The basic transmission structure of a planetary gearbox consists of four main components: the sun gear, planet gears, internal gear ring, and stage gears. By utilizing the planet gears, this gearbox achieves power splitting and enables simultaneous engagement of multiple teeth, delivering exceptional performance. It is commonly used in conjunction with stepper motors and servo motors to reduce rotational speed, increase torque, and match inertial loads. This type of gearbox finds extensive applications across various industrial sectors, including lifting and conveying equipment, construction machinery, metallurgy, mining, petrochemicals, construction machinery, light industry and textiles, medical devices, instrumentation, chemicals, shipbuilding, weaponry, and aerospace.

Regardless of the specific type of gearbox product, each has its own strengths and weaknesses as well as suitable application scenarios. As to whether a helical gear planetary gearbox or a spur gear planetary gearbox is better, it depends on the particular operating conditions and cannot be generalized. The editor has compiled the following key differences for your reference, hoping they will be helpful to those who are selecting a planetary gearbox.

1. Appearance:
Helical gears are gears that are offset and placed on cylindrical gears.
When the spur gears are arranged, there is no misalignment.

2. Meshing degree of internal gears and gears:
For the manufacture and assembly of spur gears, many thin-sheet spur gears are both uneconomical and difficult to produce. Therefore, gears are now manufactured as integral units with teeth oriented along a helical path.
Unlike spur gears, helical gears generate undesirable axial forces. However, the benefits they offer in terms of vibration reduction and increased strength far outweigh the drawbacks caused by axial thrust and the slight increase in manufacturing costs. Therefore, in the manufacture of gear reducers, helical gears are preferred over spur gears.

In a spur gear planetary reducer, the gears engage and disengage directly as a whole; therefore, the impact force during the transition from engagement to disengagement is significant for spur gears.
In a helical planetary gearbox, as the gears engage, the contact line gradually changes from short to long and then back to short again—a process of gradual meshing. Therefore, from the moment helical gears begin to engage until they disengage, the impact force is minimal and the meshing quality is excellent.

3. Gear overlap coefficient:
The overlap factor of helical gears is greater than that of spur gears.
A helical gear has a helix angle. As the gears are running, both helical and spur gears exhibit an overlap in the face contact ratio; moreover, helical gears have an additional overlap coefficient in the axial direction. Because helical gears have more overlapping surfaces, their load-carrying capacity is higher than that of spur gears.

4. Transmission error:
The teeth of a helical gear are centered around the gear itself, and their contact surfaces are inclined straight lines.
The engagement contact line of straight teeth is a straight line parallel to the gear axis.
Therefore, the gear error of helical gears is less than that of spur gears.

5. Torque transmission and efficiency differ.
Straight-tooth planetary reducer: With the motor shaft directly connected, the straight teeth engage directly, resulting in lower torque transmission compared to helical-tooth planetary reducers and lower transmission efficiency.
Helical gear planetary reducer: Mounted directly beneath the motor shaft, helical gears mesh with each other, delivering greater torque transmission compared to spur-gear planetary reducers. The transmission system is smooth, boasts high tensile strength, and features high efficiency.

6. Accuracy
Helical gear planetary reducers have higher precision than spur gear planetary reducers. Helical gears have higher precision than spur gears.
Straight-tooth planetary reducers: First-level precision is around 10 arcminutes, with a maximum of 6 arcminutes.
Helical planetary reducer: First-stage precision is around 5 arcminutes, with a maximum of 1 arcminute.

7. The support methods for the planetary carrier are different.
The planetary carrier for helical gears must adopt a double-support structure. A helical planetary reducer has two support points; its bearing and gear carrier are integrated into one unit. Each hole must be precisely aligned, both vertically and horizontally, with absolutely no deviation whatsoever. Helical-geared precision reducers offer advantages such as high torque, high rigidity, high output accuracy (high efficiency, low noise), low backlash, and high positioning accuracy.

8. Noise and Vibration:
The main drawback of spur planetary reducers is that they tend to generate vibration and are relatively noisy.
Helical planetary reducers produce less noise and vibration.

Straight teeth can be supported either by a dual-support or a single-support structure. However, when a straight-tooth planetary reducer has only one support point, the gear will shift to the opposite side under load, leading to increased noise, greater friction, and excessive deformation if the load is too high. Over time, this can result in reduced rigidity and diminished precision.

Overall, helical planetary reducers offer higher precision and lower deviations compared to spur planetary reducers.