Among the reducer family, planetary reducers are widely used in servo, stepper, and DC drive systems due to their advantages such as small size, high transmission efficiency, wide reduction range, and high precision. Their function is to reduce speed, increase torque, and lower the load/motor moment of inertia ratio while ensuring precise transmission. In the planetary reducer industry, the German company NEUGART is undoubtedly the world's most famous manufacturer and the top seller in China. The company boasts world-class mechanical engineers and excellent equipment, and its products are sold in over 100 countries and regions worldwide. In recent years, some users have experienced reducer output shaft breakage due to improper installation and other human factors, resulting in unnecessary losses for their businesses. Therefore, to better assist users in utilizing planetary reducers effectively, this article analyzes the causes of reducer and drive motor shaft breakage and details how to correctly install planetary reducers. One issue is shaft breakage due to non-concentricity . Some users have experienced drive motor output shaft breakage after several months of equipment operation. Why did the reducer twist and break the drive motor's output shaft? Upon examining the cross-section of the drive motor's output shaft, we found it to be almost identical to the reducer's output shaft. The outer edge of the cross-section is brighter, while the color of the cross-section darkens towards the center, eventually ending at the break. Figure 2 shows a photograph of the cross-section. This clearly illustrates that the main reason for the breakage of the drive motor output shaft is misalignment during the assembly of the motor and the reducer! When the concentricity between the motor and the reducer is well ensured, the motor output bearing only experiences rotational force, resulting in smooth operation. However, when misaligned, the output shaft bears radial force from the input end of the reducer. This radial force, acting over a long period, will force the motor output shaft to bend, and the direction of bending will continuously change with the rotation of the output shaft. For every revolution of the output shaft, the direction of the lateral force changes 360 degrees. If the concentricity error is large, this radial force will cause the temperature of the motor output shaft to rise, continuously damaging its metal structure. Eventually, this radial force will exceed the radial force that the motor output shaft can withstand, leading to the breakage of the drive motor output shaft. The greater the concentricity error, the shorter the time it takes for the drive motor output shaft to break. When the output shaft of the drive motor breaks, the input end of the reducer will also bear radial force from the motor. If this radial force exceeds the maximum radial load that both can withstand, it will also cause deformation or even breakage of the reducer input end. Therefore, ensuring concentricity during assembly is crucial! Intuitively, if the motor shaft and the reducer input end are concentric, the fit between the motor and reducer will be very tight, with their contact surfaces tightly connected. If they are not concentric during assembly, there will be gaps between their contact surfaces. The left image in Figure 3 shows a good assembly between the motor and reducer, while the right image shows a poor assembly where the motor shaft and the reducer input end are not concentric. Similarly, the output shaft of the reducer can also break or bend, for the same reasons as the breakage of the drive motor shaft. However, the output force of the reducer is the product of the drive motor output force and the reduction ratio, which is greater than that of the motor, making the reducer output shaft more prone to breakage. Therefore, users should also pay close attention to ensuring the concentricity of the output end assembly when using the reducer! 2. Shaft Breakage Due to Insufficient Gearbox Output Besides shaft breakage caused by poor concentricity of the gearbox output assembly, the following are some other reasons why a gearbox output shaft might break: First, incorrect selection leading to insufficient gearbox output. Some users mistakenly believe that as long as the rated output torque of the selected gearbox meets the working requirements, it's sufficient. This is not the case. Firstly, the rated output torque of the motor multiplied by the reduction ratio should, in principle, be less than the rated output torque of a similar gearbox provided in the product catalog. Secondly, the overload capacity of the drive motor and the maximum working torque required in practice must also be considered. Theoretically, the maximum working torque required by the user must be less than twice the rated output torque of the gearbox. This principle must be strictly followed, especially in some applications. This is not only to protect the gears inside the gearbox but, more importantly, to prevent the output shaft from being twisted off. This is mainly because if the equipment is installed incorrectly, the output shaft of the reducer and its load may become stuck. In this case, the overload capacity of the drive motor will still cause it to continuously increase its output force, potentially causing the output bearing of the reducer to experience a force exceeding twice its rated output torque, thus breaking the output shaft. Secondly, during acceleration and deceleration, if the instantaneous torque experienced by the reducer's output shaft exceeds twice its rated output torque, and this acceleration and deceleration is too frequent, it will also eventually cause the reducer shaft to break. Considering that this situation is relatively rare, it will not be discussed further here. III. Correct Installation of the Reducer Correct installation, use, and maintenance of the reducer are crucial for ensuring the normal operation of mechanical equipment. Therefore, when installing a NEUGART planetary reducer, please strictly follow the following installation and usage guidelines, and carefully assemble and use it. The first step is to confirm that the motor and reducer are intact before installation, and to strictly check whether the dimensions of all parts connecting the motor and reducer match. This includes the dimensions and tolerances of the motor's positioning boss, the input shaft, and the reducer's groove. The second step is to unscrew the screws on the dustproof hole on the outside of the reducer flange, adjust the PCS system clamping ring so that its side hole aligns with the dustproof hole, and insert and tighten the Allen wrench. Then, remove the motor shaft key. The third step is to connect the motor and reducer naturally. During connection, it is essential to ensure that the reducer output shaft and the motor input shaft are concentric and that their outer flanges are parallel. Inconsistent concentricity can lead to motor shaft breakage or reducer gear wear. Furthermore, during installation, never use a hammer or similar object to strike the motor, as excessive axial or radial force can damage the bearings or gears. Always tighten the mounting bolts before tightening the clamping bolts. Before installation, wipe the rust-preventive oil off the motor input shaft, locating boss, and reducer connection parts with gasoline or zinc-sodium solution. This ensures a tight connection, smooth operation, and prevents unnecessary wear. Before connecting the motor and reducer, ensure the motor shaft keyway is perpendicular to the clamping bolts. To ensure even force distribution, first screw on the mounting bolts at any diagonal position, but do not tighten them completely. Then screw on the other two diagonal mounting bolts, and finally tighten all four mounting bolts one by one. Finally, tighten the load bolts. All load bolts must be tightened and checked using a torque wrench according to the specified fixed torque data. For specific torque upper limits, please visit www.awd.com.cn or consult Beijing Awd Company. The relevant data for right-angle reducers are not entirely the same as those for linear reducers of the same model; please pay attention. *The correct installation between the reducer and mechanical equipment is similar to the correct installation between the reducer and the drive motor. The key is to ensure that the output shaft of the reducer is concentric with the shaft of the driven part. IV. Conclusion With the continuous development of global industry, the role of planetary reducers in the transmission field is becoming increasingly prominent. We hope that planetary reducers will bring you more convenience and benefits in future use!