Fig. 5

Relationship between the contraction force of the telescopic actuator when the inside air pressure is − 75 kPa to the length of the actuator. The contraction force was almost constant when the length was in the range of 45–85 mm, which was due to the fact that the telescopic actuator changed its length significantly from atmospheric pressure to approximately − 10 kPa. When the length of the actuator was in this range, the inside air pressure was nearly constant, resulting in a constant contraction force. A steeper increase over 85 mm could be attributed to the change in the cross-sectional area by dents on the surface of the actuator