Project based learning (PBL) is commonly applied in engineering education, and evaluated positively in terms of learning outcomes and student engagement. However, ensuring depth of the taught material and limiting the workload per teacher is not obvious when implementing PBL, especially for large student populations. Here we share a practical framework to prepare and execute project based learning for groups of approximately 150 BSc students in Mechanical Engineering. We show how a team of Instructors and Teaching Assistants (TAs) allows reducing the workload of individuals in the preparation, execution, and grading phases of the project. In the preparation phase, pairs of TAs draft sections of the project manual that are tested and improved by different pairs of TAs. During project execution, the role of TAs is twofold: (1) They co-supervise two project groups together with one staff member, answering basic and administrative questions. (2) They act as experts for the project groups on the topics that they helped develop, which are sometimes outside of the direct scientific scope of the instructors. Therefore, the TAs act as more knowledgeable others in Vygotski’s theory of constructive learning and therefore provide effective scaffolding, preventing students from getting stuck at places of difficult learning. The instructors (10 staff members, mainly of our research group) take responsibility for the execution and assessment phases to ensure quality, but at a strongly reduced workload because of TA involvement. The implementation schedule for the preparation, execution, and assessment phases of the project are included in the supplementary materials, as well as an example project description on Covid-safe train cabins.