Perhaps the most apparent is to improve precision, which 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 components as well as lubricants. In general, be prepared to pay out more for quieter, smoother gears.
Don’t make the mistake of over-specifying the electric motor. Remember, the input pinion on the planetary must be able manage the motor’s output torque. Also, if you’re using a multi-stage gearhead, the output stage should be strong enough to absorb the developed torque. Certainly, using a more powerful motor than necessary will require a larger and more costly gearhead.
Consider current limiting to safely impose limitations on low backlash gearbox gearbox size. With servomotors, output torque is certainly a linear function of current. Therefore besides safeguarding the gearbox, current limiting also 
protects 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 get rid of noise from such an assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Therefore the gearhead can 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 fast acceleration and deceleration, a servo-grade gearhead could be the only sensible choice. In such applications, the gearhead could be seen as a mechanical springtime. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft movement.
Servo-grade gearheads incorporate many construction features to minimize 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 kind of bearings supporting the output shaft depends upon the load. High radial or axial loads usually necessitate rolling element bearings. Small planetaries could get by with low-cost sleeve bearings or other economical types with relatively low axial and radial load capacity. For bigger and servo-grade gearheads, heavy duty output shaft bearings are usually required.
Like the majority of gears, planetaries make sound. And the faster they run, the louder they obtain.
Low-backlash planetary gears are also obtainable in lower ratios. Although some types of gears are generally limited to about 50:1 or more, planetary gearheads prolong from 3:1 (one stage) to 175:1 or more, depending on the number of stages.
