Coaxial planetary reducer (gear reducer), also known as in-line reducer (reducer), the drive shaft and output shaft are on the same rotating shaft. Coaxial planetary reducers usually take the form of spur gears. Spur gears are available in different versions.

For a single spur gear, the axes of the individual spur gears are parallel and fixed to each other. The rotation direction of the input shaft and output shaft is determined by the number of gear pairs, which can be in the same direction or in the opposite direction.

Even though a single spur gear is not in principle a coaxial planetary reducer, concentricity can be achieved using two pairs of gears with a total of four gears. In doing so, the two gears are aligned parallel on one axis.

A special type of coaxial planetary reducer is the reducer. Unlike a single spur gear, not all shafts with planetary gears are stationary. Spur gears also have internal teeth. For planetary gear reducers, multiple spur gears run on concentric tracks between the gears with internal teeth and the gears with external teeth. Hence the name planetary gears. The specific design of these coaxial gearboxes has given the coaxial arrangement of the input and output shafts.

Another feature of planetary gears is that not all spur gears have to rotate about their own axis to transmit torque. Spur gears with internal teeth are usually fixed and make the drive shaft and output shaft rotate in the same direction.

Planetary gear reducers have excellent power density compared to single spur gears. This is achieved by the fact that the torque can be distributed to the orbiting spur gear and thus to the meshing of multiple teeth. This means that an extremely compact design and high efficiency can be achieved. Multiple gear ratios can also be achieved by a single tandem arrangement in the same spur gear with internal teeth. The overall multiplier is derived from the product of the individual diets for each planetary phase.

The conversion of speed and torque is the same as that of a single spur gear. For example, with a gear ratio of 10:1, torque increases by a factor of 10, while speed decreases by the same factor. (not counting transmission loss)

The advantages of coaxial planetary reducer:

Input shaft and output shaft are arranged coaxially

very high efficiency

very high power density

compact design

Suitable for a wide range of applications

Easy implementation of multi-stage gearboxes and therefore high transmission ratios