Gearbox

What is a Gearbox?

A gearbox is a mechanical device utilized to increase the output torque or change the speed (RPM) of a motor. The motor's shaft is attached to one end of the gearbox and through the internal configuration of gears of a gearbox, provides a given output torque and speed determined by the gear ratio.

Physical Properties

The physical components of gearboxes vary from one gearbox type to another, as well as differences between manufacturers. Most gearboxes are constructed from steel materials such as iron, aluminum and brass. Unlike other gearbox types, spur gearboxes can also be made with plastics such as polycarbonate or nylon. Other than the raw materials used, the orientation of the gear teeth play a major role in the overall efficiency, torque and speed of the system. Straight gear teeth gearboxes are typically used in low-speed applications. These gearboxes can be noisy, and may have lower overall efficiency. Helical gearboxes are typically used in high-speed applications. These gearboxes are quieter in operation than straight gear teeth gearboxes, which may improve their overall efficiency.

Types of Gearboxes

There are many types of gearboxes manufactured throughout the world. One of the main differences between individual gearboxes is their performance characteristics. Choosing from the various gearbox types is application dependent. Gearboxes are available in many sizes, ratios, efficiencies and backlash characteristics. All of these design factors will affect the performance and cost of the gearbox. There are several types of gearboxes which are listed below:

Bevel Gearbox

Bevel Gears

There are two types of bevel gearboxes which include either straight or spiral teeth gears. Straight bevel gears have straight and tapered teeth and are used in applications requiring slow speeds. Spiral bevel gears have curved and oblique teeth and are used in applications requiring high-performance, high speed applications.

Straight Bevel Gearbox

Spiral Bevel Gearbox

Figure 1: Straight Bevel Gearbox Figure 2: Spiral Bevel Gearbox

Physical Properties

Bevel gears are typically constructed from cast iron, aluminum alloy or other steel materials but vary between manufacturers.

Note: Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Bevel Gears

Bevel gearboxes use bevel gears and are mainly used in right angle applications with the shafts in a perpendicular arrangement.

• Print Press

• Power Plants

• Automobiles

• Steel Plants

• Hand Drills

• Differential Drives

Advantages of Bevel Gears

• Right angle configuration

• Durable

Disadvantages of Bevel Gears

• Axes must be able to support forces

• Poorly cut teeth may result in excessive vibration and noise during operation

Helical Gearbox

Helical Gears

Helical gears are cut at angles which allow for gradual contact between each of the helical gear teeth. This type of innovation provides for a smooth and quiet operation. Gearboxes using helical gears are applicable in high horsepower and efficient applications.

Helical Gearbox

Figure 3: Helical Gearbox

Physical Properties

Helical gears are typically constructed from cast iron, aluminum allow or iron material but may vary depending on the manufacturer.

Note: Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Helical Gears

Helical gears are widely used in applications which require efficiency and high horsepower.

• Oil Industry

• Blowers

• Food and Labeling

• Cutters

• Elevators

Advantages of Helical Gears

• Can be meshed in parallel or cross orientation

• Smooth and quiet operation

• Efficient

• High horsepower

Disadvantages of Helical Gears

• Resultant thrust along axis of gear

• Additives to lubrication

Spur Gearbox

Spur Gears

Spur gears are made with straight teeth mounted on a parallel shaft. The noise level of spur gears is relatively high due to colliding teeth of the gears which make spur gear teeth prone to wear. Spur gears come in a range of sizes and gear ratios to meet applications requiring a certain speed or torque output.

Spur Gearbox

Figure 4: Spur Gearbox

Physical Properties

Spur gears are typically constructed from metals such as steel or brass, and plastics such as nylon or polycarbonate. The material used to construct spur gears may vary depending on the manufacturer.

Note: Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Spur Gears

Spurs gears are used in applications requiring a decrease in speed with high output torque.

