Norcim rc electronics page 21……
John Whitehead starts this page with his ‘Retro Radio Control Project’…
Having lived for some time on planet Earth, John has been through the early radio control times where if you wanted to control models by ‘radio’, then you had to set about and build the radio !
In the following notes, John covers some of the thinking behind producing a Home Brew radio control system that conforms with the technical requirements for use of the 35MHz R/C band here in the UK and EU EMC requirements.
In the distant past, during the introduction of the 35MHz FM band for model radio control in the UK, several electronic kit manufacturers offered radio kits that were tested and passed for use of this model control frequency by the ERA (Electrical Research Association) Test House. One of the manufacturers was ‘Micron Radio Control’. John has acquired original printed circuit design of the micron system along with the original electronic components used. So a replica has begun!
The following notes are taken from John Whitehead Emails of progress of the ‘RETRO’ project which include some interesting practical DIY technology which David and I found brilliant!
To begin with, some background from John Whitehead:-
Having been involved with radio control modelling since 1961, I've watched the hobby grow from being rather basic and quite expensive into an age of high technology yet generally speaking affordable. 1961 I used a cumbersome McGregor Ivy carrier wave system running on 27mhz with heavy batteries and limited reliability. Transistors were still an expensive novelty and most equipment used valves. Within a matter of a few years, multi-channel proportional control had almost taken over as the preferred method of controlling our models. Today we are able to buy a reliable system operating in the 2.4ghz microwave frequency spectrum for as little as £26.
The 35mhz band introduced around 1980, has been a major turning point in providing a very solid and reliable radio link conveying control commands to our models. The early 70's saw many UK manufactures evolve offering well made quality RC systems. There were several suppliers of DIY kit products, Micron was one such very popular company selling easy to build transmitters, receivers, servo kits and other well designed items. Micron has always been my favourite UK supplier of affordable reliable RC. Electronic design complexity was reduced to a minimum without compromising performance, whilst their electronic designs were easily comparable to many commercially available RC systems.
The march of technology has seen the industry change dramatically with the advent of programmable semiconductor devices. Many if not most commercial transmitters have some form of user programmability. High end RC product is without doubt very sophisticated and packed with features such as “model memory”. Large liquid crystal programming displays are commonplace. For some of us “older generation” there's a small price to pay in having to commit many of these complex features to memory. Thumbing through a large comprehensive owners manual at the flying field to find how to reverse a servo is not uncommon.
To this end, I started looking back to the 70's and 80's RC systems which have limited but perfectly adequate functionality. I fly mode 1, have just two thumbs, and with easily accessible servo reverse, joystick trims, this seemed to be a perfectly adequate solution to flying. There's a reasonable degree of interest on forums with the resurrection of older RC gear. Those old unused transmitters from the 70's and 80's are now considered to have reasonable residual value. Many modellers have migrated to use the 2.4ghz band. This has left the 35mhz band relatively quiet and uncrowded.
With an active interest in both modelling and electronics, I decided to turn the clock back and collect components to build a “retro” transmitter. A set of joysticks, case and telescopic aerial was easily sourced. The Norcim website has details for the ideal solution by way of two mating designs for the stick encoder and RF transmitting section. Printed circuit designs were easily produced using a free downloadable CAD programme which requires a very small learning curve. (Express PCB) The RF board has been copied as accurately as possible from original Micron data. The encoder board is a winner using “bog standard” easily obtainable parts, and a low component count. This item is claimed to have very low current consumption, sure enough when checked it is amazingly low at just 1.7 m/a.
And more info from John via email :-
Good morning Terry
I was visiting SLM to
collect 2 pairs of sticks to make myself 2 retro transmitters. 2.4ghz holds little interest for myself and whilst 35mhz is
available, I intend using this band.
It occurs to me that there's no way round producing a decent approved RF section that is other than cloning the excellent Micron design. Modeling and electronics are two of my retirement passions, but I also get great satisfaction from producing high quality printed circuit boards and have done for many years.
