ATV - Adjustable Travel Volume.
This is used to set the throw of the servo, either side from the center reference position.

For example, if your throttle servo is not quite fully shutting off the carburetor, put the throttle stick in the down position, make sure throttle trim is completely down, enter edit mode (display shows ATV), move the cursor across to 3 (throttle being channel 3) using the arrow keys, then press the + or - data input keys until you can see the carburetor completely closed.

For adjusting the throw for full throttle, move the throttle stick to full, and again use the + and - data input keys. The only other channel that may need ATV is ch 5, which is often connected to a gyro remote gain-control line. With the Futaba, you can ATV a channel from 120% to 30% on both the high side, and low side. (see HOLD for a graph explaining servo percentage numbers)

D/R - Dual Rate:
This is like a switched ATV if you like, but unlike the above adjustment, D/R applies to both up and down stick positions equally.

Dual Rate can only be applied to cyclic and rudder. This feature switches the throw of the servo between one value (usually maximum [default] )and some reduced value. At a reduced value, full movement of the sticks produces only partial movement of the servo, sometimes it gives more precise control for hovering.

Arrow the cursor across to the channel that you want to adjust, and locate the D/R switch for that channel to the position that is to be modified, then increase/decrease the percentage effectiveness of the servo using the + and - data keys.

EXP - Exponential:
This modifies the effectiveness of the joystick at the center, compared to full positive or full negative positions.

There are two settings for channels 1 thru 4, selected by the elevator, aileron, or rudder exp. switches. (The exponential on ch 3 changes the effectiveness of the joystick at low throttle positions and is not really worth fiddling with.) Normally, exponential is used to desensitize the cyclic around center stick, and for this a negative value is entered (say -15% to -25%).

For the ruder channel, you can experiment with a (small) positive value, say +5% to +10%.

This makes the rudder control more sensitive at center stick, and can offset the effect of the gyro countering your stick movement.

REV - Reverse:
Depending on the make and model of your helicopter, you may require a servo to rotate either clockwise, or anti-clockwise, when a joystick is moved from low to high position.

Each channel can be selected to rotate the servo in either way. It is important to check the operation of each servo after installation, to confirm that the servo moves the linkage rod in the correct sense from low to high joystick position.

If the direction is wrong, select that channel to reverse it.

F/S - Fail-safe:
If the Rx (receiver) does not receive a signal from your transmitter, or the signal is swamped by interference, the Rx will revert to a predetermined condition. This condition can be selected for each channel to be either :

• Hold the last position prior to losing signal, or
• Switch to a nominated value.

If your Rx looses signal, its fairly well a forgone conclusion that the model will crash, but nevertheless its a good idea to set up, at least the throttle channel, so that your model doesn't fly off over the horizon.

I usually set all channels to F/S mode.

Leave the cyclic at center, the rudder at center, and the collective at about one third position, and the throttle hold switch operated.

Thus the model will come down, which makes it a lot easier to find the remains than if the throttle was held at its last position, which may well have been full throttle. A further consequence of setting ch 3 (throttle) to a F/S setting is that it enables the Rx's "battery fail-safe" mode.

If the Rx battery voltage falls below a certain value (around 4.2 volts), the Rx switches only the throttle channel to the F/S percentage value, while still operating all other servos as normal.

The Rx will stay in this mode until you move the throttle joystick to match the F/S position, and will then return the throttle channel to normal control. The practical upshot of this, is that you are flying along, and notice the engine drops to a low throttle setting (because the F/S has been set with throttle hold activated).

You immediately go into autorotation panic mode, and reduce the collective to a very low position to do your descent. The battery fail-safe mode is cancelled by this moving of the throttle to a position equal to, or lower than, the F/S setting, and when you flare at the bottom of the descent, the throttle will work as per normal and you can do an ordinary landing. The model has succeeded in its attempt to get your attention.

It is now time to check the Rx battery.

PMIX - Programmable mix:
This is used for any special setups that are not catered for in the normal mixing modes.

One possible use is to mix the rudder channel into the throttle channel such that if you do a pirouette against the torque of the engine, a little more throttle is added to compensate for the extra power demand, and conversely reduce throttle for pirouettes which are in the same direction as motor torque.

T-NR - Throttle positions:
It is unlikely that the power from the motor will vary in a linear manner with the opening of the carburetor.

We need to modify the throttle settings at various stick positions to a) give correct RPM at half stick (which is where we want to hover), and b) to stay at constant RPM from half stick to full stick.

The movement of the throttle stick is divided into quarters. Each quarter can be given a percentage setting using the + and - data input keys.

These percentage numbers range from 0% (no throttle) to 100% (full throttle), and should not be confused with "servo position" percentage numbers which range from -100% to +100% (a range of 200%). The arrows above the numbers 1 to 5, show the current throttle stick position, the arrows blow show the cursor position.

