This is awesome, great inspiration and education for Drones creation. Check out this quote from the article.
Multi-rotors fly with remarkable speed and stability because they have a number of points of thrust, not just one. Each works against and with other thrust points—and with and against gravity—to move the craft along three axes, and, if needed, hold it steady in one position.
A multi-rotor pitches, rolls, yaws, and hovers by varying the speed of its motors (each connected to a fixed-pitch propeller) individually, which varies thrust (for pitching and rolling) and torque (for yawing). This type of aircraft, however, is inherently unstable unless “balanced” by a very powerful flight control computer, one that can analyze aircraft attitude and position, then provide control inputs (as motor speed rate changes) orders of magnitude faster than a human’s ability. Think of trying to balance a baseball atop the tip of a pencil: You’re not really “balancing” it, but constantly moving the pencil under the baseball in a dance with gravity to get a few brief moments of relative stability. But most people don’t have the eye-hand coordination for such a feat. Similarly, until recently, sensors and computers simply couldn’t work fast enough to use multiple thrust points to control a small aerial vehicle.
Over the past few years, the electronics industry has made great strides in the development of micro-electromechanical systems and inertial measurement units. These include tiny, solid-state, multi-axis gyroscopes for spatial orientation and accelerometers to measure change in velocity to guide multi-rotor and other types of aircraft. Manufacturers also produce micro-electromechanical magnetometers for navigation, and pressure sensors (barometers) for altitude determination.
(see article above)