I'm able to design and produce boards quickly on a one off basis using simple home made kit and pre-sensitized copper laminate. Express PCB cad program is free, downloadable, versatile and easy to use. As your Micron RF board carries applicable approved status, do you still have details of the foil layout to enable reproduction?
A local ham component supplier is still listing 2k159 coils, (Jabdog Tipton)and using exactly the same components as shown in the circuit on the website, I am hoping to reproduce a "retro" transmitter.
The following drawings show the details of the ‘micron type approved’ transmit section which will be used for the 35MHz RETRO transmitter. The picture below left is taken from a Micron transmitter kit drawing. The picture below right is a clever reproduction of the micron copper side printed circuit board by John Whitehead. No original circuit boards now exist. The board fastens directly to the bottom 6BA screw of the aerial socket, exactly as the original. The copper layout is exactly as the original. Homework has been well done.
The boards I make have always been as good as commercial ones in terms of being sharp with no fringing. I do like your layout method with so little copper to etch off.
The mask is made by printing the exact image via my Epson ink jet printer on to Overhead Projector film. (cheap) This Epson SX210 is incredibly accurate. I can often do a prototype board start to finish in a few hours.
It's all "terribly expensive kit".
Home made UV light box. 2x 12" tubes. 555 timer.
Sainsbury's cornflakes dispenser for the etching bath.
Tubular glass fish tank heater.
Commercial photo sensitive PCB "alkaline developer" costs a bomb, I use DRAIN CLEANER.
A tub of caustic soda/sodium hydroxide costs £1-39 and makes about 150 litres!
The sodium hydroxide is diluted 1 teaspoonful to 500ml of water.
As soon as I have some boards "pickled", I'll send you images.
Hopefully there should be two images attached of the pcb mask. The process is a doddle, but not aware of others making pcb masks the same way.
The copper foil image is printed onto paper using the free to download Express PCB program. A small piece of clear OHP film is taped directly over the printed image. The paper is then fed back into the printer correctly orientated.
The inkjet overwrites onto the OHP film and registration is staggeringly accurate. This film objects to being fed into the printer as a whole A4 sheet. A complete sheet would be wasted with a tiny layout in the centre. I manage to about a dozen small masks out of one sheet. It's odd stuff with an almost sandpaper surface one side, yet perfectly see through. Some may suggest I'm a bit tight, I do tend to squeak when I walk.
The mask is placed directly onto the sensitized PCB and exposed to UV for 40 to 60 seconds, then developed with Sodium hydroxide.
The first picture below shows the negative produced on overhead projector film using the Epson SX210 Inkjet printer. The second picture is of the completed micron transmit section PCB using identical manufacturers components spec.
The picture to the left is the Spectrum Analyzer Trace taken from the ERA (electrical research association UK) test house data produced in 1981. A fully working sample of the UK Micron kit transmitter was supplied to the ERA for compatibility of the then new 35MHz NBFM radio control modelers radio band. This radio band was and still is, dedicated for the use of model aircraft control Only. It is totally exclusive for model aircraft control. No other users can legally use this band. It is the only model aircraft radio frequency that is exclusive to model flyers here in the UK.
Other radio bands have become available in the UK for model control but they are all ‘shared by other users’ (see page 20 of Norcim for details).
The ERA spectrum Analyzer trace data shows that the micron 35MHz transmitter was more than capable of working alongside 35MHz FM narrow band systems using 10KHz spacing spot frequencies. Indeed it was actually better than some. Looking closely at the trace, the 40db limit at 15KHz of the generated sidebands could almost suggest the possibility of 5KHz spot frequency use. (only a possibility though to simply show how clean the transmit section is. Other technical factors do come into play). So for club use the micron Retro Transmitter will be more than compatible with present day systems.
John has also developed a very neat compact version of the micron transmitter Encoder unit for the Retro Transmitter. This is a simple four channel coder based on the micron circuit. It provides the basic operation of four servos including servo reverse rotation using non-polarized plugs from each joystick control pot. Operation is simplicity itself. This unit does not need any form of outside ‘test house’ testing procedure. The reliability simply boils down to the electronic circuitry which has been around for over four decades. Working examples of the micron R/C PPM encoder, over 40 years old, still exist today.
