Quadcopters are Unstable? Explanation to How Drones Fly

Quadcopters are Unstable? Explanation to How Drones Fly

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Drones are so popular nowadays because it’s very easy to start flying. Did you know that the quadcopter design is inherently unstable? There are electronic systems helping you fly your drone passively the entire time.

A drone flies in the air, obviously, and so it deals with some 3D physics your land-bound human body doesn’t encounter everyday. There’s no floor to help it regain balance, there’s nothing to stop it from spinning in circles, etc.

To help you understand your drone better we’ll start with some aircraft 101.

In the air, an object can move vertically, as well as horizontally and forward-backwards. What’s important is that it can also rotate in any of these directions. To make it understandable, let’s use imagination. Imagine your head as an aircraft. Imagine you’re  flying forward going where your nose is pointing.

Okay, so how can we change our trajectory? You can nod, so your nose goes up and down. Or you could shake your head, so your nose goes left and right. Or you could do an impression of a confused puppy and tilt your head. That leaves your nose pointing the same direction but your head rotated.


Now in aircraft lingo:

nod = pitch
shake = yaw
tilt = roll

What do these things mean for an aircraft? The pitch would control the altitude. The yaw would control the horizontal direction. The roll would control how many spins you do.

Now let’s take a look at a quadcopter.

Since a quadcopter is symmetrical, one important thing to do is to pick a direction to be forward. Usually LED lights will indicate the direction. The magic of the quadcopter design is that it can control all three types of rotation simply by changing the rotor speeds. The pilot still controls it by telling it how much thrust, pitch, yaw, and roll to have.

I won’t bore you with detailed explanations of how it performs everything. Here’s a simple break down.

To go higher it increases its thrust. Easy.

To change its yaw, a diagonal pair of rotors will spin faster than the other pair. In a quadcopter two diagonal rotors spin CW and the other two spin CCW. If one pair spins faster than the other, the whole quadcopter will rotate.

To change its roll or pitch, an adjacent pair of rotors spin faster. This lifts the pair’s side higher, tilting the quadcopter.

Algorithms translate your control inputs into appropriate rotor speeds. The truth is, drones with more than one rotor are inherently unstable. It seems counter-intuitive, like how can a table with 4 legs be less stable than a table with 1 leg?

The fact is each rotor needs to spin at precise speeds to counterbalance the other three. Taking wind into account, small random disturbances will stack up and knock the aircraft out of equilibrium.

A quadcopter only flies when it has passive electronic stabilization systems to counteract disturbances and bring the drone back into equilibrium. With microprocessors, solid state gyroscope and accelerometer technology advancements, quadcopters are possible. It’s a blend of machine precision and human controls.

High end camera drones have plenty of computer aid in stabilization and are super easy to fly, not to mention smooth. Many use GPS to keep them hovering in a precise location and height. Other drones emphasize pilot control, retaining much of the recreational appeal of RC helicopters.

Nowadays the question is: how much automation do you want?

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Futurist, architecture grad, drone connoisseur. I'm passionate about new and fresh things that will change the world. For example, I love dank internet memes. Also drones are very cool.

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