- Motor
magnets are made from a lot of different materials - Neodymium,
Samarium Cobalt and Alnico. which magnet material is best?
- Motor
magnets can be designed with magnets cemented on or embedded.
Which is the better design?
- I
hear a lot of debate about brush and brushless motors. What
are the benefits of a brushless motor design?
- Why
would I choose an outside rotor over an inside rotor? What
are the advantages and disadvantages of each?
- I've
seen both cube and cylindrical shaped motors. Is there a
performance difference between the two shapes?
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 speak with a design engineer at Moog
who can address your particular needs and discuss magnet choices
with you.
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.
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.
A: Inside
rotor designs provide lower rotor inertia, outside higher
rotor inertia.
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 motors because they
offer a high torque to size ratio.
