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DIY Motor Construction & Invention :

Welcome to the DIY motor construction and invention page !! Here you can see all kinds of motors and power generators on display. You can also see how we can build a motor in the DIY way using simple tools and off-the-shelf material. Then you are on your way to invent your own motor and build a working prototype. Note that motors can be classified by electrical behavior, shape, construction, operating principle, and application, etc.. So a detailed description of a motor may look like variable reluctance single-sided linear 3-phase stepper motor. But we just take the type description one by one and highlight the characteristic relevant to this type. You can then combine them to invent many types of motors and geneators with the characteristics that you need. Ready ? Let's go DIY inventing our motors.

Motor and generator are the power engine of machinery. It is also called dynamo to describe motors that are generators when turning it by external force. Although the motor was invented more than 100 years ago, recent years see new motor type appearing to meet specialised demands. Just to name a few, there are ac motor, dc motor, ac/dc motor, synchronous motor, permanent magnet motor, induction motor, stepper (stepping) motor, switched reluctance motor, hybrid stepper motor, driving with single phase / 2-phase / 3-phase / 4-phase / 5-phase, have 2-pole / 4-pole / 6-pole 8-pole and other pole numbers. Motors can be brushed or brushless, slotted pole or slotless. By shape and construction, we have toroid / toroidal motor, disc motor, princted circuit (PCB) motor, iron core / coreless motor, linear motor, and voice coil motor. By function, we have servo motor, traction motor, and vibration motor. By topology, we have radial field motor, axial field motor, and trasverse field motor. To make a choice, the main criteria are often related to optimizing certain motor performance indexes. Meaning of these indexes for generator is similar.

Performance index Meaning and implication
Efficiency (%) The percentage mechanical output from electrical input.
Voltage (V) The voltage for the motor to operate at running speed.
Power (W) The electrical input it is designed to take.
Power density (W/kg) How heavy the motor is to achieve a certain power. It is a good index to assess quality of design optimization.
Flutter (%) The speed variation due to uneven force at different position of rotation. An index important in VCR and CD drives.
Torque (N.m) The rotational force output.
Rotor inertia (kg.m^2) The inertia to acceleration. High torque low inertia is ideal for fast response. But high inertia can reduce flutter.

The above list is far from complete. It is heavily related to the application and we can define additional indexes according to our needs. For example, torque to diameter ratio for handheld screwdriver.

Now, let us open all kinds of motors we can find and see its internal construction. Then we shall find ways to do it the DIY way to invent our motor using simple hand tools and readily available material.

1. Simple DC motor

Simple DC motor consists of a permanent magnet stator, and rotor coil with a commutator near one end to properly provide current to the coil. It is the lowest cost motor solution. It can also be made very small easily. For low power design, its power desity is often very high.


2. AC/DC motor

AC/DC motor is like DC motor with electromagnet as its stator. If you change polarity of input, the polarity of both rotor and stator changes at the same time. So it can run using either AC or DC power supply. For small power, DC motor can be made smaller with permanent magnet; for large power, the AC/DC motor can save on cost of magnet and avoid the difficulty in handling a large magnet.


3. Brushless DC motor

Brushless DC motor consists of a permanent magnet rotor, and stator coil controlled by electronic circuit to provide proper current. Without a commutator, it can run more quietly and last longer. It can also be made very thin if needed. Computer fans that require 24 hours nonstop operation are usually brushless DC motors.


4. Induction motor

Induction motor is like brushless DC motor but uses an almost solid aluminium / iron core rotor. Running on AC input, the induced current in the aluminium bars force the rotor to follow the rotating magnet field formed by the AC input. It is the simplest and one of the most reliable motor type.


4. Disc motor

Disc motor is brushless DC motor with many poles for the stator coil so that it can run at low and very stable speed. That is, low flutter. It can be found in CD players, video cassette and other tape drive systems. On the other hand, it is possible to take a disc motor from a retired CD player to make a hydroelectric or windmill generator because it can run smoothly at low speed to generate voltage high enough to drive LED.

There are other variations of the disc motor. One of them do away with the iron core and just use copper wires formed to the required coil shape. In this case, the magnetic field that make the motor move is along the axis of rotation and so called axial field motor as opposed to the typical radial field motor.


5. Printed circuit motor

Printed circuit motor is another form of disc motor in which the coil is formed on a printed circuit board (PCB). There is no need to form the coil windings one by one and the coil pattern can be controlled exactly as designed. It can make very thin motors.


6. Stepper / Stepping motor

Stepping motor is similar to brushless DC motor but with many more poles formed as a result of many teeth on the surface of the stator and rotor. It is a clever design that avoids using many magnets or to make a magnet with finely spaced poles. It is very easy to control and provide high precision positioning. With relatively high torque for its size, very often it can be used to directly drive a robotic arm or other mechanism.


7. Others
There are also linear motors. In most cases, it is the unfolding of a rotary motor into linear form. Sometimes, the stator is extended to much longer than the moving part. To the extreme, the magnetic train has a stator with length of many miles.





Building our own PCB motors
Many of the motors require precise machine parts. They are not easy to build with hand tools. The magnetic attraction to disrupt weak structure and pull components to one side further increases the difficulty. Among the above mentioned motor types, the PCB motor can be build by layouting out a PCB. The other parts are relatively easy. See the PCB motor in action ;-)



Building our own disc motor
To further simplify matters, we build a disc motor by hand wounded coil. The diameter of the motor is about 100mm. It is large enough to allow use of big magnets and can tolerate error of a few mm deviation from designed shape for the coil. Very strong rare earth metal magnet is used to increase the output. The rotor carrying the magnets rests above the stator coil with a disc type bearing. This is a generator, so there is only one coil and no electronics to control the current flow. It generates alternative current that can be used to drive two light emitting diodes that is turned on for opposite polarity of the output. If it is well constructed, a iron ring can be put at the back of the coil so that it closes the magnetic path better. The stronger magnetic field can generate more power at same speed. But the torque needed to turn the generator is also increased.



Building our own windmill
Now we can add a windmill above the rotor to generate electricity. Cut plastic or paper cups in half, then use a scrap CD as the base to hold 6 regularly placed cups which are the blades of the windmill. But this is a very convenient horizontal windmill that can turn for winds from any direction. To add some fun to the project, let's draws 6 frames of animation loop and see the motion repeats itself as the wind blows.



Demonstration














 

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