Futaba GY401 User Manual

Using the AVCS mode correctly

An AVCS gyro is an angular velocity command type gyro. The gyro con­stantly compares the transmitter rudder operation signals and gyro internal
reference signal (transmitter rudder neutral signal) and controls the helicop­ter tail rotation speed accordingly. Therefore, for the AVCS function to
operate normally, the rudder neutral signal must be memorized in the gyro
before flight.

•Rudder neutral signal memorization methods

[Method 1] When the gyro power is turned on, the transmitter rudder signal
automatically received at that time is assumed to be the neutral signal and
is memorized. The gyro is normally used in this state.

[Method 2] Rapidly switch the transmitter sensitivity switch between the
AVCS and normal modes at least 3 times at a 1 second or shorter internal,
then set the switch to the AVCS mode position. The monitor LED flashes
instantaneously and the rudder signal is memorized. If the trimmer was
moved during flight, the memorized neutral position can be updated to the
current neutral position by repeating this operation. When performing this
operation, land the model and hold the rudder stick in the neutral position.

•Rudder neutral check method

In the AVCS mode, the servo does not return to the neutral position even
when the rudder stick is returned to the neutral position. When you want to
check the servo neutral position during linkage neutral check, etc., select
the normal mode, or remain in the AVCS mode, and move the rudder stick
left and right at least 3 times at an interval of 1 second or less, then imme­diately return the stick to the neutral position. This operation returns the
rudder servo to the neutral position.

•AVCS mode usage precautions

In the AVCS mode, always set revolution mixing to OFF. If revolution
mixing (pitch->rudder mixing) is ON, the pitch operation signal changes
the rudder neutral position. The gyro judges that an angular velocity com­mand was received and rotates the tail, therefore, the neutral position
changes.

The model flies in the same rudder trim position (including sub trim) as

Mounting Precautions

Always use the accessory sensor tape to
install the gyro to the fuselage.

This is necessary to securely fasten the gyro to the
fuselage so that operation of the gyro does not transmit
unwanted fuselage vibrations directly to the sensor.

When mounting the gyro, provide a little
surplus so that the gyro connection cables
are not too taut.

If the gyro cables are too taut, the gyro will not display its
full performance. If the gyro peels, control will be lost
and result in a dangerous situation.

When using the gyro with a helicopter,
install the GY401 at least 10cm from the
drive motor.

The drive motor generates strong electromagnetic noise.
This noise may interfere with the gyro sensor and cause
erroneous operation.

Mount the GY401 so that metals or other
conductive objects do not touch the gyro
case.

The GY401 uses a conductive resin case to reduce
electromagnetic interference. Because the surface of the
case is conductive, metal objects may cause a short
circuit.

Insert the connectors fully.

If a connector works loose due to vibration during flight,
control may be lost and result in a dangerous situation.

Always check the direction of operation of
the servos.

If you attempt to fly the model when a servo operates in
the wrong direction, the fuselage will spin in a fixed
direction and enter an extremely dangerous state.

turn the power off and on again. When turning on the
power, set the transmitter switch to the AVCS position
and turn on the transmitter power switch, then turn on the
gyro power.

Do not operate the rudder trimmer while
flying in the AVCS mode.

When the power is turned on, the GY401 assumes that
the rudder stick is in the neutral position. If the rudder
trimmer is moved during flight, the neutral position will
change.

Avoid sudden temperature changes.

Sudden temperature changes will cause the neutral
position to change. For instance, do not fly the model
immediately after removing it from inside a heated
vehicle in the winter and an air conditioned vehicle in the
summer. Let the model stand for about 10 minutes to
allow the temperature inside the gyro to stabilize before
turning on the power. Also, consider sudden temperature
changes when the gyro is exposed to direct sunlight or is
installed near the engine. Take measures so that the gyro
is not exposed to direct sunlight.

When using the gyro in the AVCS mode,
set revolution mixing to 0% or OFF.

In the AVCS mode, all rudder corrections are made by
the GY401. Therefore, if rudder mixing is ON, the model
will operate the same as if the neutral position changed.

Special Markings

Pay special attention to the safety at the parts of this manual that are indicated by the following marks.

