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 world carrier linked to the gearbox output. The bearings that support the planets on the carrier need to bear the entire brunt of that torque transfer.
Or, in extreme cases, they could select angular get in touch with or tapered roller bearings, both 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. 1st, there is typically hardly any room in a planetary gearbox to incorporate the kind of bulky bearings that may tolerate high axial forces.
The existence of axial forces makes things completely 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 excess axial forces amount to little more than a hassle. Gearbox designers will most likely upsize the bearings to support the additional forces.
Since they don’t need to withstand any axial forces, spur gear bearings perform just a supporting role in the functioning of the gearbox. The bearings simply need to support the rotating gear shafts, however they do not really play an active Helical Gearbox function in torque transfer.
Helical Gears Place 
Greater Demand on Bearings