Second, the planet gear bearings have to play an active role in torque transfer. Planetary systems split the torque input from the sun gear amongst the planet gears, which transfer torque to a planet carrier connected to the gearbox result. The bearings that support the planets on the carrier have to bear the entire brunt of this torque transfer.
Or, in acute cases, they could select angular contact or tapered roller bearings, both of which are created to withstand axial loads.
In planetary gearboxes, however, it’s a lot more difficult to create around these axial forces for just two related reasons. Initial, there is typically very little area in a planetary gearbox to incorporate the type of bulky bearings that can tolerate high axial forces.
The existence of axial forces makes things very different for the bearings that support helical gears. But it is critical to make a distinction between fixed-axis and planetary gearboxes. In fixed-axis gearboxes, the additional axial forces total little more than a hassle. Gearbox designers will most likely upsize the bearings to support the 
additional forces.
Since they won’t need to withstand any axial forces, spur gear bearings perform just a supporting function in the functioning of the gearbox. The bearings simply need to support the rotating equipment shafts, but they do not play an active role in torque transfer.
Helical Gears Place Better Demand on Bearings
Helical Gearbox information and also myths.