Mark Meaning

Operation Precautions

Never move the fuselage for about 3 sec­onds after turning on the gyro power
(shared with receiver).

Since the data inside the gyro is automatically initialized
as soon as the power is turned on, if the fuselage is
moved, the neutral position will change. If this occurs,

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when the power was turned on (neutral position memorized in the gyro).
When flying in the AVCS mode, set the rudder trim to the same position
under all flight conditions, including hovering and idle up. In the AVCS
mode, the gyro automatically trims the rudder so that trimming during
flight and other precision rudder trim adjustments are unnecessary.

Other precautions

•DS switch setting precaution

When the DS switch is set to the ON position, the rudder servo is driven by
approximately 270Hz high-speed pulses. This mode is for use with Futaba
digital servos only.

When using servos that are not compatible with high-speed
pulse drive, other than digital servos, never set the DS switch
to ON.

The servo may be destroyed.

•Operation of trimmers, etc.

Miniature trimmers and switches are used with the GY401 to reduce its
size. When operating the trimmers and switches, always use the miniature
screwdriver supplied and do not apply excessive force.

•Servo small step operation

When the model is static, the servos may move a small step. However, this
is because the gyro sensitivity is set to a high value and is normal.

One point advice

•Relationship between servo horn length and gyro sen­sitivity

Gyro sensitivity also changes with the length of the servo horn.
When the sensitivity is too low, length the servo horn. Conversely, when

hunting does not stop, shorten the servo horn.

Check the operating time of the receiver,
gyro, and servo batteries at the adjustment
stage and decide the number of remaining
flights while allowing a margin.

Fuselage Maintenance
Precautions

Do not turn the sensitivity trimmer with
too much force.

The trimmer may break. Always use the miniature
screwdriver supplied to make adjustments.

Make positive maintenance of the fuselage
tail section a habit.

The rigidity of the tail section has a large effect on gyro
performance. Therefore, loose supporter and tail pipe
aging also have a large effect on the characteristics.

Service the fuselage with a little vibration
as possible.

Fuselage vibration has a very adverse effect on gyro
performance.

Procedures which may lead to a dangerous condition and cause death or serious injury to the
user if not carried out properly.

Procedures which may lead to a dangerous condition or cause death or serious injury to the
user if not carried out properly, or procedures where the probability of superficial injury or
physical damage is high.

Procedures where the possibility of serious injury to the user is small, but there is a danger of
injury, or physical damage, if not carried out properly.

Symbol: ; Prohibited ; Mandatory

©FUTABA CORPORATION 2000, 7

1

FOREWORD

The GY401 is a high performance, compact, light weight AVCS
(Angular Vector Control System) gyro developed for model
helicopters. Because the sensor and control circuit are integrated,
it is simple to install.

Applicable servos

Gyro performance largely depends on the servo used. The
higher the speed and response of the servo, the better the gyro
sensitivity and performance. From this standpoint, a digital
servo is perfect for use with this gyro. The S9253 high-speed
digital servo developed especially for gyro use is recommended.

2

FEATURES

•AVCS system

Since rudder trim changes caused by wind and other meteorologi­cal changes and front, rear, forward, reverse, and other helicopter
attitude changes are automatically cancelled, tail (rudder) opera­tion is easy, making it perfect for 3D flight.

•SMM gyro sensor

Use of newly developed extremely low drift SMM (Silicon Micro
Machine) gyro sensor virtually eliminates rudder trim changes
during flight.

•Digital servo compatible (DS mode)

DS mode makes it compatible with Futaba digital servos. Maxi­mizes the high-speed response performance of the digital servo.

•Remote gain function and mode switching func­tion

Remote gain function allows sensitivity switching from the trans­mitter and mode switching function allows AVCS/normal gyro
mode switching.

•Integrated, compact, and lightweight

Compact size (27x27x20mm) and light weight (27g) realized by
high density mounting technology.

•Conductive resin case

Conductive resin case improves EMC (electrostatic and electro­magnetic interference) resistance.

