The model was based on a 3 DOF helicopter from Quanser. Two DC motors are mounted at the two ends of a rectangular frame and drive two propellers. The motors axes are parallel and the thrust vector is normal to the frame. The helicopter frame is suspended from an instrumented joint mounted at the end of a long arm and is free to pitch about its center. The arm is gimbaled on a 2 DOF instrumented joint and is free to pitch and yaw. The other end of the arm carries a counterweight such that the effective mass of the helicopter is light enough for it to be lifted using the thrust from the motors. A positive voltage applied to the front motor causes a positive pitch while a positive voltage applied to the back motor causes a negative pitch. A positive voltage to either motor also causes an elevation of the body (pitch of the arm). If the body pitches, the thrust vectors result in a travel of the body (yaw of the arm) as well. The vertical base is equipped with an eight-contact slipring. Electrical signals to and from the arm and helicopter are channeled through the slipring to eliminate tangled wires, reduce friction and allow for unlimited and unhindered travel.