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RADIO CONTROL
BY BOB YOUNG
Multi-channel radio control
transmitter; Pt.8
This month we will deal with the more
complex programming functions which
can be provided in this very advanced
R/C transmitter.
But first, let’s get this month’s grizzles, whinges and additions out of
the way. In Pt.6 (July, 1996), which
dealt with the construction of the
transmitter case, Fig.2 showed
the wiring arrangements for the
various control elements. In this
drawing set, mention is made of
the connecting cable for these
functions being a blue/white/
blue 3-core ribbon cable.
As these leads are intended
for reversing, the blue/white/
blue was to indicate that polarity
was not important on these connectors. The b/w/b also matched the
transmitter interior which is all in
blue and white and it added to the
internal appearance. The cable was
ordered weeks before that article was
written and the order clearly stated
blue/white/blue.
Months passed and still no cable.
The July issue came out, still no cable. Finally, the big day arrived. The
delivery docket stated b/w/b, the
invoice stated b/w/b but it
appears the production
people decided that
red/white/blue
would look
much better.
As I was
desperate
for cable by
this time I
had no alternative but
to use the r/w/b ribbon and to my
amazement, the production people
were absolutely correct. The finished
transmitter did look much better,
especially since I had increased the
cable length after looking at the July
issue photos. The leads now run neatly
around the sides of the case.
From now on, all leads will be
red/white/blue as dictated by the
cable manufacturers. This has one
advantage in that it removes the
need to paint a dot on one side of
the connector (recommended in the
July issue), as it is now very easy to
determine visually if the lead is normal or reversed.
All jokes aside, this business of
quality control is driving me nearly
insane. Almost without exception,
every major component has been
returned due to lack of quality or
correctness. My heart is in my mouth
every time I open a new batch of
components. From powder coating
to pots, I have sent back more components than I have accepted. Under
these conditions, delivery promises
mean nothing, and even now I am still
struggling to get the project running
smoothly with regards to deliveries.
However, I digress.
The wiring in those July photos
looked totally disorganised. By increasing the lead length, it is now possible to run the leads right around
the outside of the case (see photo).
This was mentioned in the July issue but not highlighted. The lengths
shown in Fig.2 of the July issue were
the corrected, longer values.
The addition of the frequency interlock key, as
described in the text, eliminates the possibility of
two transmitters operating on the same channel.
82 Silicon Chip
Fig.1: the frequency interlock key, developed by the Author, cuts off the
power to the transmitter while it is plugged into the charging socket.
When the transmitter is in use, the key is removed and hangs on a key
board in the club.
Another nice touch added to the
kits is the inclusion of self-adhesive
cable clamps which stick to the case
sides and secure all the cables neatly.
These are made out of the large
headed split-pin type paper clips,
available at any stationers. The legs
are clipped in length and covered in
heatshrink and the heads stuck to the
case side with double-sided foam tape.
They sit flat against the wall, can hold
a large number of cables and are dead
easy to open and close, in order to add
and remove cables; in other words, the
ideal cable clamp.
Also, since the July issue, I have
found a source of components for
crimp connectors which allows me to
crimp my own leads. These feature a
housing similar in size to the Futaba
servo connector housing but less the
polarising flange. These are fitted with
high contact pressure, gold-plated
pins. All kits will henceforth use these
connectors which will be pre-crimped.
These connectors are of a higher
quality and are less fiddly to assemble
than the original solder connectors.
They also have one large flat face
which is ideal for a self-adhesive
numbering label.
A sheet of self-adhesive numbers is
now included in all kits as an aid in
identifying the leads. The following
list gives the lead numbers in production transmitters:
The view inside the case from the rear. The operating channel is set by the
plug-in crystal near the centre top of the photo. The interconnecting wiring is
now laid around the perimeter of the case for a much neater appearance.
1. Throttle pot
2. Aileron pot
3. Elevator pot
4. Rudder pot
5. Switch 1 (outside left)
6. Aux 1 pot (left)
7. Switch 2 (inside left)
8. Switch 3 (inside right)
9. Aux 2. Pot (right)
10. Switch 4 (outside right)
Please note that these numbers are
not meant to correspond with those
given in the channel allocation table
in the August issue.
As I have no idea which switch you
will use for what application, I cannot
possibly match these numbers to the
channels. They are only a guide to
identifying the leads.