AVCS Gyro

Conventional gyros send control signals to the
rudder servo only when the tail of the helicopter
moves. When the tail stops moving, the control
signal from the gyro becomes zero. Conversely,
the AVCS gyro continues to send control sig­nals to the servo even when the tail of the
helicopter stops moving.

The following sequentially describes the con­ventional gyro and the AVCS gyro.

Operation of Conventional Gyro

Basic operation is described by considering the
case when the helicopter is hovering under
cross-wind conditions. With a conventional
gyro, when the helicopter encounters a cross­wind, the force of the cross-wind causes the tail
of the helicopter to drift. When the tail drifts,
the gyro generates a control signal that stops the
drift. When the tail stops drifting, the control
signal from the gyro becomes zero. If the cross-

Thank you for buying a GY401 AVCS gyro.
Before using your new gyro, please read this manual thoroughly and
use the gyro properly and safely. After reading this manual, store it
in a safe place.

• No part of this manual may be reproduced in any form without prior permis­sion.

• The contents of this manual are subject to change without prior notice.

• This manual has been carefully written. Please write to Futaba if you feel that
any corrections or clarifications should be made.

3

SET CONTENTS

The GY401 comes with the following accessories:

•GY401

•Mini screwdriver
(for adjustments)

•Double-sided tape
(3 sheets)

GY401 Ratings

(Integrated sensor type AVCS rate gyro)

• Control system:
Digital advanced PI (Proportional Integration) control

• Gyro sensor:
SMM (Silicon Micro Machine) system vibration gyro

• Operating voltage: +4 to +6VDC

• Operating temperature range: -10˚C to +45˚C

• Dimensions: 27 x 27 x 20mm

• Weight: 27g (including connector)

• Functions:
Gyro operation direction switch, DS mode switch, Control delay
trimmer, Limit trimmer, Remote gain control, AVCS/normal mode
switching

wind continues to cause the tail to drift in this
state, the "stop" operation is repeated until the
tail faces downwind. This is called the
"weathervane" effect.

Operation of AVCS Gyro

Conversely, with an AVCS gyro, when the
helicopter encounters a cross-wind and the tail
drifts, a control signal from the gyro stops the
drift. At the same time, the gyro computes the
drift angle and constantly outputs a control

1M23N08102

•S9253
(Only a set w/servo)

S9253 Ratings

(Digital servo for gyro)

•Speed: 0.08sec/60˚(at 4.8V)

•Torque: 2.0kg-cm(at 4.8V)

•Dimensions: 40x20x36.6mm

•Weight: 49g

signal that resists the cross-wind. Therefore,
drifting of the tail can be stopped even if the
cross-wind continues to effect the helicopter. In
other words, the gyro itself automatically cor­rects (auto trim) changes in helicopter tail trim
by cross-wind.

Considering operation of an AVCS gyro, when
the tail of the helicopter rotates, the servo also
rotates in accordance with the angle of rotation
of the tail. When the tail stops rotating, the servo
judges that it has stopped in that position. This is
the auto trim function.

4

GY401 F

Monitor LED

Indicates the operating status of the GY401. The display
contents are shown below.

Gyro Operation Direction Switch (DIR)

Switches the gyro control direction. It must be
switched according to the direction of rotation of
the main rotor and the direction of the rudder
linkage. If the rudder servo moves in the cancel­lation direction when the nose of the helicopter
moves, the operating directions are good.

•If you try to fly a model with a clockwise rotation
rotor when the gyro operation direction is reversed,
the nose will turn to the left and result in a danger­ous situation.

DS Mode Switch (DS)

Digital servo (DS) mode switch. The ON position is
the high-speed output mode for digital servo only.

When using a normal servo, always set this switch to
the OFF position. If it is set to the ON position, the
servo will be destroyed.

UNCTIONS

Rudder control signal operation speed trimmer. Conversely, to stop hunting, charac­teristics can be improved by adjusting the delay. When the trimmer is turned clock­wise, the delay increases.

•When using high-speed servos such as a digital servo, set the delay trimmer to "0".

