A still growing number of software concepts and framworks have been proposed to meet the challenges in the development of more and more complex robotic systems, like humanoids or networked robotics. The issue of hard realtime, however, has not been the main focus of such concepts, but is essential for building and controlling mechatronic systems. Here we discuss the specific demands of complex mechatronic systems and present a software concept, the "agile Robot Development" (aRD) concept, we developed at our institute. We show that the performance of current computing and communication hardware allows for a flexible component based concept with distributed execution even in hard realtime with rates in the kHz range.