June 2015. Update. John W has rescued a variety of Micron transmitter case parts that were destined for the skip!
A quick update.
The first picture (left) shows the RF and Encoder modules installed.
This next picture (right) shows the 2+2 AA NMH cells installed in each end cheek. This battery positioning is good for RF grounding giving maximum transmission. (hands virtually holding the battery packs).
(left) showing the encoder in bottom and fixed
to front of case, this allows easy access to the servo reversing plugs. Similar
sized scraps of PCB used with nuts soldered to foil then 2mm screws with short
insulating plastic stand offs to fix. Stand offs made from bits of
scrap snake tube. The mounting plate attached with some good double sided tape.
Next picture shows the novel Battery state indicator. I could have gone for a fancy cmos oscillator to flash the low battery LED but decided to stick with a simple approach.
8v2 zener switching a BC547. Selecting the LED type was easy, a couple of extra 1N4148 completes the picture. Simple as it is, this is repeatable and the switching point for the Red warning led is within a few millivolts across 6 of these indicator modules. Size is about 15X10mm.
The posh open gimbal sticks all need pots, Martin at SLM is "on the case" ....fingers X'd. Some versions use the old Cermet tracks, others have pots with small diameter shafts which I've never seen before. These are nice sticks and I'd like to use them rather than the other types on offer. 5K Cermets are like rocking horse manure now. Years ago these were the ‘standard’ used in servos and joystick units. They lasted for years but unfortunately needed cleaning every few hours of use. These servo pots were the first to develop jitter around center. Fortunately an aerobatic flyer found that if a liberal dollop of ‘Rocol ASP’ Anti Scuffing Paste (molybdenum grease) was applied to the pot on assembly, then the pots would last for months or even years between cleaning. Few manufacturers used this solution before changing to other pots.
THE ‘PATRIOTIC TRIO’ of Retro Tx’s, based on Micron parts, is shown above. These work on the 35MHz radio control band.
All the best,
There are other Retro Transmitters from John in the pipeline based on different but cherished transmitter types that have survived almost half a century! A word or two from john now….
recent retro upgrade for my pal "the Diesel Dave" with a Hitec RF module and one of Phil Greens little PIC encoders
suffered a bizarre problem. (this was the Delta
TX) Extend one section of aerial, the Corona RD820II receiver simply shuts
down. Phil does advise hanging 100n wiper to ground on the TX pots, sure enough
that seems to have cured it. Image of the Delta and a Swan 6. These are also
These TX's are waiting collection, both had pot decoupling ‘cumpasitators’ added. (sorry! John has developed his own electronic jargon!).
There could well be more updates on this one so keep watching. And thanks for reading !
Meanwhile a BIG change of subject ;-
David C has designed an intriguing device for radio control aircraft. Development is still ongoing. The unit is called a ‘VTU’ (Vertical Thrust Unit). The diagram to the left shows the outline of the device without giving too much detail away as patents are involved.
The device when mounted in a model aircraft gives an appreciable vertical thrust, assisting the models altitude. Test gliders using prototype VTUs have flown to considerable height simply from a hand launch in a flat field. The device can be switched off from the Tx for eventual landing. The VTU sits inside the fuselage at the Centre of Gravity. Side vents allow airflow intake and a square hole in the bottom of the fuselage is necessary for operation of the vertical thrust pipe. The device suits high or low wing models. Powered models have surprisingly short take off and landing using the device. With Delta wing test models, the VTU is best placed a couple of inches behind the CG where the thrust forms a ‘cushion’ of air under the wing allowing very slow controllable nose up landings.
The device uses a ‘resonant chamber’ effect. Both the input and output are simply out of phase resonant tuned pipes (motorcycle technology) and should not be tampered with. A forward air speed of around 6mph excites the air in the resonant chamber which begins violent oscillation of the chamber at around 40KHz per second. This produces a rush of air downwards from the exhaust pipe. This frequency cannot be heard by the human ear so the device is extremely quiet. The solenoid coil plugs directly into a receiver plug giving proportional or on/off operation if preferred.
