Types of Gearboxes

A Quick look at Gearboxes 

A Gearbox is a common mechanical component, found in just about any mechanical device that has spinning parts. Gearboxes are toothed, mechanical transmission elements used to transfer motion and increase output torque between machine components.

The Operating Principle of a Gearbox:   

A motor is designed to provide a certain torque and speed range.  Generally, motors work most efficiently (converting the most input power to output torque) at higher speeds (>1000 rpm).  Motors are also easier to control at higher speeds.  Designing and building a new motor for each application’s torque and speed requirement is cost prohibitive.  However, changing gearsets in a gearbox to achieve the desired torque and speed is quite simple. 

Typically, motor manufacturers will have a range of motors and a range of gearboxes, and the designer can mix and match as their application needs change.   

The shaft of the motor is connected to the first gear stage, which then transfers torque and speed through the internal configuration of gears.  The torque and speed provided by the output shaft will be determined by the gear ratio.  The gearbox essentially trades speed for torque.  Although the output speed is reduced (divided) by the gear ratio, the output torque is increased (multiplied) by the gear ratio.  The gearbox efficiency is then applied to calculate the output torque.

Types of Gearboxes: 

There are many different types of gearboxes, including: helical, coaxial helical inline, bevel helical, skew bevel helical, right-angle, spur, planetary and others.  Many trade-offs exist with different types, including mechanical size, reduction ratios, ability to back-drive (this can be desired or not), backlash (the amount of free play in the gearbox when reversing directions). 

This article focuses on spur gearboxes and planetary gearboxes.

Spur Gearboxes: 

The most common gears are spur gears, which are also called straight-cut gears.  They have straight teeth that are cut and inserted parallel to the gear’s shaft on a circular gear body.

Spur gears are used in mechanical applications to increase or decrease the speed of a device and to multiply torque, by transmitting power from one shaft to another through a series of mated gears. 

In mated pairs, spur gears are arranged in a parallel offset configuration to transfer mechanical power.  Simple in design, spur gearboxes are cost-effective, durable, reliable and provide a positive, constant speed drive to facilitate daily industrial operations.  Spur gearboxes, for a comparable reduction ratio, are shorter than their planetary counterparts.

Haydon Kerk Pittman offers a cost-effective series of spur gearboxes, featuring sintered steel gears to best complement our motors.  These gearboxes, when added to Haydon Kerk Pittman motors, offer greater flexibility to the designer for low duty applications.  Spur gearboxes provide an offset output shaft and are offered with sleeve or ball bearings.  Optional lubricants are available for extreme temperatures, and Delrin gears can be used to reduce noise.  Additionally, shortened housings are available for select ratios.   

The simplicity of the spur gear tooth design allows for both a high degree of precision and easier manufacturability. The main disadvantage of spur gears is that the power is transferred from one gear to another by a single tooth on the gear, producing more noise than if the power was transmitted across several gears.  Spur gears are typically used for lower speed applications, but they can be used for higher speeds if noise is not a critical factor.

Planetary Gearbox:

A Planetary Gearbox has a central Sun Gear and is surrounded by three or four Planet Gears. These are all held together through an outer ring gear with internal teeth. This design distributes the power equally from several teeth on the sun gear to several teeth on the planet gears.  A Planetary Gear System achieves a high torque in a small space, thus being a popular choice in cutting-edge technologies like robotics and 3D printing.

The planetary gearbox is designed for endurance, accuracy and precision.  This type of gearbox increases the lifespan of equipment and optimizes performance of the driving motor.  Planetary gearboxes come with a variety of mounting options, including a dedicated flange or a shaft collar.

A simple planetary gear set is made up of three main components:

1. The sun gear that sits in the center (central gear)
2. Multiple planet gears
3. The ring gear (outer gear).

The ring gear provides an even load distribution between the sides of the planet gears.  The carrier plate either contains another sun gear that drives the next stage of planet gears, or an output shaft. 

The central sun gear takes a high-speed, low-torque input and drives several rotating planet gears, which decreases the carrier speed, but increases the torque.  The simple design is a highly efficient and effective way of transferring power from a motor to an output. Single-stage gearboxes can deliver over 90% of the input power. 

Haydon Kerk Pittman offers a series of planetary gears with different ratios and stages.  The planetary series provides a centered output shaft for servo and continuous duty power transmission applications.  Planetary gearboxes are offered with plastic or metal gears and can be customized with sleeve or ball bearings on the input and output shafts.  Plastic gears in the first stage of multi-stage gearboxes can reduce audible noise at high running speeds.

Which Gearbox is Right for you?   

Selecting a Gearbox:

Like motors, gearbox selection requires careful consideration. With various gearbox choices, including spur, planetary and many others, designers should consider the following questions when selecting a gearbox:

Gearboxes are configured to be integrated directly with PITTMAN motors

For more on finding the right gearbox, click here: