On a brushed DC motor we had two wires. Apply a voltage and it's spins. On a
brushless motor, however, we have three wires. So does that mean that they're power,
ground, and signal? [buzzer] Okay maybe it's forward, reverse, and ground! [buzzer] Okay it's more
complicated than that but not by much. In this AddOhms episode, we're going to
look inside of a brushless DC motor and talk about how YOU can control them.
[Music Playing]
Sometimes you'll hear a brushless DC motor called a: B-L-D-C. As their name
suggests, there are no brushes. The commutation occurs electrically, not
mechanically. Wait! What does commutation mean anyway?
Well using the Google we can
see that commutation is the process of commentating. Seriously? Okay commutate
comes from the Latin word, "exchange." And that's the key. Commutating is
interchanging the current through the coils to make the motor spin. So let's
get back to the BLDC. Remember there is a rotor and a stator. In this design the
armature is part of the stator. When the current flows through the armature a
magnetic field is generated, and that allows the rotor to rotate. So the
three wires from the outside connect to the twelve coils in this design. The
coils are arranged in a pattern that keeps the rotor moving. The difference
from a brushed motor is that there is no commutation ring. This means that three
external wires are our ONLY way to keep the rotor spinning! Which means.. you can't
just apply a DC voltage to any pair of them. Now let's simplify and talk about
just three coils. Electrically they have a common connection. With three external
connections called "U", "W" and "V." Each connection gets two
transistors: one connected to ground and one connected to the supply voltage. This
circuit is similar to an H bridge. Just like that we can use a specific
pair of transistors that allows us to control which coils are turned on, and
which direction current flows It's just a matter of developing a sequence.
Backing up for just a second, I should point out that each of the coils is
called a phase. Since there are three, this is a three phase motor. Our internal
example showed twelve coils... Which is still a three phase motor, because they
are connected in groups of four. You may also see a single phase BLDC but we'll
come back to that. Now this circuit, you could build it using discrete MOSFETs
and then control the speed with a microcontroller. However you probably
want to just use an ESC instead. Okay! I swear I'm not trying to make this video
a complete alphabet soup! An ESC is an electronic speed controller. Here I have
an example from my quadcopter. Inside of this yellow package are the transistors,
decoupling capacitors and some circuits to help control the sequencing. For
connection to a microcontroller I just need to connect a PWM signal. ESC's can
be designed with many other features like an electric brake, the ability to
reverse, or special ramp curves. The point is, in most cases, when you use a BLDC
you'll also want to use an ESC. Here's a typical brushless motor that pretty much
breaks everything I've just said. It's a standard fan. Maybe one you might use in
a PC build. It's a BLDC, but unlike the quadcopter motor, it's a single phase.
And, you might notice it only has two wires... yeah, okay, sometimes they have
three but the third one is just for temperature. So how can this be a BLDC
and only have a positive and negative wire? It's because inside of the motor
are the electronics that do the electrical commutation.T he main positive
to a brushless DC motor is that there are no mechanical brushes.
This means no internal sparks and almost nothing to wear out. Now, controlling them
means a little bit of extra cost ,but, you know, the external controller or
built-in driver that's not going to be very much. In a future AddOhms Motor
Tutorial, we'll look at stepper motor, which personally these are my favorite
kind of motor. And the reason is it is basically a Brushless DC Motor! So when
that video is available, I'll let you know. All you have to do is subscribe to
this channel or follow AddOhms on all the social medias. And in the meantime, if you
have questions about motors or other electronics leave them with this video
or visit the AddOhms forum. Remember if you can't figure it out just AddOhms! ...Maybe...
I should say AddOhms one more time?