Single Channel in the 21st Century - current state of play

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Phil_G
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Single Channel in the 21st Century - current state of play

Post by Phil_G »

Single Channel in the 21st Century - current state of play (post recreated from backup)

We are a friendly bunch of flyers (though admittedly slightly odd...) who share a love of R/C as it was back in the very early days, when life was much simpler and the joy of steering a model around the sky was a very new experience.

Long before multi-channel proportional radios were available, the vast majority of R/C models had just rudder control, nothing more, and these models were controlled by a simple transmitter with just one feature - a button. Pressing the button would give full rudder - all or nothing.

Although typical Single-Channel R/C set would cost the equivalent of a couple of hundred pounds or more today, this was the most affordable way into R/C in the 60s and therefore the most popular. Though immense fun when things went well, a typical R/C set of the day was far from reliable, and chasing a fly-away was all part of the ups and downs of what was then a very experimental hobby.

Today we are able to recreate the 1960s Single-Channel flying experience with absolute authenticity, but
also with complete reliability - and flying 'on the button' is immensely rewarding!

Whilst many S/C models are slow, stable designs based on free-flight principles, many are far from that - fast, aerobatic, highly responsive and a real adrenalin rush! The 'Sharkface' by Eric Clutton is such a model, originally for an .049 Babe Bee glow, at one stage the designer fitted a 1.5cc diesel for a really hair-raising performance! Today, electric motors are so convenient and quiet that they are often chosen over internal combustion engines, and their power delivery can equal or exceed their glow equivalents:
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gem_sharkface.jpg
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So what is this 'transmitter-with-a-button-and-not-much-else'?
A 2.4g Single-Channel set is based on a purpose built, custom encoder which when coupled to a 2.4g RF
module, a battery and a button, becomes a 'new age' Single Channel set. There are a few alternatives for the encoder itself, mine is generally available ready-built & tested to anyone interested in building a S/C 2.4g tx - see the projects page of www.singlechannel.co.uk and email Phil for details - whilst Martins is a DIY Arduino project. Others have home-brewed their own, remember Dave Kay's 'Oxo tin' tranny at Ponty?

These sets accurately imitate a typical 1960s radio control set, with a few optional bells & whistles. The encoder makes it a simple job to convert any old S/C transmitter to 2.4ghz, and there are several photos of converted sets on the '2.4g Conversions' page.

My own prototype was a veroboard-and-maplin-box semi-immitation of an RCS Guidance System and first flew back in 2009. Since then the design has been in constant development and refinement on a commercially produced PCB and over 1000 have been supplied to date, to S/C enthusiasts all over the world.
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rcsgs24g.jpg
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The emulation within the encoder firmware includes sequential or compound escapement operation, using a state-machine software model of the Elmic escapements taken from timings in a 1965 magazine. "Sequential" means that the rudder alternately moves left then right with each press of the button. It helped to remember which way you last turned, but the technique was to just press and see which way the model reacted - if it turned as intended, all well & good - if not simply releasing and pressing again would give the desired effect.

"Compound" or "Selective" escapements worked slightly differently - one press would always give right rudder. Left rudder was achieved by pressing, releasing and pressing again. One dog-walker down at the park who'd been watching me fly on the button asked "is it morse code?" which, whilst amusing, isnt far from the truth! Imagine sending morse code using the single-channel button. Excuse the digression for a moment but the dog-walkers explanation does describe very well how we operate a S/C transmitter!
Right rudder would be a morse 'T' which is _ (Beep...)
Left rudder would be a morse 'A' which is ._ (Bip beep...)
Some models had a kick-up elevator, activated by a press, release, press, release, press which in morse would be a 'U' .._ (Bip bip beep...)
and finally, some had a quick-blip throttle control which sequenced high, low, high, low and so on, which we can call 'E' . (Bip...)
Ok, its stretching the point, but to anyone who has never seen a S/C transmitter maybe it helps!
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skyleader.jpg
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The emulation optionally drives an ESC (speed controller) for throttle control with electric power, and has motor delay and slow-start for sequential rudder-only models, audio and visual warning of motor start,
three motor run timers... silent mode (for gliders), the compound mode includes kick-up (or down) elevator, & quick-blip throttle... it has individual servo reversing, throw adjust, two range-test modes, config saved to flash, audio confirmation, 'next turn direction' cheat LEDs for sequential, - etc etc etc... and it also will drive a 'real' rubber escapement connected to the receiver via a channel switch.

