# Selection Calculations for DC Gear Motor

2020-06-01

DC gear motor, also known as gear motor, is the one that adds a complete set of gearbox based on the common DC motor. The role of the gearbox is to provide a lower speed and higher torque. That’s also the reason why it is called high torque low rpm DC gear motor. At the same time, the different reduction ratios of the gearbox can provide different speed and torque. This greatly improved the use of the DC motor in the automation industry. However, when selecting the type of DC gear motor, the following parameters (transmission ratio and power) should be calculated and the key points of selection should be paid attention to.

#### Calculation of DC Gear Motor Parameters:

Transmission ratio calculation:

The theoretical range of first-stage transmission ratio is “n motor = (6-20) *n output = (6-20) *360r/min”. The theoretical range of first-stage transmission ratio is “n motor = (8-40) *n output = (8-40) *360r/min”. Then, the motor power and speed have been calculated. If you need to pay attention to the torque, it can also be calculated to be T=9550P/n or T=973P/n, so that you can select the motor model.

Power calculation:

Static power calculation:

Linear motion: P = V/F * 1000η(P-w: static power, F-N: running resistance, V-m/s: running speed)

Rotational motion: P=M*N/9550η (P-w: static power, M-N.m: torque, n-rpm: rotational speed）

Dynamic power calculation:

Rotational motion: P=Jt*Nt/91200*tA*η (P-w: dynamic power, Jt-Kg.m: rotational inertia, n-rpm: rotational speed, tA-S: starting time)

Linear motion: inertial force F=ma; (m-kg, a-m/s: starting acceleration)

#### Elements of Gear Motor Selection Calculation:

1. Confirm the way to use DC gear motor as well as the application scenarios, and list the factors like environmental requirements before the purchase;
2. Determine what type of DC gear motor is needed and what power and performance requirements are needed including low power, high torque, low speed, noise, energy consumption and parameters;
3. Determine the output shaft torque and the method of installation and maintenance of DC gear motor (even it is a small DC gear motor);
4. Determine the input shaft speed and reduction ratio;
5. Select DC gear motor according to the size of the flange. If the output shaft torque is not enough, return to step 2 and conduct the process again;
6. Make sure whether the working temperature and backlash can meet the needs (also can be the first step);
7. Conduct the load motor torque calculation; It plays an important role in motor service life and it is also noteworthy that whether the maximum torque value(TP) of acceleration exceeds the maximum load torque of the motor.