• Cut-to-Length

• Packaging

• Speed Control

• Construction

• Power Plants

Advantages of Spur Gears

• Cost-effective

• High gear ratios

• Compact

• High torque output

Disadvantages of Spur Gears

• Noisy

• Prone to wear

Worm Gearbox

Worm Gears

Worm gears are able to withstand high shock loads, low in noise level and maintenance-free but are less efficient than other gear types. Worm gears can be used in right angle configuration. The worm gearbox configuration allows the worm to turn the gear with ease; however, the gear cannot turn the worm. The prevention of the gear to move the worm can be used as a braking system. When the worm gearbox is not active, it is held in a locked position.

Worm Gearbox

Figure 5: Worm Gearbox

Physical Properties

Worm gears are typically constructed of aluminum, stainless steel and cast iron. The material used varies depending on the manufacturer.

Applications of Worm Gears

Worm gears are used in applications requiring high speeds and loads and can be configured for right-angle applications.

• Mining

• Rolling Mills

• Presses

• Elevators/Escalator Drive Systems

Advantages of Worm Gears

• High precision

• Right-angle configurations

• Braking system

• Low noise

• Maintenance-free

Disadvantages of Worm Gears

• Limitations

• Nonreversible

• Low efficiency

Planetary Gearbox

Planetary Gears

Planetary gearboxes are named so due to their resemblance to the solar system. The components of a planetary gearbox include a sun gear, ring gear and planetary gears. The sun gear is the central gear which is fixed in the center, ring gear (annulus ring) which is the outer ring with inward-facing teeth, and the planetary gears which rotate around the sun gears and mesh with both the sun and ring gear.

Planetary Gearbox

Figure 6: Planetary Gearbox

Physical Properties

The sun, ring and planetary gears of a planetary gearbox are constructed of aluminum, stainless steel or brass. The material used varies depending on the manufacturer.

Note: Gears made from steel materials can be noisy when coming into contact with other gears and also make them prone to wear.

Applications of Planetary Gearboxes

Planetary gearboxes are used in applications requiring low backlash, compact size, high efficiency, resistance to shock, and a high torque to weight ratio.

• Slewing Drives

• Lifts

• Cranes

• Machine Tools

• Automotive

Advantages of Planetary Gears

• High power density

• Compact

• Highly efficiency in power transmission

• Greater stability

• Load distribution among planetary gears

Disadvantages of Planetary Gears

• High bearing loads

• Complex design

• Inaccessibility

Types of Gear motors

As the name states, a gear motor consist of an electric motor (brush less, brush, AC, servo) and gear reducer, also referred to as a gearbox, integrated into a simple package. A gearmotor combination reduces complexity and lowers costs in designs requiring high torque low speed output. Gearmotors can be manufactured to be integral or be combined as separate components. Gearmotors which have the motor and gear reducer sharing the same shaft is what is meant by integral. Anaheim Automation offers a wide selection of stepper gearmotors, brushless gearmotors, DC gearmotors and AC gearmotors integrated with either spur, planetary or worm gears.

Gearmotors are used in many applications in industrial applications as well as in everyday household appliances. Industrial applications include cranes, lifts, jacks and conveyor machines. Everyday household appliances gearmotors are used in are washing machines, mixers, clocks, hand tools like drills and dryers.

How do Gearboxes Work?

All gearboxes work in a similar fashion. The directions the gears rotate are dependent on the input direction and orientation of the gears. For example, if the initial gear is rotating in a clockwise direction, the gear it engages will rotate counterclockwise. This continues down the line for multiple gears. The combination of different size gears and the number of teeth on each gear plays a significant role in the output torque and speed of the shaft. High gear ratios allow for more output torque and lower speeds, while lower gear ratios allow for higher output speed and less output torque.

A planetary gearbox works relatively the same. A planetary gearbox system is constructed with three main components: a central sun gear, a planet carrier (carrying one or more planet gears) and an annulus (an outer ring). The central sun gear is orbited by planet gears (of the same size) mounted to the planet carrier. The planet gears are meshed with the sun gear while the outer rings teeth mesh with the planet gears. There are several configurations for a gearbox system. Typical configurations consist of three components: the input, the output and one stationary component.

