STEM activities and educational robotics practices, could contribute positively to science curriculum teaching by increasing students’ predisposition and positive responce for sciences. One of the main reasons why public schools (and teachers as a concequence) are skeptical about adopting STEM/Robotics activities during teaching, is the large cost involved, plus the “closed” SW/HW solutions offered by STEM manufacturing companies. With our paper, we aim to break that barrier, by presenting an efficient and cost effective STEM approach for mathematics and programming, using open SW/HW solutions like Arduino platform, Scratch4Arduino coding and recyclable materials for robot design. We break our work in two stages: In the first stage we describe how a student could easily built its own experiment robot using recyclable materials (paper, wood, etc) and in the second stage we design and demonstrate STEM activities related to obstacle avoidance. To this end, students are encouraged to take part during the teaching process, to experiment, to interact and built SW/HW materials and to follow a “hands – on” approach under constructive constructivism guidelines. In other words, students will design and implement their experiment robot using recyclable materials and program it to behave in a way so as to use it in STEM activities. The acquisition of new knowledge and their participation in building their own robot will give students the motivation to experiment further. Overall, the ultimate goal of this paper is to engage students in STEM activities in order to develop critical and computational way of thinking, to work in teams, to collaborate, to exchange ideas and to build their experimental robots using recyclable materials.