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‫And now let's look at how those forces in moments are created by those propellers.

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‫Let's start from the top few of the drone.

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‫We have four motors, motors, one and three rotate counter-clockwise and motors two and four rotate

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‫clockwise.

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‫Why is it necessary that two of them rotate in the opposite direction to the other two?

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‫Well, let's think of a helicopter hovering in the air.

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‫What will happen to it if you lose its tail?

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‫Let's say that you shut it down.

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‫Now you only have the big propeller working.

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‫The Newton's third law says that if you push an object with a specific force, then that object pushes

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‫you with a force that is equal in magnitude and opposite in direction.

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‫A similar thing happens with rotations inside the helicopter.

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‫You have some kind of engine that applies to work to the main rotor that makes it rotate.

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‫And so the rotor applies to talk to the rest of the helicopter, which is equal in magnitude, but opposite

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‫in direction.

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‫In other words, as the main rotor rotates counterclockwise, the rest of the body will rotate clockwise

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‫and vice versa.

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‫Of course, the helicopter will rotate slower than the rotor.

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‫However, that is due to the fact that the mass movement of inertia of the helicopter around the axis

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‫of rotation is bigger than the one of the rudder.

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‫Remember mass moment of inertia, resistance to rotation.

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‫The bigger it is, the harder it is to rotate the object.

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‫And so the objective of the tail in the helicopter is to create a counter torque that keeps the chopper

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‫rotational at rest.