• Created by Unknown User (anttijma), last modified by Unknown User (henritur) on 10.12.2014

Introduction

First we had to think of a really crucial technology concerning mankind. We thought of a generator, since it is almost the only source to generate electricity. The generator was already taken so we thought of another invention which has a great impact on our everyday life. Combustion engine was one invention that crossed our minds, but we thought that it really wasn’t that good, because it uses fossilized energy sources and one day it will become obsolete. We decided to choose electric motor, because it uses electricity to transform it to kinetic energy. Electricity could be produced with sustainable methods and therefore electric motors will be the future choice.

What makes it so important? Most electric innovations are run by electric motors and nowadays electricity is used everywhere. The motors are very flexible concerning especially sizes of the engine. We couldn’t imagine a combustion engine which could fit in your pocket, but there are really small electric motors. Electricity (fuel for the engine) is easy to transport and electric motors itself are basically pollution free.

Theory        

Our next task was to think about the physics involved in the invention and application of the electric motor. We had all studied quite a lot of physics before so it was pretty easy to come up with many formulas that have an effect in the physics of an electric motor. Main thing in this face was that we found out that it actually engages a lot of different applications of physics. The main areas of physics were mechanics, magnetism and electricity. Below is some of the formulas involved with this innovation.

 

Magnetism
  • Magnetic force
    F⃗ =qv⃗ ×B
    F=qvBsinθ
  • Electromagnetic induction
    e=−dΦ/dt
    Φ=BA
    e=−NABd/dt

 

Mechanics
  • Newton
    F=ma
  • Circular motion
    a=v^2/r
    v=2
    a=
  • Energy
    Ep = mgh
    E    k = 1/2mv2
    Ep + Ek = Etotal

 

Electricity

 

Electric Power
P = V I
P = R I2
P = V2/ R

 Electric Current

I = V / R
I = P / V
I = (P / R)^½

 Electric Resistance

R = V / I
R = V^2/ P
R = P / I^2

 

 

Electrical Motor Efficiency

μ = 746 Php / Pinput_w where
μ = efficiency
Php = output horsepower (hp)
Pinput_w = input electrical power (watts)

 Electrical Motor - Power

 P3-phase = (V I PF 1.732) / 1,000
where P3-phase = electrical power 3-phase motor (kW)

 Electrical Motor - Amps

I3-phase = (746 Php) / (1.732 V μ PF)             (7)
where I3-phase = electrical current 3-phase motor (amps)

 

 

Searching information was the most fun to do, because at this stage we decided to build our own electric motor. We did this decision based on the fact that there are a lot of reliable sources where we could find information on electric motors and we actually found some basic models already. We listed several links from the internet what we used to get the information. All the links seemed really reliable, also because we can inspect them in a critical common sense manner.

So basically what we found out is that the very raw basic function of an electric motor is that it’s based on at least two magnets, which create rotational motion. The essence of the electric motor is an electro magnet. It is essential, because to create the rotational motion the polarity of the magnet has to be changed at the right time. It will keep the motion going. The motion is based on magnetism. North and south poles tend to attract each other and south and south or north and north poles on the other hand tend to repel each other. So when the electro magnet is connected to a battery it will get polarized and thus get affected by either repelling force or attracting force. It will turn a half round over the axle and stop. Now the point is to change the polarity of the electro magnet just before it stops, so it will continue the motion, but to the other way. This will create the continuous rotational movement which is common for a motor. There are other applications as well and especially the number of poles may vary on depending on the type of the motor.

In the above picture there are two magnets in the motor: The armature (or rotor) is an electromagnet, while the field magnet is a permanent magnet (the field magnet could be an electromagnet as well, but in most small motors it isn't in order to save power).

Questions about electric motors

Why does the coiling have an effect on the rotation direction of the motor?

It doesn’t affect the direction of the rotation. The only thing that affects it is the direction of the current applied to the coil. You can make difference in the outcome of an electric motor by using different coiling techniques.

The simulation results show that the winding method has no effect on electromagnetic field distribution. However, it is able to affect the magnitude of the magnetic field and induced current. In three winding methods (solenoid winding, pancake coil winding and multi layer winding), the pancake coil winding makes the coil produce the biggest magnetic flux density and current density. The magnetic field attenuation of the coil in pancake coil winding is the slowest. (Effect of the Different Winding Methods of Coil on Electromagnetic Field during Transcranial Magnetic Stimulation. Shuo Yang, Guizhi Xu, Lei Wang and Xiu Zhang)


What are the most commonly used electric motor parts?

 

- Stator
Is usually a permanent magnet (or magnets) around the edge of the motor case which remains static, therefore it’s called a stator.  The stator may act as the field magnet, interacting with the armature to create motion, or it may act as the armature, receiving its influence from moving field coils on the rotor.

- Rotor
Rotates because the wires and magnetic field of the motor are arranged so that a torque is developed about the rotor's axis.The coil is inside the stator and it’s mounted on an axle that spins around at high speed.This is called the rotor. The rotor also includes the commutator.

- Coils (armature)
An electromagnetic coil is an electrical conductor such as a wire in the shape of a coil, spiral or helix. In electric motors coils are used as stator, rotors or both. Their purpose is to generate a magnetic field.

- Commutator
A commutator is the moving part of a rotary electrical switch in certain types of electric motors or electrical generators that periodically reverse the current direction between the rotor and the external circuit, therefore creating the continuous loop that is better known as circular motion.

