Electric Motors

This page covers electric motors

Claimed by Komal Hirani: khirani6

The Main Idea

Electric Motors

Motors convert electrical energy into mechanical energy. Our everyday routines heavily rely upon the electric motors in common applications such as refrigerator compressors, water pumps, elevators, clocks, and cars. Electric motors are a common application of the torque that a magnetic field exerts on a current-carrying coil. In order for motors to function the way that they do, the current-carrying coil needs to turn continuously. In order for the current-carrying coil to turn in such a way, you need to make electrical connections to the coil in such a way that just as it is coming to its stable position, you reverse the direction of the current. A simple way to achieve this continuos motion is through a "split-ring commutator" that automatically changes the direction of the current through the coil at just the right moment. Metal tabs make contact between the battery and the commutator, which allows current to flow and for the motor to rotate.

Below is a picture that shows the overall design of a single-loop motor driven by direct current (DC):

A Mathematical Model

A motor's mechanical output is calculated as follows:

[math]\displaystyle{ P_{em} = F\times{v} }[/math] (watts).

with Force (F) expressed in Newtons and velocity (v) expressed in meters per second.

To calculate the motor's efficiency, you divide the mechanical output power by the electrical input power:

[math]\displaystyle{ \eta = \frac{P_m}{P_e} }[/math]

Generators

Commercial generators rotate a loop of wire in a magnetic field. This is the ideal construction because it is much easier to arrange and it experiences very low friction on the axle. The magnitude of the magnetic force on a charge carrier q is F=qvBsinθ. Additionally, the magnetic force is uniform throughout the wire, thus motional emf is the force multiplies by the length, divided by the charge… emf=2vBwsinθ. This equations can also be written as emf=wB(hw)sin(wt). The current inside of this type of current varies in a sinusoidal. This type of current is known as alternating current or AC. AC is what comes out of the wall while direct current or DC is what flows through a battery. Direct current is one-direction current, while alternating current in bi-directional.

Check out this awesome video to help understand the different between AC and DC

Media:"https://www.youtube.com/watch?v=SAvYvfg41FU"

A Mathematical Model

Calculate the work done on a generator...

When a loop is rotated through a small angle ∆θ, we move each end a short distance [h/2 ∆θ], thus...

                          ∆W=2[IwBsinθ][h/2 ∆θ]

dividing this result by ∆t....

                  dW/dt=2[IwBsinθ][h/2  dθ/dt]=I[Bwhωsinθ]

this can be rewritten as...

                            dW/dt=I[RI]=RI^2

This calculation give the power dissipated in the resistor at this instant. Essentially this tells that a generator is not "generating" something from nothing. Instead it is converting mechanical power into electrical power.

Connectedness

How is this topic connected to something that you are interested in? a. Motors are heavily used in robotics, which is something that I have been interested in ever since I was on my high school's robotics team. In robotics, we heavily rely upon motors to power the robot and allow the robot to perform as it is supposed to. I am interested in going into the robotics industry, particularly the electronic component of the industry, so knowing how motors work is very useful to me.

b. Generators are connected to my everyday life because the provide energy to the power-grid that ultimately allows the United States to function in the manner that it does. Something as simple as turning on a lite bulb or charging a cell phone would simply not be possible without generates. I guess I could say I am interested in maintaining the quality of life I have right now, so I am definitely definitely interested in generators.

How is it connected to your major? a. Even though I'm a Computer Science major, I want to eventually go into the robotics industry. In robotics, when coding for any robot, you need to know how the electronic components of the robot are able to produce energy for the robot to function. You need to be able to write code that is able to be translated by the CPU and will allow each controller and motor to function.

b. Generators are related to my material science and engineering because scientists are now looking to harvest power, "generate power", from nano-scale systems. Researchers are doing this with many different materials and synthesis methods. The idea behind nano-scale thermoelectric, magnetic, and/or electric power generation is a hot research topic among leading material science researchers in the field.

This image shows the schematic for a nano-scale system that generates power from acoustic vibrations.

Is there an interesting industrial application? a. Like I said, motors are heavily used in robotics in order for robots to properly move and carry out the tasks the robot was programmed to do. Robots such as the robotic arm pictured below need motors in order to generate enough power for the arm to move in different directions:

b. The industrial applications of generators are endless. The generators can be coal, water, or nuclear based and the construction of each one of these is a huge part of industry. Then there is the actual generation and allocation of power, which involves the entire power grid. All of this is super fascinating because there are rising concerns about the potential affects of the destruction of the power grid. These affects could have detrimental affects on all aspects of life. Unless you live of the grid, chances are your life would be turned upside down.

History

In the early 1800's, Orstead, Ampere, and Faraday laid down the foundation for building electric motors by introducing the basic principles of electromagnetic induction. In 1820, Orstead had confirmed that there was a relationship between electricity and magnetism. In the same year, Ampere invented the solenoid and discovered Ampere's Law, which helps describe magnetic fields produced by motors and solenoids. In 1821, Faraday successfully converted electrical energy into motion and created the simplest form of the electric motor. In 1832 however, William Sturgeon introduced the first ever commutator DC electronic motor, and later on in 1837, Thomas Davenport created a DC motor for commercial services and received the first US electric motor patent, which is why a lot of people associate him with the first person to invent the electric motor.

Michael Faraday also discovered the operating principle of electromagnetic generators between the year 1831-1832.The principle, later coined as Faraday's Law, simply put is that an electromotive force is generated in a conduction which encircles a changing magnetic flux. The first generators that were made were disk generators and direct current generators. Later come alternating current generators. As science had developed so to have the generator technology. Generators are now designed in both DC homopolar and MHD generators, as well as AC induction, linear electric, variable speed constant frequency generators. They exist on vehicles, bicycles, sailboats, and are essential components to every aspect of our daily life.