Detailed design of the flight principle of the drone
The rotor, much like the wheel, is one of humanity’s most fascinating inventions. It has revolutionized how we interact with the sky. The four-rotor drone, for instance, has turned into an aerial camera that fulfills many people’s childhood dreams of flying and seeing the world from above.
If you’ve ever played with a bamboo pole, you might understand how a rotor works. When you spin the pole rapidly, it generates lift, allowing it to rise into the air. Similarly, multi-rotor drones use motors to spin their propellers, creating lift that enables them to fly. For example, in a quadcopter, when the combined lift from all four propellers equals the total weight of the drone, it can hover steadily in the air.
As a kid, I used to watch Doraemon and Nobita flying around using their magical bamboo poles. I always dreamed of soaring through the skies, looking down at the world below. But if someone really tried to build a real-life version of that today, I wouldn’t want to wear it. Because the result would look something like this:
[Image: A person spinning uncontrollably due to the rotation of a single propeller]
The propeller spins wildly, and the person spins in the opposite direction. That’s not exactly the smooth flight we imagine. Nobita ends up spinning so fast that he can’t even see the scenery with Shizuka.
This happens because of Newton’s third law: for every action, there is an equal and opposite reaction. As the rotor spins, it exerts a counter-torque on the motor, causing the whole body to rotate in the opposite direction. This is why helicopters have a small tail rotor to balance that force and keep the body stable.
Back to the quadcopter, its four rotors also produce this counter-torque. To prevent the aircraft from spinning out of control, the rotors are arranged so that two spin clockwise and two spin counterclockwise. This way, the forces cancel each other out, keeping the drone stable in the air.
As shown in the diagram, M1 and M3 rotate counterclockwise, while M2 and M4 rotate clockwise. The counter-torque from M2 and M4 cancels the torque from M1 and M3, ensuring the drone doesn’t spin like Nobita did. This setup allows the drone to remain steady and maneuver smoothly.
Now, let's talk about how a multi-rotor drone moves. It can fly forward, backward, left, right, or even rotate in place—all by adjusting the speed of its propellers.
Vertical movement is straightforward. When the drone needs to ascend, all four propellers speed up, increasing lift. When it needs to descend, they slow down, reducing lift. The key here is that all four must adjust at the same time to maintain the drone’s stability. If just one or two change speed, the whole aircraft could tilt or spin.
For in-place rotation, the drone uses the counter-torque effect. If M2 and M4 (the clockwise rotors) speed up while M1 and M3 (the counterclockwise ones) slow down, the drone will rotate counterclockwise. This is how it turns without moving forward or backward.
Horizontal movement is a bit more complex. Unlike airplanes that use wings and engines to move horizontally, multi-rotor drones rely on tilting. For example, to fly forward, the rear propellers (M3 and M4) speed up while the front ones (M1 and M2) slow down. This causes the drone to tilt forward, and the lift now has a horizontal component that pushes it forward.
[Image: Drone tilting forward to move forward]
Similarly, if the front propellers speed up and the rear ones slow down, the drone tilts backward and flies backward. By adjusting different combinations of propeller speeds, the drone can move in any direction—left, right, forward, or backward.
So, after going through all that, does the flight principle of a multi-rotor drone seem simple? It actually is, compared to older methods of aerial photography.
Before multi-rotor drones became popular, people relied on fixed-wing planes and helicopters. Fixed-wing aircraft needed long runways for takeoff and landing and couldn’t hover. Helicopters, while more flexible, had complicated structures with many moving parts, making them hard to maintain.
[Image: A fixed-wing plane taking off]
[Image: A helicopter in flight]
In contrast, multi-rotor drones are simpler, easier to operate, and require less maintenance. This made them ideal for consumer use, especially in the growing field of aerial photography. Today, they dominate the market, thanks to their ease of use and versatility.
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