Perhaps the most apparent is to improve precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the guts distance of the tooth mesh. Sound is also suffering from gear and housing materials in addition to lubricants. In general, expect to pay more for quieter, smoother gears.
Don’t make the error of over-specifying the motor. Remember, the insight pinion on the planetary must be able handle the motor’s result torque. Also, if you’re using a multi-stage gearhead, the result stage must be strong enough to absorb the developed torque. Certainly, using a better motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque can be a linear function of current. Therefore besides protecting the gearbox, current limiting also protects the motor and drive by clipping peak torque, which can be anywhere from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are at the same time in mesh. Although it’s impossible to totally remove noise from this assembly, there are several ways to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Therefore the gearhead could be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for quick acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead may be seen as a mechanical spring. The torsional deflection caused by the spring action adds to backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate many construction features to reduce torsional stress and deflection. Among the more prevalent are large diameter result shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads tend to be the costliest of planetaries.
The type of bearings supporting the output shaft depends on the load. High radial or axial loads usually necessitate rolling 
component bearings. Small planetaries could get by with low-cost sleeve bearings or additional economical types with fairly low axial and radial load ability. For larger and servo-grade gearheads, heavy duty result shaft bearings are usually required.
Like the majority of gears, planetaries make noise. And the faster they operate, the louder they obtain.
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