What Is Planetary Gearbox?- Definition And Overviews

What Is A Planetary Gearbox?

An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other. A carrier connects the centers of the two gears and rotates to carry one gear, called the planet gear or planet pinion, around the other, called the sun gear or sun wheel.

The planet and sun gears mesh so that their pitch circles roll without slip. A point on the pitch circle of the planet gear traces an epicycloid curve. In this simplified case, the sun gear is fixed and the planetary gear(s) roll around the sun gear.

An epicyclic gear train can be assembled so the planet gear rolls on the inside of the pitch circle of a fixed, outer gear ring, or ring gear sometimes called an annular gear. In this case, the curve traced by a point on the pitch circle of the planet is a hypocycloid.

The combination of epicycle gear trains with a planet engaging both a sun gear and a ring gear is called a planetary gear train. In this case, the ring gear is usually fixed and the sun gear is driven.

Why Is It Named A Planetary Gearbox?

The planetary gearbox got its name because of how the different gears move together. In a planetary gearbox, we see a sun (solar) gear, satellite (ring) gear, and two or more planet gears. Normally, the sun-gear is driven and thus move the planet gears locked in the planet carrier and form the output shaft.

The satellite gears have a fixed position in relation to the outside world. This looks similar to our planetary solar system and that is where the name comes from. What helped was that ancient gear constructions were used extensively in astrology for mapping and following our celestial bodies. So it was not such a big step to make.

In practice, we often speak from the perspective of the use of planetary gearboxes for industrial automation. That is why we call the sun-gear the input shaft, the planet gears, and carrier the output shaft, and the satellite gear (or ring gear) the housing.

An epicyclic gear train (also known as a planetary gearset) consists of two gears mounted so that the center of one gear revolves around the center of the other.

Possibilities Of Planetary Gearboxes

It is possible to realise different speeds and turning directions with the same construction. This can be achieved by, for example reversing the gearbox, which offers the following possibilities:

Driven sideSolid worldTo be driven sideResult
Input shaftHousingOutput shaftReduction
Input shaftOutput shaftHousingReverse movement + Delay
Output shaftInput shaftHousingDelay
Output shaftHousingInput shaftAcceleration
HousingOutput shaftInput shaftReverse movement + Acceleration
HousingInput shaftOutput shaftDelay
In- and output shaftN.A.Housing1:1

Check out our article: What is Shaft?

Where Is The Planetary Gearbox Usually Used (In The Transmission)?

Where is the planetary gearbox usually used (in the transmission):

  • In a robot to increase the torque
  • In a printing press to reduce the speed of the rollers
  • For precise positioning
  • In a packaging machine for reproducible products


What does a planetary gearbox do?

A planetary gearbox is a gearbox with the input shaft and the output shaft aligned. A planetary gearbox is used to transfer the largest torque in the most compact form (known as torque density).

Where is planetary gearbox used?

Planetary gear train (PGT) has been widely used in the transmissions of helicopters, automobiles, wind turbines, aircraft engines, etc. The main advantages of this transmission are its high efficiency, its compactness, its large transmission ratio, its large power-to-weight ratio, etc.

What is planetary shaft gearbox?

Planetary Gearboxes are a type of gearbox where the input and output both have the same center of rotation. This means that the center of the input gear revolves around the center of the output gear and the input and output shafts are aligned.

Are planetary gears good?

That’s because planetary gearboxes offer high torque transmission with good stiffness and low noise in a footprint that’s more compact than that of other gearbox types.

Why do drills use planetary gears?

Internals. Cordless drills are usually slow rotating drills with a maximum speed of 1000 rpm or even less. To reduce the speed of the DC electric motor and to increase the torque a planetary gearbox is used.

What is a 3-stage planetary gear?

Instead of the drive shaft, the planetary carrier contains the sun gear, which drives the following planet stage. A three-stage gearbox is obtained by means of increasing the length of the ring gear and adding another planet stage. A transmission ratio of 100:1 is obtained using individual ratios of 5:1, 5:1, and 4:1.

What is planetary gear motor?

A planetary gear motor mimics a planetary rotation system; the input shaft drives the central gear, also known as the sun gear, which then turns the surrounding gears, also known as planet gears.

