|
 | MacGregor Industries have kindly given
me permission to reproduce some good articles that appear in their Modeller's Guide 2000, and these will appear from time to
time in ModelFlight. Here's the first, on Radio Range
Testing - something which is always mentioned as a 'must' in all the
beginners' books but which I have never before seen spelled out in
detail. I hope you will find it interesting and helpful. |
| The second item is a bit specialised and is a helpful guide to
setting up the TeleBee Heading Hold gyro, sent to me by Frank
Drecchio, a model flight enthusiast from Maryland, USA. |
| Finally, there's a brief item of news for helicopter fans. |
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radio range testing
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Range checks are quick and easy to perform, and could well show up
potential problems with even the best of r/c installations.
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| BEFORE using any
remote-control radio system, it is always a good idea to perform a check
to verify the operating range of the system.
It is not necessary to verify
the range with the transmitter aerial fully extended as a check with the
transmitter aerial in the retracted position will give representative
results. As a rough approximation, the range on the ground with the
aerial up will be ten times that obtained with the aerial down although,
of course, if the retracted aerial is particularly long or short, this
will affect the figure.
One transmitter only
Since
transmissions from other transmitters in the vicinity can affect the
result, the test should take place with only the test transmitter
operating. Ideally, a clear open field should be used as a test area,
but a test along a path or road will be satisfactory provided that an
allowance is made for the localised, signal-distorting effects of parked
cars and other large metal objects.
Two people are
needed for the test. One should take the transmitter with the aerial
retracted and operate it as if flying the model, moving a control stick
to operate a servo in the model. The other should walk away from the
side of the person holding the transmitter, with the model held at right
angles to the direction of walking so that the transmitter and receiver
aerials are approximately parallel.
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The
radio signals are emitted from the side of the transmitter aerial. Only
a very small signal is sent out from the top, along the aerial's axis.
Similarly, the receiver picks up the strongest signal when its full
length is exposed to the transmitter. If the receiver aerial is held in
a straight line and pointed at the transmitter, only the diameter of the
receiver wire is available to pick up the signal and the result will be
a very short range. For these reasons, it is recommended that the
transmitter aerial is not pointed at the model and the receiver aerial
is arranged in two dimensions so that whichever way the model turns,
there is always a good length of exposed aerial to pick up the signal.
Taking the end of the receiver aerial to the top of the tail fin is
strongly recommended.
Ground absorption
The ground absorbs radio signals and makes them weaker. As a model moves
away from the ground, the available transmitted signal gets much
stronger and because of this, the air range might be two or three times
the ground range.
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Seventy paces
 With
the model at waist height, a range of at least
70 paces should be obtained and can be
verified by observing the servo or control surface on the model. The
servo should smoothly follow the transmitter commands without chattering
or hesitation. If the model is held lower, the range obtained will be
less and if the model is held higher, the range will be more. Pointing
the receiver aerial at the transmitter will dramatically reduce the
range. |
 TeleBee
Gyro set-up
by FRANK DRECCHIO
Anyone who is contemplating the
purchase of a TeleBee or Arcamax PI gyro or has
purchased one and cannot understand the instructions (especially the
Telebee) may want to read this.
This is how I set up my Telebee; same
for Arcamax PI.
Inhibit all mixing to the tail rotor,
rev-mix, offset, etc, centre the trim on the Tx and zero the electronic
trim if any. Do not adjust the gain on the gyro, leave it at the default
setting. Set your rudder ATV to 100% on both sides.
The cube part of the TeleBee is the
sensor unit and has all the electronics in it. The connector box has no
electronics in it. You should remove the four Phillips screws in the
bottom of the sensor case and take off the case bottom. Stick a piece of
very thin foam tape (thin wing saddle tape is good) inside the case
bottom and then reassemble the case. This keeps the electronics inside
the case from moving around. Now mount the cube on a flat level surface
on the helicopter. Use CSM foam tape or Zeal mounting gel. The tape that
comes with the TeleBee is no good. Ignore the two arrows on the case.
The Phillips screws face the ground. Mount the connector box with the
same type tape or gel.
You will notice that the two cables
supplied have male plugs on both ends. You will have to supply your own
cable to plug into the servo output if you need an extension. Plug the
gyro into your rudder channel using one of the supplied cables and plug
the rudder servo into the gyro. Plug the other cable (aux) into a spare
channel that has a two position switch. The jack on the sensor unit (the
cube) is not used - it's for factory set-up only; do not plug anything
into it.
Set the AUX channel ATV to 50% to
start. set both sides; one is for Normal mode, the other will be for
Heading Hold mode. |
Now you need
to set up the helicopter for a stable hover mechanically. Determine that
the gyro is operating in the correct direction. Turn on the Tx first
then the Rx. Wait about a minute without moving anything. Now you have
to find out if you are in normal or HH mode. If the servo slowly drifts
one way or the other, you are probably in HH mode. You can verify by
moving the rudder stick. If you move the stick to the right, the servo
will not go back to centre unless you move the stick to the left and it
will drift if you centre it. In normal mode, the rudder will follow the
stick movements. Set the switch to standard mode for now. Now give a
right rudder command from the Tx and note which way the servo arm moves
(pushes or pulls). Now pick up the helicopter by its head and jerk the
nose to the left. The servo should give a right rudder response. If it
doesn't, simply flip the reverse switch on the gyro sensor and test
again.
Turn one of your tail rotor blades 90
degrees in its holder and with the throttle/collective all the way down,
mechanically adjust the blade so it is more or less parallel to the tail
boom. This is your rough starting point for a test hover.
You now need to hover the helicopter
into the wind in NORMAL mode. Adjust the linkage until the gyro holds
the helicopter straight. Do not use the electronic sub-trim for this or
the rudder trim on the Tx face. It must be a pure mechanical adjustment.
If it "hunts" back and forth, beep down the gain a tiny bit at
a time (AUX switch again, not the gain on the sensor) until it stops and
then just a tiny bit more. When the helicopter will hover without
turning you can now set the HH mode.
Shut it down and switch the
two-position switch the other way. You will see the rudder servo drift
one way or the other. Now you can use the rudder sub-trim feature on
your Tx to stop the drift. Do not use the trim on the Tx face. You
simply flip back and forth from normal mode to heading hold mode and
keep beeping the sub-trim until the drift stops. It will drift after
about 15 seconds or so no matter how carefully you adjust the sub-trim,
but that is not important.
Your TeleBee is now set up. You cannot
use any mixing while in HH mode at any time. You can, however, use your
rev-mix and offset if you to use the gyro in normal mode only. To get
the maximum benefit of HH you will need a fast servo - 0·11 seconds or
less transit time. |
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  I
see in the model press that MacGregor Industries now have exclusive UK
distribution of JR Propo radio control products, having taken over the
distribution from
J Perkins. This means that Macgregor's now distribute
the complete range of JR radios and helicopters - something they have
apparently wanted for some time.
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