What is a coreless motor?

What is a coreless motor? It is similar to a cored DC motor in that it has brushes and a commutator. You also get brushless varieties. However, the difference is that the rotors windings are wound in a skewed (or honeycomb) fashion to form a self-supporting hollow cylinder, which is usually epoxied for stability.

The stator, which sits inside the hollow cylinder, is made of a rare earth magnet, such as Neodymium, AlNiCo (aluminium-nickel-cobalt), or SmCo (samarium-cobalt). The brushes in a coreless motor can be made from precious metal (e.g. silver, gold, or platinum) or graphite. The wire cylinder distributes the magnetic field throughout the structure when an electrical current is applied to the leads connected to the brushes and commutator, which interacts with the rare earth magnet to produce a force and rotate the shaft.

Coreless motors open up a wide variety of possibilities for use in robotics. A few applications include their extensive use in prosthetics, insulin pumps, laboratory equipment, and X-ray machines – all requiring high accuracy positioning.

Pros

Small, lightweight, and compact design.
Low noise and vibration operation.
Highly efficient (approximately 90%).
Longer life due to less electro-erosion.
High acceleration and deceleration rates.
Linear speed/torque characteristics allowing for easier control.

Cons

Significantly more expensive.
Cannot handle thermal overloads as there is no iron core to act as a heat sink for the rotor windings.
Requires additional electronics (e.g. decoders).