Abstract
In this paper, based on electromagnetic theory and geometrics, the electromagnetic field of the worm coils for the drive is researched. A coordinate system is established and equations of the toroidal helical slots for three phase coils on worm are presented. By means of equation for magnetic vector at any point near coil, magnetic vector near single phase toroidal worm coils is introduced. Hence, the total magnetic vector near three phase toroidal worm coils is obtained as well. Simulation results show: near toroidal worm, as a static current is applied to its one toroidal coil, a toroidal electromagnetic field is formed; when the 3-phase source is connected to the coils of the worm, a toroidal circular rotating electromagnetic field will drive several planets rotate about their own axial. And by means of magnetic forces between teeth of the planet and stator or worm, the rotor will be driven to rotate about its own axial and an output of low speed and large torque can be obtained.