For example: one possible configuration is the sun gear as the input, the annulus as the output and the planet carrier remaining stationary. In this configuration, the input shaft rotates the sun gear, the planet gears rotate on their own axes, simultaneously applying a torque to the rotating planet carrier that in turn applies torque to the output shaft (which in this case is the annuls). The rate at which the gears rotate (gear ratio) is determined by the number of teeth in each gear. The torque (power output) is determined by both the number of teeth and by which component in the planetary system is stationary.

How are Gearboxes Controlled?

The output of a motor (i.e. stepper, brush less, AC and brush motors) is used as the input of the gearbox and controls the speed at which the gearbox rotates. The configuration below illustrates the driver controlling the external motor, which is connected as the input shaft of the gearbox. As a result, when the driver is powered, the motor shaft rotates inside the gearbox causing the output shaft of the gearbox to rotate. The output speed and torque is dependent on the internal configuration of the gearbox.

How to Select the Appropriate Gearbox

When considering a gearbox, many factors need to be considered to meet specific application requirements:

Gear Ratio

Gear ratios are defined as the correlation between the numbers of teeth of two different gears. Commonly, the number of teeth a gear has is proportional to its circumference. This means that the gear with a larger circumference will have more gear teeth; therefore the relationship between the circumferences of the two gears can also give an accurate gear ratio. For example, if one gear has 36 teeth while another gear has 12 teeth, the gear ratio would be 3:1.

Output Torque

Output torque is dependent on the gear ratio used. To obtain a high output torque, a large gear ratio would be selected. Using a large gear ratio will lower the output shaft speed of the motor. Inversely, using a lower gear ratio, a smaller output torque value would be delivered into the system, with a greater motor speed at the output shaft. This statement illustrates the relationship that both torque and speed are inversely proportional to one another.

Speed (RPM)

Speed is proportional to the gear ratio of the system. For example, if the input gear has more teeth than the output gear, the result will be an increase in speed at the output shaft. On the other hand, having the reverse scenario with more gear teeth at the output compared to the input will result in a decrease of speed at the output shaft. In general, the output speed can be determined by dividing the input speed by the gear ratio. The higher the ratio the lower the output speed will be and vice versa.

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

Figure 8: Fixed-Axis vs. Planetary Gear System

In Figure 8, 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

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.

Advantages of a Gearbox

• Low noise level

• High efficiency

• High reduction ratios

• Increase in output torque

• Decrease in output speed

• Durable

Disadvantages of a Gearbox

• More costly than other drive systems

• Proper lubrication is necessary for smooth running

• Poorly cut teeth may result in excessive vibration and noise during operation

• Quality matters and adds to cost

Troubleshooting

Problem: Gearbox Becomes Hot
Solution: The exterior temperature of the gearbox may become hot due to several reasons. Please refer to the following information, take the necessary steps to solve this issue. If the gearbox temperature is excessive, please consult the manufacturer.

1. Ambient temperature is above advised level - If the ambient temperature is too high, it may diminish the efficiency of the gearbox. Install a cooling fan or move the application to a more viable location.

2. Proper ventilation - Proper ventilation is necessary, not only for the gearbox but for all electrical/mechanical equipment to function properly. Ensure that there is adequate air flow in the area of the equipment to allow for system cooling.

3. Improper shaft alignment - The first step is to check the alignment of the input shaft of the motor to the gearbox. It is necessary that the input shaft of the motor be aligned with the gearbox to ensure the proper use of the gearbox.

4. Overload - Decrease the load of the gearbox and observe if the temperature lowers. If not, your application may require a larger gearbox model.

5. Lubrication – Poor lubrication for the bearings and gears. Consult with the manufacturer regarding warranty information.

6. Improperly mounted bearings - Reassembly may be required of the gearbox. Consult with the manufacturer regarding warranty information.

Problem: Loud/Vibration Noise
Solution: Loud or vibration noises can be due to many different sources discussed in this section.

1. Improper installation - Improper installation may be a result of loose bolts or misalignment between the motor and gearbox. Tightening loose bolts and aligning the motor and gearbox may solve the issue of excessive noise.

