The purpose of this paper is to present a unified methodology for the derivation and implementation of the continuous dynamics (equations of motion) and discrete dynamics (transition equations) that comprise the hybrid model of an passive biped robot. A developed general model derivation procedure is presented which generates a complete mathematical model for a selected underactuated bipedal robot. The generated mathematical models are implemented in Simulink using the Stateflow tool. The functionality of the proposed approach has been demonstrated using several case studies. [ABSTRACT FROM AUTHOR]