What are planetary gears made of?

The planetary gear is a type of gear system comprised of spur gears. In planetary gearing (also known as epicyclic gearing), a center gear, called a sun gear, serves as the input and driver of the set. Three or more “driven” gears (referred to as planets) rotate around the sun gear.

Who invented planetary gears?

Ibn Khalaf al-Muradi, was an Andalusian engineer. Al-Muradi was the author of the technological manuscript entitled Kitāb al-asrār fī natā’ij al-afkār. It was copied and used at the court of Alfonso VI of León and Castile in Christian Spain in the 11th century.

What is a planetary carrier?

The planet carrier is in rotational motion holding the planets that rotate around themselves with a rotation sense which is the opposite of the planet carrier. The planets are in mesh with the ring and sun gears. The ring gear is fixed while the sun rotates at a different speed from the planet carrier.

How does a planetary differential work?

Torque is transmitted to the sun gears through the planet gear. The planet gear revolves around the axis of the carrier, driving the sun gears. If the resistance at both wheels is equal, the planet gear revolves without spinning about its own axis, and both wheels turn at the same rate.

How to Select Planetary Gearbox?

  • STEP 1: Select the reduction ratio.
  • STEP 2: Calculate the output Torque (Nm)
  • STEP 3: Find the service Factor.
  • STEP 4: Calculate the Rated Torque.
  • STEP 5: Select the Model from the Catalogue.
  • STEP 6: Verify the thermal rating for the selected model.
  • STEP 7: Verification of hollow frame.

Do planetary gears have backlash?

Planetary gears are more compact and less expensive than other types. And for a given output torque, their power transmission capability per unit volume is unmatched. Efficiencies of 95% per stage or better (at rated load) are typical. Low-backlash planetary gears are also available in lower ratios.

Do planetary gears increase torque?

The planet gears are mounted on a joint carrier that is connected to the output shaft. The rotational speed of the output is lower than that of the drive, and the torque of the output is higher in reverse proportion. The more gear wheels mesh with each other, the higher the torque.

What causes planetary gears to fail?

The planetary gearbox is exposed to high-speed reduction mostly because of its capability and compact size. Faulty design is not only the reason for gearbox failure, manufacturing, and material handling can be one. In a planetary gearbox, noise is usually no worse, and often better than standard gear-and-pinion reducers.

When should I use planetary gears?

Planetary gears are often used when space and weight are an issue, but a large amount of speed reduction and torque are needed. This requirement applies to a variety of industries, including tractors and construction equipment where a large amount of torque is needed to drive the wheels.

How are planetary gear ratios calculated?

What is planetary DC motor?

A planetary gear motor mimics a planetary rotation system, the input shaft drives the central gear, also known as the sun gear, which then turns the surrounding gears, also known as planet gears. They also feature a very compact, low-weight design in their Class.

How do planetary gears shift?

As the sun gear turns, it causes the planet gears to rotate in place along the inside of the ring. This motion, in turn, rotates the output shaft in a reverse direction.

What is true about planetary gear sets?

A planetary gear set is comprised of an outer gear ring that’s called the ring gear. Inside, you have a sun gear that has a fixed point in the center and a planet gear (or gears) that rotate about the sun gear.

How many gear ratios are in a planetary gear set?

Single-stage planetary gearhead ratios range from 3:1 to 10:1. Gear ratios cannot exceed 10:1 because pinion gears can be made only so small. Gear ratios greater than 10:1 are possible with an additional planetary stage, although this normally increases length and cost.

When was the planetary gear invented?

The sun and planet gear are a method of converting reciprocating motion to rotary motion and was used in the first rotative beam engines. It was invented by the Scottish engineer William Murdoch, an employee of Boulton and Watt, but was patented by James Watt in October 1781.

What is a planetary winch?

Planetary winch, as the name implies, is designed with a planetary gearbox. It is a sort of small winch machine that has gained popularity due to its compact size, smooth operation, simple maintenance, low noise, and good resistance to torque loads.

How do planetary gears increase speed?

The output of the second stage planetary gear mechanism uses a large diameter gear to drive the pinion to continue to increase speed. All gears use helical gears to make the transmission smoother.