Perhaps the most apparent is to increase low backlash planetary gearbox precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound can be affected by gear and housing materials as well as lubricants. In general, expect to spend more for quieter, smoother gears.
Don’t make the error of over-specifying the motor. Remember, the insight pinion on the planetary should be able deal with the motor’s output torque. What’s more, if you’re using a multi-stage gearhead, the result stage should be strong enough to soak up the developed torque. Obviously, using a more powerful motor than required will require a bigger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is certainly a linear function of current. Therefore besides protecting the gearbox, current limiting also shields the engine and drive by clipping peak torque, which may be from 2.5 to 3.5 times continuous torque.
In each planetary stage, five gears are concurrently in mesh. Although it’s impossible to totally remove noise from this assembly, there are many methods to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Thus the gearhead could be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more expensive than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In such applications, the gearhead could be viewed 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 output shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads have a tendency to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads generally necessitate rolling element bearings. Small planetaries could manage with low-price sleeve bearings or other 
economical types with relatively 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 run, the louder they obtain.
Low-backlash planetary gears are also available in lower ratios. Although some types of gears are usually limited by about 50:1 and up, planetary gearheads extend from 3:1 (solitary stage) to 175:1 or even more, depending on the amount of stages.