The advantages of pulley drive include: belt pulley transfer energy to ease load impact, pulley drive running smoothly, low noise, low vibration; belt pulley transmission is simple, easy to adjust; belt pulley transmission for pulley manufacturing and installation accuracy is not like meshing transmission strict; skin belt wheel drive with overload protection function; The two axle center distance of belt drive is larger. Belt drive has the disadvantages of: the belt pulley transmission has elastic sliding and skidding, the transmission efficiency is low and the accurate transmission ratio can not be maintained; when the belt pulley transmission passes the same large circumference force, the contour size and the pressure on the shaft are larger than the meshing transmission; the belt wheel transmission belt has a shorter life span. The diameter and size of pulley of all kinds of mechanical equipment are designed according to the speed reduction ratio, and according to the speed of the motor and the speed of the motor itself. Working speed / motor speed = drive wheel diameter / moving wheel diameter *0.98 (sliding coefficient), such as using steel as the material of the pulley, the required line speed is not higher than 40m/s, such as the use of cast iron material, the demand line speed is not higher than 35m/s, motor speed and pulley diameter conversion ratio, speed ratio = output speed: input speed = load pulley circle circle. Diameter: circular diameter of motor pulley. The diameter of the circle and the reference diameter are the same, the diameter -2h= nodal circle diameter, the H is the base line trough depth, the different types of V band h are different, Y Z A B C D E, the base line slot depth is h=1.6 22.75 3.5 4.8 8.1 9.6 respectively. The circle diameter of the belt pulley is the theoretical diameter of the belt pulley, which is a bit like the diameter of the dividing circle of the gear. Generally, it is expressed by PD. The outer circle is generally expressed by OD. The conversion formula of the different grooved nodal circle and the outer circle is different. Generally, we can easily measure the outer circle of the pulley, and calculate the nodal circle.SPZ:OD=PD+4; SPA:OD=PD+5. 5; SPB:OD=PD+7; SPC:OD=PD+9.6. The minimum outer diameter of A or SPA is 80mm. If it is less than this size, especially in high speed, the belt is prone to delamination and cracks at the bottom. SPZ belt, small wheel is not less than 63mm. At the same time, attention should be paid to the techniques and tension of the belt installation, too easy to skid, too big to damage the belt and bearings.