Tips and notes
F X - 4 0
radio control system. Never power an ignition system from the
receiver battery; a separate battery is essential. Be sure to use
properly suppressed spark plugs, plug caps and shielded igni-
tion cables. Keep the receiving system as far away as possible
from any ignition system.
20.9 RANGE CHECKING
The new, ultra-fast PCM G3 system transmits fourteen chan-
nels at a resolution of 2048 steps, i.e. it transmits very large
quantities of data in a short time. This is achieved by the use of
a special four-level FSK modulation process. A reasonably
high level of receiver signal is required if the system is to
decode it reliably at the receiver end. If the signal level is
inadequate or fluctuates - or even suffers interference - the
receiver attempts to regenerate the data signal. However, this
only works up to a particular threshold, after which it switches
automatically to hold-mode or fail-safe. The larger the quantity
of data a system transmits, the higher the signal level required
at the receiver. This is the simple - but not unexpected - fin-
ding from information technology research.
Poor servo lead deployment, or the use of particular brushless
speed controllers etc., may result in a reduction in the received
signal by up to 16 dB (a factor of 6), i.e. only 16% of the maxi-
mum signal strength is present at the receiver.
For models powered by jet engines (turbines) it is fundamen-
tally essential to connect the ECU via the robbe servo sup-
pressor filter, No. F 1413. Turbine ECUs generate such high
levels of interference that they may reduce effective range by
about 50% if no servo suppressor filter is fitted. The same filter
should also be used if a battery backer is installed in the
model, as the filters fitted to most battery backers are inade-
quate.
If any additional signal reduction occurs in flight, perhaps due
to changes in attitude of the model (aerial orientation) or other
sources of interference, brief ‘hold’ periods are the inevitable
result.
WE RECOMMEND THAT YOU CARRY OUT A RANGE-
CHECK BEFORE EACH SESSION WITH YOUR MODEL
We strongly advise that you make it a matter of routine to carry
out a range-check before you operate any new model, and
whenever you have fitted a new receiver. Note that the model
should not rest on the ground for this; instead position it about
1 - 1.5 m above the ground. You can use a plastic or wooden
table as a support, with the model raised on it using a cardbo-
ard or wooden box. Never use a metal support such as a cam-
ping table. There should not be any conductive materials close
by (metal fences, cars etc.), and even your friends and assis-
tants should not be standing in the immediate vicinity.
• First switch the model on, but with the motor not running.
• Walk slowly away from the model, operating one control
surface slowly but constantly.
• While you move away from the model, watch the associa-
ted control surface and observe whether it deflects or stays
still. If possible, ask a friend to help you; he or she should
be able to see the model clearly, and observe the control
surface you are operating.
• As you increase ground range, rotate the transmitter to left
and right occasionally in order to simulate different aerial
positions relative to the model.
• To avoid ‘hold-mode moments’, the effective range of the
FX-40 under these conditions should be around 60 metres
with the transmitter aerial removed.
• If this part of the range check is successful, repeat it with
the motor running (caution: the model must be held secu-
rely for this test).
• The range you now obtain should only be slightly lower than
the previous figure (approx. 20%). If it is significantly redu-
ced, then the power system is causing interference to the
receiver. You should be able to minimise this effect by run-
ning through all the measures outlined above, and optimi-
sing them as far as the model allows.
20.10 SWITCH HARNESS
It must be possible to operate the receiving system switch
easily, without mechanical restriction, i.e. the cut-out in the
fuselage side must be large enough to avoid obstructing the
mechanism. In powered models with internal-combustion
engines, the switch should be mounted on the opposite side
to the exhaust, to avoid the danger of oil penetrating the hou-
sing and soiling the contacts. If your model is fitted with a
large number of high-power digital servos we recommend the
use of standard commercial dual-battery power supply sys-
tems.
20.11 INSTALLING SERVOS
When installing servos in a model, always use the rubber
grommets and brass eyelets supplied. When you fit the servo
retaining screws, ensure that they are not tightened beyond
the point where the brass eyelets make contact top and bot-
tom; if the rubber grommets are compressed to this point,
their ability to absorb vibration is lost.
The following diagram shows two typical methods of moun-
ting servos.
Diagram “A” shows a wooden servo plate. Diagram “B” shows
the use of a plastic or aluminium plate.
In RC model cars the servos are usually fitted in the openings
provided for them in the RC installation plate. Robbe quick-
release servo mounts are a good choice for model boats. Ple-
ase take great care over mounting servos, as they are sensi-
tive to vibration.
20.12 SERVO TRAVELS / SERVO OUTPUT ARMS
Each servo must be able to move through its full arc of travel
without being mechanically obstructed by the control surface
or its linkage. This applies in particular to the carburettor lin-
kage. The “full throttle” and “idle” settings must be determined
by the stick positions; never by the throttle’s mechanical end-
stop. If you ignore this warning, the servo motor will be under
almost full load constantly, and will consume an extremely
high current.
A range of servo output arms is available for robbe servos, and
they are illustrated in the picture on the next page. The dra-
wing also shows the angular change per spline segment.
Servos with splined output shafts permit fine mechanical
adjustment of the servo neutral position. The position is adjus-
ted by undoing the retaining screw and lifting off the output
device.
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1Nut
2 Washer
3 Rubber grommet
4 Metal eyelet
5 Aluminium plate
6 Screw
1 Woodscrew
2 Washer
3 Rubber grommet
4 Metal eyelet
5 Wood
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