DC motors - how is it made? How it works?


Uploaded by pcbheaven on 27.03.2010

Transcript:
Welcome to PCB Heaven Techlabs
Today i will show you what's inside a DC motor
I have prepare myself a model of a DC motor for this reason
and as you can see this is fully functional
it can rotate eitherway clockwise and counterclockwise
and on the back side
you can see the bearing that holds the shaft
and the shaft itself
and the two poles that the motor is powered from
Instead of breaking the motor appart
and explain each part as i take it out
I would rather prefer to go backwards
and i will start from a scratch and build the motor from the beginning
I strip the motor
This is the basic part of the motor
this is the shaft
and on the shaft
the two electromagnets are welded
actually these are only the cores of the electromagnets
they still lack of the coils
and the coils are actually the ones that i will start with making the motor
The coils are made of thin single-core wire from copper
that it has no plastic shielding outside
instead it has a special paint
and this will prevent the short-circuit between the windings
This would be the fist coil of the electromagnets
the motor has actually two electromagnets something that doesn't happen
in the real life
but this motor is made only for educational purposes
and i tried to keep is as simple as possible
So, these are the electromagnets
and now it's starting to look a motor again
and it's time to give some power to the coils
This is the tricky part of the DC motor
So, to provide the power i need to build something that's called
commutator
The commutator is actually a ring
This ring is above the electromagnets
and it is fixed on the shaft
This ring rotates along with the shaft
and the ring is made of NON conductive material, this is very important
On the perimeter of this ring there are two other parts
That they are made of conductive material
This is the first part of the commutator
And it must be able to stand friction in high revolutions
you will see later why
On the other side of this ring is the other half of the commutator
again it is made of the same conductive material
It has the same wire to provide power to the coils
Now both electromagnets have their wire ending connected to the commutator
Now look closer to these pieces
They are actually NOT connected together
There is a gap between them
And on a real motor this gap is times smaller than a millimeter
On the other side there is the same gap
and now let's take a look around
So, we have make the commutator piece
Now it's time to put something to hold the shaft in position while rotating
and what would be better than a set of nice ball bearings
The motor has actually two bearings
One above the commutator and one under the coils
The bearings are very inportant on the motor
And actually the bearings along with the brushes
are the parts that wear off on a motor
According to the theory of operation of DC motors
The electromagnets rotate inside a magnetic field
So now we need to make a magnetic field
And this field will be made out of two permanent magnets
placed one opposite the other
now this is the first piece
This piece of permanent magnet has it's north pole facing the coils of the motor
The coils will rotate in front of this magnet
and they will be actually in a very close distance
1 or 2 millimeters for small motors
And now we need the other half of the... another magnet
with the other pole facing to the coils
This magnet has the South pole facing to the coils
Between these two magnets there is a permanent magnetic field
and the coils will rotate inside this magnetic field
I will continue making my motor
The itnernal parts are almost ready
what I need now is a way to provide power to the coils
while they rotate.
Remember that the poles of the windings of the coils are both connected
to the two pieces of the commutator
There's another part, called, the "brush"
And this is actually why this kind of motor is called "brushed" motor
The brush is a piece of metal that acts like spring
On one end,
there is a conductive material very durable, to friction
like the one used for the commutator
usually this is made out of carbon
The metal will push this piece on the commutator
and so it will make contact between these two
on the other end of thie piece
there is the power connector of the motor
this is where you connect the power actually.
The current goes from the power connector through the metal spring
and throught the carbon connector directly to the commutator
and then its provided in both coils
And of course there is another brush opposite this one
with the same structure and operation of course
It will give power to the other piece of the commutator.
Now, watch what happens while the shaft is rotating.
The brushes have always the same polarity
as provided by the power supply,
but as the shaft rotates,
the polarity driven to the coils is changed,
because every time...
for example the left commutator goes one time to the positive
and one time to the negative power supply
And this is how the electromagnets change their polarity.
That's the tricky part of the DC motor.
Now it's time to put it all together,
and i will put the housing of the motor.
It has a proper place of course for the ball bearing.
And the electromagnets are also fixed on the walls of this housing.
That's the housing.
Our motor is almost finished.
Its time for the final part.
I don't really know
the name of this part.
I will call it a cover, actually its a cover! It covers everything.
And it also has a place for the bearing on top.
It will hold the bearing on top,
and it also has two holes for the power terminals
And the motor is ready.
Fully functional.
Everything in position, that's it!
Thank you for watching this video and don't forget to visit
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