The paper deals with torus-shaped automatic equalizer with vertical axis the body of which is placed relatively to the rotation axis. Automatic equalizer with torus-shaped adjustment mass moving freely within the autoequalizer's body both circularly and crosswise. Automatic equalizer's torus-shaped form reduces to the minimum the force of resistance when the ball moves, but simultaneously decreases the chance of launching the automatic equalizer in the autobalancing regime. The main task of the research is to determine the torus-shaped cross-section's size effect on the ball's motion mode. The automatic equalizer is made up of the mathematical model with two differential equations. Differential motion equations in rotor system with automatic equalizer are investigated by the hep of SPRING software, whith allows to calculate the ball motion.