Quadrotor helicopters are micro air vehicles with vertical take-off and landing capabilities controlled by varying the rotation speed of four fixed pitch propellers. Due to their rather simple mechanical design they have grown to popularity as platform for various research projects. Despite most of them being individually highly successful, they are typically tailored to a specific purpose making it hard to utilise them for further research and education. In this paper, we present the novel design of the I4Copter quadrotor. It has been developed to provide a stable demonstration quadrotor platform for various kinds of research and education projects targeting cross-field challenges in real-time and embedded systems, distributed systems, robotics and cybernetics. The modular and open architecture of our platform allows an application-specific, fine-grained extension, adaption and replacement of software and hardware components. The safe extensibility is supported by strict tempora...