# The selection method of motor is introduced

To select a motor, you must first acknowledge the torque of the motor operating point and the required motor speed (i.e. the rated speed) under this torque. Based on this can be recognized requirements of how much standard motor can meet this requirement.

The rated speed and torque of the motor determine the output power of the motor. In terms of two motors with exactly the same standard, the output power is different due to the different speed and torque. Large torque, high speed motor, its output power is large, of course, the current should be increased.

The calculation method of output power is as follows:

P2=1.028×10 ×T×N unit: watt (W)

Where: T-- load torque unit: g/cm (g.3m) N-- load speed unit: RPM

For the same motor, when the torque is constant, the motor speed is proportional to the voltage. That is: the higher the voltage, the higher the speed. For example, a 12V motor has a load speed of 5000rpm under the rated torque, and when the voltage is increased to 24V, the load speed is about 10000rpm.

For the same motor, the load speed is inversely proportional to the load torque. That is: with the increase of load torque, motor speed will decline. For example, if the speed of a motor is 5000rpm at 200g. Cm, when the load torque is greater than 200g. Cm, the speed of the motor will be lower than 5000rpm. When the load torque is less than 200g. Cm, the motor speed will be higher than 5000rpm.

Generally speaking, the load torque of the motor should be the same as the rated torque of the motor. Because, when operating under rated torque, the motor is near the highest power point. When the load torque is greater than the rated torque, the motor is in overload operation, which will affect the heating and service life of the motor.

The torque of the motor is usually expressed by g.3m (g/cm). The conversion relation with other torque units is:

G. 1 cm = 0.098 mNm = 0.014 oz - in

1 MNM = 10.2 right to m = 0.142 oz - in

1 oz = 7.056 in mNm right = 72.0 m

The conversion link of length unit is: 1mm=0.039in Lin =25.4mm

1g=0.035oz loz=28.35g