# Design and Development of a Climbing Robot for Wind Turbine Maintenance
## 2 Materials and Methods
### Climbing Robot Model Design  
The overall mechanical design of the wind turbine climbing robot is shown in Figure 3. The design consists of three parts: the driving mechanism, winding mechanism, and body frame. The embedded microprocessor and other electronics accessories are attached to the body frame. The driving mechanism is adopted for obtaining maximum climbing speeds and includes the mechanism for up-down motion. The robot utilizes four DC motors to climb on the circular truncated cone tower being power supplied by a 12 V DC power. The DC motors provide high torque and high power to drive the robot up and down motion along the tower surface. The body frame is made of two parts to have a lightweight structure, ease of installation and transport. It supports all the driving wheels and holds the winding mechanism with the two stepper motors and steel rope. The main functions of a stepper motor are to wind and unwind the steel rope within its ideal traction force. Once the climbing robot is set up on the tapered wind turbine tower, the frame is locked and uses a tension force to grip it. This special winding mechanism maintains a safe distance of the robot to the tower diameter surface. The stepper motor together with the steel rope is a primary mechanism that adjusts the different diameter of the circular truncated cone tower to grip on the surface without falling to the ground. With this design, the robot has the potential to adapt to the tapering tower diameter structures and provide mobility capabilities to examine the circumference of the tower.  
The entire system of climbing robot is made up of two body frames that have a winding mechanism, dimensions as reckoned with both side views and top views are shown in Figure 4. The robot has two body frames with a height of 45 mm as shown in Figure 4a, a length of 500 mm as shown in Figure 4b, and each body frame weighs 2 kg. It is made of aluminum alloy 6061 material which is lightweight and economical. Figure 4b  
Figure 3: Wind turbine climbing robot model.  
shows the robot rubber wheels in contact with the wind turbine tower with the distance of 427.44 mm from M1 to M3 and from M2 to M4, which will constantly change as the robot moves along the tower surface. The tapering wind turbine tower is made of steel material with an average base diameter of 400 mm and the top diameter is 330 mm. If the robot is at the lower segment of the tower, the diameter distance is increased and as it moves upward, the diameter distance decreases. This change in diameter leads to a variation in length and forces. The electronic control circuit and the distance sensor attain the ideal traction force of the robot to move up-down the tower. The mechanical design is carried out with the aid of 3D modeling software Autodesk Inventor. The force analysis was performed to check the capabilities of the robot to climb in a circular truncated cone tower and holding onto the tower surface at a gradient angle. The robot weight, wheel torque, traction force, and the coefficient of friction between the wheel tires and tower surface were taken into consideration. It is important to determine the inclination angle and the wheel torque at an equilibrium state where the robot moves with constant speed to attain the synchronization of body frame as it climbs the tower. Then, all forces, the inclination angle and the torques can be managed to meet the climbing scenarios needed.