How to Setup the centering on a Tail servo with a Rate/Heading Hold Gyro for the EXI/Exceed 450 line of Helicopters
If you have taken your tail apart
NOTE: I recommend 7-8mm for the distance from tail servo ball to the servo center. Closer to 7 is better than 8.
is always good to use reference pictures of your mechanical setup when
putting things back together. The Heli MFG website is a good reference
but so are your own pictures. I prefer to take complete pictures of all
my new helis using a digital camera and saving them. Use a tripod with
no flash. Using a timer helps so that the camera is not shaking during
the picture. That takes nice photos without the glare or reflection of
Whenever putting the tail back together, make sure your belt is on correctly.
The belt should have a 90 degree twist in it. Start w/ it straight down the tube then twist it so that when the main rotors turn CW (looking from the top) that the tail gear turns CCW looking at it from the right. The thicker part of the tail blade is the leading edge. Make sure the tail blades/holder is on correctly. Minimize slop during re-assembly. The best way to measure slop is to remove the linkage from the tail servo. Hold the linkage in your finger and grab the tail blade and move the tail servo linkage by hand looking for slop. Also look for resistance. Some screws need to be tight but not too tight. A good holding tail has slop and friction/resistance minimized.
the Servo and Gyro polarity
Verify you have your Tx servo reverse and gyro reverse set up correctly.
Set Gyro in rate mode.
Looking from the back of the heli, Move the rudder stick to the right, the tail slider should move to the left. If not, use reverse on the servo.
now, hold the tail slider in your finger tip. pick up the heli and jerk it CCW (nose left). Tail slider should jerk to the left. If not, reverse your gyro. If your gyro does not have a reverse switch, you have to rotate the gyro about the tail boom axis. (Esky 704A gyro would have the label facing right vs. left for example).
Setting up Radio and centering the Tail Servo
Set up your radio with zero subtrim and rudder trim. Set up your tail servo horn on the servo so that it is 90 degrees at center rudder. Verify that Moving your rudder right makes the tail slider move left (when looking from the tail of the heli). Slide your tail servo on the boom to the position that yeilds a couple degrees of right rudder. Make sure the tail servo mount is tight enough on the boom to keep it from moving easily but not so tight that you can't manually slide it up and down the boom. Set your gyro to rate mode. Hover the heli and then note if it is drifting right or left (nose left or nose right). If it is drifting NOSE LEFT, you need more right rudder so move the servo mount forward. If it is drifting NOSE RIGHT, then move the servo mount backwards. Do all this WITHOUT touching the Tx trim which should still be in the center. Once your satisfied, tighten down the tail servo mount.
Now turn off the heli, turn it back on again so the gyro can initialize and try it out in HH mode. If it drifts one way or the other in HH mode, use your rudder/tail trim. For the lesser priced gyros (less than $120) It is not unusual for each flight to require a little rudder trim towards the beginning of each flight. Also, some HH gyros will drift as they warm up. Allowing the helicopter to acclimate to the environmental temperature can usually minimize drift during flight.The goal of this method of adjusting the tail servo is to make it so that if you accidently switch into Rate mode, it will not spin wrecklessly one way or the other in a hover. Also, it allows a more consistant throw in each direction allowing the HH gyro to correct movment better.
Other useful tips:
Gyro Bench Test
Gyro Trim Setup