equation to calculate efficiency of worm gears

worm gear. In these widely used speed reducers, a worm gear drives a worm wheel to provide output motion at a right angle to the motor shaft . 

 These speed reducers are often the best value for applications in which the motor and reducer are coupled in-line with the driven shaft, Figure 5. Their efficiency usually ranges between 95 and 98%, regardless of speed ratio. Cost is competitive with worm gear motor where the center distance is 2-in. or more.

The worm gear and worm wheel have non-intersecting, perpendicular axes, and the meshing action between gears occurs over a relatively large contact area. This meshing action consists primarily of a sliding motion that creates friction between the gears.

Worm gear efficiency varies significantly when lead angle, friction factor and gear ratio changes.