Light mobile robotpsilas weight design is a important problem which decides function and ability of mobile robot. In this paper, a total design method is advanced. There are many factors to consider, include mechanical part, electrical part, and task part. Each parts of robot must be carefully calculated and designed. There are many experiences in it. A light mobile robot is carefully analyzed as an example. The method can help mobile robot designers on how to design a robotpsilas weight quickly and not waste time and money.