2. Input speed too high - Lowering the input speed may help reduce the noise.

3. Overload - Decreasing the load may help reduce the noise. If not, a larger-sized model gearbox will be required.

4. Worn or damaged bearings - Worn or damaged bearings may need to be replaced. Consult with the manufacturer regarding warranty information.

5. Lubrication - Gears/bearings need to be properly lubricated for cohesiveness. Consult with the manufacturer regarding warranty information.

Problem: Input/Output Shafts Do Not Rotate
Solution: Before going through the below instructions, ensure the motor shaft rotates to isolate any problem with the motor or gearbox.

1. Proper installation - Ensure that all bolts connecting the motor to the gearbox are securely fastened.

2. Gear teeth are worn - Need to replace worn gears. Consult your dealer for warranty information.

3. Gears in locked position - Gears may need to be replaced due to wear and tear. Another possibility would be that a foreign object may need to be removed from within the gearbox, causing the gears to be in the locked position. Consult your dealer for warranty information.

Problem: Gear Teeth Wear
Solution: Wear and tear on gearboxes is natural occurrences. Proper use and system maintenance can help extend their lifetime of the gearbox.

1. Proper installation - Ensure that all bolts connecting the motor and the gearbox are securely fastened.

2. Excessive load - Wear and tear on the gear is caused by contact with other gears. Reducing the load will lower the tension the gears make with one another. If a higher load is required, using a larger gearbox may be necessary.

3. Input speed too high - Lowering the input speed may help reduce the amount of wear and tear on the gears.

4. Ambient temperature is above the advised level - If the ambient temperature is too high, it may diminish the efficiency of the gearbox. Installing a cooling fan, or moving the application to a more viable location may resolve this application.

Cost of a Gearbox

The price of a gearbox varies and is typically affected by size, accuracy specifications, backlash, and the gear ratio, as well as the specific manufacturer. Gearboxes with a backlash in the range of 30 arc-minutes may cost as low as $500. The cost for gearboxes with a backlash value under 5 arc-minutes will cost more than gearboxes with high backlash values. Below is a list of gearbox products offered by Anaheim Automation. Comprehensive specifications and pricing is available on our website at AnaheimAutomation.com, for each of the offered types:

• Economy Gearboxes

• High-Grade Gearboxes

• Right-Angle Planetary Gearboxes

• Rotating Output Flange Gearboxes

Formulas

Motor Torque x Gear Ratio = Torque at the Wheel

Input Shaft Speed (RPM) / Gear Ratio = Output Shaft Speed

Gear Ratio = Teeth on one gear : Teeth on a second gear

Example: If one gear has 60 teeth and a second gear has 20 teeth the gear ratio would be 3:1

Where are gearboxes used?

Advancements in technology and the evolution of gears have made more efficient and powerful gearboxes to be developed and manufactured at lower costs. Toothed gear systems have evolved from fixed axis gear systems to new and improved gears including helical, cycloid, spur, worm and planetary gear systems. Gearboxes are widely used in applications that require desired output speed (RPM), control the direction of rotation, and to translate torque or power from one input shaft to another.

Gearboxes are used in a variety of industries:

• Aerospace – In the aerospace industry, gearboxes are used in space and air travel, i.e. airplanes, missiles, space vehicles, space shuttles and engines.
• Agriculture – In the agriculture industry, gearboxes are used for plowing, irrigation, pest and insect control, tractors and pumps.
• Automotive – In the automotive industry, gearboxes are used in cars, helicopters, buses and motorcycles.
• Construction – In the construction industry, gearboxes are used in heavy machinery such as cranes, forklifts, bulldozers and tractors.
• Food Processing – In the food processing industry, gearboxes are used in conveyor systems, the processing of meat and vegetable products, and packaging applications.
• Marine Industry – In the marine industry, gearboxes are used on boats and yachts.
• Medical – In the medical industry, gearboxes are used in surgical tables, patient beds, medical diagnostic machines, dental equipment and MRI and CAT scan machines.
• Power Plants – In power plants, gearboxes are implemented in transformers, generators and turbines.

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