David has negotiated with two manufacturers in China and is confident that quantity manufacturing price will be around £5.00 per unit including packaging and English instruction sheet.
The NordaveVTU should be available shortly at your local model shop at the competitive price of around £25.00.
News article written 1/4/2015
David C has just finished a revamp of an old favorite model originally designed by Vic Smeed with the plan published in ‘Aero modeller’ magazine.
Yes the Tomboy was an Aeromodeller plan dating back to 1955. The plan catered for two versions 36” span for 1cc engines and 44” span for 1.5cc engines. I built the latter but then thought it looked ridiculous so I sawed off the end bays of both the wing and the tail plane. Consequently mine is a unique 40” span version. I did consider fitting an ED Bee and flying it ‘radio assist’ on 2.4GHz but, not relishing the messy exhaust, I have fitted a brushless motor and real radio (35MHz Fleet mini/micro gear). It did have a former life with a brushed and geared 300 motor which was hardly powerful enough to pull it aloft with an eight cell NiCad battery.
For vintage effect, a dummy replica of an early ED ‘Bee’ diesel engine was made up and fitted. The resulting quiet operation will baffle most vintage modelers!
This kind of stuff really takes us back to the REAL aero modeling days and we will keep you posted on how this one flies.
And finally the well-used trio of Micron 35 MHz receivers have been pensioned off…..
After 20 years of sterling work in many of David’s model aircraft the Trio of Micron receivers are being pensioned off for a while. They will be replaced with 2.4 Gigahertz units to work with the new transmitters of the day (Feb 2017).
Micron produced many radio control electronic kit receiver versions during their decade (Plus) of UK production. Early versions were AM (amplitude modulation) receivers and those of you who are old enough to remember, will associate AM receivers with things called ‘glitches’. This phenomena showed itself at least once during several faultless flights. Usually at speed and under perfect transmitter control, the model would suddenly…Only for a split second.. drop a nose and violently bank, just to continue flight after, as if nothing had ever happened!
This was an annoying characteristic of model aircraft AM receivers. Fortunately ‘glitches’ rarely, if ever, happened on the landing approach.
Signal ‘reflections’ from the transmitter were to blame. A hill or a metal hanger or a cooling tower at the flying site provided several reflected transmissions at the moving receiver. The distance of each reflected signal arriving at the receiver were all out of phase producing a ‘flutter’ of the arriving signal at the receiver. AM receivers used ‘Automatic Gain Control’ circuitry which occasionally found this difficult to deal with resulting in the Glitch.
FM radio control had been envisaged, designed and developed in Germany and was selling well, two years before we in the UK took any interest.
Micron, Fleet along with Skyleader were the first here in the UK to get FM systems to the market place. 27MHz was the UK Radio Control band so all new FM systems were developed to work on this band. Some difficulty of the New FM receivers working alongside the existing majority of AM receivers was found. Initially this was a problem but with so many imports of FM equipment already ordered from the Far East by UK wholesalers…. a strange thing happened. Knowing that the future was definitely FM, …………the importers ganged together to filter all existing AM equipment out into the market place on the understanding that only FM equipment would be imported in the future. This move got around the problems of the new FM systems not liking the old AM systems. Worth a mention at this point is the fact that Micron saw the problem of FM working alongside existing AM systems and their first FM receiver was often demonstrated flying within a few feet of six AM transmitters which were switched on at the time. No Problem. The first Micron FM receiver however was a mixture of both AM with AGC followed by FM demodulation. Micron was individual and had no problem. However within a year or so, the sales at the model shop were all FM. So the unique micron system was no longer needed. Micron’s later receivers were smaller using the available FM chips that everybody else was using. The picture above shows Microns ‘Competition FM Receiver’ it worked really well and I used this version mostly for my flying. It was a development of the ‘Micron Dual Conversion receiver’ but did not have the problems of Dual Conversion Receivers in the UK. Unfortunately the Micron Competition Receiver kit had to be dropped by Micron owing to impending UK receiver testing. It emitted more than 1 Nano-watt of it’s Xtal activity from the flex aerial. A transmission that would have been difficult to detect just a few feet away.
Thanks for reading !