Norcim rc electronics club page 8……
MEMORIES FROM THE LONG MARSTON MODEL AIR SHOW. STRATFORD-UPON-AVON. UK…………
The pictures begin with World Champion Ali Machinchy and his Viper Jet 2M. Low passes were recorded at over 300 miles per hour at this event.
The large petrol prop aircraft displays were impeccable with some almost impossible low level manoeuvres.
Several thousand spectators including non flying family outings, enjoyed this two day event organized by the Avondale M.F.C.
We will be there next year !
MIKE HAWKINS is into some real retro R/C gear!!!!!
I’m real sorry to change the subject so quickly here but I had some mail from these two guys, which bristled the three or four hairs left on the back of my neck! The pictures attached with this mail show the type of transmitter that started off the whole of this hobby of ours during the 1940’s. The first pictures show Mike’s single channel transmitter built from scratch but to a spec from yesteryear! Probably late 1940s. Anyway I will let Mike fill in the pictures (as it were).
I have been modelling since about 1955 and used to fly free flight on Chobham common near Ascot where I grew up. About 1957 I watched a guy fly a model with radio and he actually brought it back and landed nearby! This was for me! I made a Vic Smeed “Electra” with an ED “Boomerang” radio system and powered with an ED “Hunter” diesel. It was marginally successful due to my inexperience but put me on the right road. Finding this radio “stuff” very interesting I then went on to becoming a Radio Ham and subsequently a career in electronics. However model aircraft has always been my major passion (I still have my old control line handle!) and I think always will be.
Some while back I was discussing “the good old days” with a couple of aeromodeller/radio ham friends and we decided it would be good to replicate a system to show the young ones how easy they have got it today, so the project was born. See accompanying photos, the transmitter is now finished and tuned and works very well and remarkably stable for its design but I put that down to modern components and better construction techniques that experience has brought. I now have to build the receiver, which will be an Ivy single hard valve (3S4) but with a transistor relay eliminator circuit. The model is to be the good old KK “Junior 60” which I already have built and is flying using modern radio on two channels and powered by an Australian Taipan 2.5cc diesel. I am also the Secretary of the Hobart Model Aircraft Club, http://www.hobartmodelaeroclub.org.au please visit our site.
The second picture on the right shows Mike’s circuit boards. The board to the left of the picture with the dual gate valve is the carrier transmitter itself while the unit to the right of the picture is a later antenna matching circuit designed by the legendary electronic guru F.C. Judd.
Mike has recently sent more details of further digging back into the past with the resurrection of a legendary single channel receiver and escapement from now our planets leaders in R/C technology! (Japan).....Wow it is good to see how it all started!
A member of our club (also a radio ham) has given me an OS receiver & escapement that he had used in the 1950’s, see attached photo, but unfortunately he does not know what happened to the transmitter, anyway the object being to use this in the project instead of building a receiver. As my time is very limited this is what I shall do. I have not powered it up yet but I am assured that it was working ok when last used in about 1958! By the way you are very welcome to use anything I send you for your website.
73’s until next time VK7DMH.
Many thanks for that Mike. The valve receiver is to the left of the picture probably works on a 45 volts battery supply with another 2 volt battery for the valve heater. The relay (to the right of the glass valve) looks of the ‘polarised’ type. These used an internal magnet to keep the normally closed contacts together. These relays were very sensitive and would respond to a very small change of coil current when receiving the Tx signal. A typical value of current change flowing through the relay coil when receiving the transmitter signal was often as low as one and a half milliamps! Unfortunately very sensitive mechanical devices (relays) obviously suffered from vibration…..so invariably these receivers had to be hung inside a fairly large airframe using four elastic bands. The petrol and diesel engines of the day often caused havoc with their vibration. The ‘escapement’ (the equivalent in their time of today’s servo) is shown on the right of the picture. They used their own usually 4v5 dry battery. Escapements were often a ‘converted’ relay but the coil windings were chunky and allowed a few hundred milliamps to flow. Escapements because of this healthy current flow used quite strong spring return mechanisms and did not seem to be worried too much by vibration. Fitting of these escapements often involved direct contact to a fuselage former. Escapements used a longish (12 inches) rubber band which was wound up to a hundred or so windings. As the escapement clicked with each command from the transmitter it produced sequential left and right rudder. Unfortunately, if engine vibration caused the receiver relay to chatter…… All of the pre wound rubber band windings for control of the model could be lost within a few seconds and no further control over the model was achievable!