Limit Trimmer (LIMIT)

Sets the maximum travel of the rudder servo. Move the rudder stick to the
left and right and adjust the limit trimmer so that the servo operating angle
do not strike the linkage. During flight, the servo will not operate beyond
this angle and the linkage is protected. When the trimmer is turned clock­wise, the servo operating angle increases

Sensitivity Switching Connector

Gyro sensitivity switching signal input connector.
Connect to the receiver sensitivity switching
channel (normally CH5). This connector is also
simultaneously used to switch between the AVCS
and normal operation modes. Since this connector
is a single wire signal line, do not pull it force­fully.

Rudder Input Connector

Connects to the receiver rudder channel (CH4)
output connector.

Rudder Servo Connector

Connects the rudder servo.

(Monitor LED display)

Control Delay Trimmer (DELAY)

Relationship between transmitter sensitivity
adjustment and gyro operation sensitivity
and operation mode

The gyro sensitivity becomes zero when the transmitter sensitivity
switching signal is in the neutral position. The sensitivity can be
adjusted over the deflection width of the signal by operating in the
AVCS mode at the + side and in the normal gyro mode at the - side
of the neutral position.

When the transmitter has a gyro sensitivity switching function
(T9ZHwc Series, T8UHPS, etc.), and the transmitter GYRO setup
screen sensitivity setting is 50%, the GY401 gyro sensitivity be­comes zero. When the setting exceeds 50%, the gyro enters the
AVCS mode and the sensitivity becomes 100% at 100%. At set­tings lower than 50%, the gyro enters the normal gyro mode and
the sensitivity becomes 100% at 0%.

When sensitivity setting is performed by transmitter switch channel,
AVCS mode and normal gyro mode switching is performed by
switch position. The sensitivity of each mode is set by the rudder
angle adjustment function (ATV, AFR, etc.) of the respective
channel. When the ATV or AFR set value is 90%, the gyro sensitiv­ity becomes 100%.

Transmitter with gyro sensitivity switching function
(T9Zwc, FF8S, etc.)

(Example of sensitivity setting with T8UHPS) (Example of sensitivity setting with T6XHS)

Idle up

switch

（NORM）

（IDL1）

（IDL2）

The figure above is an example of use of the gyro sensitivity switching
function (GYRO) to switch hovering (AVCS mode), idle up 1 (AVCS
mode) and idle up 2 (normal gyro mode) by SW-E and to set the gyro
sensitivity to 80%, 60%, and 60%, respectively.

[Setting procedure]

1. Call the transmitter advance menu GYRO setup screen.

2. Press the cursor key and display the switch selection screen. Press the

data key and select SW-E.

3. Press the cursor key and display the hovering sensitivity NORM screen

and set hovering sensitivity to 90%.

4. Press the cursor key and display the IDL1 screen and set the IDL1

sensitivity to 80%.

5. Press the cursor key and display the IDL2 screen and set the IDL2

sensitivity to 20%.

* The values above are the values when the sensitivity channel reverse

function is normal.

(Transmitter setup screen)

AVCS mode

80%

AVCS mode

60%

Normal mode

60%

between transmitter set value

Relationship

and gyro sensitivity

Transmitter

set value

100%

75%

50%

25%

0%

sensitivity

AVCS sideNormal side

Gyro

100%

50%

0%

50%

100%

LED display Gyro operation state

Rapid flash Displayed while data is being initialized at power ON.
Steady light Indicates that the gyro is operating in the AVCS mode.
Off Indicates that the power is OFF, or the gyro is operating

in the normal gyro mode.

Slow flash Displayed when there are no rudder operation signal being

input from the transmitter. At this time, the rudder servo
does not operate.

Intermittent flash Alarm display when the power was turned on in the

normal gyro mode. For the rudder neutral signal to be
read correctly, set the transmitter to the AVCS mode
and turn on the gyro power again.

Double flash Displayed when the rudder signal from the transmitter

in the AVCS mode is different from the neutral signal
memorized in the gyro. Also flashes when the rudder stick
was operated.

Single flash Displayed only when the transmitter sensitivity switch is

rapidly switched between the normal and AVCS positions
at least 3 times, then returned to the AVCS position and
the transmitter rudder stick was rapidly moved to the left
and right at least 3 times. After this display goes off, the
rudder is in the neutral position.

