DC Servo Motor: Spur Gearbox VS Planetary Gearbox

A DC servo motor with a built-in gearbox can provide a better cost-effective solution compared to similar products composed of various parts. However, deciding which type of gearbox is suitable for the application scenario is determined by many factors, such as: backlash, efficiency, maximum torque, speed, reduction ratio and price.

Generally, the two commonly used reducers or reducers are spur gears and planetary gears. Generally, compared to the planetary unit, the spur gear reducer is simpler and cheaper, and is suitable for low torque application scenarios. The maximum torque of a spur gear is limited because each gear in each stage bears the entire torsional load. Planetary gearboxes, on the contrary, in planetary gearboxes, multiple planetary gears share the load. Here, the input shaft drives a central sun gear, which drives the planetary gears. Each planetary gear simultaneously transmits torque to a rotating support plate linked to the gear output shaft.
At the same time, a factor that determines the load bearing capacity is the material used in the gear. Usually, sintered nickel steel is used. Because the sintering process can economically produce net shape gears that are closer to tolerances. In addition, because the material is porous, it can withstand lubrication better than rigid gears. However, cut gears tend to be more durable. And for application scenarios that require higher torque, this is a better choice. However, whether it is the gear material, especially in the case of high speed and high load, adequate lubrication is very important. Here, the planetary gearbox has a better advantage. Because the oil flying out from the sun gear is sucked and captured by the planet gears and the carrier plate. The spur gear type, on the other hand, shakes the lubricating oil from the gear. This is why the planetary gearbox has a higher speed rating.
　　 Another one, consider backlash and reduction ratio. Backlash is a way of measuring position accuracy, usually expressed in arc minutes. For example, a typical spur gearbox has a backlash of approximately 10 arc minutes. The planetary gear is only about half. The reduction ratio of planetary gearboxes or spur gearboxes is usually several hundred to one. Spur gearbox, if one gear input shaft is coupled with another gear input shaft, it provides approximately 6:1 reduction. In comparison, the planetary unit can reach a reduction ratio of 10:1 at each stage. For a better reduction ratio and proportional output torque, multi-stage gears and gear sets need to be increased. The increased number of stages will increase the reduction ratio and output torque but this will increase the overall length and reduce the efficiency of the machine. The output torque is expressed as:
　　Out = N motor
　　Motor is the torque of the motor, and N is the reduction ratio and efficiency. A typical single-stage spur gearbox, for example, has an efficiency of about 90%. The second-level model has an efficiency of about 85%. Most planetary gearboxes have a single-stage efficiency of 97%, while the two-stage efficiency is 94%.

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