solving standard problems in mechanical engineering(Task that I did recently at university)

The question:

You are supplied with output data from the CAD model of a prototype car brake disc. The data states the mass moment of inertia of the brake disc about the rotational axis. You are required to:

1. Determine the mass moment of inertia experimentally by oscillating the brake disc as a compound pendulum.	See the theory on the following page. You should consider the design of your experiment including: - How many swings should be counted (see Measurement and uncertainty Lab, simple pendulum part) - Likely sources of error and their magnitude, think about the things you will need to measure and time. – See the reaction time exercise on Moodle.
2. Use theory from lectures and any other relevant sources to estimate the mass moment of inertia via hand calculation.	See question 2 from the Rotational Dynamics Tutorial (29th January- 4th February) You will need to make assumptions, these should be clearly stated in your report.
3.    Develop/Design another experimental method that could be used to determine the mass moment of inertia for the object. This should include: a.    The underpinning background theory for the method b.    The method for gathering the required data c.    The process for analysing the gathered data	Suggested methods you may wish to investigate are given below, this is not an exhaustive list: i.      Falling mass (dynamics) (e.g. Question 5 of the Rotational Dynamics tutorial) ii.     Torsional pendulum ii.     Tri-filar suspension When researching ideas we suggest you search for methods/labs for determining the mass moment of inertia of flywheels. You do not need to carry out this experiment, it should be part of your report as an appendix.
4.    Present your findings, including a discussion of your results and the stated value from CAD.

 My answer to the question above...

❖ Abstract In this experiment we attempted to swing a brake disc twenty times and measure the time that it takes it to do that amount of swings using a timer.

The brake disc was set up on it inside ring to let the disc set freely then we moved it on it axes to either left/right side and let it swing, meanwhile one of the student in my group was holding a timer to get the most accurate results for the 20 swings.

We repeated the same process for four times to reduce the uncertainty for our own results, then by calculating the results and put it in the right equations we were able to calculate the Mass Moment of Inertia.

❖ Theory In order to find the mass moment of inertia I had to use many equations that been used for previous experiment such as the Pendulum experiment. By taking the average value from the provided data I was able to find the frequency f which I got it by dividing 20 by the average value of the time F = 𝑆𝑤𝑖𝑛𝑔𝑠 𝑇𝑖𝑚𝑒 𝑡𝑎𝑘𝑒𝑛 , from that I got the time period which is equal to one over frequency. Then I calculated the angular velocity ω, ω = 2 𝜋F. Afterward I Had to find the value
of radius of gyration about the centre of gravity 𝐾𝐺, ω = √
𝑔 ℎ 𝐾𝐺2+ℎ2
 . I rearranged the
equation to calculate 𝐾𝐺, 𝐾𝐺2= (𝑔 ℎ 𝜔2
) - ℎ2. In the end to get to calculate mass moment of inertia 𝐼𝐺 I used this equation 𝐼𝐺 = m 𝐾𝐺2. But I think all could be written in one equation which could make calculations easier by replacing 𝐾𝐺2 and ω to get: 𝐼𝐺 = 𝑚 𝑔 ℎ (2𝜋𝑓)2 − ℎ2

❖ Experimental Methods The method was to put the brake disc on a small rod like shown in picture and move it to the side by small distance on it axes and let it go with initial speed of 0, and measure how long does it take for the disc to make 20 full oscillations, this experiment were repeated 4 times for more accurate measurement, using the same conditions and move it exact the same distance we were able to get four different measurement but close enough to be accurate of this experiment.


