In the development of intelligent mechatronic systems, a gap of tools and methodologies appears to exist, when technical requirements meet physical behavior modeling. Consistency between requirements, development and modeling is not fully achieved and more sophisticated methods seem to be needed. The meaning of requirements in terms of intelligent mechatronic systems is pointed out. Challenges in obtaining technical requirements are worked out by literature review. The influence, identified as most crucial, is domain knowledge. This challenge of the right assumptions considering domain knowledge is reinforced by the, in literature, predominantly applied discrete models. An approach for a solution of these challenges is presented at the end of this paper.