# Study of a Small Robot for Mine Hole Detection
## 4 Hardware Circuit and Program Design  
### Hardware Circuit Design  
The small robot for mine hole inspection also needs to detect the environment inside the coal mine hole, mainly including methane content, temperature, humidity, mine hole depth, and stratigraphic conditions, under the condition that the motion state is controllable. Figure 10 shows the hardware circuit composition of the robot; the hardware circuit of the robot consists of a master control module, a motion control module, a detection module, and an image module. The main control module is composed of an STM32F101R6 microcontroller, a power supply circuit, a crystal circuit, a Micro-USB circuit, etc., which form the control core of the circuit. The motion module is responsible for the robot's movements. It contains MY36 GP-3626 DC brushless (MYDJ, Shenzhen, China) planetary gear motors to provide power, which can provide a maximum torque of 100 kg, and 42 HD1403 GT891 stepping motors to execute the variable diameter movements, which can provide a maximum thrust of 130 N and smooth and controllable movements. The detection module contains a methane detection sensor, a temperature and humidity sensor, and an optical encoder. The sensor detects the methane concentration, temperature, and humidity, and the optical encoder records the number of motor drive revolutions, deduces the robot displacement, and derives the depth of the mine hole. The image module consists of a camera and LED auxiliary light source, which takes pictures of the hole wall and passes the picture to the upper computer via the main control module, which analyzes the stratigraphic condition.  
To account for the phenomenon of the presence of gas and water inside coal mine boreholes, the circuitry of the mine borehole-detection small robot needs to be safely designed.  
In order to avoid an explosion, the robot's power must be strictly limited, and the total power should be limited to 12 W according to the requirements. The design uses  
Figure 10: Hardware circuit block diagram.  
Figure 9: Universal joint.  
a cable to power the robot, and the power consumption of the robot is mainly from the driver module, the STM32, and the light bulb. The maximum power of the selected driver module is 9.12 W, and the power of the lighting lamp is 0.5 W. The operating current of all peripherals is selected as 36 mA, so the maximum power of the STM32 is 0.12 W, and the total power of the robot is less than 9.74 W. Low power prevents explosions caused by sparks due to sudden changes in current, leading to glow discharges in the event of a circuit breakage fault. At the same time, the circuit is sealed and fixed to isolate the circuit from external gases, thus reducing the risk of explosion.  
In order to avoid short-circuiting the robot due to the accumulation of water, the robot needs to be designed to be waterproof. The electrical equipment of the mine hole-detection small robot is placed in a functional compartment for sealing and treated with sealant. The exposed equipment is waterproofed with IP68-rated products. The functional compartment inside the robot is fully sealed and treated with rubberized waterproof mats and sealant at the places where the wires pass through.