❖ Results Task 1: Ave value = 17.19+17.29+17.18+17.21 4 = 17.217≈ 17.22 s 𝑓 = 20 17.22 =  1.161 𝐻𝑍

𝑇𝑝 = 1 𝑓
 = 1/1.161 = 0.861 s 𝜔 = 2𝜋𝑓 = 7.29 rad/s
ω = √𝑔 ℎ 𝐾𝐺2+ℎ2

𝜔2 = 𝑔 ℎ 𝐾𝐺2 + ℎ2
 𝐾𝐺2= (𝑔 ℎ 𝜔2 ) - ℎ2 = 9.81×68.5 ×10−3 7.292− (68.5 × 10−3)2 = 7.949× 10−3
𝐾𝐺 = √ 7.949 × 10−3

𝐾𝐺 = 89.161x10−3

𝐼𝐺 = m 𝐾𝐺2= 3.55 × 7.949 × 10−3 = 0.0282 Kg.𝑚2
 Uncertainty: Standard deviation = √∑(𝑟𝑒𝑎𝑑𝑖𝑛𝑔𝑖−𝐴𝑣𝑒𝑟𝑎𝑔𝑒)2 𝑛 𝑖=1 𝑛−1 = √(17.19−17.22)2 4−1
 = 0.01732
Standard Uncertainty = 𝑆𝑡𝑎𝑛𝑑𝑎𝑟𝑑 𝑑𝑒𝑣𝑖𝑎𝑡𝑖𝑜𝑛 √𝑛 = 0.01732 √4 = 8.66𝑥10−3.

Task 2:  I broke the brake disc to three shapes the out-disc part(shape1), the ring which is the middle part(Shape2) and the small inside-disc(shape3). I didn’t include with my calculation the chamfers and the small holes, because their mass is too small to be considered in our experimental sample. The density 𝜌 = 7200 kg/ 𝑚3 from the CAD drawing.

Shape1: 𝑟𝑜 = 119.5𝑚𝑚, 𝑟𝑖 = 68.5𝑚𝑚 and the thickness = 12mm 𝑉1 = 𝜋(𝑟𝑜2 − 𝑟𝑖2)𝑡 = 𝜋(0.11952 − 0.06852) × 0.012 = 3.614× 10−4 𝑚3 𝑚1 = 𝜌 × 𝑣1 = 7200 × 3.614 × 10−4 = 2.6 Kg 𝐼1 = 𝑚1 2 (𝑟𝑜2 + 𝑟𝑖2) = 0.0246 𝐾𝑔.𝑚2

Shape2: : 𝑟𝑜 = 72.5𝑚𝑚, 𝑟𝑖 = 68.5𝑚𝑚 and the thickness = 4mm 𝑉2 = 𝜋(𝑟𝑜2 − 𝑟𝑖2)𝑡 = 𝜋(0.07252 − 0.06852) × 0.004 = 7.087× 10−6 𝑚3 𝑚2 = 𝜌 × 𝑣2 = 7200 × 7.087 × 10−6 = 51.02× 10−3 Kg 𝐼2 = 𝑚2 2 (𝑟𝑜2 + 𝑟𝑖2) = 0.2537 × 10−3 𝐾𝑔.𝑚2

Shape3:  𝑟𝑜 = 68.5𝑚𝑚, 𝑟𝑖 = 31.75𝑚𝑚 and the thickness = 8mm 𝑉3 = 𝜋(𝑟𝑜2 − 𝑟𝑖2)𝑡 = 𝜋(0.06852 − 0.031752) × 0.008 = 9.259× 10−5 𝑚3
𝑚3 = 𝜌 × 𝑣3 = 7200 × 9.259 × 10−5=  0.6666 Kg  𝐼3 = 𝑚3 2 (𝑟𝑜2 + 𝑟𝑖2) = 1.8999 × 10−3 𝐾𝑔.𝑚2

Total: 𝐼 = 𝐼1 + 𝐼2 + 𝐼3 = 0.02675 Kg.𝑚2 ≈ 0.027 Kg.𝑚2


❖ Discussion By looking at Task1 the answer was pretty accurate, but to get to the definitive answer I went through a lot of calculations and rearranged some equations too, I had to consider the difference in units and change some values from millimetres to metres.

In Task2 the answer wasn’t too accurate although calculation process was very slow and distractive so there was very high chance of making mistakes, some very small values like chamfer and the small holes was hard to calculate so I had to ignore it small value comparing to the disc value.

