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Brushless Permanent Magnet Motors

Coercives’ standard and custom designed Brushless DC motors enable optimal solutions to be provided to the application.

Magnets

These motors feature high performance rare-earth permanent magnet materials covering a range of grades of Samarium Cobalt and Neodymium Iron Boron in order to address differing application requirements, where the particular characteristics give the optimal balance (trade-off) for the specific application .This may be governed by extreme ambient temperatures or high power densities or high coercive forces as an example.

Lamination Materials

These are similarly selected to suit the requirements, having developed considerable experience using a range of materials from the Silicon Steels , Nickel Alloy Steels and Cobalt Alloys (Vanadium Permundur), the latter providing the highest possible flux density.

Configuration

Motors can be supplied in both housed and frameless configurations meaning either as a wound stator/PM rotor set (which can be advantageous in directly mounting to the driven component- hence no coupling requirement) or as a housed motor with bearings, output shaft and or gearboxes, feedback devices, special cooling features (fluid , forced air or conduction cooling) etc.

Motor Geometry

This is one of the parameters that is modelled for the application. It is difficult to generalise but for a servo control application looking for fast response the geometry tend towards a ratio of diameter to length of less than 1. However, for high torque direct drive applications the converse design of the typical pancake torquer will enable maximum mechanical advantage to be gained , generating the torque at the maximum radius .The pole number tends to be significantly higher in these designs . Regardless of this, it may be that system requirements dictate the motor geometry irrespective of optimal efficiency or servo response, if you need a large hole through the motor rotor, to pass optical beams or services etc then a motor will be configured accordingly. Frequently this means you have a “thin ring” design to limit overall mass.

Power Supply

The motor winding, within reason can be designed to accommodate the available supply whether the application operates from high voltages and relatively low currents – such as with long transmission lines, or requires to operate on low voltages but with higher current capacity. The winding can be designed for trapezoidal or sinusoidal back emf wave forms for 6 step or sine wave motor drives.

Efficiency

It is easy to be misled by efficiency figures in general and eye catching percentage efficiencies well into the 90’s - but they must always be considered relative to your application demands and constraints .Certainly efficiency can be optimised as the important parameter of your systems requirements, however this is always a trade off. The highest efficiencies as well as utilising various motor design considerations are also achieved by addition of very good motor cooling .Brushless motors already due to their architecture inherently allow far better cooling than motors with rotating windings, such as Brushed Motors. However to extract maximum heat fluid cooling techniques are frequently used especially when high 90’s figures are quoted. More typically the percentage efficiency will be in the 80’s for an air cooled design operating optimised for efficiency.

Cooling

Motors can be designed to utilise a variety of cooling mediums from conduction only, air , forced air and fluid cooling. Many of Coercives’ designs operate with fluid cooling whether through direct immersion or indirectly , such as in marine applications .In this latter case the motor will be designed to be resistant to the cooling medium.

Life and Reliability

Brushless Motors tend to be inherently reliable in their technology (see previous comments on motor design aspects) and if correctly engineered and matched to the application provide very long service life, which is why the technology is widely employed in the most demanding applications.

The Company’s own considerable experience in dealing with anything from the more benign to extremely hostile environments and high reliability demands as placed by programs from Defence, Space and Marine enables designs to be produced to give many years of maintenance free service life .

Fault Tolerant Design. In some applications, such as aerospace, fault tolerance can also be incorporated into the design to increase system reliability. Examples are duplex design features with redundant windings and separated electrical circuits, such that in the event of a fault condition there is a second drive channel.

In a housed motor bearing failure should be the life limiting element , therefore it is imperative that the motor operating conditions and environment are carefully considered in bearing selection ,mounting , rating and loading . With a rapidly advancing range of bearing materials , lubricants , configurations and tolerances this makes correct selection for application vital in satisfying the specification and life. Consider, long periods of inactivity may lead to lubricant migration or cause increase in stiction, combined with short periods of operation or small angular rotational movements as encountered in some optical systems, then failure to adequately address this in suitable bearing design will lead to premature product failure.

Environmental

Coercive can provide its experience in designing products for a wide range of applications demanding ultra low or high ambient temperatures, vibration, shock, acceleration, extended life, vacuum, out-gassing (optical)

Summary

  • Optimised brushless dc motor technology
  • High Efficiency
  • Housed or Frameless
  • Powers 1W to 100KW Outputs
  • Product Size – Diameters from 10mm to 750mm
  • Speeds to 100,000 RPM
  • Wide Operating Temperature Range
  • Hall Effect , Resolver /Encoder or Back EMF Feedback
  • Trapezoidal , Sinusoidal Driven
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