Planetary Gearbox

The essential parts of a planetary gearbox can be divided into four main components. In the center of the gearbox is the sun gear with external teeth, which is driven by the motor. The power is transmitted to the rotating spur gears, known as planet gears. These are mounted on a planet carrier, which also forms the output shaft and ensures power transmission at the output. The orbit of the planetary gears is limited by a toothed wheel with internal teeth, the so-called ring gear. This usually also forms part of the gear housing.

The number of teeth of the planetary gears can be freely selected in theory, as it has no influence on the overall transmission ratio. They are only responsible for transmitting the torque. Usually, the input and output of planetary gears are arranged coaxially. Due to this and the condition that all gears in mesh must have the same module, the equation for the pitch diameter d=m*z results in the following condition for the number of teeth of the planet gears (please note: number of teeth of the ring gear is always negative).

m(z_{1}+2z_{p}+z_{2}) = 0 \rightarrow z_{p} = \frac{-z_{1}-z_{2}}{2}

Due to display issues, the formula is shown below in the form of a picture

The number of teeth of the planetary gears thus always corresponds to half the difference between the number of input and output teeth for simple planetary gear units.

The number of planetary gears can vary, but in industrial applications it is at least three. As the number of planetary gears increases, the transmittable torque can be increased by distributing the load over a larger number of tooth meshes.

Characteristics
Since a planetary gearbox contains several planetary gears, several tooth meshes occur at the same time during operation. This power split ensures that, compared to other gear types, a higher efficiency and thus also a higher transmittable torque is possible with a more compact design.

The gear ratio of a planetary gearbox results from the ratio between the ring gear and the sun gear. If the size of the ring gear is kept constant, the ratio can be changed by changing the number of teeth of the sun gear and the planet gears. The smaller you choose the sun gear, the larger the gear ratio will be.

For technical reasons, a ratio greater than 10:1 should not be selected, otherwise the number of teeth of the sun gear will be too small. A higher ratio is required, several planetary gear sets can be arranged in a row in the same ring gear or in two fixed ring gears. This constellation is then called a multi-stage planetary gear.

Planetary gearboxes are suitable for counterclockwise and clockwise rotation as well as for continuous, alternating and intermittent operation.

3 Planetary Gearbox Types
Here are the three main planetary gearbox types and their specs:

Shaft Output
With this gearbox, the housing of the gearbox is mounted straight on the machine. The planetary gears are located in a rotating carrier, and the ring is fixed to the carrier, delivering drive to the shaft and resulting in rotating shaft output.

Shaft output gears can deliver up to 113,000 N.m. (Newton-meters) torque.

Spindle Output
This type of planetary gearbox is similar to the shaft output gears. The only difference is that the output is supplied as a flange.

Spindle output gears can deliver up to 113,000 N.m. (Newton-meters) torque.

Wheel Drive
The planet gears in this high torque planetary gearbox type are attached to a wheel carrier and go round the ring gear.

Wheel drive gears can deliver up to 332,000 N.m. (Newton-meters) torque.