It’s often asked, how can a quadrocopter fly at all? Actually, it is quite simple…
There are two different propellor-rotations. The front and back propellor turn clockwise, while the left and right propellors spin counter-clockwise. To hover, all propellors rotate at the same speed. When doing so, the forces between the clockwise props on one hand, and the counter-clockwise props on the other hand, are balanced out. This makes the quadrocopter hang steady in the air.
To be able to fly in one direction, the quadrocopter will be brought out of balance. The speed of the propellor that opposes the desired direction is increased. This makes the quadrocopter tip over in a certain direction. Example: to fly forward, the back-propellor has to turn faster. This is called “pitch” or “nick”. In this MK community “nick” is the preferred name for the forward/backward-movement. Left and right movements are called “rolls”.
Turning around it’s vertical axe is called “yaw”, but in German it is referred to as “gieren”. To be able to yaw you need a force to turn around. This is produced by changing the speeds between the forward/backward props and the left/right props. Example: to be able to yaw clockwise, the forward/backward propellors will turn faster and the left/right propellors will slow down a little. This makes the quadrocopter turn clockwise, while maintaining the same height.
For a stable flight, you need a controller. The main task of such a controller is to make sure that the Mikrokopter stays steady in the air. It uses data from several sensors and calculates the speed for each individual propellor. Basically the controller also compensates for external disturbances like wind. The controller is programmed with (open-source) software that holds all logic to keep the Mikrokopter balanced

Source: www.mikrokopter.de

And some videos.

MikroKopter – HexaKopter from Holger Buss on Vimeo.

MikroKopter – Storm from Holger Buss on Vimeo.