After waiting 5 weeks for one of my parts turning up, yet again i had a B400 that still wouldnt fly.

But as i have swapped all servos for hitec metal geared ones i could at least find if these are working ok

All cyclic works fine, all servos acting as the should, mixing ok etc

The problem is with my tail, i noticed that the servo horn was not centered after setting up a week or so before, so i let gyro initialise, unscrewed the horn and re centered.

Spooled up the heli to find it would spin in both directions for no reason, no trim would remove this. If i counter acted the initial spin then it would stay still for a few seconds until i powered down, once the throttle was reduced in any form the heli would immediatly spin wildly out of control

Ive took it up to my lhs and they think the gyro might be shot, they said again the servo wassnt centred, re centered it again and then found that with left rudder the servo would go straight back to center but with left it would not center just creep there, this was not due to H H gyro function, it was in rate mode

Any ideas ?

Do you still have the stock tail servo. You could do a quick test and put it on and see if it does the same thing. If it does you might have a bad gyro, but I have not heard of any gyro's going bad. When you set up the tail did you do it in standard rate mode. When I set up my tail I have zero degrees of pitch on the tail blades with no rudder input. Did it work before with the hitec servo? In the past I also set up the tail servo by bypassing the gyro. I would connect the tail servo directly to the rudder pin on the receiver. Then when I got everything set up I would reconnect the tail servo to the gyro. Also have you changed any settings on the transmitter besides the subtrim? Did you accidently hit the rudder trim on the transmitter?

Nick

You mentioned that you replaced the tail servo as well as the others. You need to reverse all 4 servo settings in the TX, you will (I think) also have to reverse the servo control switch on the gyro.

One way to check:

Fire it up stationary on the bench and move the rudder stick left, the tail blades should tilt to push the tail right (leading edge of the blade to the right to push the nose left for any newbys following along)

Now push the tail to the left and the gyro should tilt the tail blades the same way, ie, trying to push the tail back to the right. If not, gyro switch is reversed and there is no way on earth you would be able to fly it!! When it starts to move, the gyro pushes the servo the wrong way, causing it to move more in the wrong direction, so the gyro puts even more force in there. A never ending pirouette is the net result, in which ever direction it last moved.

To make sure the servo horn is centred without having to unplug anything, just set it for no gain at all, ie, 50% on the DX6i TX. Mechanically center the horn - but do not use subtrims - that comes next.

Once you have that setup correctly, with the gyro in HH mode and at about 50% gain (ie 75% gain on the DX6i TX) make sure that the servo can not drive the tail control too far, may have to move the ball link in another hole on the servo arm, then move stick left then gently release. Servo arm should move bout halfway back to centre and stay (not creep). Then try same thing in opposite direction. If it is creeping, it will only be doing it from one side, use subtrim until you get this out.

This is the method used in the Finless Bob videos - I have found it works pretty good.

Sounds like exactly what was happening to mine. I didnt have any mods to it yet. The solution... I got a brand new one from my lhs, who sent my old one back to be fixed. They been flying heli's for over 5 years and couldnt figure it out. replaced gyro, replaced everything one at a time. The new one works great.