This paper discusses the modeling of serial manipulators with flexible link
s and joints. The model of a flexible link includes bending in two perpendi
cular directions and torsion around the longitudinal axis. Second-order str
ain-displacement relationships, coupled with curvatures' as generalized coo
rdinates, are used to represent the foreshortening effect. Then, the dynami
c equations are exact to first order in terms of the generalized coordinate
s associated with the flexible links. These generalized coordinates and the
ir first time-derivatives are assumed to be small (of first order). The mod
el developed captures all the important phenomena, such as stiffening due t
o the angular speed or buckling due to large payloads. The dynamic equation
s are developed recursively using Jourdain's principle to allow an efficien
t symbolic implementation. The equations associated with the flexible links
are reformulated to enable off-line symbolic integration. The gyroscopic e
ffects of motors with reducers are included.