To increase students' sense of ownership, the present study incorporated elements of Challenge-based learning (CBL) into a mechanical engineering course. CBL is a desirable pedagogy adopted by many universities of technology. Although the boundaries and constraints of a regular course hinder the application of CBL, some of its benefits can be retained. In this paper, we investigate a second-year mechanical engineering course which aimed to give students autonomy in choosing their modelling projects, to facilitate students' ownership of their learning processes. The mixed-methods analysis of the intervention reveals no particular benefits of the intervention on pilot students' ownership, compared to a control group. The qualitative analysis suggests that implicit and explicit factors constrain ownership development, namely the anticipated difficulty level and official constraints for selecting projects. Our findings suggest that, currently, there could be too simple assumptions about how providing students with autonomy in selecting their projects allows for student ownership.