❖ Conclusion By comparing the results and the process I came to conclusion that CAD is faster and more accurate to provide with a good valuation of the mass properties, therefore its essential for an engineer to considerable CAD skills in order of saving much time and much effort.


❖ Appendix An alternative method I though of is by hanging the brake disc using a sting attached to it from the very top of the disc then by rotating the disc on it Y axes clockwise then release it when the string have enough tension to rotate the disc anticlockwise, at the release time a timer should start and then you count how many turns did the disc make until it start rotating clockwise again, then you count the total turns until the rest position of the disc.

By finding the string tension and the weight that affect the force diagram you will be able to find the force and from there you can find the acceleration and from the acceleration we can find the radius of gyration about the center of gravity and in the end we find the mass moment of inertia.

The End
My result came out to be 48% not quite sure where my mistakes was (since we don't get a feed back with where I made mistakes) but hopefully you find my assignment helpful and intersting enough for you.
Thank you

TeslaCoin - The Currency to Finance Free Energy - "Nikola Tesla Vs. JP M...

Explain the principles (rules) that underpin reporting and recording accidents and incident.

An accident is an unplanned or uncontrolled event which has led to or could have led to injury to people, damage to plant, machinery or the environment or cause some other losses.

An incident is an instance of something happening; an event or occurrence.

Accident and incidents are things that could happen in any engineering workplace or organisation during the work. A worker is more vulnerable to and accident because they are more present in the workplace than the visitors and the employer. Because of this the reporting and recording of accidents and incidents becomes very important to the engineering organisation, so they must have the health and safety reporting system in place, especially when that reporting underpins from the RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations 2013) which lies under the health and safety at work etc act 1974. This puts duties on employers, the self-employed and people in control of work premises (the Responsible Person) to report certain serious workplace accidents, occupational diseases and specified dangerous occurrences.

RIDDOR is the law that requires employers, and other people in charge of work premises, to report and keep records of: work-related accidents which cause deaths, work-related accidents which cause certain serious injuries, diagnosed cases of, certain industrial diseases; and certain dangerous occurrences. All that must be reported to the relevant enforcing authority, either the local authority's Environmental Health dept. or the Health and Safety Executive (HSE), without delay.

All incidents are recorded, however not all are reported. Accident and incident are reportable. Types of injuries which are reportable include the death of any person, specific injuries to workers which include fractures, other than to fingers, thumbs and toes, amputation of an arm, hand, finger, thumb, leg, foot or toe,  any injury likely to lead to permanent loss of sight or reduction in sight in one or both eyes, any crush injury to the head or torso, causing damage to the brain or internal organs, any burn injury including scalding covers more than 10% of the whole body’s total surface area or causes significant damage to the eyes, respiratory system or other vital organs and Any loss of consciousness caused by head injury or asphyxia.
Only responsible persons including employers, the self-employed and people in control of work premises should submit reported under RIDDOR.

The information provided through recording and reporting enables the enforcing authorities either Health and Safety Executive (HSE) or local authority Environmental Health, to identify where and how risks arise, and to investigate serious accidents.

All incidents can be reported online but a telephone service is also provided for reporting fatal and specified injuries only.

A report must be received within 10 days of the incident. Accident are reported on the online form F2508

And in the end the HSE and local authority enforcement officers are not an emergency service it’s just who is responsible to for the accident and incident recording and reporting.

Controlling Hazards 3

Describe how control measures are used to prevent electrical accident.

A hazard is anything that may cause harm or injury. A control measure is any measure taken to eliminate or reduce the risk of injury or bodily harm when the workers doing them job and treating with equipment might cause harm for himself and for anybody around him. Control measures include actions that can be taken to reduce the potential of exposure to the hazard, or the control measure could be to remove the hazard or to reduce the likelihood of the risk of the exposure to that hazard being realized. A simple control measure would be the secure guarding of moving parts of machinery eliminating the potential for contact.

