I try to do exactly what Kelly says regarding lengths of the control arms.

I usually run a separate bellcrank so the tension on the steering cables is not dragging on the servo shaft,
the servo drives the bellcrank with a separate link.

There's a very fine line between adequate tension on the cables & stopping the retract from locking down,
a LITTLE slack is needed. If the nosewheel folds your just a passenger. As the wheel retracts the cables
go slack, a cable tie used as a tensioner or a couple of light rubber bands to maintain some tension on the
cables & prevent them catching on things in the model.

John.