What Is a Planetary Gearbox And How Does It Work?
There are several reasons why you might be considering a planetary gearbox for your next automotive application. Aside from being ideal to connect to any type of motor, they’re considerably more effective in generating higher speeds, speed reduction, and ensuring higher output torque.
This makes these nifty little components a firm favourite in a huge variety of motion control projects. What is a planetary gearbox and how does it work? Keep reading as we answer a few of the more popular questions surrounding planetary gearboxes and their applications.
What Is a Planetary Gearbox?
A planetary gearbox also called an epicyclic gearbox, is a gear unit commonly used in drive technologies. As an integral part of automatic transmission applications, planetary components are remarkably versatile. Essentially, the output shaft and input shaft both share the same center of turning.
How Does a Planetary Gearbox Work?
All of Assun’s planetary gearboxes are meant for use in DC motors and servo motors. This is because their high-precision planetary gearboxes boast a few impressive advantages, some of which include system rigidity compactness, and superior torque. That said, let’s explore how an average planetary gearbox works.
The term “planetary gearbox” comes from the concept of planets revolving around the sun in the solar system. The gear system in this epicyclic system works similarly by having one central gear around which other gears rotate.
The central gear in the center of the planetary gearbox is known as the “sun gear”. In most cases, this is the input gear. The outside is made up of two or more outer gears, or “planet gears”.
A rotating ring gear surrounds the planet gears and holds the whole system together, connecting the planetary gear carrier. This planetary gearing system is connected to the output shaft. Planetary gears are proportional to the fixed ring gear which creates the rotation.
As the carrier keeps the outer gears in the basic form, the gaps are set. A basic planetary gear set or train is made up of three components: the sun gear, several planet gears, and the outer or ring gear.
We’ve included a short clip to more clearly explain how a planetary gearbox works below.
A Simple Planetary Gearbox’s Main Components
Essentially, a planetary gear train, also called an epicyclic gear train, works as a coaxial speed reducer or increaser consisting of two gears.
Average planetary gearboxes are made up of four basic components. A motor drives a central sun gear in the middle of the gearbox. The power generated is then transmitted to rotate around spur gear, also commonly referred to as planet gears.
These in turn are mounted on the planetary carrier which also creates the output shaft which also enables power transmission at the output. A toothed wheel with internal gear teeth creates a ring gear which limits the orbit of the planetary gears.
AssunMotor’s Planetary Gearbox (Exploded View)
What Is The Main Purpose of Planetary Gears?
For the most part, epicyclic gears, are used as speed reducers. This means they increase torque by slowing down the motors (brushed, brushless or servo motor).
In terms of torque and speed, planetary gear motors are more effective in producing higher speed and torque. This is largely attributed to the multiple contact points situated between the gears. In fact, the planetary gear system is able to accept higher input speeds and also reduce speeds of up to 10:1 for most standard designs.
How Efficiency Are Planetary Gearboxes?
Generally, you can expect an efficiency of 97% of energy input from your planetary gearbox. That equates to an efficiency loss of only 3% per stage. Energy is therefore transmitted through the gearbox rather than being lost on other mechanical losses within the actual gearbox.
Where Are Planetary Gearboxes Used?
Planetary gear systems are used for a variety of purposes. For the most part, these planetary gear trains are used in projects where space is limited. This is because they’re typically smaller than many other types of gearboxes.
Planetary gears can be used in a host of different modern automatic transmission applications. Additionally, they’re a common addition to equipment and most industrial machines.
The most significant examples are listed below.
- Wheel-drives
- Inside packaging machine for reproducible products
- Auger & drilling drives
- Conveyors
- Winch drives
- In printing presses to decrease the speed of the printer rollers
- Coil tubing injectors
- Bicycles acceleration hub
- They form part of robot components to increase the torque
- Cutter head drives
- Medical scanners
- Slew drives
- Pumps
- Hoist drives
- Renewable energy products
Tips For Choosing a Planetary Gearbox
Since not all gearboxes are the same, you’ll need to ensure that you’re choosing the perfect one for the project on hand. When you’re considering a planetary gearbox for your application, it’s important to keep the pointers listed below in mind.
- Features to look for: Backlash, torque density and ratio required will depend on the type of application you’re creating.
- Environment: Choose a planetary gearbox with the right type of housing to avoid dirt, dust and moisture from entering the gearbox and damaging the inner components.
- Space: Always check the space available in your application—the good news is that you can always opt for a smaller planetary gearbox to suit your application. Speak to a specialist to get the right-sized planetary gearbox to ensure that your application works as required.
Advantages & Disadvantages of Planetary Gearbox
As with all other types of gearboxes, compound planetary gears have their own set of pros and cons to consider. Consider the advantages and disadvantages of epicyclic gearing as you shortlist your options.
Advantages
- No backlash: Gearing is very accurate with almost no backlash.
- Modular: Since it’s modular, most planetary stages can be stacked.
- Output shaft: Coaxial arrangement means no offset output shaft.
- Gear life: Increased gear life at similar loads.
- High power density: Several planets share the load.
- Size: Planetary gears are compact and boast low weight, making them easy to use in many different applications.
- Torque: High torque transmission possible.
- High efficiency: Planetary gear systems have about 95% higher efficiency due to low rolling power.
- Versatile: Can be used in hydraulic motors and electric motors and can be used in everything from printers to medical equipment.
Disadvantages
- Noisy operation: Planetary gearheads often have higher noise levels. Some types, however, such as the ones in the Assun product range guarantee to be quieter.
- Load sharing: If the gearing isn’t accurate, load sharing won’t be effective as the gears must always be bevelled with helical teeth.
- Lubrication: A planetary gear must generally be grease lubricated to prevent wear. Many users might prefer an oil bath option.
- Cost: To ensure low backlash and longevity, the cost can be higher. This is usually because they are composed of more components than other types of gearboxes.
- Loads: High bearing load often leads to early wear in the dead stud.
What Are The Different Types of Gearboxes?
Planetary gear sets are categorized into three different gear types. The options you can choose from are listed below:
1) Wheel-Drive
Essentially, the sun gear moves the surrounding planetary components attached to the planet carrier in wheel-drive. As this happens, the planet gearset circulates around the outer ring gear.
Connecting the wheel directly to the gearbox easily optimizes the size of the system. Generally, a wheel-drive planetary gearbox can be utilized in instances requiring 332,000 N.m torque.
2) Shaft Output
Housed in a tuning carrier inside a shaft drive gearbox means the sun gear runs the surrounding planetary components. Since the ring part remains fixed with the turning carrier drive, the housing part of the system is secured directly to the machine.
This makes the output a turning shaft. That said, the range of an output shaft gearbox can easily deliver an output of 113,000 N.m torque.
3) Spindle Output
Essentially, spindle output planetary gearboxes work the same way as shaft outputs. The difference is that the output is delivered as a flange. As with the shaft output, spindle drive planetary types are used in applications with a torque of 113,000 N.m.
Conclusion
With our informative article, it should now be much easier to understand how planetary gearboxes work. More good news is that Assun’s small planetary gearboxes are not only compact but precise as well. You can expect smooth operation, reduced noise and optimum transmission efficiency.
Furthermore, our blog’s main purpose is to educate users to best use incremental encoders for their different projects. Assun Motor will also assist customers with the right products and components to fit and improve your current project!
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