Conventional mobile robots typically use a wheel or crawler mechanism for locomotion. However, these robots often get stuck in narrow spaces. To mitigate this issue, we propose an innovative flexible mobile robot named “MOLOOP” in this study. The proposed robot has double-looped and hermetically-sealed structure and all ground-contact-area moves to the same direction. Three synchronized flexible crawlers generate the driving force within the robot body. The crawler, named “HS crawler,” comprises of loop-connected flexible bags. The entire body of the robot is flexible; therefore, the robot can pass through narrow terrains with adaptive shape changes. However, in terms of power and size, performance improvement is necessary for the practical use of the robot. This paper describes the improvement of HS crawler performance, which directly affects the driving force, traveling speed, and size of the robot. For the purpose of high input pressure, this study reinforced the flexible bags of the crawler using fibrous materials. This reinforcement realizes the power-up and downsizing of the flexible bags. The new crawler achieves a performance of 3.43 Nm torque and 39.0 mm/s traveling speed, compared to a torque of 0.23 Nm and traveling speed of 3.0 mm/s of the previous crawler. Additionally, the width of the new MOLOOP changed to 270 mm from 420 mm because of the downsized crawler. Furthermore, a dedicated mechanical valve was developed. This valve achieves a flow rate of 2.39 L/min as compared to 0.92 L/min of a commercially available solenoid valve. Moreover, the traveling speed of MOLOOP increased from 3.0 mm/s to 9.0 mm/s. The prototype robot successfully passed through a narrow terrain with a minimum width of 200 mm (robot width: 270 mm).

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