FEATURE Drives, Controls & Motors

The fundamentals of motor gearbox selection

Ian Williamson, chief design engineer at EMS, shares his expert insight into motor gearbox design specifications S

imply put, a motor gearbox is a mechanical unit consisting of a series of integrated gears, which can alter motor speed and torque. The torque

output is inversely proportional to the speed, and gearboxes are mainly applied to motors to increase torque by reducing the speed. While the basic principles remain the same, there are a number of other factors to consider when choosing an appropriate gearbox.

Top design specifications To pinpoint the ideal motor gearbox is to look at the application it will go into – right from the beginning of the selection process. This insight will uncover the gearbox’s specifi c demands and requirements, leading to a successful fi nal product. However, there are some essential specifi cations that must also be studied, including torque, speed, current and operating voltage. These features must be balanced with the customer’s performance aims, preferred price and target quantity, to ensure the product works well and is commercially viable. Customers can choose the best fi tted

standard gearbox to their specifi c application based on all these factors, but a bespoke solution allows complete tailoring to requirements. These can be designed to suit additional factors, such as product space, output drive confi guration and product mounting points. Self-locking of the motor gearbox and integration of mechanical slipping clutches can also be considered.

When working with a standard component, there is likely to be a compromise on features, which means the fi nal product performs well, but not to its maximum potential. A bespoke solution considers all component requirements and the fi nal product as a whole, right from the beginning of the project. By tailoring each aspect of the component to the application, more benefi cial features can be integrated to tick all of the customer’s boxes, and in a smaller space. Standard motor gearboxes can require a degree of adaptation to work well in an application and, therefore, bespoke gearboxes are often more compact.

24 June 2021 | Automation Left to right: Gearboxes

High power density motor systems Many customers seek to fi t a highly- functional unit into a small or complexly- shaped space, which can be achieved with an effi cient, high-power motor matched with a custom gearbox. An example of a challenging area to work with is in interior automotive applications, where space is shared with many other equipment pieces, rendering standard components typically unsuitable.

Another application of these motor systems is in the prosthetics industry, where the resulting product must be slim, lightweight and comfortable whilst still delivering enough power to perform everyday functions.

Small yet powerful motor systems are also suitable in healthcare applications, including stairlifts, where powerful systems must provide suffi cient drive to move patients up and down stairs. Yet, the system must also be compact for easy integration into the stairlift without negatively impacting its aesthetics or wider performance.

Complementary parts A magnetic or optical encoder, for example, can easily be added to the motor to deliver precise control over speed and positioning. If accurate sensing is required upstream of the motor or at the output of the gearbox, a bespoke solution can allow integration of the encoder elsewhere in the gear train. Other sensing options include potentiometers for position control or microswitches for endstop detection. Another potential add-on is an

electromagnetic brake, which can be fi tted to the gearbox to provide holding torque once the power is removed. This allows the system to come to a full stop and hold a position at a reasonably high torque for a long time, particularly useful in medical devices.

Mechanical slipping clutches are also a popular option, commonly used to protect against overloads. They can be integrated internally or into a product geartrain – wherever the output of the product is required to slip at a particular overload torque or the internal gear train needs protecting from shock loads.

Working with a UK manufacturer Communication is easier between a customer and a local manufacturer, allowing close support throughout the whole project timeline. It also allows physical meetings when possible, to help the manufacturer fully understand the component’s end application, or to help the customer gain clarity on the production steps needed to make their product. EMS is UK-based, with design engineers at its manufacturing facility in Poole and a sales team around the country. Our design expertise and wealth of experience, combined with our commitment to eff ective communication with our customers, ensures an optimal motor system is chosen that is ideal for the end application. CONTACT:


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