When writing this post, I really wanted to incorporate some pun on “making your head spin,” but it just wasn’t working out. Nonetheless, today’s post will provide the briefest introduction to the world of motors.
Motors are an important part of our daily lives that shows up even where we least expect it. We notice that motors are in cars and ceiling fans but they even show up in computers for DVD-drives, phones for vibration, electric toothbrushes, vacuums, and more!
First, I should clear something up, people often use the terms engine and motor interchangeably; however, there is a slight difference between the two:
Motor – Something that provides motion
Engine – Something that converts thermal (like heat) energy into mechanical work
So what? This means that engines are a kind of motor, but not the other way around. Gas powered-cars have engines that burn gasoline to make them move, but electric cars don’t; however, you CAN say both of them have motors. Rocket engines that burn fuel are also a kind of motor because they provide motion, but the motors in your computers, toys, and toothbrushes are not engines.
The most accessible kinds of motors are electrical so we will be focusing on those in this post.
The three types you will mainly using are DC, Stepper motors, and servos.
DC motors are simplest and cheapest motors available for projects and are made of the minimum parts needed for a motor to function which are the stator and rotor.
The stator is the stationary or non-moving part of the motor (the red and blue curves), and the rotor is the rotating or moving part of the motor (the grey part). The stator is made of permanent magnets like the ones that stick pictures to fridges and are aligned so that opposite poles face the inside. The rotor is wrapped by thin copper wire many times in a coil that is directly connected to the battery or power supply.
When current flows from the positive end to the coil, it energizes the coils and creates a magnetic field that repels the magnet on the stator with the same polarity. As the coil moves to the other side, it switches polarity and repels the other magnet. This process repeats constantly to create motion. DC motors with no encoder (more on this soon) have two leads, one for positive and one for negative; however, switching them simply causes the motor to move in the opposite direction, so wiring it wrong is not a big deal.
The simplicity of these motors make them perfect for motion which doesn’t need to be precise like for moving a car, robot, propellor, or a fan. DC motors can also be purchased with built-in gearboxes to make them more powerful.
A servo takes the DC to new level with precise motion and comes in continuous or limited motion varieties.
A servo consists of a DC motor, a set of gears to make it more accurate and powerful, a horn to attach different kinds of attachments and a circuit board, but what’s that weird brass colored thing sticking out of the top of the circuit board? That, my friends, is a potentiometer. Potentiometers are useful as knobs controls for many applications, but here it is what makes the servo so accurate. In this case, the potentiometer acts as a sensor that turns when the DC motor does. The controller, measures the voltage across the potentiometer to figure out exactly where the servo horn is positioned. This limits the amount they can move to around 180 degrees depending on the servo. Continuous motion servos are more like DC motors with gearboxes, so although you can control them fairly precisely, it’s not nearly as good as their limited motion counterparts. When you attach them to a controller like an Arduino, you have three leads, power (usually red or orange), ground (usually black or green), and signal (white or yellow).
Servos are not good for moving cars, but are perfect for precisely controlling something that doesn’t need to go round and round, like a robot arm, claw, or rotating head or like the elevator, aileron, or rudder of an airplane.
Steppers are an interesting combination of the power and continuous motion of a regular DC motor with the precise motion of a servo.
Just like the other motors, the stepper has a stator and a rotor, but it gets a little strange from here. First, the stator is not a permanent magnet. Instead, it is made of separate coils indicated by the numbers 1-4 shown above; however, most motors only have two separate coils. The rotor is made of a series of permanent magnets on the outside edge shown by the little teeth on the red gear. These magnets are arranged so that they only line up with one coil at a time. As each coil is energized in order, the rotor turns so that the next set of teeth lines up with the coil. As this process repeats, the stepper makes its way around shown by the yellow slice. Don’t be fooled, this process can happen really quickly, allowing the stepper to move swiftly and accurately. This makes steppers perfect for moving larger robot arms in arcs or X and Y axes. When you’re wiring a stepper, you’ll notice you have way more wires than you ever thought you needed for a motor with 4, 6, or even 8 wires! Not to worry, there’s an important reason for that. Common steppers pretty much come in two common varieties: bipolar with 4 wires and unipolar with 6 wires. We will not be covering 8 lead steppers here.
A bipolar motor can be simplified as having two DC coils with two leads a piece:
Check the datasheet or website for your motor to figure out which color wire corresponds to which lead, or you can use a multimeter with a continuity test. The leads that make the multimeter beep are indicate leads connected to a single coil.
A unipolar motor adds to connections to the middle of each coil. This allows you to use it as bipolar, by ignoring the middle leads. By connecting the middle wire to ground, you can energize half the coils to move the motor in one direction or energize the other half to move the motor in the opposite direction.
Now you can go out and get your projects moving! For an idea of where to start, here are a few projects we have made that you can use for inspiration: