In order to investigate the contenders for the best direct drive motor on the market today, we first need to look at the criteria that might contribute to a motor making the cut. For the purposes of this article, we are going to look at the laundry sector and what factors contribute to the 'best direct drive' laundry appliance motor.
There are a number of manufacturers producing direct drive motors for laundry appliances today and there will be one available to suit almost every application that requires an electric motor. These will either be in catalogues or off-the-shelf, or fully customised motors to suit a specific set of criteria.
How good a direct drive motor is will depend entirely on how well a company can design and manufacture it. There are numerous options available from manufacturers and there are a host of factors that will influence which might be best, or best for your application. Many of these factors will require careful consideration before any decisions can be made. There are functional parameters to think about, such as what torque and speed is required, along with basics like physical size and other constraints. We will highlight just a few key factors here to ascertain what criteria might go into the best direct drive motor.
Every washing machine requires a drive system to rotate the drum. Traditional washing machines use a belt driven or gearbox driven motor to do this, while more commonly now, direct drive systems require no belt and very few moving parts, making them a far better option. Along with a host of other benefits, the direct drive system has become the gold standard in washing machine motor technology today.
When we think about customer pain points with their laundry appliances, what are the main points of contention? Wash quality, spin speed, performance or efficiency, cost, and noise/vibration are all factors to consider. It may also be all about energy efficiency, sustainability or the product's longevity.
Depending on your application requirements, some or all the above-mentioned factors will be important to some degree. Many of them can be addressed with a good direct drive motor, so when it comes to creating a new application, which ones are on the top of your list to enhance or refine? We know the great benefits direct drives offer in many different applications, such as higher efficiency, low noise, less physical size and more precise agitation etc., but what are some of the most important factors contributing to the best-in-class direct drive motor?
Let's dive into a few of the top contenders.
Motor noise and vibration are two of the most important factors when it comes to optimising laundry appliances. But what are some of the factors that contribute to reducing noise and vibration?
There are many factors that can impact this. One is the electromagnetic force which can cause various levels of vibration within the motor. In order to successfully reduce this and reach minimum torque variation, it is necessary to avoid frequencies that may resonate with other parts of the motor or system and potentially generate more noise, leading to vibration.
Other ways of mitigating vibration/noise are to consider altering the structural or mechanical parts. For example, modifying the existing design by making it denser. Changes such as this will, however, have an impact in terms of the final cost or even weight of the finished product. Manufacturing is also vitally important in terms of variability. You will need a very robust and capable manufacturing process that can deliver to the individual specifications required.
Another solution, although not commonly used, is to increase the air gap - however this may compromise the motor's performance.
Finally, other non-magnetic related factors worth noting here include product assembly e.g., bearings not aligned correctly, and air movement which can potentially cause a fan-like noise. Controllers and the control method can also be contributors to added noise.
The two key factors contributing to the efficiency of a laundry appliance are minimising energy consumption and effective heat management. In order to maximise the efficiency of the appliance, a highly optimised motor and drive system is essential. There is also a large emphasis on the continued efficiency of water heating, as this is the main consumer of power. Ideally, manufacturers will be aiming for the least amount of energy consumption, while minimising the amount of heat created. These factors combined will help to refine the motor for peak performance.
Fine tuning the electromagnetic design by optimising the overall use of materials, for example, is key to driving efficiency. This may include simply not using more steel or magnets than is needed in production.
The search for more efficient direct drive motors needs to be balanced with the cost implication. Ideally, manufacturers want to create the most efficient motor in the most cost-effective way. The large appliances market, which includes washing machines, is very competitive and to meet customers' expectations, cost is a critical factor in the decision-making process.
In order to create the highest levels of efficiency, there is inevitably going to be a trade-off with cost. Using premium materials or better magnets for example, will contribute greatly to overall efficiency, but will of course impact cost. The controller will also contribute to the motor's overall efficiency, as will the choice of software used with the controller.
The factors that will contribute to the torque/weight ratio reach from motor topology to material selection and utilisation to mechanical design complexity and to the individual cooling solution inside the final application.
In order to increase power density, a premium level of materials can be used - again at a higher price point. The form factor can also be changed, for example making the motor size thinner so the drum can be larger but occupy the same amount of space within the unit. The power density remains the same, while the physical form has changed.
Another contributor to the torque/weight ratio is the use of plastic rotors instead of steel. Both manufacturing methods have their benefits and trade-offs. Plastic moulding is cheaper, effective and generally quieter as it reduces noise in applications (in washing machines for example). However, it can be less reliable if the manufacturer has not specified the correct material and does not have the manufacturing experience required. Many manufacturers prefer to use steel, as it can require less manufacturing experience and is sure to last, however it is more expensive and can drive additional noise.
When searching for the 'best direct drive' motor, we have seen there is a list of factors that can contribute to taking this crown. We have focused on laundry as an example and highlighted several of the key factors that should be considered when looking for the best-in-class motor. It really is all about your application and what specifics you require. For many applications, there will be an obvious choice to use, or options will be severely limited. On the flipside, some applications may afford the option of using a number of different motor types. Of course, this is just a snippet of what will go into the final decision-making process, so it is important to evaluate the pros and cons of each motor type and how (or if) they cover the key requirements of your application.
Read more about direct drive motors here.
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