Helical Inline Gear Motors Helical gears are not specifically much like worm or bevel gearbox systems. They are actually an alternative to spur gears where the tooth are parallel to the axis of the gear itself. For helical spiral bevel gear motor example, within an inline application, you could have 
either spur OR helical gears. An inline helical gearbox electric motor will usually be quieter and may bring higher loads than motors utilizing a spur gearbox. They could be more expensive in initial price, and manufacturers need to account for axial thrust. Nevertheless, the actual fact that the helix position can vary from 15 to 30 degrees allows for flexibility with regards to design. They are used in in-line applications as well as 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 permits more teeth to be engaged at the same time as one’s teeth roll across one another.
There are myriad types of gearing. Some manufactures use spur gears rather than helical gearing, for example. 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 usually common are planetary gear systems, where in fact the one gear is totally within the other. In addition they require grease lubrication plus they must be built with expensive materials to be able to maintain a long-lifestyle and bearing integrity. A simpler variant, internal gearing, suffers from the same problems and can only be used with parallel shaft.
Finally, hypoid gearing may be best understood since similar to bevel gearing, but with the gear axes not intersecting. The sliding actions can create large amounts of high temperature and the alignment requires great care.