Coreless DC Motor—A Quick Reference Guide

Thanks to brilliant engineering minds over the past few decades, society now enjoys the smooth working of advanced motor drives in various industries. Innovative DC motors that improve productivity and make life easier for consumers & businesses have are being produced in various types, and each one of the models have got its own pros and cons.

Among all the different motor types, coreless DC motor have always been outstanding in performance since its invention. Is the coreless motor a type worth considering for your industry? We will discuss coreless DC motors in detail so you can determine its value for your application.

What is a Coreless DC Motor?

An easy way to understand why coreless motors are so unique is to compare them to regular DC motors. A regular brushed DC motor has an inner iron core around which coils are wound, so the rotor is made of heavy iron laminations. In contrast, a coreless motor has no inner iron core component, thus it’s called coreless.

Coreless DC MotorInstead of the heavy iron core, in a coreless DC electric motor you’ll find:

  • Housing which guides the magnetic field and acts as a magnetic return path.
  • A hollow cylinder, also called a basket, with copper coils wound in a self-supporting honeycomb or skewed pattern.
  • The permanent magnet which fits inside the basket and therefore sits inside the rotor. An air gap separates the magnet and the housing. The magnet produces the magnetic field.
  • Brushes and commutators usually made of precious metals.
  • Bearings that support the rotor so it can rotate around the magnet.

The unique design means a coreless DC motor is definitely not a lower quality product when compared to DC motors with inner iron cores. To compensate for the mechanical strength because lack of an iron core, the innovative coil design had been adopted to improve the mechanical strength of the rotor.

Of course, DC motors often have to handle high torque levels. In the absence of an iron core, epoxy—often glass—is added to rotors of coreless DC motors. This epoxy strengthens the rotor coils, so they don’t get damaged easily.

The absence of the heavy inner core has many advantages, discussed in detail later in this article. 

Recommended read: Brushless vs Brushed Motors: Which is Suitable for Your Project?

Coreless DC motors can be divided into two types based on their different rotor shapes:

  • Disc shaped rotors: In this category you’ll find pancake rotors as well as three-coil and printed rotors.
  • Cylindrical rotors: Some cylindrical rotors have inside fields while others have outside fields. The latter has the smallest mechanical time constant.

To sum up, the coreless DC motors offer exceptional precision driving and use unique winding designs to enable the high output & control from very compact sizes.

The History

This dynamic coreless DC type has been around for about 80 years (mid 1930s) but wasn’t popular from the start, as they were expensive. Technology evolved and eventually in the 1960s motor manufacturers could produce them at a price that made them economically viable for industries to purchase and use.

The many benefits paired with a lower price tag quickly made coreless DC motors one of the favourite type in many industries.

Advantages and Disadvantages of a Coreless Motor

The benefits of coreless DC motors stem mostly from its physical attributes that provide you with the following:

  • High efficiency paired with compact design: When purchasing an ironless DC motor, you can have an efficient motor which is lighter compared to many others on the market. Coreless DC motors usually have less current loss, making it more efficient overall than cored types.
  • Low drawing current: It doesn’t draw as much current as some other motors, so when powered by a battery the battery will last longer.
  • Optimised functioning: If you’re looking for a DC motor that can handle acceleration and deceleration very quickly, the coreless DC motor design is an absolute winner. It handles these conditions well since it has got lighter rotors and doesn’t cause as much inertia as other motors.
  • No cogging: A coreless motor never produces a scenario where the rotor and the stator magnetic circuits get misaligned. This means, unlike in many other motors, there is no cogging and the motor can run very smoothly.
  • Safety and durability: Without iron core, there’s less chance of arcing and sparks that often occur between a cored motor’s brush & commutator. Your coreless motor will last longer and you won’t have much EMI (electromagnetic interference).
  • Easy control: Users appreciate that you can easily control the motor and manage its speed.
  • Low Noise levels: It runs quietly.

Of course, the perfect DC motor is yet to be designed, so you have some drawbacks you need to manage. In a coreless electric motor there’s no heat sink for the winding, so to cool the machine down, your DC motor’s housing must have good thermal conductivity. This is especially important if your motor will often speed up and slowdown in rapid succession.

In the case of overheating, the motor will break down because the windings’ bonding adhesive will lose its efficacy. Thus, coreless DC motors won’t be able to handle an overloaded system as well as a cored motor.

Applications of Coreless DC Motors

The advantages mentioned above lead to the coreless DC motors to becoming a popular option where precision, efficiency and durability are essential.

Practical applications of a coreless DC motors include:

  • The healthcare industry: They can be used to power dialysis pumps, CPAP machines, surgery tools and ambulatory infusion pumps. 
  • Robotics: Engineers install them in positioning systems and small wheel systems in robot projects.
  • Automation & Actuators: These motors can be used in precise automation systems and high accuracy actuators.
  • Laboratories: Engineers can use it to drive small but effective equipment such as pumps, stirrers and centrifuges.
  • Office equipment: Thanks to their small size, effective motors can be installed in printers, card readers and other office equipment, without the need to make the products bigger.
  • Audio/visual equipment: Pan and tilt drives for cameras & audio turntables can be fitted with effective motors that work quietly.

Conclusion

Almost a century after the first coreless electric motor was invented, the market is now flooded with them for good reason: they work powerfully, precisely and efficiently without requiring much space.

Who knows what they will enable engineers to invent in the next 80 years?

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