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DC Gear Motor vs Planetary Gear Motor (SG-555 vs PG-36)

Jiaming CaiAugust 23, 2023

In this article, DONCEN MOTOR will share the structure comparison and efficiency difference of two different geared motors ( Planetary geared motor and DC geared motor) We will use the most popular SG-555 series and PG-36 series as the objects of this test. In order to ensure the consistency of the comparison. For the SG-555 series, we choose a spur gear gearbox (tower gearbox) with a reduction ratio of 1:100K. For the PG-36 series, we choose a planetary gearbox with a reduction ratio of 1:99.5K. Let’s do it.

What is a Gear Motor?

Geared motor is mainly composed of a gear structure and a motor. The speed of the output end of the motor is reduced through the gear structure, and the torque is increased. Geared motors are widely used in low-speed, high-torque fields such as robots, automation, smart home and etc.

gear motor explosion diagram
Gear Motor Diagram

DC Gear Motor: structure and working principle

The spur gear motor adopts the traditional tower gear structure, and its internal gear is divided into double tooth structure. The input end of the motor is meshed with the first-stage gear through the head wheel to achieve step-by-step deceleration, and finally the power is output to the output shaft of the gearbox. This is a simple and proven design available in a wide range of sizes at affordable prices and is often used in applications requiring higher torque but lower speed.

However, there is an efficiency problem with the spur gear reduction motor, which is mainly attributed to the inefficient use of space for the spur gear reduction structure. The deceleration structure is simple and the utilization rate is low.

Planetary Geared Motor: structure and working principle

The planetary gear motor adopts a planetary gear structure, which mainly includes a sun gear, a planet gear, a planet carrier and an internal ring gear. The sun gear is driven by the input shaft of the motor, while the planet gear rotates around the sun gear and meshes with the internal ring gear to achieve step-by-step deceleration. This structure is extremely efficient and precise and is suitable for applications where space is limited.

For engineers, planetary gearmotors are attractive due to their compact design and high efficiency. The ball bearings used reduce friction and improve overall efficiency. Planetary geared motors are often used in applications requiring high precision and efficiency.

Gearbox Efficiency Comparison (Geared Motor vs Planetary Gear Motor)

Real knowledge comes from practice. In order to more accurately understand the efficiency difference between the tower gear structure and the planetary gear structure. DONCEN Motor will use the same motor with different types of reduction gearboxes to conduct an efficiency test.

Gearbox :In order to ensure the accuracy of the test results, we use the SG series of spur gearboxes with a diameter of 37mm and the PG-36 series planetary gearboxes with a diameter of 36mm. The gear ratio of SG series is 1:100K. The gear ratio of the PG-36 gearbox is 1:99.5

Motor :As for the motor, we chose the same 12V 6000rpm DC555 brushed DC motor. This is also the most commonly used brushed DC motor on the market.

SG-555 Test report

SG555126000-100K Test report
SG555126000-100K Test report

PG-36555 Test report

PG36555126000-99.5K Test report
PG36555126000-99.5K Test report

Gearbox Effiency Compare (DC Gear Motor vs Planetary Gear Motor)

The dynamometer records the current, speed and output power of the motor under different torques at the output shaft end of the motor under the condition of a fixed voltage. Here we mainly compare two key POINTs. One is the maximum output power point of the motor, and the other is the maximum efficiency point of the motor.

Max Output Power Point Compare

UAP 1 WN.mrpmP2 WEFF

We can see that at the maximum output power point. The PG-36555 series with planetary gear reduction structure is larger in torque and power than the SG-555 series with the same reduction ratio. The difference is probably in the range of 20%.

Max EFF Point Compare

UAP 1 WN.mrpmP2 WEFF

at the point of maximum efficiency. The output power of the planetary gear motor is 11.5W, while the output power of the gear reduction motor is only 8.9W. At the same time, at the same speed, the PG-36555 can output a torque of 2.05N.m, but the SG-555 motor can only output a torque of 1.6N.m.


It can be seen from our test report. In the case of the same gear ratio, the efficiency of the planetary gear structure will be greater than that of the spur gear structure. If you need a cost-effective geared motor, consider using a spur geared motor in your application. If your project is applied in high-precision and high-efficiency fields, you can consider using a planetary gear structure.

If you have any questions about which gear motor to choose for your application, please contact DONCEN MOTOR. We have a professional team of electrical engineers to add value for your solution.

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