Electric Motor Basics

Every day almost 10 million electric motors are manufactured around the world.  Electric motors convert electric energy into mechanical energy, and can be operated with AC power from an electric outlet or with DC power from a battery.  In the under-10 horsepower output range, there are three basic types of motors being manufactured today:

AC Induction Motors

This type of motor is currently the workhorse motor for constant speed applications. They are found in a wide range of appliances, such as mixers, washing machine agitators, and refrigerators.  AC induction motors do not require drive electronics, although quite often these are added in an effort to improve their performance. 

AC induction motors have medium to poor efficiency, depending on how well they are matched to their load.  As more products switch from single speed to variable speed, this limitation is becoming more important.  For example, the induction motor in a fan (or a mixer or a washing machine) might be 65% efficient when operated at its maximum speed setting, but far less efficient at its lower speed settings.

DC Brush Permanent Magnet Motors

Currently hundreds of millions of these motors are produced each year (mostly outside the U.S.) for low duty-cycle, low load applications.  This is the most inexpensive type of motor to manufacture.  Typical applications include automotive auxiliary systems (windshield wiper, seat adjust, window lift, etc.), power tools, and other portable devices.  DC battery power directly drives these motors.  The term “brush” refers to the sliding contacts between the non-rotating part of the motor and the rotating armature.

DC Brushless Permanent Magnet Motors

The brushless PM motor is the fastest growing segment of the motor market.  These motors have the highest potential for efficiency and provide the highest peak torque and peak power values per unit volume. Permanent Magnet motors require electronic drive modules, which convert AC line power to DC power and control the motor’s speed.  The brushless PM motor is the primary technology for the high performance servo motors used in precision positioning applications such as robots, machine tools, medical analysis equipment, semiconductor machines, surface mount equipment, and many other applications where dynamic response is required. 

The NovaTorque motor technology is a unique type of brushless Permanent Magnet motor.

Radial and Axial motors

A different way of categorizing motors is into radial and axial motors.  The vast majority of all motors today (whether they are AC induction, DC brush, or DC brushless) are radial motors.  A typical radial motor has a rotating hub which is assembled onto a rotating shaft.  This hub fits inside – and is encircled by – the stationary stator assembly.  The stators have copper wire wound around them, and are orthogonal to the shaft.  Looking at a cross section of a radial motor, the field poles and copper windings are arranged like the radii of a circle.  Magnetic flux is generated across the air gap in a radial direction (hence, the term “radial” motors).

In axial motors, the field poles and copper windings are parallel to the axis of the motor.  Axial motors have been around since the 19th century, but they have been used only in very specialized situations.  They typically have a form factor with a very large diameter relative to the length of the motor, so are sometimes called “pancake” motors.  In the standard axial motor design, there is a fixed air gap area for any given motor diameter, so the only way to produce more torque is to use stronger (and more expensive) magnets.

NovaTorque motors are axial motors, because their field poles and copper windings are parallel to the motor’s axis.  However, they use an entirely different design than other axial motors.  Instead of being limited to magnets with a 2D flat face on the end of a field pole, NovaTorque motors use a 3D conical magnet structure to increase the pole face and air gap area.  In many respects, NovaTorque motors can be thought of as a hybrid between radial and axial motors which combines the best features of each type.

 

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