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What is a brushless motor?

What is a brushless motor?

One of the common questions we get, is what is a brushless motor? And customers requiring support to understand whether they have a brushless motor on their bike or not.

Almost every eBike these days uses a brushless motor. Old ebike generally have brushed motors.

The simple answer

The simple answer is that a brushed motor has two wires, and doesn’t need any kind of clever control. You can pretty much plug it straight into a battery and it will work. The disadvantage is eventually the brushes wear out, and they also waste energy.

A brush less controller has 3 motor wires, and usually has 5 extra small sensors wires. It doesn’t waste any energy with brushes, and it has to be connected to a suitable controller otherwise it won’t work.

An example of a brush-less motor cable with 3 motor wires and 5 sensor wires:

hall effect brushless motor cable

Brushless motor cable with hall sensors

The Techy answer

 

So let me explain first what is a brushed motor?

These are like the motors that kids make at school in science class. You have a coil of wire in between two magnets. When you put current through the wire, it turns in order to align with the magnets, and then it stops.

In order to keep the coil of wire turning, the direction of the current needs to change as it rotates around, and to do this there are metal brushes which brush up against the central bit of the motor that spins and conduct current to it.

A simple brushed motor

So what’s the difference with a brushless motor?

The important thing is to remember it’s all about how you keep the motor spinning round continually. In a brushed motor, the brushes change which coils the current goes into for you, this happens automatically as it turns and the brushes brush over different coils.

In a brush-less motor, the changing of the current is achieved using a controller, and sensors. The controller tracks what position the motor is in, and selects which 2 of the three motor phases to send current down in order to keep it moving around.

So what’s inside a brushless motor? Most brushless motors these days use very strong permanent magnets around the outside, and coils of wire inside conducting current.

Here’s a more simple image showing the construction of a brushless motor:

A brushless motor

Current is only ever flowing through a few of the coils at any one time, and when current is flowing through a coil it acts like a magnet and pushes away any other magnets near it that are of the same orientation (remember the north pole of a magnet will push away the north pole of another magnet). So when you put current through some of the coils, they will push or pull the magnets around the outside, turning the motor, until they have lined up so that there is no more force. Then you need to put the current through a different set of coils to push it round the next bit. Controlling this is the job of the motor controller which I’ll talk about in another blog.

Here is a picture from one of the factories in China where our motors come from. You can see the copper coils of wire in the middle and the black magnets around the outside.

A stack of brushless motors from our factory

Brushless motors at our factory

So there you have it, that’s essentially how a brushless motor works.

In the next blog I’ll talk about motor gearing and geared motors v.s. direct drive motors.