This was quite an undertaking by authors Ed Sweeney
and Fred M. Marks. They reported on practically every radio control system that came new onto the market
in 1969 and printed the findings in the 1969 Annual edition of American Aircraft Modeler. That was still
the era of galloping ghost systems with reeds, rubber band-powered escapements, and some of those newfangled
things called transistors. By 1969, some of the transistors had graduated from germanium to silicon.
The authors actually get into a little detail on the dual conversion receivers with their IF frequencies
and selectivity - music to the ears of a radio guy.
From the R/C perspective, as the song goes, "These are the good old day," not the days of the old
equipment shown here.
1969 Radio-Control Equipment Survey
(see page 2 for the
Comprehensive directory of all 1969 systems from single channel to full-house digital, with data
on controls, circuits and cost.
Text by Ed Sweeney; commentary on digital by Fred M. Marks
THIS radio survey is the first of its kind in several years. The market recently has changed vastly.
Today's modeler has a choice of three types of control systems inexpensive dry-battery-operated sequential
sets, medium-priced proportional systems of up to three independent controls, or going first class with
full-house multidigital proportional. Each of these categories offers fine quality equipment suitable
for different applications. Some systems are expandable to more controls, some are kits, and some are
just for sport or fun flying.
Our survey is designed with two purposes: 1) to be a buyer's guide of what's available in each category,
showing what it operates, how it works, and what it costs; 2) to give enough technical information for
a meaningful comparison between the features of each system, including data that provides possible interchangeability
between one system and another.
For effective presentation we have limited this year's survey to systems manufactured in the U. S.
or Canada, but including equipment manufactured abroad for sale here provided service-after-sale
is available, too. We are interested only in systems for sale in 1969 and those units continuing from
1968 in full production for 1969. Discontinued, or no-longer-in-production systems, are not shown, although
they may be available brand-new at some hobby shops.
No evaluation of control systems is made. All the equipment mentioned is top rate,
excellent in design and performance, and of reasonable price. It would be impossible to fully review
and evaluate each set. No systems are knowingly excluded.
The groups: The role of a sequential system is two-fold.
First, it started R/C. All we had when Walt Good, Chet Lanzo and Jim Walker first tried R/C were
escapements, tubes, ground-based car-battery-powered transmitters, and rabbit-ear antennas. Now we have
very light, simple, compact, dry-battery (the cheapest kind), and highly refined sequential systems.
Second, we have more elaborate sets with motorized sequential actuators operating with pulse-counter-equipped
transmitters, which are hand-held units, and superhet receivers.
Three most appealing features of sequential systems are low-cost purchase and operation, non-wagging
single-channel action, and easy use. For glider flying, low-current consumption is important. Sequential
systems with only occasional command operation allow the least battery supply, yet powerful servo movement
when called for. All a small glider needs is steerage and occasional elevator trim; a sequential set
does the job fine. Small-field, and trainer types also go great with sequential rigs.
A proportional single-channel system, or anything up to three channels, is our medium-priced spread.
Proportional usually means bigger and more expensive batteries, mechanically better servos, continuous
communication between transmitter and receiver, a pulser in the transmitter, and more elaborate output
from the receiver. Weight is generally more than with sequential systems. But, proportional is better
because it is easier to fly and more like the real thing. The cost is usually worth the performance
Pulse proportional systems can be very simple and use light batteries, such as sets with magnetic
actuators. Smooth-working linkages are essential, and only small planes of less than 19 power are recommended.
For learning to fly, especially if one will some day get an elaborate multi-function system, rudder-only
pulse with add-on motor control is great.
Most rudder-only systems can be expanded to servo action with Galloping Ghost servos or with dual-servo
high-pulse-rate systems. This is elementary and dependable multi flying. Again, control installation
is more critical but the performance is still better. Current drain is higher, so bigger batteries will
be needed. Better pulsers are essential for good operation, and bigger-than-19 planes can be flown.
Some pulse-servo proportional rigs can be expanded with kits for servo amplifiers, decoders, and
the like. So doing, is fun in itself and gives one a real multi system, although with only two proportional
and one trimmable function. Such sets offer variable pulse width, variable pulse rate, and solid signal-on
and solid signal-off. This gives rudder, elevator, and motor controls.
Feedback servos for two proportional and one trimmable operation can be built and will be available
in kit form. Therefore, you can expand up to this performance.
The best of the medium-priced range are the three-channel proportional systems with all-feedback
independent functions. Transmitter has usually one two-axis control stick and a proportional, or positionable,
lever to operate a proportional feedback servo for such operation as throttle. Servos are the same as
in the full-house systems, and most of the transmitters and receivers are identical with the bigger
rigs. In fact, many of the three-channel systems can be expanded by their manufacturer to more than
three channels for additional expense, or at least the servos, battery packs and charging equipment,
can be used with a new transmitter and receiver, offering more functions. One or more additional servos
would be needed.
With three functions, there is no limit to what can be operated - big-engined planes, large soaring
gliders, boats, cars, etc.
It is common practice to use three-channel sets in planes normally flying with four-channel rigs.
