Most researchers develop real-time applications with C, including programming hardware with C and using a Real Time Operating System (RTOS) that is written in C to manage the task environment. In this paper, we research a different approach by using Java to develop a real-time application. We implement an example real-time project, onboard computation of a coaxial helicopter Lama, with a Java based Sun SPOT to control the hardware and a Java RTOS (JARTOS) running on top of the Sun SPOT to manage the processes. This project enables us to answer several questions regarding to real-time system development with the Sun SPOT. At last, we conclude this paper with the experience we gather during the development.