Electrically powered personal mobility is expected to emerge as a new mode of transportation, in response to impending socioeconomic issues such as urbanization, global climate changes, demographic changes, and increasing number of single-person households. Yet, in the transition, the market for each usage of personal mobility such as passenger transportation, delivery of goods, assisting the less abled, or pastime recreation is not big enough for mass production of each model. This may preclude most enterprises from entering the market. The paper presents a prospective, and realistic solution: modular design to produce a number of variant models based on a common platform, and further modularization of the platform itself, to achieve a high degree of the economies of size. It is shown that using this extended modular design strategy, threewheeled vehicles with two front wheels or those with two rear wheels, for example, can be developed based on a common mid-portion of the platform. Such extensive modular design is relatively easy for electric personal mobility because of its small number of components, simple architecture, and easily separable groups of components. Furthermore, the paper illustrates the collaborative roles of industrial designers (ID) and engineering designers (ED) in each step of the preliminary design process adopted here. Personal mobility designs developed in this work demonstrate the importance of such collaborative efforts; for example, engineering design for dynamic stability and package layout design affect each other, so clear communication and compromise between ID and ED is crucial. Overall, the paper sheds light on a prospective direction for electric personal mobility to become one of the major mobility means in the near future.