I thought we’d begin this little odyssey with a brief recap of Single Channel (S/C) operation as it was in the 60’s. If you were around during those early days a lot of this will be familiar and it might even jog a few dormant memories, some good and some not so good!
If you arrived on the scene a little later, bear with me, you might take some convincing that we were actually able to fly these things!
In the 1960’s the most affordable and therefore the most popular radio set was a single channel transmitter and a super-regenerative receiver, with a rubber-driven escapement controlling just the rudder.
The super-regen type of receiver would respond to almost any transmitter in range and therefore models had to be flown one at a time.
This actually caused very little trouble and we were happy to share airtime very courteously!
|A typical 1960’s single-channel transmitter had just two features, and one of those was the on/off switch. The other, the one and only control, was a push-button, a bit like your doorbell.
In the receiver was either a relay or a transistorised switch, which followed the operation of the transmitter button, so in fact the whole outfit was basically a remotely operated on-off switch. The receiver relay was wired so that it switched power to the coil of the escapement when the transmitter button was pressed and so the armature of the escapement followed the operation of the pushbutton. The escapement was driven by a long rubber motor, wound up with a few hundred turns and attempting to spin the rotor of the escapement, which it was prevented from doing by a pawl on the resting armature.
|In a sequential escapement such as the Elmic Conquest, operating the armature released the rotor for a quarter of a turn, equating to right rudder. Releasing the armature would permit the rotor to turn another quarter turn, settling at neutral rudder. The next armature operation would release the rotor for another quarter of a turn, giving left rudder, and on releasing the button (and therefore the armature) it would complete the 270-degree cycle and come to rest at neutral. Sequential escapements simply gave left and right alternately, and you had to remember which way you turned last. Operation was very fast as the rubber powered rotor was not slowed mechanically, the escapement emitting a loud ‘clack’ as it deflected the rudder.|
|A compound escapement such as the Elmic Commander had stops at 90 and 270 degrees, but omitted the ‘neutral’ position at 180 degrees. The rotation had to be mechanically slowed to allow a reasonable speed of keying the button, and this is how the ‘one press for right’ and ‘two-pulses for left’ method was achieved.
|The Compact compound escapement had a further stop at about 355 degrees, where the ‘kick-up’ elevator function would be triggered on the third press of the button, and a ‘quick-blip’ circuit which triggered the throttle escapement if the rotation passed through 45 degrees whilst the button was released.
Timing the keying of the button was quite critical and had to be well rehearsed - flying a 3-function single channel model was a real skill!
|The Corporal was a two position throttle escapement - operated by a quick-blip of the transmitter button, it would alternately open and close the throttle.|
|Four of Shauns working Single-Channel demo rigs. from the top down:
ED Escapement plus Terrytone super-regenerative receiver
Futaba Single Channel with rudder plus motor actuators and Macgregor Superhet receiver
Rand LR3 GG setup, (more on the G/G page)
and a Macgregor super-regen again with an Elmic 'Compact' and 'Corporal' rubber-driven compound escapement setup giving selective rudder, kick-up elevator. and quick-blip throttle. Note the clever Elmic 'Sidewinder'.
A development of the Elmic rubber-driven escapement was the motorized equivalent for example the Climax ‘Unimite’ compound 'motorized actuator' (they didn't call it a servo back then). Both worked in much the same way, one press for right, two for left.
The Unimite was incredibly noisy, and could be plainly heard from a model flying hundreds of feet above.
Single-channel models were more often than not rudder-only and inherently stable models were the simplest and most successful. On the other hand, by choosing Compound escapements, a fully equipped single channel model would have rudder, one way elevator (usually up but down was often used in gliders) and a 2-position throttle. All these controls were 'bang-bang' all or nothing, there was no proportional movement, no stick to follow. All the control surface movements involved nothing more than rubber bands and mechanical means, no electronics were used other than in the radio itself.
The radio itself was rarely 100% dependable in those days, and the rubber band driving the escapement could easily run down during a long flight, which of course meant no further control was possible. Radio failures, interference and expired rubber meant that retrieving a fly-away was an occasional necessity. This is where the noisy Unimite was a godsend for finding a S/C slope-soarer buried under four feet of bracken. Made the sheep scatter like ninepins too.
Despite the shortcomings of the equipment, it was of course a lot of fun, and fun is the reason we do this hobby, right? Wouldn’t it be great if we could have a modern, reliable equivalent of the old single channel sets?
The ingenuity shown by early R/C designers was incredible. Here we have another of Shauns demo rigs, kitted out with a 'Full House' single channel setup having SIX individual functions!
This system used an especially clever escapement called a "Bonner Varicomp". These could be cascaded almost ad-infinitum and in this rig we have two Varicomps, a Fred Rising clockwork throttle actuator, and a buzzer (just to show the sixth function).
This would give left, right, up, down, throttle and another auxiliary function (ie the buzzer) which could be a bomb drop, flaps, retracts... on Single Channel in the 60's !!!
