In this paper, we propose a formation method that can specify the position of each robot in a group. The robots are assumed to be heterogeneous and identified. Also assume that a formation is composed of some equilateral triangles. The method is verified through some simulations. When applying the method to a real robot system, it needs to obtain IDs and relative positions of the robots. We further propose the measurement system using wireless communication and ultrasonic sound. Such a system is evaluated in the estimation accuracy of relative positions through some experiments in a simulated environment.