Second, the earth gear bearings have to play an active role in torque transfer. Planetary systems split the torque insight from the sun gear amongst the earth gears, which in turn transfer torque to a planet carrier connected to the gearbox result. The bearings that support the planets on the carrier have to bear the full brunt of this torque transfer.
Or, in extreme cases, they could select angular get in touch with or tapered roller bearings, both of which are made to withstand axial loads.
In planetary gearboxes, however, it’s a lot more difficult to design around these axial forces for just two related reasons. First, there is typically very little space in a planetary gearbox to include the type of bulky bearings that can tolerate high axial forces.
The existence of axial forces makes things completely different for the bearings that support helical gears. But it is important to make a distinction between fixed-axis and planetary gearboxes. In fixed-axis gearboxes, the additional axial forces amount to little more than a Helical Gearbox hassle. Gearbox designers will often upsize the bearings to support the additional forces.
Since they won’t need to withstand any axial forces, spur gear bearings enjoy just a supporting role in the functioning of the gearbox. The bearings should just support the rotating gear shafts, however they do not really play an active function in 
torque transfer.
Helical Gears Place Greater Demand on Bearings