I have a nexus also and have had the same problem with no tail rotor control. I found the tail rotor pitch change arm loose on the left hand thread brass bushing this causes a lot of slop and when the gyro tries to work it just keeps going around and when you try to work the rudder controls it will become really erratic. If you find this I suggest drilling a small hole in the brass bushing in the center area where the control arm runs also a small hole in the top of the control arm hookup bushing almost directly across from the pin. This will let you oil all bushing or bearings and the tail rotor shaft under the pitch control arm. This is only my opinion.