Electricity can kill or severely injure people and cause damage to property. All these accidents are reported to the Health and Safety Executive (HSE). However, you can take simple precautions when working with or near electricity and electrical equipment to significantly reduce the risk of injures your workers and others around you.

Whenever possible consider the best way to control a hazard is to apply the control at the source of the hazard. The ultimate control is actual removal of the hazard from the workplace. Controls the hazards do not exactly remove the hazard, but provide information’s to alert the worker that a hazard exists.

Controls at the worker include personal protective equipment (PPE), training in safe work ways, administrative procedures and disciplinary actions. Controls at the worker may be subject to human mistake and should be considered the last alternative in a list of hazard controls, especially in the case of PPE For example, sometimes workers don’t wear their PPE correctly and that sometimes make the controlling hazards more difficult and hard to Implementation.

The basic element of any management program for PPE should be an in depth evaluation of the equipment needed to protect against the hazards at the workplace. The evaluation should be used to set a standard operating procedure for personnel, and then train employees on the protective limitations of the PPE, and on its proper use and maintenance.

Using PPE requires hazard awareness and training on the part of the user. Employees must be aware that the equipment does not eliminate the hazard. If the equipment fails, exposure will occur. To reduce the possibility of failure, equipment must be properly fitted and maintained in a clean and serviceable condition.

Administrative controls, administrative controls include adopting standard operating procedures or safe work practices or providing appropriate training, instruction or information to reduce the potential for harm and adverse health effects to persons. Isolation and permit to work procedures are examples of administrative controls.

Those using or working with electricity may not be the only ones at risk. Everyone around the worker who treating with the electricity is amenability to the burning dangerous because of Short circuit during the worker do his job. In order of that there are too many precincts to controlling these hazards for example, choose equipment that is suitable for its working environment, make sure that equipment is safe when supplied and that it is then maintained in a safe condition and make sure that equipment is safe when supplied and that it is then maintained in a safe condition.

All electrical equipment, including portable equipment and installations, should be maintained to prevent danger; this is a requirement of the Electricity at Work Regulations 1989. These Regulations state principles of electrical safety and apply to all electrical systems and equipment.

There is an increased risk of this happening if the equipment isn't used correctly, isn't suitable for the job, or is used in a harsh environment.

More complicated tasks, such as equipment repairs or alterations to an electrical installation, should only be carried out by people with knowledge of the risks and the precautions needed.

You must not allow work on or near exposed, live parts of equipment unless it is absolutely unavoidable and suitable precautions have been taken to prevent injury, both to the workers and to anyone else who may be in the area.

Overhead power lines, over half of the fatal electrical accidents each year are caused by contact with overhead lines. When working near overhead lines, it may be possible to have them switched off if the owners are given enough notice. If this cannot be done, consult the owners about the safe working distance from the cables.

555Timer circuit assignment VERY RARE

Explanations of each component

LED:

An LED (light-emitting diode) is a semiconductor device that emits visible light when an electric current passes through it. The LEDs can help indicate the status of the circuit.

Resistor:

The main function of resistors in a circuit is to control the flow of current to other components. It can protect other components from getting burnt or destroyed. In the circuit the resistors are protecting the LEDs from receiving too much current.

Capacitor

A capacitor stores the electrical energy and gives this energy again to the circuit when necessary. It is used to maintain a power supply temporarily when the battery is off.

555 timer:

IC The 555 timer is an integrated circuit as a chip which is used in a variety of timer, pulse generation, and oscillator applications. This device consists of 8 pins. Pin 1 is connected to ground. Pin 2 is the trigger, which works like a starter’s pistol to start the 555 timer running. Pin 3 is the output pin. Pin 4 is the reset pin, which can be used to restart the 555’s timing operation. Like the trigger input, reset is an active low input. Pin 5 is the control pin. Pin 6 is called the threshold. The purpose of this pin is to monitor the voltage across the capacitor that's discharged by pin 7. Pin 7 is called the discharge. This pin is used to discharge an external capacitor that works in conjunction with a resistor to control the timing interval. Pin 8 is connected to the positive supply voltage.