Frequency interlock
There is one correction for the August article. It stated that the charge
plug must be a 2.5mm non-shorting jack. This should read “3.5mm
non-shorting”. In the kit will be found
two 3.5mm jack plugs. One is for the
charger while the other should be fitted
to the frequency key as shown in Fig.1.
This plug/key combination forms the
basis of the Silvertone Frequency Interlock system.
Under the rules of operation for the
Silvertone Keyboard frequency control
system, each transmitter has its own
individual key which is inserted into
the Keyboard to reserve the frequency and bandwidth required for the
transmitter.
The only person allowed to insert
or remove a key in order to reserve
a frequency is the operator of the
transmitter on that frequency. Thus,
the logical position for the key at all
other times is for it to be plugged into
the transmitter, thereby rendering it
inoperative.
The plug/key combination performs
this function. When it is inserted into
With the back of the case on, the
channel-setting crystal is instantly
obvious. Only one transmitter may
use this channel, for obvious reasons.
October 1996 83
Fig.2 (left): detail of
the mixing inputs and
outputs. Any channel
may be mixed with
any other and multiple
mixes are possible.
Fig.3: this diagram shows how the various micro-shunts (shorting
links) must be placed across TB10 if the configuration module is
not used.
the charge socket located on the bottom right of the transmitter control
panel, the +9.6V line is open circuited,
thereby rendering the transmitter inoperable even if the switch is left on.
When the operator wishes to switch
on, he takes his transmitter to the
Keyboard and checks to see if his
frequency is clear. If it is, he then
removes his key from the charge socket and inserts it into the Keyboard.
Thus, we now have a true frequency
interlock system. If the key is in the
Keyboard, the transmitter is cleared
for transmission. At all other times,
the key is in the charge/interlock
socket on the transmitter so that the
latter is inoperative.
Bingo, no more inadvertent shoot
downs by transmitters accidentally left
on in the transmitter pound!
There is an interesting sidelight to
this story. When Silvertone invented
and patented this system in 1969, the
importers went berserk for the simple
reason they would have had to pay
a royalty on every transmitter sold
in this country, had the system been
officially adopted in Australia.
They kept the system out of official
use with a particularly vindictive campaign until about two years after the
patent had expired. Then the very people who so vehemently campaigned
against the system were the very first
to start manufacturing and selling it
when the coast was clear.
Today the system is known as the
Australian National Frequency Con84 Silicon Chip
trol System and is approved for use
by the MAAA at all national contests,
although the frequency interlock aspect of the system is never mentioned.
However, every Silvertone transmitter produced since 1969 has featured
frequency interlock.
Simple mixing programming
This explanation will concentrate
on the basic principles involved rather
than covering every possible combination of mixing. Once the principles
have been mastered, the rest falls into
place quite easily.
Four simple mixers are built into
the standard Mk.22 encoder module.
Two are inverting and two are non-inverting. These are located at the top
righthand corner of the module and
consist of a quad op-amp IC (LM324),
four mix volume pots, and a double
row 8-pin header plug. Fig.2 shows
these controls in detail.
In radio control parlance, a mixer
is essentially a variable gain buffer
amplifier, necessary to prevent reverse
mixing when the channel inputs and
outputs are connected together.
Thus, a mixing amplifier is necessary for each mixing function. The
input of the mixer is connected to the
output of the control channel and the
output of the mixer is connected to
the input of the mixed channel. If you
are confused by this explanation, you
may like to refer back to the article on
mixing in the December 1995 issue.
Mixers 1 & 2 are inverting while
mixers 3 & 4 are non-inverting. A
non-inverting mixer will give the
same direction of rotation in the mixed
channel as the primary control channel. An inverting mixer will give the
opposite (reverse) direction of rotation
in the mixed channel to the primary.
Any channel may be mixed with
any other channel and multiple channel mixing is possible. Referring to
Fig.3 (repeated from page 73 of the
August 1996 issue), the pins numbered 1-8 carry all control input data
to multiplexer IC5, including dual
rate switching. The pins identified
by letters are the outputs from the
control stick potentiometers via the
gain control pot wipers (see the circuit
diagram in March 1996) and are used
in certain complex mixing functions.
When discussing mixing, the primary
control channel from which the mix
data is to be derived is considered to
be the output channel.
