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Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/63506

### **Abstract**

Underwater robots are currently utilized to evaluate water quality and the undersea landscape. Small-sized underwater robots are especially useful in improving the spatial resolution of the measurements, yielding high-quality data. This chapter describes a small-sized fish-like robot, with its surface composed of a flexible thin plastic film. Its internal components, including an actuator, could be encapsulated in the plastic film using a vacuum packaging machine. To simplify the waterproofing and pressure resistance properties of the fish-like robot, its internal components can be filled with insulating fluid. The plastic film on the surface has electromagnetic-wave-transmit‐ ting properties, allowing sensors to be arranged within the device, enabling assess‐ ment of its autonomous locomotion using infrared sensors. Robot attitude can be altered, based on geography of its internal components, floating blocks, and insulat‐ ing fluid. This attitude could be especially determined by the differences in densities between the floating block and insulating fluid. Evaluation of attitude control showed that an insulating fluid heavier than water allows a large variation.

**Keywords:** fish-like robots, underwater robots, flexible mechanism, vacuum packag‐ ing, plastic film