SN7447

IC The IC7447 is a BCD to 7-segment pattern converter. This chip is used to drive 7 segment display. The SN7447 takes the Binary Coded Decimal (BCD) as the input and outputs the relevant 7 segment code. This IC has active low outputs which are made to switch on and off particular LEDs of the display. All the 8 anode legs uses only one cathode, which is common.

SN7493

IC This is an up counter which is capable as acting as a multi-modulus counter. The 7493 has an internal architecture of 4 asynchronously connected J-K flip flops in toggle mode. Only a few pins in this IC are essential. The IC 7493 would be given input DCBA from the IC 7447 and the rest of the display connections are the same with the current limiting resistors. This process is simplified with this IC.

7 segment

display A seven-segment display (SSD), is a form of electronic display device for displaying decimal numbers. This display is arranged in a way in which it can display all numbers from 0 to 9. In this circuit, the display is used as a timer where the numbers increase from 0 till 9. 

Complete description of the circuit function.

Here is the circuit diagram of a seven segment counter based on the counter SN7493 IC. This circuit can be used in conjunction with various circuits where a counter to display the progress and add some more attraction.

The IC7493 changes when a pulse is applied. At the output the counter begins at 0. The maximum it would reach is 1. It has the input- following characteristics of the clocked D flip-flop but has two inputs, which are known and J and K. If the 2 outputs are different then the output takes the value of J at the next clock edge. The counter changes its count every time this happens. One of the outputs is equal to 2 inputs. The previous input which is stored latches and for this reason, the counter starts going up in numbers instead of continuing as a 0. Generally, synchronous counters count on the rising-edge which is the low to high transition of the clock signal and asynchronous ripple counters count on the falling-edge which is the high to low transition of the clock signal.

The 555 timer IC provides a very versatile, effective, and easy-to-use astable mode. It can also have the mark-space ratio altered almost limitlessly. A mark space ratio is present in this circuit due to the use of impulses. Mark space ratio in a pulse is the ratio of the duration of the positive-amplitude part of a square wave to that of the negative-amplitude part. An increase in current will lead to a decrease in frequency.

The used inputs of IC 7493 are given as inputs DCBA of the IC 7447 and the rest of the display connections are the same with the current limiting resistors. The required resetting connections have to be made. The 7493 has an internal architecture of 4 asynchronously connected J-K flip flops in toggle mode. Counting the flip flops can be achieved by changing the state on each of the clock cycle. The output of the flip flop completes one whole cycle after 2 clock cycles. Using this output as the input for the second would result in the second flip flop cycling at half of the rate of the first. Increasing the number of flip flops would increase the times you divide it by half. The SN7447 converts the binary data to digital code. The 7447 chip is used to drive 7 segment displays. The inputs DCBA often come from a binary counter. The way it is done is that the 7447 circuit decodes the binary coded decimal which it can then assign logic 0 for low and 1 for high.

Complete description of the circuit function.

Here is the circuit diagram of a seven segment counter based on the counter SN7493 IC. This circuit can be used in conjunction with various circuits where a counter to display the progress and add some more attraction.

The IC7493 changes when a pulse is applied. At the output the counter begins at 0. The maximum it would reach is 1. It has the input- following characteristics of the clocked D flip-flop but has two inputs, which are known and J and K. If the 2 outputs are different then the output takes the value of J at the next clock edge. The counter changes its count every time this happens. One of the outputs is equal to 2 inputs. The previous input

which is stored latches and for this reason, the counter starts going up in numbers instead of continuing as a 0. Generally, synchronous counters count on the rising-edge which is the low to high transition of the clock signal and asynchronous ripple counters count on the falling-edge which is the high to low transition of the clock signal.

