# Design and Development of a Climbing Robot for Wind Turbine Maintenance
## 3 Results and Discussions  
The scaled-down climbing robot design verification was tested in an indoor experimental setting. The first prototype testing was conducted to evaluate the performance of the winding mechanism and its locomotion. Figure 10 shows the winding mechanism that is prompt from the distance sensor to attain the proper tension force to ensure good traction for climbing. Once the precision measured on the four rubber wheels is obtained, the robot started its mobility to go up straight on the tower. The robot requires 3 s to cover the upward mobility of the tapered tower height of 1200 mm and the tower diameter for climbing 330-400 mm. The robot has dimensions of 500 mm \(\times\) 164.96 mm\(\times\) 45 mm for each body frame, with an average weight of 2 kg per body frame.  
Figure 11 shows the climbing process of the robot in a circular truncated cone tower. This reveals that the robot traction force from the winding mechanism has to be greater than the robot gravity force in climbing along the tower surface with an average speed of 120 mm/s, which shows a good performance of the tapering tower diameter structures of a wind turbine. The sufficient traction force coming from the steel rope and stepper motors demonstrated its absolute necessity to create friction on the robot wheels as it climbs. The robot may ascend and halt along the tower surface and continue ascending in the tower without slipping. As the robot descends along the tower, it also generates a strong traction force from the winding mechanism and requires a contact pressure decrease as the stepper motor unwinds the steel rope. The adaptability of the different diameter  
Figure 10: Climbing robot at the bottom part of wind turbine tower.  
Figure 9: Winding mechanism flowchart.  
of the wind turbine tower, as it climbs through a circular truncated cone shape, caused no problem.  
Figure 12 shows that the robot weight is 8.2 kg and includes the entire electronics assembly module and electric wires and maximum payload capacity of 4.4 kg with a safe factor of two. The result shows that the climbing robot can withstand the different load on the robot body frame without consuming power. The stability against breaking or slipping from the torque of the winding mechanism is sufficient for the robot to perform the climbing process in a circular truncated cone tower.  
The experiment testing results show that the prototype design of the climbing robot can perform its winding mechanism and locomotion along the tower with 1.67\({}^{\circ}\) inclination angle, as shown in Figure 13. The test allowed to exhibit the limit state of climbing a tower that the robot needs to provide an ideal force of traction to support all the weight of the climbing robot. The critical point is the equilibrium weight of each body frame that needs to be compensated for the equal distribution of force but in totality the scaled-down prototype climbs successfully on the tapered tower.  
Figure 11: Climbing robot in the middle part of wind turbine tower.  
Figure 12: Climbing robot payload capacity.  
Figure 13: Wind turbine climbing robot physical test model.  
Table 3 shows the specifications of the climbing robot while Table 4 shows the specification of the DC motor for its locomotion and stepper motor for the winding mechanism. Figure 14 shows the current swing of the four DC motors with and without load. The value of the current during the climbing process was measured to be within a 1.4 A range. As the robot has a load, the DC motor current shows an erratic swing due to the several factors needed in the climbing process. The data are generated during the preliminary climbing scenario test run as shown in Figure 15: it climbs 1150 mm (1.1 m) up in around 10 s. The average speed of the robot to go up and down is 120 mm/s with the