This is done by electronic or mechanical coupling of rudder function with ailerons. If mechanical, a
linkage does the job; if electrical, a second parallel-wired servo is used. Flying with coupled aileron
and rudder is not too different from having independent functions and is better sometimes, as with high-wing
The user can further modify the three-channel set to have so-called 3-plus-1 action. Here, a set
of microswitches on the throttle servo cuts in or out the electronically coupled rudder servo. Primary
servo is aileron. One way to set this up is with coupled functions at full high throttle and full low
throttle, but to have ailerons only at all intermediate engine speeds. Switches just close contact in
the signal lead to the digital servo.
To add meaning to the three functional economic groups, we will give as brief as possible description
of single-sequential-function gear up through multi full-house digital.
In single-channel the use of one tone transmitted by a constantly on carrier or radio frequency is
the information to the receiver for operating a control.
In sequential single-channel, the tone causes a switching action of an escapement or servo. An escapement
is a rubberband-powered device on which rotating arm is released and caught by movement of an armature
controlled by a magnet from the receiver. A linkage operates the control surface from the rotation of
the arm. In the escapement is a shaft, hooked to the wound-up rubber band. The shaft and arm are allowed
to rotate a quarter or so turn from neutral, giving a mechanical output. So, indirectly, the tone moves
the shaft, and the device has several points in the rotation at which it can be stopped. These points
give neutral, right-rudder, left-rudder, and a third position (which is actually neutral rudder but
allows wiper contacts to trigger another device), and these are in sequence.
A motorized sequential actuator does the same thing as the escapement, only wiper contacts replace
the armature and rotating shaft. Movement of servo is powered by a motor. The same functions are available
in the same sequence.
The tone of the single-channel set can be turned on repeatedly with a pulser. Tone-on gives rotation
of servo motor one way, and tone-off gives opposite rotation. With linkages and gearing, the rotation
gives right- and left-rudder movement. Therefore, if the tone is turned on as much as it is off in a
given period of time, the rudder goes equally right and left. To the airplane this is neutral effect.
At the control stick on the transmitter we can vary the percentage of on-off time, and at the plane
have variable rudder positions. Rudder position is proportional to control-stick position. Thus, we
have pulse and proportional operation. The above describes rudder-only pulse proportional.
A Galloping Ghost system adds another operation available with the one tone, that of changing the
rate of the pulsing. This can be done without affecting the percentage of on-off time and therefore
is a second independent pulse proportional function. Galloping Ghost servos respond to the pulse-rate
changes for the elevator functions. Usually, the rate range is four to 12 pulses per second, with six
pulses per second for neutral. The function is mechanically detected by the servo.
Since the GG servo oscillates back and forth, not making a full revolution, we can obtain a positionable
function by having an arm on a gear downstream of the output gear for rudder, that is moved several
degrees when the rudder gear makes a full rotation. By the direction of full rotation of the rudder
gear, the arm of the down-stream gear is moved forward or backward. This is normally hooked up for the
motor-speed control. Full rotations either way are achieved by solid-on or solid-off tone; the control
is trimmable, and during throttle changes, the rudder wags at neutral and the elevator in up elevator.
This throttle arrangement is mechanically detected pulse omission, or more simply, solid-on or -off
Briefly, a two-servo single-channel system operates just like Galloping Ghost, except at much higher
pulse rates and with electronically detected pulse-rate changes. In all systems fast pulsing is down
elevator and slower pulsing is up elevator. More elaborate decoder single-channel systems with three
servos are possible, but none are described in the survey. The third servo, for motor control, would
operate on electronic pulse-omission detection.
A digital system, whether it is a one, two, three, or as many as eight functions, is a basic pulse-width
device. Here, the transmitted radio frequency is pulsed on and off - not a tone. The pulses are electronically
measured with reference to time and position within a set of pulses or a frame. Each servo gets one
of these pulses. In the servo an electronic amplifier adjusts the servo position to correspond to the
percentage of on-off time of each pulse.
The servo does not pulse at all- this is called feedback-servo operation. More detailed description
follows in the discussion of multi-digital proportional. What is given here is reference with single-channel
pulse systems only.
The survey of digital systems will attempt to be more than a simple listing of equipment available
from various manufacturers in that specific performance is given where available. In setting up such
a survey, the primary question is "What is important to the survey reader and why is it important?"
We will establish this rationale here in the hope that it will make the survey most meaningful.
It appears that flyers generally fall into distinct classes: those who couldn't care less what makes
the thing tick so long as it ticks, those who wish to learn the rudiments of the equipment in the hopes
that it will aid them in selection of a system the most useful to them, and those who like to build,
or at least maintain and repair their equipment. I feel that there will be data here useful to all.
For the prospective buyer: Those preparing to purchase their first set will generally
be guided by price, intuition, and what the local pros (if any) prefer. The following observations apply
in terms of the utility and mechanical arrangement of the systems.