Transmitter with ATV function
(T9Z, FF8, FF7S, FF6S, etc.)

Sensitivity

switch
(CH5)

(Forward
position)

(Backward

position)

The figure above uses the CH5 ATV function and is an example of switch­ing to hovering (AVCS mode) in the switch forward position and to idle up
(normal gyro mode) in the backward position) and setting the sensitivity of
each mode to 80% and 60%, respectively.

[Setting procedure]

1. Call the CH5 ATV screen.

2. Pull the CH5 switch forward and set the ATV rate to 72%.

3. Push the CH5 switch backward and set the ATV rate to 54%.
However, when sensitivity switching is performed with the CH5 switch, the
AVCS mode cannot be used at both hovering and idle up. The AVCS
mode and normal gyro mode are switched by switch position.

*The values above are the values when the sensitivity setting channel

reverse function is normal.

(Transmitter setup screen)

AVCS mode

80%

Cannot be set
in this range.

Normal mode

60%

between transmitter set value

Relationship

and gyro sensitivity

Transmitter

set value

90%

45%

10%
10%

45%

90%

AVCS side

0%

Normal side

Gyro

sensitivity

100%

50%

0%

50%

100%

5

Mount and adjust the GY401 as described

USE

below.

Use the miniature screwdriver supplied and
operate the GY401 switches and trimmers so
that excessive force is not applied.

Installing to fuselage

(1) Gyro installation

GY401

Fuselage gyro bed

Always install the GY401 using the
double-sided sponge tape supplied.

(2) Gyro connection

Connect to rudder servo.

(3) Servo selection

When using a digital servo (S9253, S9250,
S9450, etc.) as the rudder servo, set the DS
switch to the ON position.

(4) Rudder servo linkage check

Set the transmitter gyro sensitivity switch to the AVCS position and
turn on the transmitter power, then turn on the gyro power (shared with
receiver). Since the GY401 initializes the data when the power is
turned on, set the rudder stick to the neutral position and do not move
the helicopter for approximately 3 seconds.

If the monitor LED lights, the gyro is operating in the AVCS mode.
When the power is turned on in the normal mode, the monitor LED
will display an alarm by flashing intermittently. Set the sensitivity
switch to the AVCS position and turn on the gyro power again.

Next, switch the transmitter switch to the normal gyro mode position
and check the linkage.

In the rudder neutral position, connect the linkage

Perpendicular

Move the rudder stick to the left and right, and check the direction of
operation of the tail rotor. If the tail rotor rotates in the wrong direction,
adjust the direction with the transmitter reverse function.

so that the servo horn and control wire are
perpendicular.

(5) Gyro sensitivity setting criteria

The gyro sensitivity differs with the servos used and the fuselage.
Generally, the faster the servo operating speed, the higher the gyro
sensitivity. Also, when the main rotor speed is raised, the tail sensitivity
of the helicopter itself rises and the gyro sensitivity at idle up must be
dropped below the sensitivity when hovering. This tendency is greater
with 60 class helicopters than with 30 class helicopters.
Start sensitivity adjustment with a gyro sensitivity of 70 ~ 80% when
hovering and 60 ~ 70% during flight as the criteria and search for the
best sensitivity for the helicopter used.

(6) Gyro operation direction check

If the rudder servo moves to the left when the nose of the helicopter
moves to the right, the gyro direction is correct.

If the rudder servo operates in the reverse direc­tion, switch the switch.

Since the switches are close to each other,
switch them carefully.

When the rotor rotates clockwise, if you try to fly while the
gyro direction is wrong, the nose will rotate to the left and
result in a dangerous situation.

(7) Limit setting

Move the rudder stick to the left and right and adjust
the limit trimmer so that the servo operating angle
does not strike the linkage. During flight, the servo will
not operate beyond this limit and the linkage will be
protected. If the setting is too low, the gyro perfor­mance will be affected.

Install the gyro so that the bottom of the
gyro is perpendicular to the direction of
the main rotor shaft axis. Changes of
this axis are also reflected in the roll and
pitch directions.

