Part 1 of 2: Electrical Motors
How motor technology evolved over two centuries, and how it works to drive modern life
Electric motors work by converting electricity into controlled magnetic fields to induce a rotation.
BY JEREMY LOSAW
The growing popularity of electric vehicles has thrust electric motors into the spotlight, but it is a tale more than two centuries in the making.
The roots of electric motor technology date to the early 1800s and the foundational research around electromagnetism. Through generations of design and innovation, electric motors have been developed to be one of the most highly efficient power transmission devices and a key component in industrial and consumer devices.
Often shrouded under the cloak of an electric car body or the housing of a consumer product, electric motors have emerged as a hidden hero that we use in our everyday lives.
In this two-part series on electric motors, I will discuss the history and fundamentals of electric motor technology before exploring practical applications and prototyping techniques in Part 2.
The history of electric motors parallels that of the development of electricity.
The late 1700s and early 1800s brought about dramatic innovations in electricity, such as Alessandro Volta’s invention of the battery and Georg Ohm’s work that described some of the first mathematical descriptions of electricity. However, it was Hans Christian Ørsted who unlocked the relationship between electricity and magnetism.
In 1820, he observed that a compass needle moved when in the presence of an electrified rod. This concept became the foundation of electric locomotion.
Further innovations followed quickly: English physicist William Sturgeon developed the first motor that could power industrial machines; Americans Thomas and Emily Davenport were granted the first electric motor patent in 1837. These early motors were commutator-, or brushed-style motors that necessitated a physical connection between the rotating armature and the magnetic stator (the stationary portion of an electric generator or motor).
In the late 1800s, as Thomas Edison and others were working out the details of electric lighting, Nikola Tesla and Galileo Ferraris were independently developing brushless, or induction, alternating current (AC) motors. This technology unlocked the power of electric motors for widespread uses. Soon after they became a staple of industrial products, powering anything from cable cars to mining equipment while replacing human, water and animal power.
Over time, electric motor technology advanced to the point it is today to efficiently power cars, consumer goods and industrial applications of all types.
How they work
Electric motors work by converting electricity into controlled magnetic fields to induce a rotation. The two main ingredients that make up all electric motors are the magnet and electric coil.
The coil is wound in such a way that when power is applied to it, it creates a magnetic field, which is also called an electromagnet. In magnets, opposite poles attract each other and so when the coils are energized, the fixed magnet tries to align itself (north pole to south pole) and find its equilibrium.
This action of the magnet and electromagnet trying to pull themselves into alignment induces the axle or rotor of the motor to move. If the electric field switches before the system equilibrates, the shaft of the motor will continue to spin to try to align to the new state of the electromagnetic poles. If this is done fast enough, the motor will spin continuously in its never-ending attempt to find its elusive equilibrium until the power is cut.
The two broad types of electric motors are brushed and brushless. A motor falls into one of these categories based on the arrangement of the magnets and the coils.
All electric motors have a rotor and a stator. Predictably, the stator is the housing that stays stationary and the rotor is the part that rotates. The magnets or the coils can be on either the rotor or the stator.
Brushed motors have the magnets in the stator and the coils are on the rotor; therefore, they also require conductive brushes that are mechanically and electrically in contact with the rotor to provide electricity to the coils while still allowing the rotor to spin. Brushless motors have the magnets on the rotor and the coils in the stator. The magnetic field is created by the coils in the stator and induces the magnets on the rotor to move without the need for brushes.
Brushed motors tend to have more startup torque and are easier to control. However, the brushes increase the drag on the rotor; plus, they have lower top speed and slow down faster when the power is cut. Also, brushes are a consumable that need to be replaced when they wear out. They can be powered directly from a battery or a wall wart (AC to DC wall converter) but require a controller if variable speeds are required.
Brushless motors have lower startup torque but high RPM and need very little maintenance. They cannot be run directly from wall power without intermediate circuitry or a controller to dose out electricity to the coils in the right way to keep the rotor spinning.
Electric motors are used in devices from cell phones to freight trains and seemingly everything in between. Motors are all around us in our homes, The vast majority of us unknowingly carry around one or more with us all day long, as there are tiny haptic motors inside wearables and cell phones that buzz us when we get a call or reach our step goals.
In our kitchens, motors run inside blenders and other cooking tools; rotate the turntables inside of microwaves; and pump coolant in our refrigerators to keep our food cold. Motors inside our computers spin disk drives and provide cooling air to keep them running properly.
Motors are ubiquitous in our tools, too. Drills, grinders, sanders, saws and even 3D printers use electrical motors to help us get our jobs done. There are also myriad applications in industrial and medical devices that provide us with the products and services we need and desire.
While often hidden from view, cloaked by an aesthetic housing or mounted deep inside the guts of a machine, electric motors are integral to modern life.
In Part 2, I will explore some different types of motors and how they can be used to bring prototypes to life.