In this paper, the biomimetic modular robot research that mimics pill bug will be introduced. Pill bug moves by legs and rolls its body when it faces hostile situation. The proposed system was also imitated by the linear motion of earthworm, and in order to escape dangerous situations such as Armadillium vulgare, they themselves are able to round the its body into a ball shape being protected from predator, i.e., in order to passive defense exercise, we use to the split solenoid. The proposed robot has not only a simple structure composed of cores, coils and wires, but it also enables bidirectional actuation and high speed locomotion regardless of friction condition. The optimal input voltage with respect to maximum speed is approved. After the theoretical analysis as to stroke and power, I have verified it using a finite element analysis and experiment.