This paper describes a service- and scenario-driven software architecture for the ambient assisted living infrastructure currently under development in the Robot-Era project. Involving the end-users from the start, the project integrates an ambient sensor network with an advanced knowledge-representation and planning system and three different robots for outdoor, condominium, and indoor service roles. We explain the design decisions for the userfriendly and medium-cost service robot, with a focus on the integration of the ROS-based sensing and manipulation capabilities with precise indoor navigation and the PEIS middleware for ubiquitous robotics.