What are the coreless motors?

by Josafatt Bernocchi

12 Novembre 2020

What are the coreless motors?

Are you sure you know about coreless motors and their advantages? If the answer is "not much" or "just a little", then this article is for you.

Let's start with a definition: a coreless motor is a brushless or brushed motor with a coil wound on itself and not on iron. For this reason, it is also called ironless.
motori brushless coreless e ironcore

The winding of coreless motors has a typically "oblique" or "honeycomb" design to create a dense, self-supporting weave that is then held in place with the use of epoxy resin. In brush motors, the stator is composed of rare earth magnets and is located in the most internal part of the motor, while for brushless motors the magnet, always internal, is the rotor part.

The selection of rare earth magnets and the construction technology of the coreless motors guarantee maximum power in the smallest possible package.


So why choose a coreless motor?

This innovative design offers several advantages, not least the elimination of the cogging effect. Cogging is an effect that machine builders do not like, typical of conventional permanent magnet motors. This effect can be defined as the "snap" that occurs when the tooth is aligned with the opposite magnet and passes through the intermediate unstable magnet. To learn more about cogging, please refer to this article. As you can easily guess, the absence of this effect will allow the great advantage of a more fluid and uniform motion.

motori brushless coreless

A further advantage of coreless DC motors is their low level of electromagnetic interference (EMI) - in fact, the presence of the external ferromagnetic structure allows interference to be confined. This is particularly advantageous when there are other EM signals within the application, such as those produced by smartphones or medical devices. Coreless motors can also be used in battery-powered devices, as they absorb little current thanks to their characteristics.

Other advantages are long operating lifetime, high overload capacity (no iron saturation), excellent heat dissipation, low inertia, high torque and speed, compactness and lightweight.

High efficiency is a significant advantage. In coreless motors, the absence of the ferromagnetic core means the elimination of iron losses, which guarantees significantly higher efficiency when compared to traditional iron core direct current motors. In coreless motors, the rotor mass and inertia are reduced, producing more rapid acceleration and deceleration. These are key performances in high dynamic applications.

You will also be pleased to learn that coreless DC motors are available in brushed and brushless versions. As the name suggests, the difference is whether the brushes are present or not. In the former, the current commutation in the stator windings and changes in magnetic field orientation is provided by brushes and commutator, in the latter they are generated electronically with the rotor position being given by special "hall sensors".

schema motori brushless coreless e brushed coreless

Needless to say, every type of coreless motor (with or without brushes) has its pros and cons and, in turn, reference applications. For brushed coreless motors, there are also fundamental differences in brush materials - typically graphite or precious metals. A specialist supplier such as Servotecnica of brushless motors and brushed coreless motors will be able to provide advice on the best solution for a specific application.

Coreless DC motors are ideal for a myriad of dynamic applications, including robotics projects such as small positioning systems and pan/tilt systems. Medical devices such as prosthetics, insulin pumps, X-ray machines and laboratory equipment, also benefit from the use of coreless motors. Besides, there are numerous applications in particularly demanding sectors such as aerospace, defence and surveillance.

We could give many other examples, ranging from automotive systems, wire tensioning systems, microscopes and electric screwdrivers, tattoo machines, golf caddies and massage chairs (to name but a few). With a coreless motor, the possibilities for designers are endless.

For a more detailed comparison between coreless and iron core motors, go to our dedicated white paper.

To find out more about how and at what level coreless motors can improve the performance of your application, contact our team of specialists.

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