The 555 timer IC provides a very versatile, effective, and easy-to-use astable mode. It can also have the mark-space ratio altered almost limitlessly. A mark space ratio is present in this circuit due to the use of impulses. Mark space ratio in a pulse is the ratio of the duration of the positive-amplitude part of a square wave to that of the negative-amplitude part. An increase in current will lead to a decrease in frequency.

The used inputs of IC 7493 are given as inputs DCBA of the IC 7447 and the rest of the display connections are the same with the current limiting resistors. The required resetting connections have to be made. The 7493 has an internal architecture of 4 asynchronously connected J-K flip flops in toggle mode. Counting the flip flops can be achieved by changing the state on each of the clock cycle. The output of the flip flop completes one whole cycle after 2 clock cycles. Using this output as the input for the second would result in the second flip flop cycling at half of the rate of the first. Increasing the number of flip flops would increase the times you divide it by half. The SN7447 converts the binary data to digital code. The 7447 chip is used to drive 7 segment displays. The inputs DCBA often come from a binary counter. The way it is done is that the 7447 circuit decodes the binary coded decimal which it can then assign logic 0 for low and 1 for high.

The following is a schematic drawing of the circuit. 

The following is a PCB layout of the circuit.  All the components have been set with a relevant layout and joined with tracks with each other.

The following are 3D visualisations of the circuit with the components and without the components. 

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Thanks for reading

Explain the features and characteristics and an application of types of DC MOTORS

Series motor:

A DC motor relies on the fact that like magnet poles repels and unlike magnetic poles attracts each other. A coil of wire with a current running through it generates an electromagnetic field aligned with the center of the coil. By switching the current on or off in a coil its magnetic field can be switched on or off or by switching the direction of the current in the coil the direction of the generated magnetic field can be switched 180°. A simple DC motor typically has a stationary set of magnets in the stator and an armature with a series of two or more windings of wire wrapped in insulated stack slots around iron pole pieces.

Construction of Series DC Motor

Construction wise this motor is similar to any other types of dc motors in almost all aspects. It consists of all the fundamental components like the stator housing the field winding or the rotor carrying the armature conductors, and the other vital parts like the commutation or the brush segments all attached in the proper sequence as in the case of a generic DC motor.

Yet if we are to take a close look into the wiring of the field and armature coils of this dc motor, it’s clearly distinguishable from the other members of this type. To understand that let us revert back into the above mentioned basic fact, that the motor has field coil connected in series to the armature winding. For this reason relatively higher current flows through the field coils, and its designed accordingly as mentioned below.

-The field coils of dc series motor are wound with relatively fewer turns as the current through the field is its armature current and hence for required mmf less numbers of turns are required.

-The wire is heavier, as the diameter is considerable increased to provide minimum electrical resistance to the flow of full armature current.

The DC or direct current motor works on the principal, when a current carrying conductor is placed in a magnetic field; it experiences a torque and has a tendency to move. This is known as motoring action. If the direction of current in the wire is reversed, the direction of rotation also reverses. When magnetic field and electric field interact they produce a mechanical force, and based on that the working principle of dc motor established.

Brushless DC motor

Brushless DC motor, also known as electronically commutated motors, are synchronous motors that are powered by a DC electric source via an integrated inverter/switching power supply. The rotor part of a brushless motor is often a permanent magnet synchronous motor, but can also be a switched reluctance motor, or induction motor.

 Brushless motors may be described as stepper motors; however, the term stepper motor tends to be used for motors that are designed specifically to be operated in a mode where they are frequently stopped with the rotor in a defined angular position.

Typical brushless DC motors use a rotating permanent magnet in the rotor, and stationary electrical current/coil magnets on the motor housing for the stator, but the symmetrical opposite is also possible. A motor controller converts DC to AC. This design is simpler than that of brushed motors because it eliminates the complication of transferring power from outside the motor to the spinning rotor. Advantages of brushless motors include long life span, little or no maintenance, and high efficiency. Disadvantages include high initial cost, and more complicated motor speed controllers. Some such brushless motors are sometimes referred to as "synchronous motors" although they have no external power supply to be synchronized with, as would be the case with normal AC synchronous motors.

