Perhaps the most apparent is to increase 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 components as well as 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 manage the motor’s result torque. Also, if you’re utilizing a multi-stage gearhead, the output stage must be strong enough to soak up the developed torque. Certainly, using a better motor than necessary will require a larger and more expensive gearhead.
Consider current limiting to safely impose limitations on gearbox size. With servomotors, output torque is definitely a linear function of current. Therefore besides protecting the gearbox, current limiting also defends the engine 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 you can’t really totally eliminate noise from this assembly, there are several 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 generally more expensive than lighter duty types. However, for speedy acceleration and deceleration, a servo-grade gearhead may be the only wise choice. In this kind of applications, the gearhead may be viewed as a mechanical spring. The torsional deflection caused by the spring action increases backlash, compounding the consequences of free shaft motion.
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 most costly of planetaries.
The kind of bearings supporting the output shaft depends on the strain. High radial or axial loads usually necessitate rolling element bearings. Small planetaries can often manage with low-cost sleeve bearings or additional economical types with low backlash gearbox relatively low axial and radial load ability. For bigger and servo-grade gearheads, durable output shaft bearings are usually required.
Like most gears, planetaries make noise. And the quicker they operate, the louder they get.
Low-backlash planetary gears are also obtainable in lower ratios. While some types of gears are usually limited to about 50:1 and up, planetary gearheads lengthen from 3:1 (single stage) to 175:1 or more, depending on the number of stages.