Originally Posted by zappygon
But with two motors only how is it able to move around ?
The rotor blades rotate downward into the direction of movement and upward when they reach the opposite direction. This is in addition to pitch changes, which control lift. The difference is for pitch, the change is consistent throughout the rotation, regardless of the direction of movement. For example, to move forward the rotor blades may rotate - 8°, when they reach the forward position in their rotation, while the backward side rotates +8°. At the same time, you could be giving pitch changes to climb, which causes the blades to rotate upward +5°; the net would be -3° forward and +13° rearward. Of course, these numbers are just for illustration. Actual values will vary a lot.
This is how it's done with a conventional single rotor or tandem, collective pitch heli. With the design I was working on, I was allowing only the front rotor to supply directional and pitch changes. The rear could supply compensating pitch changes, but that is all. In theory, this aids the ability to control movement and stability, as the rear rotor acts as the anchor or pivot. Having both rotors doing exactly the same thing introduces variables that are hard to control, IMO.