RE: Older transmitter with the axe
Do you still have the manual for the radio? Many older helis (and older designs like the ARK400) used discrete mechanical mixing for the rotor axes. The Axe uses CCPM, where the servos act directly on the swashplate and the transmitter processor does all the mixing instead. If the 8U doesn't have a CCPM mode, then you'll be out of luck. Specifically, it's 120 degree CCPM you're looking for.