Brushed DC Motors | AddOhms #20

Brushed DC Motors | AddOhms #20

Motors convert electrical energy into
motion. They get used in many ways from disk drives to fans to robots. This AddOhms tutorial kicks off a series on motors, starting with the simple Brushed
DC Motor. [Music Playing] AddOhms tutorials are made in part thanks to viewers. If you find these
tutorials helpful please consider participating in our patreon. First let’s look at some basics. Motors work because of permanent and electromagnets. An electromagnet is a magnet created when current flows through a coil of wire. When the electromagnet is active, it moves towards the permanent magnets
poles causing the motor to turn. Here are some basic terms: the rotor is the part
that rotates, the stator is the part that stays in place. The magnetic field is
generated by the armature. In this motor, the armature is part of the rotor. However the armature doesn’t always move Depending on the design, it can be part
of the ROTOR or the STATOR. We’re going to look at different motors throughout
this series. In this video, we are focused on the brushed DC motor. These are very cheap to make and really easy to control our simplified example is only missing
two pieces. The coils being energized in a sequence
keeps the spindle moving. But! There are only two wires! How do switch between the coils? Well the coils are wired to something called a “commutator” on the spindle. This commutator has split rings allowing the current to activate each coil in
sequence. Next let’s talk about how to control a brushed DC motor.. with a microcontroller. Motors draw too much current to connect
directly to an I/O pin. So we need a switching transistor as a driver. Now before we connect the transistor to the I/O pin we need to consider one thing. Remember the armature, or coils,
are generating a magnetic field. When the magnetic field collapses voltage builds up and current is generated. You might hear that called “Back EMF” which means:
Electro-Motive Force. That brief surge of energy can destroy a transistor! So we need to add a flyback diode across the motor. When the motor throws off its EMF, the diode will give it a path for the current to follow
dissipating the energy. Now that it is safe we can connect
a transistor to a microcontroller, and use the PWM to control or change the speed of the motor. Here’s a thought!
What if we want to go backwards? For a brush DC motor, all you
have to do is reverse the leads. But our simple driver can’t do that electrically.
So that’s when we bring in the H bridge. This circuit has four transistors with
the motor in the middle it sort of looks like an H, right?
Anyway! The microcontroller turns on two transistors at a time to change the direction current flows. You can even connect the two transistors to ground to create a simple brake. This circuit can be built with
discrete BJTs, like the 3904, or you can design with
something like the l293d. Which has all of the transistors and
protection diodes built in. The positives to a brushed DC motor are that they are 1)cheap, 2)simple to control and 3)very common These motors do have two major
disadvantages though. First the brushes on the commutator
will eventually wear out and second the physical connection between the brush and commutator generates tons of electrical noise sometimes they even produce
tiny electric arcs! So in the next AddOhms tutorial
we’ll take a look at a type of motor that doesn’t use these physical brushes. Stay subscribed to AddOhms.
The next couple of videos will cover different motor types. In the meantime if you have
questions leave them with this video or visit the AddOhms forums at Or for show notes head over to As always you can find
us around the Internets using the keyword Add Ohms [Music Playing]

58 Replies to “Brushed DC Motors | AddOhms #20”

  1. Hey, thank you for making these videos!

    For the Brushless, could you do a brief comparison between both the Brushed DC motors, and Synchronous AC motors? How to control them and such (speed directly proportional to the applied voltage on a DC motor/frequency on an AC sync one. How, despite brushless being the later, can be controlled as the former?) Also, an explanation on regenerative braking?

    Again, thank you 😀

  2. Really like the series, nice and simple. For the brushless motors would you mind explaining a hard drive motor and how to drive them from a raspberry or arduino? (3 coils, 1 common) Anyway thanks!

  3. You have suggested part numbers for a few components, but not for the fly back diode. I guess I've been lucky so far with my fooling about because I've not used one, or maybe the tiny motors I've used with no load have meant they have nothing to provide momentum that could generate electricity once the power is cut. But all that aside, what to use for that fly back diode would be good to know.

  4. I recently found you channel and became a follower, I really do liked your video, you have an awesome way of explaining things,  but to be honest there are a ton of these type videos on YouTube that control motors via H bridge controller. What do you think about taking different approach and diving in a little deeper and developing a proportional controller that includes armature and load inertia and explore the effect that it has on the stability of the system and how to tune for a critically damped response. I think it would be fun and very useful and a step above "basic hobbyist" content that is so pervasive on YouTube.  It is just a thought, thanks for your efforts and keep up the great work.

  5. the way you animate and explain makes things easy to understand. i'm kind curious, what software do you use to make it ?

  6. 2:59 That looks very similar to one of the drawings that I made for one of my want-to-do projects. Never actually built it, but I made several drawings to try to get similar functionality.

  7. Pls, would you make more electronics videos bcz your explanation and animation are too much easy to understand

  8. I have a question. I have a 9-12V DC motor and a 9 volt battery I need to make it go slower so I'm using resistors. Why is my 20 ohm resistor burning when a use the battery?

  9. Hey hocam . First of all i would like to thank to you . I have some trouble about deciding a type of motor and how should i control it ? Do you have any video or documents for that ? Thankss

  10. Outstanding channel! I love the graphics and clear explanations. Looking forward to your brushless motor video, hope you include a bit on how the ESC's drive motors and how FETs on ESC's work, particularly the voltage/current paths. Battery to ESC- power source input. Battery current to FET input, controlled by ESC MCU and gate drivers, then to ESC motor output, or maybe that deserve a video to itself.

  11. This video is even better than the one about BJTs! Subscribed! Hope to see some new videos from you soon!

  12. Your videos are simply the best on YouTube. I never understood back EMF until visually seeing it in your video. I also love how you connect theory to real world examples. Seamlessly moving from the motor, to controlling it with a microcontroller, to combining transistors to an H-Bridge to add more functionality. My thanks to you. You have helped me so much.

  13. What I don't understand about the H bridge is why the NPN transistors are being used for both high side and low side switching.

  14. I am not able to understand that part switching between the coils and how to make motor move in the opposite direction

  15. how can i make h bridge with transistors to draw high current in the motor and speed control(from mosfet)?

  16. I am struggling to choose the right diode for diagram in 2:35. My motor is 1000W 48V 20A. Wiki suggests a 1N4007 for 3A currents but I think mine will be considerably higher… Any tips? Can someone point me in the right direction? Thx!

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