Perhaps the most obvious is to increase precision, which 
is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound is also suffering from gear and housing materials in addition to lubricants. In general, be prepared to spend more for quieter, smoother gears.
Don’t make the mistake of over-specifying the electric motor. Remember, the insight pinion on the planetary must be able manage the motor’s result torque. What’s more, if you’re using a multi-stage gearhead, the output stage should be strong enough to soak up 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 limits on gearbox size. With servomotors, output torque can be a linear function of current. Therefore besides protecting the gearbox, current limiting also shields the electric motor and drive by clipping peak torque, which may 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 you can’t really totally eliminate noise from such an assembly, there are many ways to reduce it.
As an ancillary benefit, the geometry of planetaries fits the form of electric motors. Therefore the gearhead can be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are generally more expensive than lighter duty types. However, for rapid acceleration and deceleration, a servo-grade gearhead could be the only sensible choice. In such applications, the gearhead may be seen as a mechanical springtime. The torsional deflection resulting from the spring action adds to backlash, compounding the effects of free shaft motion.
Servo-grade gearheads incorporate a number of construction features to minimize torsional stress and deflection. Among the more prevalent are large diameter result shafts and beefed up support for satellite-gear shafts. Stiff or “rigid” gearheads tend 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 element bearings. Small planetaries can often manage with low-price sleeve bearings or additional economical types with fairly low axial and radial load capacity. For larger and servo-grade gearheads, durable output shaft bearings are often required.
Like most gears, planetaries make noise. And the faster they run, the louder they get.
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