Evoloid toothings are extremely helical pairs of cog wheels which can be used to build very compact and powerful gear units. The overlap lacking with smaller number of teeth is settled by the overlap ration of the helical gearing. As examples these images show two kinds of a planetary gear.

For example evolid toothing allows for construction of highly gear reducing planetary gears. These planetary gears can take much more load capacity than planetary gears with a spur toothing. Higher gear reductions / level become possible.