RE: Difficulty trimming for yaw with a CX2.
Is the helicopter Used or New? Has it flown correctly before? When you spin the blades by hand do they move freely or have some drag. If you have a voltmeter you can check the motor output pins and see if the voltage is changing with rudder inputs and by how much. That will determine if you have a bad or good 3in1 or 4in1 which ever one you have. You might have a bad motor for the lower blades. It has been a long time since I have flown the CX to know what the problem could be. Tomorrow the Guru's should be one to help out more.
Nick