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What is a planetary gear motor?

Micro DC Planetary Gear Motor

The word “planetary” has a special meaning in gear parlance. It refers to a particular arrangement of gears such that at leas one gear is an internal, or ring gear, one gear is a “sun” gear, and is mounted on the same center line as the ring gear. Additionally, there is at least one gear, called the planet, mounted on a shaft called a carrier, between the sun and the ring (in mesh with both). Generically, when either the ring or the sun is rotated (and the other held fixed), the planet gear and the carrier “orbit” the sun.

Occasionally, similar arrangements in which the carrier is fixed (preventing the planet from orbiting), and the sun (or ring) is rotated are referred to as “planetary”, but strictly speaking, these arrangements are properly referred to as “epicyclic”. (The only distinction is whether the carrier, which the planets are mounted to, is fixed or not. Visually, they look the same as planetary gear trains to the layman.


Planetary reducer function:

Transmission of motor power and torque;

Transmission and matching power speed;

Adjust the inertia match between the mechanical load on the application side and the motor on the drive side;


The composition of planetary reducer

The origin of the name of the planetary reducer

In the middle of this series of components is the core transmission component that any planetary reducer must carry: the planetary gear set.

It can be seen that in the structure of the planetary gear set, there are multiple gears around a sun gear (sun gear) along the inner gear of the planetary reducer housing, and when the planetary reducer is running, with the sun gear (sun gear) The rotation of the wheel), several gears around the periphery will also "revolve" around the central gear. Because the layout of the core transmission part is very similar to the way the planets in the solar system revolve around the sun, this type of reducer is called a "planetary reducer". This is why the planetary reducer is called a planetary reducer. 

The sun gear is often referred to as the "sun gear" and is driven to rotate by the input servo motor through the input shaft.

The multiple gears that rotate around the sun gear are called "planet gears", one side of which is engaged with the sun gear, and the other side is engaged with the annular inner gear on the inner wall of the reducer housing, carrying the transmission from the input shaft through the sun gear. The torque power comes over, and the power is transmitted to the load end through the output shaft.

During normal operation, the orbit of the planetary gear "revolving" around the sun gear is the annular ring gear on the inner wall of the reducer housing.


Working principle of planetary reducer 

When the sun gear rotates under the drive of the servo motor, the meshing action with the planetary gear promotes the rotation of the planetary gear. Finally, under the driving force of rotation, the planetary gear will roll on the annular ring gear in the same direction as the sun gear rotates, forming a "revolutionary" motion around the sun gear.

Usually, each planetary reducer will have multiple planetary gears, which will rotate around the central sun gear at the same time under the action of the input shaft and the rotational driving force of the sun, sharing and transmitting the output power of the planetary reducer.

It is not difficult to see that the input speed of the motor side of the planetary reducer (that is, the speed of the sun gear) is higher than the output speed of its load side (that is, the speed of the planetary gear revolving around the sun gear), which is why it is called. The reason for "Reducer".

The speed ratio between the drive side of the motor and the output side of the application is called the reduction ratio of the planetary reducer, referred to as "speed ratio", which is usually represented by the letter "i" in the product specification, which is composed of the annular ring gear and the sun gear is determined by the ratio of the dimensions (circumference or number of teeth). In general, the speed ratio of a planetary reducer with a single-stage reduction gear set is usually between 3 and 10; a planetary reducer with a speed ratio of more than 10 needs to use a two-stage (or more) planetary gear set for deceleration.

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Post time: Sep-26-2022