How to Select the Appropriate Gearbox ?

Gear Arrangement
Gear arrangement is an ingenious engineering design that offers various benefits over the traditional fixed axis gear system design. The unique combination of both power transmission efficiency and compact size allows for a lower loss in efficiency. The more efficient the gear arrangement, (i.e. spur, helical, planetary and worm) the more energy it will allow to be transmitted and converted into torque, rather than energy lost in heat.

Another application factor to be taken into account is load distribution. Since the load being transmitted is shared among multiple planets, the torque capacity is increased. The higher number of planets in a gear system will increase the load ability and enhance torque density. Gear arrangements improve stability and rotational stiffness because of a balanced system, but it is a complex and more costly design.

Fixed-Axis vs. Planetary Gear System

In the figure, the gear arrangement on the left is a traditional fixed axis gear system with a pinion driving a larger gear on an axis parallel to the shaft. On the right, is a planetary gear design system with a sun gear (pinion) surrounded by more than one gear (planet gears) and is encompassed in an outer ring gear. The two systems are similar in ratio and volume, but the planetary gear design has three times the higher torque density and three times the stiffness due to the increased number of gear contacts.

Fixed Axis Gear System:
Volume = 1, Torque = 1, Stiffness = 1

Planetary Gear System:
Volume =1, Torque = 3, Stiffness = 3

Other gear arrangements as mentioned in the Types of Gearboxes segment of this guide are bevel, helical, cycloid, spur and worm.

Backlash is the angle in which the output shaft of a gearbox can rotate without the input shaft moving, or the gap between the teeth of two adjacent gears. It is not necessary to consider backlash for applications which do not involve load reversals. However, in precision applications with load reversals like robotics, automation, CNC machines, etc., backlash is crucial for accuracy and positioning.