This paper presents the design, mathematical development and experimental validation of a new vibration-driven locomotion module for capsule robots. The proposed system consists of a mass moving inside a body mass. A nonlinear elastic spring is used to connect the two masses, providing the ability to enhance the resonant characteristics. Being excited by a half-sine electromagnetic force, the internal mass periodically oscillates and thus generates locomotion. The system was found to move effectively in expected direction under isotropic friction condition. Bifurcation analysis showed that the system always has period-1 motion.