# Study of a Small Robot for Mine Hole Detection
## 3 Mechanical Structure Design of Small Robots for Mine Holes
### Auxiliary System Design  
The auxiliary system is capable of realizing the radius change function of the small robot for mine hole detection. It holds the body upright, adjusts the travel state, connects multiple modules, and uses the screw nut structure to realize the radius change function, which can effectively control the radial size of the robot. As shown in Figure 6, the pusher is initially in a contracted state. When the robot starts to work, the stepping motor works on the action sleeve via the screw nut, and the spring in the action sleeve pushes the connecting rod after accumulating force, which pushes the crossbar to slide in the slide groove and holds up the pusher, forming a stable triangular structure with the drive arm. By controlling the forward and reverse rotation of the filament nut, the auxiliary system can also adjust the positive pressure between the crawler wheel and the pipe wall, thus changing the size of the friction force. The spring design of the action sleeve plays a cushioning role. When the crawling wheel encounters a minor bump or depression, the deformation of the spring will drive the slider to slide left and right, enhancing the robot's passability. Suppose the pipeline inspection class robot deviates from the pipeline axis during the working process. In that case, it will not only affect the robot's crawl performance but also the shot's quality. In order to ensure that the robot coincides with the axis of the pipe during travel, and to ensure that the robot is stable and fixed on the inner surface of the pipe, the front and rear ends of the body are supplemented with a support device, as shown in Figure 7. The tripod structure ensures that the positive pressure on each group intersects at one point; the spring structure of each foot plays a cushioning role and is adapted to the diameter-varying function of the mine hole inspection robot so that the robot maintains balance in the body when moving. Figure 5: Schematic diagram of the power system. Figure 6: Schematic diagram of the reducer structure. The design of a small robot for mine hole inspection has certain requirements for the size of the traction force, and in order to obtain a sufficiently large traction force, the friction between the crawler wheel and the hole wall needs to be increased. The friction force can be improved by increasing the friction coefficient between the crawler wheel and the hole wall and by increasing the positive pressure between the crawler wheel and the pipe wall in two ways. The first approach requires knurling the surface of the crawler wheel to increase the friction. The second approach requires the robot parts to have enough strength and stiffness to prevent the excessive positive pressure from destroying the structure of the robot, but this will result in the structure of the robot being too large to meet the size requirements of the robot. In order to increase the traction force of the robot as much as possible, the two approaches are used in combination. As shown in Figure 8, the robot is designed modularly, and multiple groups of crawling modules are connected in series to solve the problem of dimensional parameters. The robot system is divided into crawling modules and functional modules by module, and each robot is equipped with multiple sets of crawling modules and one set of functional modules. The functional modules are used to test the environment in the coal mine borehole, and the crawling modules are used to drive the robot to move. The crawling modules are connected to each other in series with universal joints. As depicted in Figure 9, a universal joint has two degrees of freedom, allowing the connected modules to rotate in both the horizontal and vertical planes, thereby enhancing the robot's flexibility. The required traction force determines the number of crawling module groups, with the load distributed across each group.