The two above pictures show the ‘Retro Man’ himself, Mike Hawkins, with his briefcase style carrier wave valve transmitter and above the clinically neat valve receiver installed ready to go! ….magic memories. Mike has kindly sent some excellent circuit diagrams of these early receivers and transmitters, Interested ? then click here.
I will let Mike Hawkins explain this latest picture which shows the superb quality of his home built retro R/C system.
Surprisingly valves are no problem the below link should be able to help, however getting the valve bases is another story! I first got into this project by being asked to give a lecture on the history of model radio control to our amateur radio group here in Hobart, I am also a radio ham (VK7DMH). I said I would build a system if I could get hold of the valves thinking it would be almost impossible and I would be off the hook. As it turned out there are loads of battery portable valves available as the transistor portables made the valve sets obsolete whilst considerable stocks of spares were worldwide. I contacted a vintage radio restore business in Melbourne looking for a 3A5 (DCC 90) and was asked how many I wanted as they had loads of brand new in stock, so the project was born. The rest of the components were obtained from redundant equipment donated by ham friends except resistors and capacitors which were new. The TX battery was made from ten 9 volt units wired in series and two 1.5 volt units wired in parallel inside a plywood box covered with blue paper and a printed logo of ‘Ever Ready’ downloaded from the above site. The HT for the RX is made up from five 12 volt remote car door lock batteries in series to give 60 volts as the original 22.5 volt layer ones are definitely not available now. The relay for the RX and the rubber escapement are original and were donated by an aero modeling friend.
David Caudrey was also one of the many who contributed during the beginnings of radio model control.
David’s valve transmitter circuit is shown to the left using a pair of large American 3D6 valves. It was built in 1958.
Pondering the pitiful power output of my latest 2.4 GHz transmitter and of metal cases vs. plastic cases, made me think of my first efforts with regard to radio ‘control’.
The bulb in series with the aerial counterpoise in the attached schematic was rated at 6V 0.3A and it normally glowed pretty brightly (say 0.2A worth) which indicated about 1.6 W into a 40 Ohms aerial even more if the ground was damp. I used to get as much pleasure from building the radio gear as I did from building the planes. Some flyers did remarkable things with single channel sequential (and still do) but for me the prospect of keeping the model in the field was reward enough and even then I didn’t put too much fuel in the tank.
How much different from todays sophisticated toys!
The plywood construction was console shaped with an aluminium panel on the sloping section. The panel carried the meter the ON/OFF switch, the grommet for the umbilical to the micro-switch and sockets for monitoring the battery voltage with a ‘Pifco Radiometer’. I still have the latter which, of 1930s vintage, might well be a collector’s piece by now.
I was very proud of the panel because it looked a bit special having been fabricated from a piece of phosphated sheet which was light olive green in colour.
Some sort of insulated terminal block was bolted to the outer case. This originally mounted aerial and spike, both of which could be removed for transporting, and I remember that one had only to press the transmitter flat to the ground for the spike to penetrate and get a good earth connection. Note! no crystal; I think I tuned with a simple absorption wavemeter aimed at the amateur radio community. This was probably cross calibrated with a signal generator at Pye where I worked at the time. At a later stage I remember improving the aerial by fitting the rod into a large and impressive coaxial cable connector which made it all more swish to my eyes.
Talking about ‘memories’…. I have recently come across an old photo of one of my models taken when I was fifteen years old! (59 years ago!). Can’t quite believe it really cos how long has the Avro 707A been going as a model? It was built from an Aeromodeller plan design by a Hugh Beisterfield? (sure that’s not spelled correct!). A lot of this is from memory and after 75 years on planet earth, things can get a little puddled at times.