It is not uncommon for the throttle curve to be "s" shaped, with percentage numbers for the five positions being something like 0% - 35% - 50% - 65% - 100%

T-Idle 1 - Idle-up 1 Throttle positions:
As above but these settings are activated when the idle up switch is selected to idle-up 1 position.

If INH is showing, this feature is inhibited. To enable the Tx idle-up switch, use cursor arrows to make the INH flash, and press + data input key. Normally idle up is used to a) increase rotor RPM for aerobatics, and b) set minimum throttle position to be a fast idle, such that the engine RPM does not drop at low collective.

T-Idle 2 - Idle-up 2 Throttle positions.
As for T-Idle 1

HOLD - Throttle Hold:
When enabled, this allows the throttle to stay fixed at a preset value regardless of stick position. This is used for practicing autorotations without shutting off the motor.

It is a good idea to operate the throttle hold switch when starting and carrying the model to the take off point, so if you do accidentally knock the throttle joystick while carrying the transmitter and model, it won't rev up.

The throttle trim remains operational regardless of throttle hold. The default value is -70%. (the naming of stick positions is -100% = throttle stick at minimum, 0% = half stick, +100% = full throttle. As the full range is therefore 200%, a value of "-70%" actually means "30% up from the bottom on a scale that is 200% end-to-end", or 15% throttle.)

PNR - Pitch normal positions:
The pitch of the main rotor blades is required to alter in a non linear fashion from low collective, through half stick, to full.

For example, if you require bottom stick to have say -2 degrees main rotor pitch, half stick to have 5 degrees pitch, and full stick to have 9 degrees, then the blades change pitch by 7 degrees from zero to half stick, but change only 4 degrees from half to full stick.

The resultant percentage values in the five PNR positions may be something like 10% - 30% - 50% - 65% - 80%.

Pitch-Iddle 1 - Pitch idle up 1 positions:
To achieve higher rotor RPM and still maintain hover at half stick, the throttle settings must be increased, and the pitch settings decreased.

Thus PIddle-1 contains the pitch settings associated with TI-1 and is activated with the Idle-Up 1 switch. The settings may be something like 0% - 25% - 45% - 60% - 70%

Pitch -Iddle 2 - Pitch idle up 2 positions:
Pitch settings for Idle up 2.

Pitch-Throttle Hold - Pitch settings when the throttle hold switch is activated:
For auto rotation practice we want minimum pitch at low stick settings (to keep the rotor blades rotating during descent) and maximum pitch at full stick (to make full use of the stored rotational energy).

The default settings of 0 - 25 - 50 - 75 - 100 give maximum range.

HV-T - Hovering Throttle:
When ON, enables the hovering throttle knob. The throttle at half stick can be adjusted on the Tx knob.

HV-P - Hovering Pitch:
When ON, enables the hovering pitch knob. These two knobs can be used to quickly adjust hovering RPM, or to bring the throttle stick back to mid position at hover.

REVO - Revolution mixing:
You need to have this selected to ON (rather than INHIBIT).

This mixing will increase the pitch of the tail rotor as the collective is moved from half to full (to counteract the increase in motor torque), and conversely will decrease tail rotor pitch when the collective is moved from half to zero.

When set correctly, this ensures the model does not twist (pirouette) in a vertical climb or descent. The UP value and DOWN value are set separately. For clockwise rotating rotors, both up and down values must show the - sign. The magic rule for clockwise rotating rotors is : The bigger the number (ignore the sign), the more the model turns right when going up, or turns to the left when going down.

(Bigger = UP RIGHT / DOWN LEFT). If the model twists to the right (i.e. twists clockwise) during a vertical climb, the UP value needs to be reduced (say, from 50 to 40). If the model twists to the left in a climb, then the UP value is too small (increase from 50 to say 60).

Similarly, if the model twists to the left when vertically descending, the DOWN value is too large. To set the DOWN value, have the collective at zero, press the cursor until the % sign flashes, and then increase or decrease the value with the data entry keys. To set the UP value you need to have the collective at full, or at least above half.

f the motor is running, make SURE you have operated the throttle hold switch, then modify the value as before. REVO is one of those things that need to be setup on a still day, with low gyro gain, but once set correctly, will enable you to perform climbs and desents without the tail wagging from side to side.

Incorrect setting is particularly noticeable when you have done a descent and flare at the bottom.

If REVO is set correctly the model will stay at the same heading as you increase the collective.

This article was contributed by Jeff Law

**Many Many thanks goes out to Jeff.

He was the ice breaker, the first to contribute an article. Took some guts knowing that a lot of people will be reading his writings, but bear in mind that we are not critics if you wish to submit an article.

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