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Now that we have the batteries charged and we know the sequence
for turning on the power, one of 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.
Click on photo to view large image with caption
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