Second, the planet gear bearings have to play an active role in torque transfer. Planetary systems split the torque insight from sunlight gear amongst the planet gears, which in turn transfer torque to a world carrier connected to the gearbox output. The bearings that Helical Gearbox support the planets on the carrier need to bear the entire brunt of that torque transfer.
Or, in acute cases, they could select angular contact or tapered roller bearings, both which are made to withstand axial loads.
In planetary gearboxes, however, it’s a lot more difficult to create around these axial forces for two related reasons. 1st, there is typically hardly any area 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’s important to make a distinction between fixed-axis and planetary gearboxes. In fixed-axis gearboxes, the excess axial forces total little more than an inconvenience. 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 gear shafts, however they do not really play an active part in torque transfer.
Helical Gears Place Greater Demand on Bearings