The thing that dates it is the fact that I constructed the brilliant Hill 2 valve receiver as a project in ‘metalwork’ at secondary school. ….HOWEVER the main thing here is the receiver, which at the time was superb. While other single channel carrier wave receivers would give a drop in supply current of around one to one and a half milliamps when receiving it’s transmitter……Mr Hill had just taken model control a massive step forward by producing a receiver that produced a massive current change of SEVEN milliamps! WOW this was a field day for the relays of the time and long gone were the very sensitive mechanical adjustment of the contacts. You could at last ‘hear’ the relay slamming in and out from (almost) the next room.! This meant also that the receiver was not so prone to vibration and looking at the picture it looks as if I’ve used soft foam to mount the receiver instead of elastic bands. An OS Pet 1.5cc glow engine (which had just become available), pushed the model with less vibration than the diesels of the time. The actuator was a modified Mighty Midget motor working on a single 1.5volt battery, giving sequential left and right rudder. Elevons were fixed with cement to give a gentle ‘up elevator’. Flying was very slow and gentle.
THE SUCCESSFUL VINTAGE TWO VALVE RECEIVER BY MR HILL
(Photo by Derek Round)
SEVERAL YEARS AFTER THE HILL RECEIVER germanium transistors came on the scene and many transistorised radio control systems began to appear. One of those circuits comes next from David Caudrey via one of his reverse engineering projects. The circuit may seem strange, as in those days most available transistors were PNP type. David has shown this circuit as we now normally view electronic circuits with the negative rail at the bottom. In the darkest past, this circuit would have been upside down with the POS rail at the bottom !
The circuit is of the Gallatrol Receiver which was a tone pulse proportional system developed by Charles Rail. This system used slow pulsing of a single ‘Mighty Midget’ electric motor to control both rudder and elevator of a model aircraft. The method used an ingenious mechanical linkage at the tail of the model to achieve this. The Gallatrol receiver circuit was designed by Doug Bolton who lived in Nottingham UK. The transmitter produced 27MHz carrier and tone pulses which via the receiver, caused the Mighty Midget motor to flick backwards and forwards, achieving the flicking of both the rudder and elevator of the model. The proportional effect on both rudder and elevator of this system in a model airplane was impressive.
Galloping Ghost Transmitters emitted sequential blocks of 27MHz ‘Carrier’ with a block of ‘Tone’ (the Carrier being switched on and off at a frequency around 1000 cycles per second). These ‘Blocks’ of transmission varied in frequency from 2 to 20 cycles per second. Also the ‘Blocks’ varied in size between 20% to 80% mark space.
Doug Bolton used a ‘TerryTone’ inspired front end super-regen receiver for this version of the Gallatrol receiver. The OC170 was one of the first germanium transistors to work at 27MHz and formed the super-regenerative front end.VT2, VT3, and VT4 amplified the ‘Tone’ part of the transmission to keep VT4 in a permanently ON state. Carrier transmission kept VT4 in an OFF state.
The following motor amplifier VT5 to VT8 drive the motor backwards and forwards performing the primitive proportional effect of the rudder and elevator of model aircraft. More detail about the Gallatrol Super-Regen front end ?
The assembly of the Gallatrol receiver is shown next for Nostalgia reasons only ! Early versions appeared in 1962 with the design drawings including the transmitter and modified Mighty Midget actuator being printed by a UK model magazine in 1965.
The above shows how ‘Radio Control’ has changed within one single generation !
THE FOLLOWING NOTES COVER ONE OF DAVID CAUDREY’S 2014 RETRO RECEIVER PROJECTS….. David had the interesting idea of using the Quench Oscillator of a valve Super-Regenerative receiver, to also supply the HT and heater voltages for a retro valve receiver. This would allow a standard 4.8volt radio control receiver battery to be used. The following circuit shows how this could be achieved. The whole receiver is now being worked on and we will cover the results as they emerge. Please note that although the following circuit has been assembled and tested, minor modifications may result from ‘work in progress’.
THANKS FOR READING!