Motors FAQs

ANSWERS TO FREQUENTLY ASKED MOTOR QUESTIONS

motors faqs

Q: Motor magnets are made from a lot of different materials - Neodymium, Samarium Cobalt and Alnico. Which magnet material is best?

A: Each magnet material has its advantages - and disadvantages. Let's look at each.

Alnico Samarium Cobalt Neodymium
Was the best available until the early 1970s.
Its main advantage is its temperature stability.
This is a high energy magnet. In its early days,it suffered from stability problems; that issue has now been resolved, making it a good, stable magnet material. Neo offers the highest possible energy. Environmental factors must be considered, however, as it is limited to 150° C and can develop corrosion problems in some environ-ments, if not coated.


There are also cost differences between magnet materials. Your best bet is to contact a design engineer at Moog who can address your particular needs and discuss magnet choices with you.

 

Q: Motor magnets can be designed with magnets cemented on or embedded. Which is the better design?

A: Again, it depends on the application. From a manufacturer's point of view, an embedded magnet is easier; the magnets are simply slid into the slots as the motor is built. From a performance point of view, the most important consideration is the speed at which the motor will be performing. Special precaution must be taken with extremely high speeds - cemented magnets have been known to fly off.

 

Q: I hear a lot of debate about brush and brushless motors. What are the benefits of a brushless motor design?

A: A brushless DC (BLDC) motor is inherently more reliable than a brush motor. They, of course, have no brushes to wear out, so they have a longer life and less downtime due to brush replacement. Because of the lack of brushes, there is no brush arcing or brush bounce. With no brush resistance, they typically provide higher speeds than brush motors. And because the winding is typically on the outside element, they offer better heat dissipation. The absence of brushes also makes the BLDC motor a more quiet (both acoustically and electrically) unit than one with brushes. Advances in electronics and power semi-conductors permit cost effective control of a BLDC motor. And BLDC motors offer the response and linearity over a wide speed range that is needed for today's applications.

Conversely, brushless designs are usually a bit more expensive. There are many applications where brush motors do a superb job. It's always best to discuss your particular requirements with a Moog applications engineer.

 

Q: Why would I choose an outside rotor over an inside rotor? What are the advantages and disadvantages of each?

A: Inside rotor designs provide lower rotor inertia, outside rotor designs provide higher rotor inertia.

 

Q: I've seen both cube and cylindrical shaped motors. Is there a performance difference between the two shapes?

A: Many design engineers choose a cube shaped motor primarily because it lends itself better to the size of the envelope with which they're working. But many choose cube shaped motors because they offer a high torque to size ratio.

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