@bnsgeyer
For my case i use the differential collective pitch to control Yaw , i dont know what mean H_YAW_SCALER =0 (Scaler for mixing yaw into roll or pitch.) and H_DCP_YAW parmameters , I started analyzing the 4.1 code of the Dual Heli part ,I will keep you posted when there is something new in this porject .