Two new designs for gravity compensated modular robotic systems are presented and analyzed. The gravity compensation relies on using zero-free-length springs approximated by a cable and pulley system. Simple yet powerful parallel four-bar modules enable the low-profile self-contained modules with sequential gravity compensation using the spring method for motion in a vertical plane. A second module that is formed as a parallel six-bar mechanism adds a horizontal motion to the previous system that also yields a complete decoupling of position and orientation of the distal end of a serial chain. Additionally, we introduce the concept of vanishing effort where as the number of modules that comprise an articulated serial chain increases, the actuation authority required at any joint reduces. Essentially, this results in a method for distributing actuation along the length of an articulated chain. Prototypes were designed and constructed validating the analysis and accomplishing the functions of a general serial-type manipulator arm.