Laszlo,
thanks for the explanation.
Yes I was wondering how effective yaw control was with the tandem or side by side configurations. In full scale aircraft, they allow the rotors to tilt through flapping hinges on each blade. Therefore it is much easier to tilt the thrust vector and minimize the torque on the fuselage.
Be careful in doing this. The rotor systems have frequencies where exciting them could cause the rotor system to couple with the aircraft structure. If you are familiar with ground resonance in full scale helicopters, then this is a rotor mode that you could encounter in your experiment. I once tried to build an RC V-22. My first design resulted in very large oscillations in the rotor systems in the opposite directions. The lead-lag mode of the rotor systems was coupling with the tube that connected the two rotor systems. here is a link to a post where I talk about the issue in more detail.
Keep me posted on your progress.
Regards,
Bill