All these comprehensive features are controlled by the button on the transmitter, and although it may sound complicated, it really is a piece of cake and is ready to go as supplied.

Its all built on a neat PCB which has connectors for either a DIY hack module or direct insertion into a Futaba compatible module. The PIC firmware is written entirely in assembler and we've been using Frsky DIY, Corona 2.4g DIY and several 'Futaba style' cased modules including Spektrum, OrangeRx and Hitec. In fact the 'Futaba style' module is the preferred method now, as it does not involve any soldering to the module. The encoder can be configured to drive a simulator too, for button bashing practise!
The whole Single Channel Emulation Encoder project was featured in RCM&E magazine in November and December 2012.

This has been a fun project, well into its seventh year now. I've really enjoyed doing this one!

Here is a sequence of photos showing a typical conversion, this example being a Macgregor MR200:
First, the donor transmitter is carefully disassembled, and the 27mhz board saved in case you might want to reverse the process. The button and switch need to be desoldered from the PCB and remounted into the case.

Here, all the parts of the MR200 conversion are laid out - the side cheeks, aerial mount, front panel with its microswitch button and on-off switch, the emulation encoder and the DIY RF module with its bind board attached:
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mr200_conv1.jpg
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Heres the emulation encoder itself. The LEDs should be made visible, so in this case they are bent around to mount through the front panel:
There are three connectors to the encoder, of which two are used. PL1 takes a standard 3-way servo plug and connects the battery and 'tone' button.
Either PL2 OR PL3 connects the encoder to the RF module. Pl2 is used for DIY ir 'Hack' modules, and PL3 is used to mount the encoder 'piggy-back' style directly onto a Futaba-style RF module. The 'Futaba' method is quite neat as it avoids the wiring between the encoder and module.
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mr200_conv2.jpg
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The encoder is mounted between the on-off switch and the button, using gyro-tape, which is a very strong double-sided tape. Clean the surfaces first with rubbing alcohol to ensure good adhesion. Ensure that none of the solder-stubs are poking throught the tape and into the metal panel.
Note the LEDs bent around and protruding through the front panel:
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mr200_conv3.jpg
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Next, using more gyro tape, we mount the RF module and its bind-board. The back cover of the MR200 is designed to be easily removed, so its no inconvenience to leave the bind button inside the case. We then wire the battery and button connections to a standard servo plug, which then connects to the encoder header PL1. The RF module connects to PL2. PL3 is unused in this example, its an alternative mount which piggy-backs onto a Futaba-style module, thereby avoiding some of the wiring up. The aerial SMA connector has to be slightly countersunk into the black Macgregor aerial mount:
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mr200_conv4.jpg
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The side-cheeks are refitted, taking care not to strip the PK screws in the soft plastic. A 2S 500mAh lipo sits at the base, connected via a JST:
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mr200_conv5.jpg
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And heres the completed conversion alongside the original 27mhz board. Result - all the fun of 1960's single-channel flying with none of the old reliability problems, several km range, no interference, no waiting your turn to fly, no running out of escapement turns... just perfect reliability!
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mr200_conv6.jpg
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...and here's a converted 'OS Pixie' radio, all ready to go:
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If you have happy memories of single-channel flying, please share your story here. Reminiscing is at least half of the pleasure of vintage R/C!

Happy landings!
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