How Do Drones Fly and Stay Stable?

A typical quadcopter drone has four rotors arranged in an X or + pattern. Pairs of diagonally opposite rotors spin in opposite directions to cancel torque. By varying the speed of individual motors, the flight controller adjusts pitch, roll, and yaw. Onboard inertial measurement units (IMUs) — combining gyroscopes, accelerometers, and sometimes barometers — feed data to the controller hundreds of times per second, making micro-adjustments to keep the craft level. GPS modules enable position hold and autonomous waypoint navigation, while optical-flow or ultrasonic sensors aid low-altitude hovering.