Bob Aberle
basic Radio Control (RC) system, the selection process, and basic installation in a model aircraft. This
month I'll get into the operation of an RC system. More detailed information using a basic training
model will be provided in following months, including the assembly and flying aspects.
For the purpose of this presentation, let's assume we have that RC model-aircraft mock-up
(containing the RC airborne components) from the previous article sitting in front of us on our
workbench. The RC transmitter is nearby. To get familiar with your new RC system you are
encouraged to operate it at home, try the various controls, and even pretend you are flying the
model! Allow yourself to get the feel of it.
Before turning on that transmitter, think for a moment about your location. If you are operating from
your home shop or garage, the important thing to consider is whether there might be an RC flying
field in the immediate area. You would be wise to check this out before turning on your transmitter for
the first time. Keep in mind that two identical RC channels can easily interfere with one another.
As a precaution, you can operate your RC transmitter for relatively short periods with the antenna
fully collapsed. By doing this you are able to operate your RC system for checkout purposes, but the
transmitted signal will be greatly reduced. Extended use of the transmitter with the antenna collapsed
might cause overheating and damage to the output stages.
A cardinal rule of RC operations is to turn on your transmitter, then turn on the receiver (airborne
pack). Use the reverse order when shutting down the system; turn the receiver off first and the
transmitter off last. (The transmitter goes on first and off last.)
If you turn the receiver on first, without any signal being broadcast from the transmitter, it is possible
for the servos to jitter (dither) or even drive to an extreme control position and stall out the servo
motor. In this condition you would have excess battery drain and might even damage a servo motor or
gear.
Make sure your transmitter and receiver battery packs have been charged properly. The supplied
dual-output battery charger should always be employed prior to operating the system. The amount of
charge placed on these batteries by an RC system dual-output charger is at a low enough level that
they can't be overcharged.
The general rule is to charge transmitter and receiver battery packs overnight, or at least for 10
hours. The only problem you might experience is if you charge for less than 10 hours. As I have
already stated, never attempt to just put back into a battery what you think you took out. Several
charging sessions for only an hour or two can quickly lead to a battery that has little, if any, charge
remaining. That is an invitation to potential control problems in flight.
Most RC transmitters will have a meter, an LCD (Liquid Crystal Display) voltmeter, or color indicator
lights that inform you of your batteries' charge status, and some even provide an audible alarm when
the battery needs to be recharged. The airborne battery needs extra monitoring while at the flying
field; we will get into that in the installment about flying.
the first steps on a new RC airborne installation is to determine that all controls operate from the
proper control sticks on the transmitter. The order in which each servo cable plugs into the RC
receiver makes the difference. For our initial training purposes we will employ only three channel
functions, such as rudder, elevator, and engine/motor (throttle) control. That will involve three servos
for a fuel-powered model or two servos and an Electronic Speed Control (ESC) for electric power.
With the transmitter and receiver powered up, move the rudder control stick, which will be on the right
side (or right control-stick assembly) on a three- or four-channel-function transmitter. Rock this stick
side to side (left to right) and observe the rudder on the model (or mock-up in this case). The rudder
should move when you operate the control stick. If, say, the elevator moves when you move the
rudder stick on the transmitter, you have to change the servo plug at the receiver.
I wish I could simply tell you that connector position one at the receiver is always rudder, two is
elevator, etc. Unfortunately no two RC manufacturers use the same convention or order. The rudder
and elevator functions will generally be on the first and second position, with the throttle on the third.
So if your rudder stick is operating the elevator, swap those first two connectors at the receiver
terminal block. Try the rudder stick again; the rudder will most likely operate properly. Try the
elevator control stick in an up-and-down motion, and the elevator will probably respond. If it doesn't,
you must try other connector positions on your receiver until the control-stick command operates the
correct control function.
Try the throttle control on the transmitter. This will be located on the left-side control-stick assembly
(on a four-channel transmitter) or on the rear of the transmitter case for a three-channel transmitter.
