Although the simplest gear systems are those with just one gear engagement area between a pair of gears, alternatives are available for applications where it is necessary to transmit a very high torque in a very small space. One option to increase power density is to use the split torque systems that were mainly developed for the aviation industry. These gear systems are based on a very simple idea: division of the transmission of force between several contact areas, thereby increasing the contact ratio. This gives rise, however, to the problem of meshing four gears (Fig. 1).