Drone Flight Controllers: How Quadcopters Stay Up

Throw a brick in the air. It tumbles. A Quadcopter is basically a brick with 4 propellers. It is naturally unstable. If one motor is 1% faster, it flips over and crashes. How does it hover perfectly still?

The 400Hz Loop

Inside the drone is a Flight Controller (a tiny computer). It runs a loop 400 to 8,000 times a second.

1. Read Gyro: “I am titling 0.5 degrees Left.”
2. Calculate Correction (PID): “I need to speed up the Left motors to push me back up.”
3. Command ESCs: “Motor 1 and 2, increase power by 3%.”

PID in the Sky

• P (Proportional): Snap back to level.
• I (Integral): Hold level against the wind.
• D (Derivative): Stop the snap so you don’t overshoot.

If the PID tuning is wrong, the drone wobbles (“Oscillation”) or feels “Mushy.” In FTC robotics, we do the same thing to make our robot drive straight. If the left wheels drag on the carpet, the Gyro senses the turn, and the PID boosts the left motors to compensate instantly. You are running “Flight Controller” software on the ground.