Gear reducers – more commonly known as gearboxes – are among the most commonplace and critical components of any complex motor.  The gear reducer controls the output from a motor, adjusting the speed and torque of the power by sending it through a series of gears. The more gears and the more complex the system, the less overall power sent to the final application.

Gearbox Housing

Broadly speaking, the number of teeth on the gears involved in the process determines complexity.  The overall ratio of the number of teeth on the input shaft to the output shaft is the transmission ratio.

Unsurprisingly, there are many different types of gearboxes, depending on an application’s needs.  Some are better at allowing large amounts of power transmission, and others are tuned to reduce the power output without damaging either the engine or the final output system.

Types of Gear Reducers

This article will discuss your selection criteria when choosing a gear reducer and the different types of gearboxes and their applications.

I.  Criteria When Selecting a Gearbox

Three main criteria are most important when making a selection:

1 – Torque

The main purpose of a gearbox is to reduce both the overall torque transmitted through the system and overall power transmission.  So, you need to know the overall torque required by your end application—most gear reducers rate according to the minimum and maximum torque they can handle.  In addition, different types of reducers are more effective at high or low torque scenarios.

2 – Reduction Ratio

In short, the inputs vs the outputs.  Applying the reduction ratio of a particular gearbox to the RPM of the engine tells you the RPM of the output.  The output RPM is also specified in the packaging and documentation for any gearbox, allowing you to match it to your usage case easily.

3 – Type of Assembly

There are three different basic types of gearbox assemblies:

• Coaxial:  Also called “inline” gear reducers, these have the inputs and outputs on the same shaft, creating an extremely compact package that is good for space-conscious designs. However, they are often limited in what reduction ratio they can achieve.
• Parallel-Shaft: As the name suggests, the input and the output are on separate parallel shafts.  These tend to be good all-purpose gearboxes when you still need everything to stay on the same plane.
• Orthogonal:  Orthogonal gearboxes are distinguished by having perpendicular input and output shafts, transitioning the power transmission by 90 degrees.  These can take up extra space but allow plenty of flexibility in overall mechanical design.

II. Types of Gear Reducers

While there is almost no limit to the types of gearboxes out there, these four designs are the most common.  One of these will almost certainly suit your intended application.

1 – Planetary Gearboxes

Planetary gearboxes are one of the most common types of coaxial assemblies.  While the casing typically obscures their insides, they’re referred to as “planetary” because the gear system involves a series of large hoops which rotate within each other, similar to the motion of the planets within a solar system.

Planetary gearboxes have a lot of advantages.  They have an excellent torque to weight ratio and are particularly well-suited for applications calling for low RPMs with high torque. They’re also excellent at dealing with fast acceleration and ramp-up. In addition, they are quite small relative to their power output and are quite energy-efficient.

The downside is that due to the complicated machinery within, they are expensive to buy and difficult to service.

2 – Worm Gear Reducers

Worm gear reducers utilize a single large threaded shaft which takes the input power and transfers it to gear works connected to the shaft. These are typically orthogonal assemblies, with the output rotated 90 degrees from the input.  They are particularly well-suited for applications where a high transmission ratio is called for and often found on machinery such as conveyor belts and winches.

One distinguishing characteristic is that the worm gear (shaft) can only spin in one direction. For one-way-only applications, this adds security and ensures the machine can never run backwards. However, it does somewhat limit their usage.

Worm reducers are also relatively inexpensive compared to planetary assemblies.  They don’t vibrate, and they are among the quietest gearbox designs. However, they tend to heat up quickly, so heat management is critical.

3 – Gear Trains

Gear trains are among the most mechanically simple gearboxes – two parallel shafts with some gears in between.  Use gear trains in situations where a single application needs a lot of power, running at a constant speed – such as assembly lines and conveyor belts.  They offer extremely efficient power transmission, with a ratio close to one.

In addition, they are inexpensive and – being mechanically simple – easy to service.  However, the gear train’s design simplicity also limits how many applications use them.  Also, they can tend to be larger than other types of gearboxes, making them better for industrial applications with plenty of free space.

4 – Bevel Gear Reducers

The distinguishing characteristic of bevel gearboxes is their angular bell crank, which allows you to switch the rotation back and forth.  This rotation ability gives them a lot of added flexibility, although applications where reversing the spin would be catastrophic should not use them.  They allow for extremely high torque and can also handle a lot of power.  They can also work well with three-phase electrical systems.

In addition, they are compact and extremely quiet.

On the other hand, they do not offer performance as efficient as planetary assemblies. Also – like planetary assemblies – they are expensive and difficult to maintain. Due to their small size and high-power output, mobile machinery such as agricultural vehicles use them.

5 – In The Future…

State of the art in gearboxes is always moving forward, and there’s an exciting new technology on the horizon: magnetic gear reducers.  Rather than using physical gears, these will use alternating magnets to control the power transmission.  Once perfected, they will have the advantage of being nearly maintenance-free.  No physical contact between the components eliminates wear and tear and eliminates the need for lubrication.  Plus, they will be able to operate in a wide range of temperatures that inhibit mechanical gearboxes.

A few magnetic gearboxes are already on the market, but they still have significant issues.  Notably, they tend to be extremely heavy and have problems generating high amounts of torque.  At present, this significantly reduces their usefulness.

However, once the technology perfects, these are likely to make inroads quickly due to the extremely long lifespan they would offer.  They would also find use in extreme environments, such as outer space or deep underwater.