While i am still a green horn with these heli's my Trex 450 was doing fine. I installed a CPII which has nothing to do with the gyro/tail and now all it will do is spin in uncontrolable circles all the right stick input and right trim will not stop it. I think i have probably screwed up a setting somewhere along the way but can't seem to find the issue. The gyro, a 401 is still plugged in to the rx (Berg 7L) as always. My tx is a 9303 airplane radio so the heli settings are limited. The tail was fine earlier. Any suggestions? I am willing to try most any thing at this point. Thank you.

Sounds like the gyro sense is reversed.

Do the following checks.

Make sure the tail is spinning the correct direction, that is, counter clockwise looking at the right side of the helicopter (nose left, tail right)

Give right rudder, make sure the tail blades change pitch so as to push the tail to the left. If thats wrong reverse the rudder channel.
Pick up the heli and turn the nose left, the tail blades should do the same thing as above, if thats backwards, reverse the nor/rev switch on the gyro.

That all seems to check out ok. Another issue is the servo is not going back to center when the rudder stick is recentered. It is holding left input or right input from the tx but not going back to center. Strange....

Thats just how heading hold gyros work. Its waiting for the heli to do what it's told, the heli is sitting there on a bench so the gyro is patiently applying rudder waiting for a reaction. Pick up the tail and move it, you'll see the servo recenter.

Told you i am a green horn. Any other ideas on what to check? Thank you for your help.

What menu are you using for your gyro gain? If using the Gyro Sense menu, with a 9303 you MUST plug in your gyro signal wire to Aux2.

Skarn

Did anyone mention, NO trim on rudder...NEVER with a 401.

Solid red gyro light after bootup?

Problem resolved thanks to my good friend and local heli expert. He was kind enough to take it home and figure it out. The tail rotor shaft gear had become seperated from the shaft. He replaced it with an upgraded metal one versus the nylon gear that the heli came with. Due to my limited experience i don't think i would have ever found this on my own. Thanks Rick aka Gyronut.

Except subtrim! Subtrim with a 401 is perfectly fine to get the servo arm at 90.

But NO trim to stop drifting....

Glad you got it working!

Skarn

You really don't want the servo arm to be at 90 at neutral with a 401, which is like the biggest myth in this hobby. The 401 needs intentional differential on the servo arm to compensate for its lack of independent limit settings for left and right rudder without binding on either side while still providing full pitch range. You just want to be sure the differential in in the correct direction (otherwise you'd be better off with 90 degrees). This also somewhat allows (in the ballpark) normal mode mechanical centering and moves the slider through TR zero degrees (the dead zone) at peak linkage speed. Alternatively, with a 90 neutral setup you either have to give up centering in normal mode (which could be bad), a lot of right rudder authority (which is bad) or else allow binding (which is seriously bad).

Since the gyrodetects yaw rotation rate and dynamically responds, it doesn't care if the linkage is squared up with the arm at neutral. It's more important that it can deliver full pitch range in either direction without any kind of binding and with good servo resolution throughout the range.

Set the servo arm at 90 degrees, center the tail pitch slider, set the servo arm length such that you get at or slightly above 100 on the limit pot without binding.</p>

Put it in HH and go fly.  Don't worry about rate mode.</p>

...until somebody accidentally gets one off the ground in normal mode(and they will)with the tail spinning at neutral stick, gets freaked out and puts it in the pits and kills someone's innocent plane.

Not if you don't even have rate mode setup on the radio! Since I never plan on flying in rate/normal mode, I don't have it set up.

Like Cuda said, center slider in rate, set limit pot so it's not binding, put it back in HHmode and never look back.

Skarn

Well, I wouldn't give up normal mode as I use it for pre-spool centering.  That way the tail doesn't have to swing all over the place before take off like it's amateur night or something.  But, to honor simplicity maybe it's too ####ing complicated. </p>

LOL, Iwouldn't say it's too complicated. But it is pretty easy to simply flip the rudder stick back and fort a few times and it will accomplish the same thing...

Skarn
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After your tail lets go, feel your servo.  My tail servo limits wereset too high and were allowing my servo to bind and go out.  I swappedout servos (the other one was toast) and gave it less total throw. It's been fine ever since.  Also, cheap servos (if that's what youhave) do terribly on the tail.  I've just started flying heli's, butthat's still what I've experienced.