- Axle
The axle is the central piece of the rotating device. Usually there are coils and commutators attached to the axle

- Brushes
A brush is a device which conducts current between stationary wires and moving parts, most commonly in a rotating shaft

                

What kind of different electric motors there are?

Electric motors operate on three different physical principles: magnetic, electrostatic and piezoelectric. The most common principle used in electric motors is magnetic. Magnetic fields are formed by the rotor and the stator in magnetic motors. The product between these two fields gives rise to a force, and thus a torque on the motor shaft. One, or both, of these fields must be made to change with the rotation of the motor. This is done by switching the poles on and off at the right time, or varying the strength of the pole. The main types are DC motors and AC motors, the former increasingly being displaced by the latter. AC electric motors are either asynchronous or synchronous. Once started, a synchronous motor requires synchronism with the moving magnetic field's synchronous speed for all normal torque conditions. In synchronous machines, the magnetic field must be provided by means other than induction such as from separately excited windings or permanent magnets. It is usual to distinguish motors' rated output power about the unity horsepower threshold so that integral horsepower refers to motor(s) equal to or above, and fractional horsepower (FHP) refers to motor(s) below, the threshold.

 

 

Electromagnetic energy to matter

Energy as a concept is very intangible. In physics energy is the ability to do work or cause changes in matter. This leads us to a conclusion that energy transfers basically to make changes on either the matter itself or to create some kind of movement (the movement can be small, fast or even invisible).

 

The energy transfer happens between at least two systems, when an amount of energy crosses the boundary between the systems. This will cause a loss of energy to at least one system and an increase of energy to the other(s). In this transaction the amount of energy is always conserved and the amount of loss to losing systems equal the amount of increase to the other systems. Energy is something that can't be created or destroyed (as far as we know), instead just transformed from one form to another.

 

An electric motor is basically a machine, which has only one job. To convert electric energy to mechanical energy. In this invention the electric energy forces the matter to move. Basic function of an electric motor is that it’s based on at least two magnets, which create rotational motion. The essence of the electric motor is an electro magnet. The electro magnet is the thing which receives the electrical energy. It is essential, because to create the rotational motion, the polarity of the magnet has to be changed at the right time. It will keep the motion going. The motion is based on magnetism. The device uses electromagnetic (or magnetic) forces to transfer the energy to mechanical energy. North and south poles tend to attract each other and south and south or north and north poles on the other hand tend to repel each other. So when the electro magnet is connected to a battery, with a charge (energy source), it will get polarized and thus get affected by either repelling force or attracting force. It will turn a half round over the axle and stop. Now the point is to change the polarity of the electro magnet just before it stops. This is done usually with commutators. Thats how it will continue the motion, but to the other way. It will create the continuous rotational movement which is common for any kind of motor. There are other applications as well and especially the number of poles and magnets may vary on depending on the type of the motor.


 

Why photons are not visible in an electric motor?

Photon is a gauge boson, which is a bosonic particle. The modern concept of photons was developed by Albert Einstein. Gauge bosons carry any fundamental interactions of nature. Photon carries the electromagnetic interaction.  Every interaction of nature is carried by gauge bosons, except gravity (see graviton theory). Photons are commonly known as the quantum of light and all other forms of electromagnetic radiation. The quantum theory suggests that energy and matter are quantized. A quantum is the minimum amount of any physical entity involved in an interaction.


Electric motors, like mentioned above, are based on magnets and electricity. Electricity is basically the movement of particles with electric charge. In metals (wires) these particles are usually electrons. In classical physics electromagnetic phenomenons are described by Maxwell's equations. Maxwell stated that an electric charge is always circulated by an electric field and an electric current is always circulated by magnetic field. Maxwell formed his equations by combining and adding laws by Ampere, Gauss and Faraday. According to Maxwell's equations electromagnetic radiation is moving at the speed of light and therefore is actually a form of light, or more accurately, light is a form of electromagnetic radiation. Electromagnetic radiation on the other hand is the waves of an electromagnetic field.  Magnetic fields are formed from electromagnetic radiation. Magnets have magnetic fields and also electromagnets have electric fields.


Now photons are the quanta of electromagnetic radiation and the carriers of fundamental interactions called electromagnetic interactions. Photons are the particles, which causes electromagnetic fields to happen. In an electric motor photons first make the electrons move (current) and then while electrons move they cause the magnetic field. When the magnetic fields interact with each other the photons carry a force between them forcing them to move. Why photons are not visible in an electric motor is, due to the visible spectrum of light. The electromagnetic radiation involved in our invention doesn’t involve any wavelengths that are visible.


What are drives?

Main article: What are electric drives

The basic function of a drive is to control the flow of energy from the grid to the process. Energy is supplied to the process through the motor’s axle. There are two different physical variables for the axle, torque and speed. To control the flow of energy, these quantities have to be controlled. The terms for the control are either speed control or torque control. Torque or speed control may be achieved with variable speed drives (VSD’s) usually in DC motors (also in AC motors) and variable frequency drives (VFD’s) in AC motors. When the drives operate in torque control mode, the speed is determined by the load and when operated in speed control, the torque is determined by the load. VSD’s can also be used to transform mechanical energy to machinery. DC motors are much simpler to control by using drives. There are almost infinite number of different types of drives, but the main functions are explained below.

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