Workings of a Brush DC Motor

choosing a dc motor

Brush DC Motor Basics

Portescap's brush DC technology originates from a design based on an ironless rotor (self-supporting coil) combined with a precious metal or carbon copper commutation system and a rare earth or Alnico magnet. It offers distinct advantages for high-performance drive and servo systems: low friction, low starting voltage, absence of iron losses, high efficiency, good thermal dissipation, linear torque-speed function. All these factors facilitate use and simplify the servo loop. For incremental motion systems where the low rotor inertia allows for exceptional acceleration, and for all battery-powered equipment where efficiency is a major concern, brush DC motors offer optimum solutions.

All DC motors are composed of three main sub-assemblies:

  1. the stator
  2. the brush holder end cap
  3. the rotor

1. Stator – The stator consists of the central and cylindrical two-pole permanent magnet, the core that supports the bearings, and the steel tube that closes the magnetic circuit. High-quality rare earth magnets ensure outstanding performance in a small envelope. Sintered bearings and ball bearings are available depending on your application loads and requirements.

2. Brush holder endcap – The brush holder endcap is made of a plastic material. Depending on the intended use of the motor, the brush could be of two different types; carbon or multi-wire. Carbon types use copper graphite or silver graphite and perfectly suit incremental motion applications where high continuous and peak torque are required. Multi-wire type uses precious metal and will guarantee low starting voltage and improved efficiency, a perfect match for portable battery-powered applications. Portescap's engineer can design endcaps that reduce electromagnetic noise to meet EMC requirements.

3. Rotor – The rotor is the heart of Portescap's DC motor. The coil is directly and continuously wound onto a cylindrical support that is later removed, eliminating excessive air gaps and inactive coil heads that bring no contribution to the torque creation. The self-supporting coil does not require an iron structure and therefore offers low moment of inertia and no cogging (the rotor will stop in any position). Unlike other conventional DC coil technologies, due to the absence of iron there are no hysteresis, eddy current losses or magnetic saturation. The motor has a perfectly linear speed-torque behavior and the running speed depends only on supply voltage and load torque. Portescap, through its proprietary know-how, has developed multiple automated winding machines for different frame sizes and continues to innovate on the winding method to increase power output.

The brushes/collectors combination is optimized to withstand a long operational lifetime at up to 12,000 rpm and provide high reliability. Portescap DC products can deliver a torque range from 0.6 mNm up to 150 mNm continuously and from 2.5 mNm up to 600 mNm in intermittent operation.

Additional Information

Rotor assembly

Brush DC motor cutaway