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 suffering from 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 engine. Remember, the insight pinion on the planetary should be able handle the motor’s result torque. What’s more, if you’re utilizing a low backlash planetary gearbox multi-stage gearhead, the output stage should be strong enough to absorb the developed torque. Obviously, using a more powerful motor than required will require a larger and more costly gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is usually a linear function of current. So besides protecting the gearbox, current limiting also defends the electric 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 simultaneously in mesh. Although it’s impossible to totally get rid of noise from such an assembly, there are several ways to reduce it.
As an ancillary benefit, the geometry of planetaries matches the shape of electric motors. Hence the gearhead can be close in diameter to the servomotor, with the result shaft in-line.
Highly rigid (servo grade) gearheads are usually more costly than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In such applications, the gearhead could be seen as a mechanical spring. The torsional deflection resulting from the spring action increases backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate several construction features to reduce torsional stress and deflection. Among the more common 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 type of bearings supporting the output shaft depends on the load. High radial or axial loads generally necessitate rolling component bearings. Small planetaries could manage with low-cost sleeve bearings or additional economical types with fairly low axial and radial load capacity. For larger and servo-grade gearheads, durable result shaft bearings are often required.
Like the majority of gears, planetaries make sound. And the quicker they run, the louder they obtain.
Low-backlash planetary gears are also available in lower ratios. Although some types of 
gears are usually limited to about 50:1 or more, planetary gearheads extend from 3:1 (one stage) to 175:1 or more, depending on the amount of stages.