Set the TRAVEL LIMIT on the 401 to 100%.
Set your rudder endpoints to 100%.
Initialize the gyro in HH mode (required always), then switch over to rate/normal mode. The servo will follow the stick and return to center when you go to normal mode.
Rudder set to NEUTRAL, sub-trim set to zero. Rudder trim set to zero.
Figure out which position of the servo arm will get you a hole so that a line through its center and the center of the output shaft is perpendicular to the tail boom. You may have to try the servo arm on in more than one position (the splines of the shaft make it so the arm will fit with the proper orientation in only one position. If you end up needing a bit of subtrim to get the output arm in the right position, use it.
With things set at neutral, set the length of the TR pushrod such that the TR pitch slider is centered in its travel range on the TR shaft.
Now, figure out the distance to mount the ball link from the center of the servo such that at full deflection, the servo arm moves at least +/- 45 degrees from neutral, without causing the pitch slider to run into a mechanical stop at either end of travel.
If you have the distance from center too long, the servo will only have to move a little bit to run the slider to its stops. AS you move the ball link inward, toward center, the servo arm will travel further and further before bottoming the slider out at either end of travel. When you find the distance out from center where you get +/- 45 degrees of servo travel, and the pitch slider doesn't come up against a hard stop at either end, that is the place to mount the ball on the servo arm.
Once you get there, again start up in HH mode, then switch to normal mode. Hover the heli. If the nose yaws left or right, adjust the linkage (shorter/longer) until the heli will hover without wanting to yaw left or right. Land, fine-tune the TRAVEL LIMIT setting on the gyro to eliminate any binding at either end of travel.
The goal here is to have the servo arm perpendicular to the tail boom at neutral, to have the TRAVEL LIMIT adjustment on the gyro as close to 100% as possible, and to have at least +/- 45 degrees of servo travel from center before the TR pitch slider bottoms out at either end of travel.
On a 450, you'll probably end up somewhere in the vicinity of 5-7 mm out from center on the servo.
Switch back to HH mode, go fly.
* Making the World Better -- One Helicopter at a time! *