Rotor

A rotor has a main body (42). A weight guide (45, 49, 51, 53, 55, 57) is recessed in the main body (42). A weight accommodated in the weight guide contacts with and rolls on a weight guiding surface. The weight swings like a pendulum about a second axis that is parallel to and offset from the rotation axis. The weight guiding surface guides the weight to keep the weight moving within the guiding surface.