Helical Inline Gear Motors Helical gears aren’t specifically much like worm or bevel gearbox systems. They are in fact an alternative to spur gears where the tooth are parallel to the axis of the apparatus itself. For example, within an inline application, you can have either spur OR helical gears. An inline helical gearbox engine will usually be quieter and may bring higher loads than motors utilizing a spur gearbox. They may be more expensive in initial price, 
and manufacturers need to take into account axial thrust. Nevertheless, the actual fact that the helix position may differ from 15 to 30 degrees allows for flexibility with regards to design. They are used in in-line applications in addition to 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. In addition, it produces less friction and allows for more tooth to be engaged simultaneously as one’s teeth roll across each other.
There are myriad types of gearing. Some manufactures use spur gears rather than helical gearing, for example. However, there isn’t as much helical spiral bevel gear motor surface contact, as noted above and consequently there is more sound and much less torque transfer possible.
Another program where noise can be common are planetary gear systems, where in fact the one gear is totally within the other. They also require grease lubrication and they must be constructed with expensive materials to be able to maintain a long-lifestyle and bearing integrity. A simpler variant, internal gearing, is suffering from the same issues and can only be used with parallel shaft.
Finally, hypoid gearing may be best understood as similar to bevel gearing, but with the gear axes not really intersecting. The sliding actions can create huge amounts of temperature and the alignment needs great care.