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The physics of staying up

A drone flying looks like magic, but it’s pure physics. Everything a drone does comes down to balancing four forces and controlling four spinning motors. Understand these and you understand every flight command you’ll ever give - by hand or by code.

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The four forces of flight

Every flying thing - a bird, a jet, your drone - is pushed and pulled by the same four forces.
Diagram of lift, weight, thrust, and drag acting on a drone

Flight is a constant balancing act between four forces

To hover, lift exactly equals weight. To climb, lift beats weight. To move, the drone tilts so some thrust points sideways.

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Hover, climb, or descend

The whole game of altitude is a tug-of-war between lift (up) and weight (down). Change how hard the motors push and you change which force wins.
Three drones showing descend (weight wins), hover (balanced), and climb (lift wins)

Whoever wins the lift-vs-weight tug-of-war decides if the drone rises, holds, or drops

Weight > Lift

Motors ease off, gravity wins, the drone descends.

Lift = Weight

Perfectly balanced - the drone hovers in place.

Lift > Weight

Motors speed up, lift wins, the drone climbs.

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How a propeller makes lift

A propeller is really a spinning wing. Each blade is shaped as an airfoil, and as it slices through the air it throws air downward. By Newton’s third law - every action has an equal and opposite reaction - throwing air down pushes the drone up.
Airfoil cross-section showing air pressure difference creating lift, with Newton's third law inset

A spinning propeller pushes air down, and the air pushes the drone up

Spin the propellers faster and they throw more air down, creating more lift. This is the drone’s throttle: more motor speed means more lift means the drone rises.

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Four motors, total control

Here’s the clever part. A quadcopter has no flaps or rudders - it steers purely by changing the speed of its four motors. Two spin clockwise and two counterclockwise, in an alternating pattern.
Top-down view of a quadcopter showing two clockwise and two counterclockwise motors

Opposite motors spin the same way; this cancels out spin and keeps the drone stable

If all four motors spun the same direction, the whole drone body would spin the opposite way (like a helicopter with no tail rotor). Alternating the directions cancels this out - which is why propeller placement matters.

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From motor speed to movement

So how does changing four motor speeds turn into “go forward” or “spin left”? By speeding up some motors and slowing others, the drone tilts in the direction you want to go, or twists to face a new way.
Top-down grid showing which motors speed up for forward, backward, turning, and climbing

Speed some motors up, slow others down - that's how every move happens

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The three ways a drone moves

Pilots describe drone motion as roll, pitch, and yaw - three ways to rotate around three axes.
Diagram of roll, pitch, and yaw rotation axes on a drone

Every drone movement is a mix of roll, pitch, and yaw

Roll

Tilts left or right, so the drone slides sideways.

Pitch

Tilts forward or backward, so the drone flies forward or back.

Yaw

Spins the drone left or right to face a new direction, without moving.
Add a fourth control - throttle (all motors faster or slower for up and down) - and you have the four inputs behind every flight, whether you push a joystick or send a command from your code.

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The four inputs behind every flight

Every command you write on Day 3 sets one of just four values: roll, pitch, yaw, and throttle. Learn them now and the code will make instant sense later.

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Try this thought experiment

Why does it drift?

If the drone drifts sideways while hovering, which force is slightly unbalanced - and how could the flight controller fix it?

Heavier drone

If you taped a coin to your drone, what would the motors have to do to still hover? What happens to flight time?
You can name the four forces of flight, explain how a propeller makes lift, describe roll, pitch, and yaw, and connect each to throttle and the two sticks.