Helical Inline Gear Motors Helical gears aren’t specifically much like worm or bevel gearbox systems. They are actually an alternative solution to spur gears where the tooth are parallel to the axis of the gear itself. For example, in an inline application, you could have either spur OR helical gears. An inline helical gearbox engine will most likely be quieter and may bring higher loads than motors utilizing a spur gearbox. They can be more costly in initial cost, and manufacturers need to take into account axial thrust. However, the actual fact that the helix position may differ from 15 to 30 degrees permits flexibility with regards to design. They are found in in-line applications along with parallel shaft applications.
The benefit of helical gears is that it produces a rolling action, is quieter, and has less vibration compared to spur gears. It also produces much less friction and permits more teeth to be engaged concurrently as the teeth roll across one another.
There are myriad types of gearing. Some manufactures use spur gears rather than helical gearing, for instance. However, there is not as much surface contact, as mentioned above and as a result there is more noise and much less torque transfer possible.
Another system where noise is common are planetary equipment systems, where in fact the one gear is totally within the other. They also require grease lubrication plus they must be constructed with expensive materials to be able to maintain a long-life and bearing integrity. A simpler variant, internal gearing, is suffering from the same issues 
and can only be utilized with parallel shaft.
Finally, hypoid gearing may be best understood helical spiral bevel gear motor because similar to bevel gearing, but with the apparatus axes not intersecting. The sliding actions can create large amounts of warmth and the alignment requires great care.