What is a quadcopter, how do quadcopters fly and what do we use them for? Unmanned delivery vehicles are no longer the future. Robotic flying workers aren’t fiction. They are here now.

Quadcopters, or drones, have been doing deliveries for Amazon for a few years now and everyone from farmers to window cleaners are using quadcopters to carry out tasks and its only a matter of time before we have quadcopter taxis and cars. But what are they and how do quadcopters even fly??

What is a quadcopter or drone?

Technically a quadcopter is a flying vehicle with 4 propellers, quad meaning 4, but people are using talking about ANY flying helicopter thing when they talk about drones and quadcopters. Also, a drone can actually be a fixed wing aircraft, or even a driverless car, but people are usually talking about the typical flying drone with horizontally mounted propellers.

For the rest of this article a drone means a flying vehicle with horizontally mounted propellers!

Although the concept is quite complex, how quadcopters fly is actually quite simple. It consists of a body, a controller, a battery and some motors. All these components work together to get the best drones in the air.

How does a drone fly up?

A drone, like all flying crafts on the earth, gets pushed into the air by forcing air downwards away from the drone, and producing a force that is greater than the gravity that is pulling it down. Because the upwards force is greater than gravity, the drone moves up.

The drone pushes the air down using propellers which spin at high speed and fling air downwards. In modern radio controlled drones the propellers are spun by efficient brushless motors.

Why brushless?

Because they are much lighter and more efficient than brushed motors, giving a higher power output from a smaller battery and lets you use a smaller motor. This means more power, less weight and longer flight times.

World Record Flight

A major concern with quadcopters is always the flight time due to the speed at which the tiny propellers need to spin because of their small surface area. Not a problem for a German called Ferdinand Kickinger whos drone stayed in the air for 2hr 31 minutes in 2016.

He did this by effectively making the drone useless. He used low-discharge rate, high capacity Lithium Ion batteries and stripped the quadcopter of every ounce of non-essential weight to reduce power draw and extend endurance. The result of this is a total lack of any features.

As a side note Kickinger is actually in the process of producing electric quadcopters that lift humans!

How Quadcopters Fly – The controls!

Most people think that drones are like helicopters, but they’re actually very different in the way they work.

In traditional helicopters the rotors (read as propellers in drone speak) spin at a constant speed with the lift being adjusted by adjusting the angle the propeller blades are set at. This is called the pitch of the helicopter rotor and sets how much air is being pushed down. If you want the helicopter to stay at a constant height the propeller blades are adjusted to give just enough lift to match the weight of the helicopter. If you want the helicopter to go up then the rotor blades are adjusted to push more air down.

The crucial thing is that in a helicopter the speed of the rotor remains constant all the time and the actual propellers (rotors) are adjusted instead.

Drones are completely different to helicopters

A drone works in a completely different way and uses fast, micro circuitry to control the drone in flight. A drones flight is completely microprocessor controlled and works by only adjusting the precise speed of each of its motors. This is all done automatically by the controller. The drone controller is usually a module in itself that automatically controls each motor speed to make the drone do what you want.

But how does the drone actually fly?

If the drone is steady in flight and holding on one position then all the motors are turning at the same speed and at a speed that generates enough downward air to keep the drone at its steady height. This is where we start at a steady height …. and then the motor speeds are tweaked depending on what you want the drone to do.

How a drone goes up and down

The lift in a drone is altered by adjusting the speed of the propellers. Faster propellers mean the drone goes up, slower propellers mean the drone goes down. To go up or down, all propeller speeds are ramped up or down by the same amount.

How a drone turns left and right

This is where the drone design is important and where it all gets a bit more complicated. To understand how this works you need to know how the propellers are set up…In particular, which direction they spin. On a quadcopter the propellers are set up to spin like this :

In a quadcopter, the diagonally opposite propellers turn the same direction as each other, the opposite direction as the other set of propellers.

Why would your propellers spin in different directions?

There is a very good reason for this that isn’t obvious at first. As with all of the drones controls, to turn a drone left or right the drone slows down or speeds up some of its motors.

Get ready for physics!

Now, cast your mind back to high school when you were supposed to be studying physics. Because of Mr Newton we know that every action has an equal and opposite reaction but what does that mean?

It means that as your propellers on your drone spin round at high speed, they essentially try to spin your motor at the same speed in the opposite direction. If you imagine the propeller setup again, with all motors spinning at the same speed they are cancelling each other’s opposite reactions out so the drone stays pointing in one direction.

So all you need to do to spin the drone in one direction or the other is to speed a set of the motors up that are spinning the same direction and slow the other set down.

What if your motor directions weren’t arranged like this?

Now if you imagine that your motor directions weren’t arranged like this, what would happen? your drone would sag on one side every time you turned it due to the lack of thrust on that side.

And that’s the simple reason the motors spin in different directions!

How Quadcopters Fly forward or backwards or sideways

Making your drone fly forward or backwards is even less counterintuitive than turning!

If you think about an aeroplane, it flies forward because the fans are blowing air backwards, pushing it forward due to the opposite reaction of the blowing. On your drone however the propellers are always pointing downwards, so how does it even move forward, backwards or sideways at all?

Its all in the propeller speeds

How do quadcopters fly? As with everything quadcopter related, the drone controls its forward, backwards or sideways motion by altering the speeds of its propellers.

To go in any direction the drone simply reduces the speed on the propeller that points in that direction and increases the speed of the propeller opposite. This has the effect of dropping the slower propeller down slightly and pointing all propellers in the direction you want to travel, this causes the air to be blown at an angle rather than straight down and pushes the drone in that direction.

Using this concept you can push the drone in any direction.

Why do drones have 4 propellers?

It should be obvious, but the drone needs at least 4 propellers to maintain flight whilst controlling its direction and position in the sky.

A quadcopter always needs at least 2 propellers to maintain height and 2 propellers for control. Note that you can have more propellers, as many as you like really, but the control systems just get more complicated.

The simple controls of a quadcopter!