12.17. Gyro setup - variable pitch tail rotor

Heading Hold Gyro setup:

First, if you are using a heading hold gyro (such as the GY240 or GY401) you must make sure your transmitter REVO MIXING option is disabled, because this option is only for non-heading hold gyros.

If you are using a Piccoboard with a heading hold module, you do not need to trim the helicopter properly without the heading hold module installed (e.g. as a yaw rate gyro). Just install the heading hold module and it should work properly as a heading hold gyro. You may need to adjust the gain however.

12.17.1. GY240 setup

There are three controls which require setup on the GY240.

12.17.1.1. Setting AVCS

Set to ON. AVCS is Futaba's name for "heading hold" and you want this enabled.

12.17.1.2. Setting DIR

  1. Turn on the transmitter.

  2. Disconnect the heli motor.

  3. Plug in the heli battery.

  4. Wait for the gyro to initialize.

  5. Turn the heli right about 20 degrees. If your tail rotor faces left(Corona) then the tail rotor blades should increase in pitch. If your tail rotor faces right (ECO, Logo) then the tail rotor blades should decrease in pitch.

  6. If the tail rotor blade pitch change is wrong, then flip the direction switch on the gyro, and retest.

12.17.1.3. Setting GAIN

  1. For the Corona, the GY240 does not hold the tail well without high gain (because it's fixed pitch) so set this to about 75%.

  2. Otherwise, set this to 50% to start. It can be adjusted later if the tail wags too much.

12.17.2. GY401 setup

There are five controls on the gyro and one on the transmitter which require setup on the GY401.

12.17.2.1. Setting DS

This should be OFF unless you are using a S9253 S9250, S9450, etc. digital servo compatible with a fast update rate. Not all digital servos are compatible with the GY401 DS mode!

12.17.2.2. Setting DIR

See the GY240 section on setting this switch.

12.17.2.3. Setting DELAY

Set this to about 50 initially.

If your tail servo is fast (<0.11 sec/60 degrees) set this to a lower value.

If your tail servo is slower or you are using a fixed pitch tail driven by a variable speed motor (Piccolo Hummingbird, etc.) then set this to a higher value.

12.17.2.4. Setting LIMIT

This controls the amount of tail servo travel.

  1. Turn on the transmitter.

  2. Disconnect the heli motor.

  3. Plug in the heli battery.

  4. Wait for the gyro to initialize.

  5. After the gyro has initialized, make sure the tail servo is at the center of its travel range (90 degrees to servo body) and the tail pitch lever is at the center of its travel range as well (90 degrees to tail boom).

  6. Turn off the AVCS mode temporarily at the transmitter.

  7. Use the rudder stick and give full left rudder and full right rudder. The tail servo should be moving moving the tail pitch slider through its full range of motion.

  8. If the tail pitch slider is not moving far enough, then you will need to increase the LIMIT control.

  9. If the tail pitch slider is moving too far and hitting the ends of travel and the tail servo is emitting buzzing sounds, then decrease the LIMIT control.

  10. It may be necessary to move the tail servo mount on the tail boom or adjust a ball link or something else to ensure that:

    1. The tail servo can move the tail rotor pitch from minimum to maximum without binding (e.g. without the tail servo making a buzzing sound).

    2. The tail servo should be centered when the tail rotor pitch is at the middle of its range. Be sure to reenable AVCS mode after setting the LIMIT control.

12.17.2.5. Setting SENSITIVITY

This is set at the transmitter on channel 5 for both Futaba/Hitec and JR radios.

If you have a transmitter with gyro support, then one of the transmitter toggle switches will switch between two gyro sensitivity settings, and there will be a menu where you can choose the two gyro settings associated with the two switch positions. In this case, set the down switch setting to 50% normal (yaw-rate) mode and the up switch position to 50% heading hold mode. If you do not have a transmitter with built-in gyro support, then you will use the landing gear channel to control the gyro sensitivity. The two gear positions (up/down) will be used to select two gyro sensitivity settings.

If you have a Futaba/Hitec (negative shift) radio without gyro support, then channel 5 settings below 50% are non-heading hold mode sensitivity and settings above 50% are heading-hold mode sensitivity. For the initial settings, set the down switch position to 25% travel and the up switch position to 75% travel.

If you have a JR (positive shift) radio, the settings are swapped, e.g. below 50% is heading hold sensitivity and above 50% is non-heading hold sensitivity. For the intial settings, set the down switch position to 75% travel and the up switch position to 25% travel.

After you have set the gyro settings, you should disconnect the motor wires and power up the helicopter to check the gyro settings. If you power up the gyro in heading hold (AVCS) mode, then the LED on the gyro will blink rapidly for a few seconds during initialization, then stay on. When you switch to yaw rate mode, then the LED will turn off.

If you power up the gyro in yaw rate (NOR) mode, then the LED on the gyro will blink rapidly for a few seconds during initialization, then blink slower. You cannot switch to heading hold mode if you power up the gyro in yaw rate mode.

12.17.3. Non-Futaba Heading Hold gyro setup

You should follow your manufacturer's directions.

In addition, you should set the subtrim step size to the smallest increment possible so you can get very fine control of the rudder neutral point so you can match the transmitter's rudder neutral point to the gyro's neutral point.

On the Futaba 9C, go to the TRIM menu and change the rudder step size from 4 to 1.

12.17.4. Yaw-Rate Gyro setup

If using a separate yaw rate gyro (not Piccoboard):

You need to enable the REVO MIXING feature on the transmitter and adjust the REVO MIX curve to effect revo mix changes.

If using any Piccoboard WITHOUT the heading hold module:

You will need to adjust the REVO MIX dial on the Piccoboard to effect revo mix changes.

The revo mix controls the speed or pitch of the tail rotor relative to the throttle position. This is required to counteract the torque generated by the main rotor blades so the heli does not yaw while in flight.

You will need to adjust the revo mix so the heli does not yaw at all throttle positions.

The best way to do this is to buy a "lazy susan" type turntable that will allow the helicopter to rotate freely while the helicopter is weighed down so it won't take off inadvertently. (Rubbermaid appears to make one which is probably suitable)

Perform preflight checks, then slowly apply throttle.

The helicopter will start to yaw as you apply throttle.

You will need to adjust the revo mix so the heli has no tendency to yaw as you slowly apply throttle. It is normal for the tail to swing a little when changing the throttle, as long as the heli does not continuously rotate while the throttle is not changing.

If the helicopter is rotating and you need to increase the thrust of the tail rotor to counteract the rotation, then you should increase the revo mix at that throttle position or turn right the revo mix dial on the Piccoboard.

If the heli is rotating and you need to decrease the push of the tail rotor to counteract the rotation, then you should decrease the revo mix at that throttle position or turn left the revo mix dial on the Piccoboard.