For a glow-fueled model you will be using a third servo to operate the engine carburetor (throttle
device). In this instance, it will be obvious when you move the transmitter throttle stick that the throttle
servo is responding. It won't be as obvious when using electric power because the ESC is substituted
for a servo, but we will get more into that next month.
Now we have the control surfaces and throttle operating from the correct control sticks on the
transmitter. The next important thing to check is the direction of the servo movement. We are going
one step further in our basic checkout procedure.
Move the transmitter rudder-control stick fully to the right side while observing the rudder's position
on the mock-up (simulated aircraft in this case!). The rudder should be deflected to the right, which
would produce a right turn in the aircraft. As you move the control stick from the neutral position to
the extreme position (such as full right), the rudder operates in direct proportion to your stick
deflection. This proportional control allows you to impart any amount of rudder control to the aircraft,
depending on how far you deflect the control stick.
Let's say that the rudder moved to the left when you applied right rudder stick at the transmitter; that
means it is hooked up backward, which could easily crash your model on its first flight. Almost all
modern RC transmitters have a servo-reversing switch for each control function. In this case, flip the
rudder-reversing switch to the opposite position.
Now move the control stick to the right, and the rudder should move to the right. Follow this same
procedure, and check to make sure that the elevator moves up when you are pulling back on the
elevator control stick.
Check the engine throttle control. With the throttle-control stick in the uppermost position, the engine
carburetor should be set for full open, which will provide full, or maximum, power. At the bottom
throttle-control-stick location, the carburetor should be almost fully closed, which will provide a low
idle speed. On a three-channel transmitter, with the throttle-control lever located on the rear of the
case, convention usually dictates that moving the lever to the outside of the case is high throttle and
moving the lever toward the inside (pulling it toward you) is the idle position.
On some of the lesser-function RC transmitters (such as the three-channel variety), it is possible to
see servo-reversing switches on the first two channels but not on the throttle channel. If this is your
problem, it will require special attention. On a glow-fueled model, you simply move the throttle
control-rod location from one side of the servo output arm to the other. That will reverse the direction
of the control. It gets more complicated in the case of electric power; let's leave that for next month.
The next item to concern ourselves with is the position of the trim levers for each channel function.
On most RC transmitters there are levers adjacent to the control stick (for rudder, elevator, and
throttle) that when moved can impart a certain small amount of control adjustment for trimming
purposes while the aircraft is in flight. These levers usually have a ratchet-type device that produces
a clicking sound when moved; this is done to prevent unwanted movement of the trim levers.
The full movement of a trim lever will usually impart approximately 15% of the full control throw. Digital
trim is being employed on some of the more sophisticated RC transmitters, in which case the
traditional lever is replaced by a push-button switch. There will be more about that when we get into
the advanced radio systems, at a much later date.
For each new model you are advised to turn on the transmitter and receiver, then position the rudder
and elevator trim levers for the middle or center position. With the throttle control stick in the high or
full-power position, move the throttle trim lever to the uppermost position.
At this point you might observe, with your hands off the transmitter control sticks, that your rudder
and/or elevator are/is not exactly at the neutral control position(s). If that is the case you must adjust
your control rods, which presumably have adjustable clevises on at least one end. By screwing the
clevis in or out, you are changing the length of the control rods, hence the position of the control
surface (rudder or elevator).
With the throttle stick at full power and the throttle trim at the uppermost position, your engine
carburetor should be full open. Again, adjusting the clevis will make this happen. Moving the throttle
control stick all the way down should make the carburetor opening almost fully closed. This will
provide a low idle speed. At this point, if you move the throttle trim lever to the lower position, the
carburetor, if mechanically set properly, will completely close and the engine will stop running.
Mechanically adjusting the carburetor control linkage can take extra patience. More advanced RC
transmitters have electronic-type dial-up adjustments that make carburetor settings easy, but I want
to keep everything simple for the moment.
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