) and Planetary Gearbox with Flange Output (SNDU Series) and is made available in various sizes such as SNP40, SNP60, SNP90, SNP120, SNP150 etc. This Planetary reducer consist of High torque capacity and low inertia and also can be used for Indexing purpose with high Accuracy. SMD Provides Reduction Ratio from 1:3 to 1:100 and any mounting modifications can be done.




Our Company Name SMD stands for SEIMITSU MOTION DRIVES as a trailblazer in the solution provider of various types of industrial Gearbox in Taiwan.