Helical Inline Gear Motors Helical gears aren’t specifically comparable to worm or bevel gearbox systems. They are in fact an alternative to spur gears where in fact 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 electric motor will usually be quieter and may carry higher loads than motors using a spur gearbox. They could be more expensive in initial price, and manufacturers need to take into account axial thrust. However, the actual fact 
that the helix angle can vary from 15 to 30 degrees allows for flexibility when it comes to design. They are found in in-line applications and also parallel shaft applications.
The advantage of helical gears is that it produces a rolling action, is quieter, and has less vibration compared to spur gears. It also produces less friction and permits more the teeth to be engaged simultaneously as the teeth roll across each other.
There are myriad types of gearing. Some manufactures make use of spur gears rather than helical gearing, for instance. However, there is not as much surface contact, as noted above and as a result there is more sound and much less torque transfer possible.
Another program where noise is definitely common are planetary gear systems, where in fact the one gear is completely within the other. They also require grease lubrication plus they must be built with expensive materials to be able to maintain a long-existence and bearing integrity. An easier variant, internal gearing, suffers from the same helical spiral bevel gear motor problems and can only be utilized 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 action can create huge amounts of warmth and the alignment requires great care.