There are three frequency bands available: 27mhz, 50mhz, and 72mhz. Not all equipment is available
on all frequencies, and the modeler is not permitted to operate in the 50mhz band without a technician's
license. There is basically no difference in performance available on all frequencies and selection
is dependent on local interference and the number of flyers in given frequency slots. Prices on 72mhz
are somewhat higher for some systems and 72mhz crystals are more expensive.
The number of channels required will generally be determined by the modeler's specific control requirements.
In general, it is felt that maximum utility is provided by purchasing a four- to six-channel system
which will cover your ultimate needs with whatever number of servos your budget will sustain.
Stick arrangements are: two sticks with trims and auxiliary levers for channels beyond four, or;
a three-axis stick with aileron and elevator controlled by the stick, rudder by knob on top of the stick,
and throttle control by a lever; or a two-axis stick for elevator and aileron, plus a separate self-centering
lever for rudder and a lever for throttle. The two-stick arrangement normally has elevator and aileron
on the right-hand stick and rudder and throttle on the left-hand stick, commonly called Mode 1. There
are a number of control arrangements such as throttle right, elevator left to separate aileron and elevator,
etc., which can be set up optionally.
Airborne equipment mounting is usually a variable feature with clip mounting, mounting brackets,
as well as the more common mounting lugs with grommets.
What performance characteristics mean: Proportional control systems in the past
were analog instead of digital. Within limits, different servos could be used with most analog systems.
With the advent of digital systems, the simple analog signal was replaced by a more complex digital
control pulse which varies from system to system and makes interchangeability more difficult.
Briefly, the digital system transmits a repetitious series of pulses about five microseconds wide,
spaced a nominal 1.5 milliseconds apart. This series of pulses will total one more than the number of
channels available. The series of pulses totals 1.5 times the number of channels, in milliseconds. This
series of pulses is followed by a pause of several milliseconds for system synchronization. This sequence
is then repetitive. The total length of the set of information pulses and the synchronization time is
called the frame length and varies for each system. The inverse of the frame length is the frame rate,
or repetition rate. Channel command variations appear as changes in the nominal length between each
succeeding information pulse.
The decoder accepts the series of transmitted pulses and decodes them sequentially to produce a pulse
for each servo. The length of this pulse is determined by the relative position of the transmitted pulse.
The characteristic of this decoded pulse determines the design of the servo. The variables associated
with the decoded control pulse are: its polarity which can be either positive or negative going; the
nominal width which you will see in the survey ranges around 1.5 milliseconds; the amount of pulse-width
variation about the nominal pulse width, usually around plus and minus 0.5 milliseconds. Thus, it can
be seen that within limits, servos can be used compatibly with systems other than that for which they
The receiver characteristics and techniques are presented, not as a measure of capability, but as
a matter of interest to illustrate how many ways the design can be done and still be successful. All
perform well and no one design approach offers an outstanding advantage over another. The sensitivity
of the typical receiver runs around one to five microvolts for full control. Those at the lower end
must be quite selective to reject unwanted signals while those with higher signal level requirements
generally have slightly higher transmitter power requirements.
Receiver selectivity is becoming an increasingly important consideration in a high-interference environment.
Typically, the required selectivity is obtained by means of a double-tuned front-end and the usual IF
strip. In some cases, RF amplification has been introduced with the advent of the Field Effect Transistor.
The high level of sensitivity achieved in digital receivers makes the use of automatic gain controls
(AGC) an absolute necessity to prevent receiver swamping and output variation with range. However, note
the multitude of ways in which it is achieved, all satisfactory!
Decoders offer an equally wide variation in technique with the use of SCS's predominant and the use
of integrated circuits increasing rapidly.
What can be forecast: Some of the trends are relatively apparent such as the reduction
of airborne system weight and Volume. Others, such as the use of new circuit concepts are not as predictable.
The weight of the average four-channel digital airborne system has been reduced from around 24 ounces
for the preceding generation to 12 to 14 ounces for the current generation. The 12- to 14-ounce weight
is achievable with discrete components and present serve mechanics and motors.
The next generation of airborne systems in the four-channel class appears to be headed for the eight-
to 10-ounce weight bracket. However, this requires the application of integrated circuit design in at
least the servo amplifiers. Just over the horizon are airborne receivers having not much over a one-inch-cube
Volume and servos weighing about one ounce.
With respect to circuitry, the use of RF amplification in the front-end will probably become universal
as has double-tuning followed perhaps by triple-tuning. The use of pre-tuned ceramic-filter IF strips
may also see extensive use, probably in conjunction with integrated circuitry.
One observation bears note by our domestic manufacturers: the introduction of frequency selection
by field-change crystals in the German-made equipment. The normal reaction is to say it can't be done
economically but remember, about three years ago it would have been emphatically stated that a 10-oz.
system couldn't be produced economically.
The second observation is based not so much on the survey as on personal observation: the impact
of kitted digital systems is having a tremendous effect on the hobby, primarily because of the price
aspect. Newcomers are coming into R/C at a sharply rising rate as a result. They then proceed to more
sophisticated equipment with the advantage of a fair working knowledge of the digital system.
Continued on Page 2
Posted May 14, 2011