To use this effectively would need such precision timing of the transmitter tone key that an electronic or mechanical pulser was probably essential, although with practise Shaun can operate all six functions. Actually flying one might be more of a challenge!
|Original REP Reptone transmitter|
|REP Gemini (successor to the Reptone) Single Channel Transmitter.|
|Futaba FR21 transmitter and super-regenerative receiver|
|Early Macgregor Single Channel Transmitter.|
|Early and later Macgregor S/C sets|
|27 Mhz Macgregors, Futaba FT3A and a Ripmax Pathfinder|
|ED (Electronic Developments) Black Prince Single-Channel transmitter|
|Shauns very early floor-standing ED valve transmitter|
|and the matching valve receiver which is remarkable compact for the era|
|This was a build-it-yourself article in RCM&E magazine, a single-channel tone outfit that could be built in relay or relayless versions|
|The RCM&E set with the printed article|
|and with its matching receiver|
|The diminutive OS Pixie, this one is a later model|
|Mainstream (later to become GEM) Single-Channel transmitter.This same hardware was also marketed by Roland Scott as the "RS Navigator"|
|...and here is Phils "RS Navigator", kindly donated by Doug C|
|The Macgregor Codamac tried to make button-pushing obsolete! It had an electronic coder which did all the 'one-for-right, two-for-left' business for you via a two-way lever. The button gave a timed quick-blip to trigger a throttle escapement.|
|A latecomer to the Single Channel scene, the Staveley Tonelock had an inbuilt left/right/quickblip coder similar to the Macgregor Codamac. This particular design was unusual in that it transmitted a continuous tone between button presses, and unmodulated carrier whilst keying. This supposedly gave better interference rejection. Without doubt it was one of the very best single channel sets ever made.|
|A better view of Shauns immaculately restored Staveley Tonelock transmitter.|
|Futaba also made a 'coder' transmitter, this outfit was kindly donated by Simon B.
It features a switchable button which can be either an automatic quick-blip, or a manual 'tone' button.
The left-right joystick uses a rotary pcb disk with wipers rather than a simple toggle-switch!
Inside are variable 'pots' to adjust the timing of the coder, with the manual button option as a back-up 'just in case'!
|The Futaba is beautifully made, these were the Rolls-Royce of sets back in their day!
This example has cleaned up nicely, just a little wear to the 'Futaba' badge. This one has a Superhet relay receiver, with fixed crystals on 'red' (plug-ins came later!).
The relay permitted use of motorised actuators in place of escapements - typically the Climax Unimite, Ripmax/Orient Minimite, or the less common Slim-Jim. A lovely set.
|The Controlaire 'Mule' single-channel transmitter was very conventional.|
|RCS Guidance System with Compound rudder & throttle escapements|
|A collection of Single Channel receivers|
|Complete MacGregor Single-Channel outfit, with MiniMac receiver|
|Although Shaun only built this Single-Channel transmitter recently, it is typical of 1960's innovation in transmitter cases!|
|Collection of Single Channel escapements|
|And a similar collection of Single-Channel servos (or motorized actuators, as they were known back then).|
|And an unusual German motorised actuator, this is
the superbly engineered Aristo Craft 'Pilot' sequential:
|A hombrew transmitter fitted with an Aristcraft mechanical coder for compound escapements.|
|Futaba FT3A Single Channel set complete, shown with Elmic Conquest sequential escapement|
|A Raven Single Channel set with receiver and elmic compound escapement.
This one belongs to Diesel Dave!
|Graupner Mikro Combi receiver, escapement and relay pack|
|Instructions & price list for Mikro Combi receiver, actuator and transmitter|
|Telecommander single-valve carrier-wave transmitter|
|Inside the Telecommander:|
|and a close-up|
|Here we have Shauns home built Windy Kreulen transmitter, alongside a recently acquired 'mystery' Stockmann & Westley transmitter - the 'Altran'.
Best guess is that this was the follow on set from the Windy Kreulen valve tone set, but I have never seen any reference to it in the modelling mags of the period. The previous owner bought it as a kit from Ron Westley. It was in a pretty poor state, The on / off switch and keying button had to be be replaced and the case also needed some panel beating back into shape. A few hours fettling and it looks original and in pretty decent condition again.
I have a feeling this Tx is an improved version of the Windy Kreulen EASYTRAN Tx . The circuit was published in Dec 1963.
|Towards the end of the 70s Micron did an innovative kit-build Single Channel proportional set, literally rudder only, just one proportional channel. The 'Elf' was absolutely ideal for small diesel powered models or for S/C gliders. Terry tells us that less than a hundred units were sold, so finding this one was a really lucky break, especially one in such good cosmetic condition - inside is another story! Soon to be resurrected for action down the flying field on 2.4ghz. Pictured alongside Phils Sharkface.|
|...and heres the original 'Elf' advertisement from RCM&E magazine:|
|A 1950's homebrew pulse actuator made by John Codd. Centrigufal bob wieghts pull the output arm which is connected to the rudder. With the servo un-powered the model was trimmed to fly left, with signal driving the servo to give right rudder. Straight flight was blip, blip, blip all the time. Hold for right, release for left. Ingenuity unlimited!|
|and another one of John's homebrews, we're not sure how this one worked as there seems to be no solenoid/detent mechanism. I can see how the wire shaft with the 'U' bend can slide to & fro to act as the detent, either side of the 'U' will catch the pawl front or back stops, but I wonder what moved the shaft?
Note the clever conversion from rotary to push-pull action.
Phils Vic Smeed Poppet on rudder-only, flown at Pontefract Park, on the 2nd Feb, 2012.
This is a test-bed for the converted 1970 Macgregor Digimac 1+1, details on the '2.4g conversions' page:
Join the Single Channel Revolution!
Phil Green & Shaun Garrity, of the Pontefract PANDAS club
For more information, please email