Electric Motor - Know Its Types, Properties and How to Choose It

WHAT ARE MOTORS?

The basic idea of an electric motor is really simple. Electricity input into it at one end rotates an axle (metal rod) at the other end generating the power to drive machine of any kind. Try this! Take a length of ordinary wire, make it into a big loop, and lay it between the poles of a powerful, permanent horseshoe magnet. Now if you connect the two ends of the wire to a battery, the wire will jump up briefly. When an electric current starts to creep along a wire, it creates a magnetic field all around it. If you place the wire near a permanent magnet, this temporary magnetic field interacts with the permanent magnet's field. You'd know that two magnets placed near one another either attract or repel. In the same way, the temporary magnetism around the wire attracts or repels the permanent magnetism from the magnet, and that's what causes the wire to jump. For small DIY projects DC motors are preferred as they are easy to manage and safe to use.

Types of DC Motors-

DC Brush Motors

DC Brushless Motors

Vibration Motors

Servo Motors

Stepper Motors

Properties of motors to consider?

Current

Current powers the motor, however, too much current could damage it. For DC motors, operating and stall current are two important factors to be considered. Operating current is the average amount of current a motor is expected to draw under typical torque. Stall current applies enough torque for the motor to run at stall speed, or 0RPM. This is the maximum amount of current the motor should be able to draw, as well as the maximum power when multiplied by the rated voltage. Heat sinks are important as they are constantly running the motor or are running it at higher than the rated voltage in order to keep the coils from melting.

Voltage

Voltage is used to keep net current flowing in one direction and to overcome back current. The higher the voltage, the higher the torque. The voltage rating of a DC motor indicates the most efficient voltage while running. Be sure to apply the recommended voltage. If the volts applied are too few, the motor will not work, whereas too many volts can short windings resulting in power loss or complete destruction.

Torque

Operating and stall values also need to be considered with torque. Operating torque is the amount of torque that the motor was designed to give and stall torque is the amount of torque produced when power is applied from stall speed. You should always look at the required operating torque, but some applications will require you to know how far you can push the motor. For example, with a wheeled robot, good torque equals good acceleration but you must make sure the stall torque is strong enough to lift the weight of the robot. In this instance, torque is more important than speed.

Velocity

Velocity, or speed (RPM), can be complex regarding motors. The general rule is that motors run most efficiently at the highest speeds but it is not always possible if gearing is required. Adding gears will reduce the efficiency of the motor, so take into account speed and torque reduction as well.

CHOOSING MOTORS AND SERVOS

It really boils down to how you're going to use the motors or what is the function of your robot. The most common example of a motor is a DC motor and its basic job is to rotate. They come in different sizes and shapes but have the basic function of providing continuous rotation. A servo on the other hand is limited in its range of motion so for instance if you put a on that servo horn and I rotate that you should be able to see that it only goes a certain distance about a little bit slightly more than 180 degrees that's the limited amount of range of motion that you get from a servo now the big benefit is that this servo will know where it's at so we can tell it to go to a definite spot in that range of motion and it will move to that spot each and every time.

That's one of the big advantages of most servos now there are other types of servos as well we have a continuous rotation type of servo that is more like the DC motor in the fact that it provides continuous rotation and the same thing applied for motors, that there are some additions to motors called encoders that you can put on a DC motor that will allow that to actually keep track of where it's at and moved to a certain position instead of rotating continually Confused right? People often wonder how do I know which one to choose in which application and so we now start considering the downsides of that specific application. We usually see that DC motors weighs a little bit more compared to Servos therefore weight becomes a consideration on the opposite side of that it has plenty of power. The servos is lightweight but not near as much powerful.

So now we look at what are we trying to build. If we have a use case which requires a lot of power say like a gear movement we use a DC Motor, if we need precise movement say in a robotic arm we use a servo. It really becomes an example or a case where you want to look at how you intend to use or need to use your up source of power and where it's going to be used that helps you decide whether we need a DC motor or a servo or maybe one that has an encoder on it that allows us to track my position but still has power or maybe a servo that has continuous rotation but we don't need the weight so those are the type of things that you're going to look at and help you decide which one you want to use.

Properties	Encoder DC Motor	Servo Motors	Stepper Motors

Current	High	Low	Low
Torque	Low	Highest	Mediocre
Torque Flexibility	Fixed	Controllable	Fixed
Micro-Stepping	Not Possible	Possible	Possible(reduces torque by 30%)
Velocity	High- Very High	Average	Low
Voltage	Low-voltage	Low-voltage	High-voltage
Heat Dissipation	High	Low	Average
Cost	Cheap	Cheap	Expensive
Feedback Analog/Digital	With Encoder- Yes Without Encoder- No Analog	Yes Digital	Yes Digital
Noise	Low	High	Very High
Driver Electronics	Simple- Brush DC Motor Complex- Brushless DC Motor	Simple	Complex