Explain the features, characteristics and application of two different types of AC motor

AC motors operate with two rotating magnetic fields on the rotor and stator respectively. Pulling or pushing the poles of the two magnetic fields along, the speed of the stator rotating magnetic field and the speed of the rotor rotating magnetic field, which is relative to the speed of the mechanical shaft, must maintain synchronism for average torque production by satisfying the synchronous speed relation. Otherwise, asynchronously rotating magnetic fields would produce pulsating or non-average torque.

The two main types of AC motors are classified as induction and synchronous.

The induction motor always relies on a small difference in speed between the stator rotating magnetic field and the rotor shaft speed called slip to induce rotor current in the rotor AC winding. As a result, the induction motor cannot produce torque about synchronous speed where induction is irrelevant or ceases to exist.

In contrast, the synchronous motor does not rely on slip-induction for operation and uses either permanent magnets, salient poles, or an independently excited rotor winding. The synchronous motor produces its rated torque at exactly synchronous speed. The brushless wound rotor doubly fed synchronous motor system has an independently excited rotor winding that does not rely on the principles of slip induction of current. The brushless wound rotor doubly fed motor is a synchronous motor that can function exactly at the supply frequency or sub to super multiple of the supply frequency.

Single-phase induction motor

Three-phase motors produce a rotating magnetic field. However, when only single-phase power is available, the rotating magnetic field must be produced using other means.

A common single-phase motor is the shaded-pole motor and is used in devices requiring low starting torque, such as electric fans or the drain pump of washing machines and dishwashers or in other small household appliances. In this motor, small single-turn copper create the moving magnetic field. Part of each pole is encircled by a copper coil or strap; the induced current in the strap opposes the change of flux through the coil. This causes a time lag in the flux passing through the shading coil, so that the maximum field intensity moves across the pole face on each cycle. This produces a low level rotating magnetic field which is large enough to turn both the rotor and its attached load. As the rotor picks up speed the torque builds up to its full level as the principal magnetic field is rotating relative to the rotating rotor. Another common single-phase AC motor is the split-phase induction motor, commonly used in major appliances such as air conditioners and clothes dryers. Compared to the shaded pole motor, these motors can generally provide much greater starting torque.

 A capacitor start motor is a split-phase induction motor with a starting capacitor inserted in series with the startup winding, creating an LC circuit which produces a greater phase shift and so, a much greater starting torque than both split-phase and shaded pole motors. The capacitor naturally adds expense to such motors.

                           

Poly-phase synchronous motors

If connections to the rotor coils of a three-phase motor are taken out on slip-rings and fed a separate field current to create a continuous magnetic field, the result is called a synchronous motor because the rotor will rotate synchronously with the rotating magnetic field produced by the poly-phase electrical supply. Another synchronous motor system is the brushless wound-rotor doubly-fed synchronous motor system with an independently excited rotor multiphase AC winding set that may experience slip-induction beyond synchronous speeds but like all synchronous motors, does not rely on slip-induction for torque production.

Nowadays, synchronous motors are frequently driven by transistorized variable-frequency drives. This greatly eases the problem of starting the massive rotor of a large synchronous motor. They may also be started as induction motors using a squirrel-cage winding that shares the common rotor: once the motor reaches synchronous speed, no current is induced in the squirrel-cage winding so it has little effect on the synchronous operation of the motor, aside from stabilizing the motor speed on load changes.

One use for this type of motor is its use in a power factor correction scheme. They are referred to as synchronous condensers. This exploits a feature of the machine where it consumes power at a leading power factor when its rotor is over excited. It thus appears to the supply to be a capacitor, and could thus be used to correct the lagging power factor that is usually presented to the electric supply by inductive loads. The excitation is adjusted until a near unity power factor is obtained. Machines used for this purpose are easily identified as they have no shaft extensions. Synchronous motors are valued in any case because their power factor is much better than that of induction motors, making them preferred for very high power applications.