Brushless Motors and Why Drones Work Better with Them
All hobbyist drones contain electric motors; without these, they’d really be fancy paperweights and not nearly as much fun. As drones run on batteries, these are of the DC (Direct Current) variety rather than Alternating Current like the motors in your washing machine and hair dryer.
You may also have heard that some DC motors are called “brushless” and that these are somehow better. What’s the difference, though, except that they don’t contain brushes, whatever those may be?
The Basics of How Electric Motors Work
As most of us were intrigued to find out as kids, magnets like it when they see the opposite pole of another magnet and try to draw closer. If they get too near a pole of the same kind, they become frightened and try to run away. Knowing this, we now have a way to turn electricity into magnetism and then into motion – this is obviously what a DC motor is all about.
When you think about it, any motor needs to have a part that moves and a part that stays still. The former is called the rotor and the latter the stator. In non-brushless motors, the stator contains one or more permanent magnets:
A coil of wire generates a magnetic field when an electrical current flows through it. This current is transmitted from the battery to the coil through wires and the gray, conductive “brushes”. This means that the direction of the current through the coil switches every half-rotation, making sure that the rotor’s magnetic field is always fighting that of the permanent magnets, generating power.
So, How Do Brushless Motors Work?
In a brushless motor, the mechanical switching action of the brushes is replaced by a Magical Box of Wonders, otherwise known as an electronic controller. Also, instead of being part of the stator, the permanent magnet is mounted on the rotor.
Each coil on the stator is switched on in sequence, attracting the opposite pole on the permanent magnet. For this to work, the electronic controller needs to know the current position of the rotor, making things slightly more complex.
Do Brushless Motors Work Better than Others?
You may already have figured out one weakness of the old-style “commutated” motors: because the brushes are constantly subjected to friction, even the hard graphite they’re made of will wear out sooner or later. This isn’t the major reason most drones use brushless motors, though.
Brushless motors, apart from being more reliable, are more powerful, smaller and more lightweight than their commutated counterparts. Because they’re also more efficient, they allow smaller, lighter batteries to be used.
Less mass to drag around is always a good thing when it comes to drones. So, the next time you feel like complaining about brushless DC motors being more expensive, don’t: you’re getting your money’s worth.