When using the GY401 with a
motor helicopter, install the
gyro at least 10cm from the
drive motor.

Connect to receiver sensitivity
switching channel (CH5).

Connect to receiver rudder
channel (CH4).

For a digital servo,
switch to ON position.

Tail control wire

Set the servo horn length based on the
model manufacturer's instructions.

Flight adjustment

In the AVCS mode, the gyro automatically adjusts the rudder neutral
position so that mechanical rudder neutral position changes are un­known. When the rudder neutral position changes substantially, a left
and right rudder error is generated and gyro performance may drop.

When making your first flight and when reconnecting the linkage, set the
mechanical rudder neutral position by first flying in the normal mode and
then flying in the AVCS mode.

(Rudder neutral position adjustment)

(1) Set transmitter revolution mixing (pitch->rudder) to 0% or OFF.
(2) Set the transmitter gyro sensitivity switch to the AVCS position. First, turn on

the transmitter power, then turn on the gyro power (shared with receiver). Since
the GY401 initializes the data when the power is turned on, set the rudder stick
to the neutral position and do not move the helicopter for approximately 3
seconds.

If the monitor LED lights, the gyro is operating in the AVCS mode.

When the power is turned on in the normal mode, the monitor LED will
display an alarm by flashing intermittently. At this time, set the sensitiv­ity switch to the AVCS position and turn on the gyro power again.

(3) Switch the transmitter gyro sensitivity switch to the normal position. At this time,

the monitor LED goes off. Lift off the helicopter and hover and adjust the rudder
neutral position with the transmitter trim lever.

Large rudder neutral position deviation may require readjustment of
the fuselage linkage.

(4) Set the gyro sensitivity to the point just before the helicopter tail begins to hunt.

When the helicopter tail hunts, set the gyro sensitivity to a lower value.
When adjusting the gyro sensitivity, increase and decrease the sensi­tivity gradually while checking.

(For other information, see "One point advise".)

This completes mechanical neutral position adjustment. Land the helicopter and
set the gyro to the AVCS mode. When flying, the power must always be turned
on in the AVCS mode and the rudder neutral position read each time.

(AVCS side adjustment)

(5) Set the rudder trim position for all flight conditions which use the AVCS mode to

the trim position flight-adjusted in the normal mode.

When using common trim in both the AVCS and normal modes, this
operation is unnecessary.

When the power is turned on thereafter, the gyro reads this trim position as
the rudder neutral position.

(6) Set the rudder stick to the neutral position, switch the transmitter sensitivity

switch between the AVCS and normal modes at least 3 times at an interval of 1
second or less, then set the switch to the AVCS position.

This operation memorizes the AVCS side neutral data to the gyro. At
this time, the monitor LED flashes once. The neutral data is also
memorized by setting the transmitter sensitivity switch to the AVCS
position and turning on the gyro power again.

Switch the transmitter flight mode to hovering, idle up and all other flight condi­tions used and confirm that the monitor LED lights.

If the LED flashes twice, the rudder trim of that flight condition has
shifted. Readjust the rudder trim.

(7) Hover and fly in the AVCS mode and set the gyro sensitivity to the point just

before hunting begins. The AVCS mode sensitivity is slightly lower than in the
normal mode.

When hunting occurs, lower the sensitivity. When adjusting the sensi­tivity, proceed slowly while checking.

(For other information, see "One point advise".)

(8) Adjust the rudder steering effect using the transmitter rudder angle adjustment

functions (AFR, D/R, etc.).

(9) When hunting occurs at pirouette stop, increase the delay with the delay trim-

mer. This hunting occurs easily when the servo operation speed is slow. If the
delay is increased too much, the tail will drift when stopping and rudder operation
will become sluggish. Adjust the delay to a suitable value.

With a high-speed servo such as the S9253,
set the delay trimmer to "0".

(10) Switch to the AVCS or normal mode, whichever your prefer. In the AVCS

mode, the tail neutral position is forcefully restrained even when external distur­bances such as cross winds occur. On the other hand, in flight, the weathervane
effect cannot be expected like in the normal mode. When the tail turns, that
attitude is maintained. Operation that sets the rudder to a suitable position is
required.