Another thought here is to find a nice smooth surface like concrete or something like that and dont even start the engine up. Just center your rudder and then give the plane a nice push and see if it goes straight or veers one direction or another, then adjust your linkage to track straight. I used to do this in my basement so the things would track straight. Also, the wheel dragging is a good suggestion to check out too. I got one collar too close one time and it drug, and made the plane track to the tight wheel side. I fly from buffalo grass, and one thing that really helped was to put a Fults dual strut nose gear on my trike planes, as that would take a lot of stress and movement off of the servo and control arm assembly.