The mixer inputs and outputs may
be found on the Mix Input/Output
connectors TB27 and TB28, located
at the extreme top right corner of the
encoder module. Fig.2 shows these
inputs and outputs in detail.
Note that there are four pins for
each mixer: an input, an output and
two for the mix IN/OUT switch. Fig.4
shows the details of the mixing patch
cord used to connect the mixer inputs/
outputs to the pins on TB10.
One patch cord is required for each
Fig 4: the mixing patch cord used to connect the mixer inputs/outputs to
the pins on TB10. One patch cord is required for each mixing function.
mixing function. The 2-wire, 2-pin
socket connects to the appropriate
mixer input/output pair with blue
to mix/in and white to mix/out. The
split leads go to TB10. The blue 2-pin
connector is connected to the primary
control (channel output) and the white
2-pin connector to the mixed channel
(channel input).
Two pins of the 3-pin socket on any
toggle switch are connected to the
switch pin pair. This provides front
panel switching for mix in/out. The
sense of the toggle switch (UP/OFF)
is determined by which two pins
are used (centre/left, centre/right). If
remote switching of the mixer is not
required, then the toggle switch may be
replaced with a micro-shunt across the
two pins. One switch or micro-shunt
is required for each mixing function.
Servo throw
That completes the description of
the basic components in the mixing
circuits. Before proceeding any further, there is a very important point to
bear in mind when setting up mixing
functions. Each mixer input has an
additive effect on servo throw and
this must be taken into account when
setting mix ratios. Failure to observe
this may result in the servo being
driven into its internal end stops with
attendant gear damage.
The Mk.22 has automatic compensation built in but it is still possible to
drive the servo into over-travel if the
mix ratios are set too high. Therefore,
be sure to check the final servo travel
with the full extremes of mixing applied, as servo travel varies with the
brand of servo used.
To illustrate the point being made
in the above warning, let us examine
the mixing process for a delta aircraft
featuring elevons (Delta mix). Such an
aircraft uses two control surfaces, one
on each wing, and each control surface
performs two functions: aileron and
elevator control – hence the name
“elevon”. Fig.5 shows the control
sequence in detail.
To bank such an aircraft, one control
surface goes up and the other goes
down, thereby imparting a rolling
motion to the aircraft. To raise or lower
the nose (pitch control), both control
surfaces go up or down, respectively.
Complications arise when one
wants to bank and climb at the same
time. If full throw on the aileron servo gives the desired rate of roll, what
Fig. 5: the control sequence for each of a variety of movements in an
aircraft fitted with elevons. Elevon controls are very complex to set up
correctly. Step-by-step instructions are included in the text.
happens when we then apply full up
elevator to impart a climbing motion
to the aircraft?
If we are turning left, then some
“up” mixed into the right elevon
(which is down in a left roll) is easily
accommodated. However, there is no
more travel available in the left servo
which is already full up.
To apply an additional pulse width
variation will only drive the servo hard
into the end stops and possibly strip
the gears. Therefore, the controls must
be mechanically arranged so that 50%
differential servo travel (one up, one
down) gives the maximum rate of roll
and 50% common servo travel (both
up or both down) gives the maximum
pitch angle.
If this is done, then we may apply
full pitch and roll commands simultaneously. Oddly enough, at this point
only one servo actually moves and it
goes to full travel.
The two commands on the opposing
servo cancel each other out and the servo remains in neutral. Elevon controls
are very complex to set up correctly,
especially when you start to consider
the reflex and unequal differential angles which must be taken into account
for the correct aerodynamic conditions
October 1996 85
Fig. 6: this revised diagram shows the configuration module socket (TB10) in the centre of the encoder PC
board. This socket was inadvertently left off the diagram published on page 73 of the August 1996 issue.
required by “tail-less” aircraft.
So let us move towards this complex
programming task cautiously and one
step at a time.
Simple 2-channel mixing
Such applications as Coupled Aileron/Rudder, Flap with elevator compensation and Main Rotor/Tail Rotor
mixing all come under the heading of
simple mixing applications and may
be accomplished with the use of the
simple programming patch cord and
the on-board mixers. Dedicated, complex mixing utilises the configuration
module and these mixing functions
will form the basis of later articles.
Coupled aileron/rudder
with dual rate mixing
In this program mode, the Aileron
and Rudder controls will be coupled
with an adjustable ratio of mix which
will change proportionally to the dual
rate ratio.
