A propeller is mounted on the shaft of the corresponding motor. The total number of motors that are needed depends on the build. For example, quadcopters use four motors, hexacopters use six, octocopters use eight, and so on.
Nowadays, brushless out runner motors are the most common type of motors used; they have minimal friction. A cylindrical shell of magnets rotates on precision bearings around a core of tightly and neatly coiled wire. The propeller is mounted at the top and is rotating at the same angular velocity as the motor. As a result, thrust is produced and the quadcopter lifts from the ground. Every motor requires reasonable maintenance; dirt should be kept out of the motor so that it can spin easily.
