Due to the use of internal meshing and several planetary wheel to share the transmission load, the planetary reducer has the advantages of compact structure, small volume, light weight, small backgap, high precision, large transmission ratio, long service life and so on, the rated output torque can be done very large. And the price is moderate. There are two kinds of straight teeth and oblique teeth.
The following is a bipolar transmission of the planetary gear box to illustrate the principle of the rotating input pinion to drive the meshing of the three planetary gear for revolution. And its revolution motion, through the planetary axis to the front bracket. At this point, the front bracket rotates in the same direction as the input rotation. The rear segment pinion connected with the front segment bracket becomes the input of the rear segment deceleration part, which is the same as the front segment deceleration part and drives the planetary gear of the rear segment to carry out revolution. And its revolution motion is transmitted to the back bracket supported by output bearing and then output. As you can see, the output axis is coaxial with the input axis and the steering is the same. Figure 2 B
Usually manufacturers will avoid the single-stage speed ratio is too large, the reason is that the output torque of the planetary reducer under the large speed ratio is significantly less than the smaller speed ratio of the same stage. This is caused by the structure of the reducer itself, as shown in Figure B-3. It can be clearly seen that when the reduction ratio is 10, the diameter of the central solar wheel is much smaller than that of other reduction ratios of the same stage, and of course the output torque is much smaller.

Fig.B-3

If you have to use a single stage with a high deceleration ratio in the deceleration ratio collocation, its output torque will become smaller. It can also be seen from Figure B-3 that if the 1/3 reduction ratio is placed at the first stage, the linear velocity is bound to be high and the vibration and noise will be relatively large due to the high motor speed and the large pitch radius of the central gear. There are a number of different ways to drive the internal structure of a planetary gearbox, but this is by far the most common one.

7.2：backlash

The accuracy of planetary reducers is often measured in a measure called a rotary backbacklash indicator, also known as a backlash or a rotary backlash. Each manufacturer production of reducer, its index is not completely the same, the test means is not completely consistent. The basic test method is: the input end is fixed, the output end is loaded in one direction with the rated load of 3%, and the rotation Angle of the output shaft is marked. Then the reverse direction is loaded with the same means, and the rotation Angle of the output shaft is marked. The difference between the two rotation angles is the back clearance of the reducer.