F X - 4 0
Position the output device in the appropriate neutral position,
push it down onto the splined output shaft, and tighten the
retaining screw. The diagram below shows a servo with push-
rod connected.
20.13 INSTALLING LINKAGES
The basic rule when installing mechanical linkages and control
surfaces is that they must be extremely free-moving, other-
wise the servos will draw excessive currents, and the effective
operating time per battery charge will be greatly reduced. At
the same time the centring accuracy of the control system will
be worse, which in turn has a negative influence on the mode-
l’s flying characteristics.
21. THE SYSTEM IN USE
All robbe-Futaba receivers continue to work with full range at
reduced voltage, down to the point where the supply voltage
falls to 3 V. The advantage of this is that the receiving system
will normally continue to work even if one cell fails completely
(short-circuit), since robbe-Futaba servos still work down to
3.6V, albeit at slightly lower speed and with reduced power.
This is very important in Winter, when ambient temperatures
are very low, otherwise any momentary voltage collapse could
cause the loss of a model.
However, there is a drawback: under certain circumstances
the user may not even notice the failure of a battery cell. For
this reason it is important to check the receiver battery from
time to time.
We especially recommend the use of a robbe battery monitor,
No. 8409, which indicates the condition of the battery by
means of a row of LEDs.
21.1 POWER-ON SEQUENCE
Always switch the transmitter on first, and only then the recei-
ver. Reverse the sequence when switching off. When you
switch the receiver on, the servos run to the neutral position.
If you are using a PCM system it is permissible to switch the
receiver on first, and then the transmitter. This offers the
advantage that the fail-safe data for all channels is automati-
cally transferred to the receiver. If you switch the receiver on
later, it may occur that one channel was already transmitted
before the receiver was ready to receive it. However, this is
only significant if the period between switching off and take-off
is less than sixty seconds, as all data is transmitted again
every minute.
We recommend that you check each function in turn by opera-
ting the associated stick or other transmitter control. Check
that each control surface operates in the correct “sense”
(direction) relative to the stick movement. If any control surface
moves in the wrong direction, that servo must be reversed at
the transmitter.
21.2 “ELECTRICAL NOISE” INTERFERENCE
If your radio control system is to operate safely and reliably, it
is essential to avoid what is known as electrical “noise” interfe-
rence. This problem is due to metal parts, such as pushrods,
the exhaust and the motor crankcase, defective ballraces etc.
rubbing against each other intermittently as a result of vibra-
tion. For this reason the linkage to the engine’s carburettor
must always terminate in a plastic clevis - never connect a
metal linkage directly to the carburettor arm without insulation.
21.3 RECEIVER BATTERY CAPACITY AND OPERATING
TIMES
This rule applies to all types of battery: at low temperatures
battery capacity is severely reduced, i.e. safe operating times
are shorter in cold weather. The safe operating time varies gre-
atly according to the number of servos connected to the recei-
ver, the stiffness of the linkages, and the frequency of control
commands generated by the pilot or operator. A standard
servo draws between 150 and 600 mA when the motor is run-
ning, and about 8 mA at idle. Super-servos and powerful digi-
tal units can draw peak currents of up to 1300 mA at full
power.
Be sure to select a receiver battery with ample capacity,
bearing in mind the likely current drain and the number of
servos in the model.
Ensure that all mechanical linkages are free-moving, and that
the servo is not obstructed in its travel. A servo running con-
stantly against a mechanical stop or limit draws a very high
current, and will also inevitably suffer damage in the long-term.
When the receiver battery is almost discharged, you may
notice that the servos respond much more slowly. The
moment you notice this, land the model immediately and
recharge the battery. To monitor the receiver battery during a
session we recommend the use of a battery controller, which
gives you a useful idea of the state of charge of the battery
between flights.
101
Retaining
screw
Pushrod
