Adjusting the Gyro
A helicopter's tail must point in one direction until you tell it to turn. This chore is handled by an electronic gyroscope. When you first get a model or when temperature or humidity changes the gyro may need to be adjusted. This is not hard to do.
You need to adjust the gyro if:
- The tail moves to the side when spinning up on the ground
- The tail moves to the side when hovering and the left stick is centered
- The tail wags from side-to-side when the helicopter is in the air
The goal is to make the tail stay still without using the left stick or the trim tab on the transmitter. You may get it close and still need to crank in some trim. And as the battery becomes discharged you may need a little yaw correction (left stick sidways) near the end of a flight. Such minor variations are okay but you might as well try to make the gyro work as perfectly as you can.
There are two kinds of gyros: 'rate' gyros adjust the speed of the tail motor to counteract torque from the main rotor and that is all. Heading Hold (HH) gyros keep the helicopter pointed in the same direction even when it is affected by wind. These deluxe gyros cost more and make the helicopter nicer to fly. Heading Hold gyros are also called AVCS, which stands for Angular Velocity Control Systems.
Ready-to-Fly models have a gyro on the 'mixing board' in the nose. The board handles co-ordination of the servos for directional and pitch control. It also has an electronic speed controller for the main motor and another for the tail motor if there is one. And it has a simple gyro with two adjusting screws.
More sophisticated heli's that are 'running separates' have individual gyros that are typically mounted just behind the rotor mast, either above or below the tail boom. Some are equivalent to the gyro on a mixing board. Heading Hold gyros are more accurate and some may be adjusted from the transmitter.
In the case of co-axial helicopters and RTF fixed-pitch or CP birds such as the Honey Bee FP, Walkera #4, Blade CP/Pro, Esky CP2, etc., you will deal with the two adjustment screws on the mixing board. One screw is labeled 'proportional'. It controls the speed of the tail motor with respect to the speed of the main motor. The other screw, which is labled 'gain', controls how sensitive the gyro is. In other words gain controls how early or late the gyro responds to changes in main motor speed.
The proportional screw is used to stop the tail from moving sideways in a single direction.
The gain screw is used to stop the tail from wagging or to make the gyro more responsive if the tail lags behind changes in throttle speed.
Gyro adjustments will not take effect until the flight battery is unplugged. This is because the gyro 'initializes'—senses the position of the helicopter—when power is first turned on. Do not move the helicopter or apply power until the flashing green LED on the mixing board, visible through the clear portion of the canopy, goes to steady green.
If the helicopter rotates as you spin it up and it gets near take off speed, use the proportional adjustment first. If it turns clockwise the gyro needs less compensation so turn the screw out, or counter-clockwise, a quarter to a half turn. If the heli is rotating counter-clockwise the gyro is doing too little. Turn the proportional screw in, or clockwise—one quarter to one-half turn. Then spin it up and/or hover it to see if the tail is more steady.
If the tail wags from side to side when the helicopter is in the air the gain is set too high. Turn it down in very small increments by turning the gain screw out, or counter-clockwise, until the tail stops wagging. You want the gain turned up just before the point where it will make the tail wag.
It may be necessary to go back and forth from the proportional control to the gain several times to get the gyro to work as well as it can. Be patient and observant and you will get it dialed in nicely.