low backlash gearbox

Perhaps the most obvious is to improve precision, which really is a function of manufacturing and assembly tolerances, gear tooth surface finish, and the center distance of the tooth mesh. Sound is also affected by gear and housing materials along with lubricants. In general, be prepared to pay more for quieter, smoother gears.
Don’t make the mistake of over-specifying the engine. Remember, the input pinion on the planetary should be able handle the motor’s result torque. Also, if you’re using a multi-stage gearhead, the output stage should be strong enough to soak up the developed torque. Certainly, using a better motor than required will require a bigger and more expensive gearhead.
Consider current limiting to safely impose limits on gearbox size. With servomotors, result torque is a linear function of current. So besides protecting the gearbox, current limiting also defends the electric motor 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 simultaneously in mesh. Although you can’t really totally eliminate noise from this 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 could be close in diameter to the servomotor, with the output shaft in-line.
Highly rigid (servo grade) gearheads are usually more expensive than lighter duty types. However, for quick acceleration and deceleration, a servo-grade gearhead may be the only sensible choice. In such applications, the gearhead may be viewed as a mechanical springtime. The torsional deflection resulting from 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 common are large diameter result shafts and beefed up support for satellite-equipment shafts. Stiff or “rigid” gearheads have a tendency to be the most costly of planetaries.
The kind of bearings supporting the output shaft depends upon the strain. High radial or axial loads usually necessitate rolling component bearings. Small planetaries could get by with low-price sleeve bearings or additional economical types with relatively low axial and radial load ability. For larger and servo-grade gearheads, durable output shaft bearings are usually required.
Like most gears, planetaries make sound. And the faster they run, the louder they get.

You’ve certainly resorted to the net to find out even more regarding low backlash gearbox because public libraries do not bring as much information about this subject as they utilised to.