In order to move freely on the window surface the robot is required linearity and rotatability.
Table 1 compares characteristics of five types of locomotion mechanisms in points of mobility and complexity of mechanisms. Table 1 says that a crawler mechanism allows good linearity but rotatability is not good, that this mechanism needs many suction cups at the minimum which are attached on outer of a crawler, and that it makes the mechanism complexity and leads increase of mass.
First prototype (P1) was developed for confirmation of performance of two drive wheels mechanism with the suction cup based on principles described at Chapter 2.2.
Fig. 2 shows the overview of the Pl. The P1 consists of two couples of stepping motor and wheel, one suction cup connected to a miniaturized vacuum pump, and control electric circuits. Electric power is supplied via cables. The total weight of the robot except power source is 1.9 [kg]. Each Specification is shown in Table 2. Vacuum pressure is controlled by manual.