The demand for monitoring from high points is increasing to support remote control and accurate monitoring. Unmanned ground vehicles with long arms are used to achieve long-term and accurate monitoring. The use of convex steel tapes is effective for achieving both high strength and lightness of the arm, which prevents the robot from collapsing or the arm from falling off. However, the previously proposed methods could not be used under tough environmental conditions such as strong winds as well as when the posture of the robot is changed. The objective of the present study is to design a novel extendable arm structure using convex tapes for outdoor usage. We designed an arm with a novel combination of convex tapes that can endure outdoor interferences. We manufactured the arm using a new method such that there is no need to separate the convex tapes. Our results indicated that the robot could extend its arm up to 4 m at a wind speed of 10 m/s and its posture can be changed to 15° in all directions without the use of additional supports such as an outrigger. This novel arm is useful for supporting remote-controlled aerial work platform outdoors such as in a disaster struck area where only tiny mobile robots can enter. This novel combination method is significant not only because it fills the gap in previous sutures but also because it does not require complex mechanisms such as the outrigger method.