How to setup the Gyro with a servo
There are different forums with movies how to setup your Gyro and servo. Check my links
The setup method I used is as follows. For more specific Gyro explanations scroll down.

Step 1.
First setup the tail mechanicaly. This means that the servo arm should be 90 degrees with no trim and/or subtrim. The tail slider should be in a angle that the tail blades are straight. Or in a little angle to overcome the torque of the motor.

Step 2.
Program your Gyro so that you can switch between normal and HH mode from your transmitter.
In my case this is the gear channel. +36% gain for HH mode and -70% for normal mode.

Step 3.
Check your servo direction and the Gyro direction. You can test it easily with the rotorblades off. Set the heli on the ground and spin up (not full throttle). Steer the rudder to check the servo direction. If the direction from your servo is reversed switch it in your transmitter. Spin up again give a little rudder. If the Gyro is reversed the heli will spin around. So disconnect the battery and switch the Gyro from normal to reverse or the other way around. Always connect the battery for the changes to take effect.

Step 4.
The potmeter "travel" on your Gyro limit the servo range. Adjust it so that there is no binding with maximum steering input. This is al done in normal Gyro mode.

Step 5.
Make a hover with the Gyro in normal mode. Counter steer the tail if it starts to drift to a direction. Land the heli and keep in mind whitch way you steer.Move the servo over the tail boom to eliminate the counter steer. Each time a little bit and make a hover to check. Repeat this procedure to center the tail without any (sub)trim. Try to achieve little tail drift as possible. If you use (sub)trim to center the tail in normal Gyro mode the servo can creep in HH mode.

Step 6.
Put the Gyro in HH mode and steer full in a direction. Quickly let go of the rudder stick. The tail should hold its maximum position. (you are in normal mode if the servo change quickly to its neutral position when you let go of the rudder stick) If the servo creeps use subtrim to filter this out. Do this for both directions. After this the tail should hold. You are in normal mode if the servo change quickly to its neutral position when you let go of the rudder stick.

Step 7.
Keep your Gyro in HH mode and make a hover. If the tail drift in one direction increase the gain. If the tail start to wag decrease your gain. Fine tune the gain for optimal performance.

Step 8.
There is a big differance in HH mode than in normal mode. You must realize a few important changes:
- the endpoints from the rudder channel adjust the piroutte speed from the Gyro;
- the endpoints from the gear channel adjust the gain from the Gyro.

Step 9.
If you use a analog servo you must use "delay" on the Gyro. For digital servos the delay is zero. In the E-sky manual the delay is used for how the servo ends a piroutte. By zero degrees the tail stops quickly. With a little delay the tail stops a bit smoother.


What is heading hold
In non-hh mode the gyro just dampens unwanted movements of the tail. To keep things simple lets say you are hovering and a constant wind hits the helicopter from the side, the gyro will keep the helicopter from suddenly swinging nose into the wind, but the helicopter will eventually drift nose into the wind. All the gyro does is to prevent any jerk type reaction. In hh mode the gyro will keep the nose pointed in the same place until you tell it to move. You can fly sideways with the rudder stick in the center and the nose will remain pointed in the same direction. If you have not used heading hold before then you will notice in fast forward flight that when you make a turn, the tail will not follow the helicopter, you have to give some rudder in your turns.
Another thing is that you'll notice the rudder stick feels different. In heading hold, the amount you move the rudder stick from center tells the gyro how many degrees per second that you want the helicopter to rotate. The gyro moves the rudder servo however much it needs to obtain the requested rotation rate. With a standard rate gyro if you did a slow pirouette (one rotation) with the wind then to keep the helicopter spinning at the same rate you would have to move the rudder stick more as the tail is going upwind and less as the tail goes downwind. But with a heading hold gyro, it will tell the rudder servo to move more or less to maintain the constant rate, you just keep the rudder stick in one place. Due to typical marketing ploys you will see many names for heading hold. They all are just different names for the same thing. AVCS = Tail Lock = Smart Lock = Heading Hold


Rudder ATV values
On a non-heading hold gyro this function in your radio is used to set how far the rudder linkage will travel. On heading hold gyros this function works completely different. It is used to set the maximum rotation rate. So what do you do about limiting the travel so as not to allow the servo to bind? Some gyros have a limit adjustment on them that you use to set this. The ones that do not require you to move the ball on the servo arm further or closer to the center of the arm to limit the travel.


Can I use rudder trim
If you are using a heading hold gyro then the quick answer is no. The reason is that heading hold gyros are looking for a centered command from the radio to keep the helicopter from rotating. If you move the rudder trim a few clicks one way or the other then a gyro in heading hold mode thinks that you wanting it to spin in that direction. Example: Say you have switched to non-heading hold mode and the helicopter is rotating left so you add a little right trim until the helicopter is still. Now when you flip back to heading hold then you will find the helicopter now constantly rotates to the right. How to trim the helicopter in both heading hold and non. The first step is to center the trim and zero the sub-trim. Next with the gyro in heading hold mode adjust the sub-trim so the helicopter does not rotate. Normally this should be zero but due to small differences in the radios as well as some gyros you may find you have to adjust the sub-trim. The next step is to switch to non-heading hold and if the helicopter drifts, then adjust the rudder linkage. If the helicopter is drifting left then turn the link clockwise, opposite if drifting the other direction.


Heli spins out of control
The cause is the reverse setting on the gyro. This is not the same as the reverse settings in the radio. To check the gyro move the rudder stick to the right, the control rod for the tail should be pulled toward the front of the helicopter. Next pick up the helicopter by the rotor head. Grab the tail boom and quickly rotate the helicopter so the nose goes to the left. Watch the control rod, it needs to move forward. If it does not then the gyro is backwards. Most gyros have a reverse switch or jumper located on the gyro, this is not done in the radio. A few gyros require you to turn the gyro upside down.


Gyro gain
This refers to the sensitivity of the gyro. When the gyro senses an unwanted movement it commands the tail servo to move in the opposite direction to compensate. How much it tells the servo to move is the 'gain'. Ideally the amount of gain should match how much the helicopter was rotated so that it stays pointed in the same direction and does not move. If the gain is too high then the helicopter over compensates. The effect you will see is the tail will bounce back and forth (aka wag). If the gain is not enough then you will notice the tail does not hold very well. When setting the gain, you want to turn it up until you see the tail 'wag' (bounce back and forth) then turn the gain back down until it stops.


How to set the gain
Gyros with remote gain: This depends on the type of radio you have and how you set it up. Some radios do not have a dedicated gyro function. For these you adjust the gain in the travel adjust (aka End Point, EPA, ATV) menu. In this menu select the gear channel (channel 5) and use the switch assigned to it to toggle between the gain setting for heading hold and non heading hold. For radios with gyro menus leave the atv's set to the default values (usually 100) and then use the gyro menu to set the gain Gyros without remote gain: This type will have an adjustment on the gyro. It is usually a small pot that you use a screwdriver to turn.


Gain values
Set your end points (ATV) to 100% and 100% for the gyro gain too. Then if the tail wags lower the gain from there. If you have to go below 85% then move the ball on the servo arm in one hole toward the center and try again.


Delay
This is a setting found on some gyros such as the popular Futaba GY401. It is used to compensate for slower servos. To set it do a quick pirouette and when you stop watch to see if the tail stops still or bounces. If it bouces then increase the delay to stop it. For a fast servo like the Futaba 9253 leave the delay setting at 0.


Source: summary of important information from different internetwebsites