To program for coupled Aileron/
Rudder, we are going to take some output from the Aileron channel and feed
it into the input of the Rudder channel
via one of the on-board mixers and the
mix select connectors TB27 and TB28.
Both the output and input programming pins are located on TB10, the
configuration port connector (Fig.3).
At this point, it is necessary to
establish whether an inverting or
non-inverting mixer is required for
your application. Such details as the
direction of rotation of the servos and
the placement of the control linkages
will all play a part here.
If the complexity of working it out
in your head proves too much, just
whack the 2-pin connector onto a
non-inverting mixer and if the rudder
moves the wrong way, plonk it onto an
inverting mixer; very scientific! The
procedure is as follows:
(1). Replace the micro-shunt from pin
2 of TB10 with the Blue socket. Next
remove the micro-shunt from the rudder input on TB10 (pin 4) and replace
it with the White socket.
(2). Connect the 2-pin socket of the
patch cord to the appropriate MIX
INPUT/OUTPUT connectors on TB27
and TB28, with the Blue lead to “IN”
and the White to “OUT”.
A close-up view of the frequency interlock key. It plugs into the charging socket
on the transmitter when the latter is not being used.
86 Silicon Chip
(3). If remote switching of MIX IN/
OUT is required, connect two pins
of the appropriate toggle switch to
the “Switch” pin pair, checking the
sense of operation as you go. If permanent mixing is required then place
a micro-shunt across the “switch”
pin pair.
(4). Adjust the dual rate ratio using
the Aileron channel ATV potentiometer in the usual manner and set the
ratio of mix using the mix control pot
associated with the mixer you have
chosen.
You are now programmed for Coupled Aileron/Rudder with dual rate
mixing.
Coupled aileron/rudder without dual rate mixing
In some cases, it may be desirable to
change the dual rate without changing
the mix ratio. In this case, replace
Steps 2 and 5 in the above with the
following:
(2). Connect one pin of the Blue
socket to pin A on TB10, leaving the
other to float free. Next, replace the
micro-shunt on pin 4 with the White
socket.
(5). Set the ratio of mix using the appropriate mixer potentiometer.
Having mastered the basics of simple mixing, and it really is simple
once you get the hang of it, the same
principles apply to all 24 channels in
the Mk.22 transmitter. Any channel
can be mixed with any other channel
and even multiple channel mixing is
possible using the same principles.
Let us now look at the more complex
task of programming for elevons. In
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this application we begin to confront
the concept of channel allocation
which really is at the heart of complex
mixing.
Referring back to our earlier discussion on elevons and comparing it now
with the channel allocation table, we
find that there are no Aileron or Elevator channels, at least in the sense that
we normally understand them.
Instead, we are confronted with a
left elevon servo and a right elevon
servo, both of which respond to Aileron and Elevator commands.
Where do we go from here? We still
have an Aileron stick on the transmitter as well as an Elevator stick. If we
allocate one to left Elevon and the other to right Elevon, I hate to think what
would happen. I do not think humans
would be too good at manually mixing
these controls.
The answer is quite simple really.
We will use cross-coupled simple
mixing in which we will mix channel
2 into channel 3 and channel 3 into
channel 2. We will also allocate the
Aileron control stick to Channel 2 and
the Elevator Control stick to channel
3. Thus, the Aileron stick reverts to
its normal action, as does the Elevator
stick.
So the programming sequence
for servos of the same rotation is as
follows:
(1). Set both the channel 2 and channel 3 vary/normal headers to the vary
position.
(2). Take two patch cords and connect
one to an inverting mixer and the other
to a non-inverting mixer on TB27 and
TB28.
(3). Connect the Blue lead from the
non-inverting mixer to pin E on TB10
and the Blue lead from the inverting
mixer to pin A on TB10.
(4). Remove the micro-shunts from
TB10 pins 2 & 3 and replace them
with the White socket from the
non-inverting mixer to pin 2 and the
White socket from the inverting mixer
to pin 3.
(5). Fit micro-shunts to the appropriate
“switch” positions on TB27 and TB28.
(6). Use both channel 2 and 3 ATV
pots and both mixer volume pots to
achieve perfect balance between the
movement on both servos.
Remember here that Aileron will
send the servos in opposite directions
(differential), while Elevator will
send the servos in the same direction
SC
(common).
October 1996 87
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