Electric Flight in Australia

 

What are cobalt and neodymium motors?

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Cobalt and Neodym motors are those that use rare earth magnets to produce the magetic flux necessary to convert electrical energy into mechanical energy. They are called rare earth magnets because both samarium cobalt and neodymium are powdered metals found in the rare earth elements of the periodic table. The powdered metal is compacted in the presence of a magnetic field and then sintered; these are man-made magnets. Once compacted the shape can only be altered using diamond abrasives. Both Samarium Cobalt and Neodymium exhibit very strong magnetic fields and resist demagnetisation very well. However, there are some differences:

Samarium cobalt magnets

  • high magnetic properties
  • very good temperature stability
  • powerful for size
  • quite expensive to produce
  • first available in the 1970s
  • suffered from stability problems in the early days, but this issue has now been resolved

Neodymium-Boron-Iron magnets

  • more recently developed
  • offer the highest possible energy - stronger than samarium cobalt
  • less expensive to produce than samarium cobalt magnet material
  • however, are prone to corrosion problems which result in loss of energy
  • also lose magnetic properties if overheated (above 150ºC)

The outcome of all this is that Neodym magnets have become the most common in our motors, especially in brushless motors where heat is not such a problem. In brushless motors the magnet material is attached to the shaft and is often wrapped in kevlar. I assume that this wrapping reduces the corrosion problem, but you still have the heat problem. The message for us as electric fliers is - make sure that you do not overheat your neodym motors. This is usually not a problem in electric glider where our motor runs are so short. However, if you are pushing your motors hard, and running for extended periods, you might be better off selecting a cobalt motor.