MODEL RADIO CONTROL ELECTRONICS 
More circuits and chat for the Radio
Control enthusiasts out there who have an interest in the electronics side of
the hobby.
Some notes about radio control
transmitter circuitry covering a 35 MHz FM circuit.
Barrie
Allen design glider for Sun electric motor. (mentioned in circuit
notes2)
Simple Speed Controller for
model boats! A PIC design with powerfet
drive
Ideas from NASA! Simple dead receiver check without even
opening the plastic!
Crystal
Meditation! Thoughts on plug-in crystals and engine vibration.
UHF with a twist!
…Malcolm’s cocktail,
for instant UHF from your transmitter!
Joystick
Wiring for home builders. Wiring for a joystick using separate
trim-pots
A Multi Servo Fail Safe for PPM systems. Alan’s
method of conserving Tx
battery use!
Radio
Control Council of the UK (not a lot of
people know about this!)
‘Car Boot’ for joysticks, servos, Rx cases, boxes, control horns, and even machines!
You
want a model electronic kit supplier? Then look no more, just click this line!
Video from the cockpit
of your model? Well not quite but nearly. It’s a start!
norcim
1 Home page with technical notes on Micron R/C kits.
norcim 2 mixture
of circuits and links and things.
norcim 4 new page more
circuits and general chat.
norcim 5 commercial receiver testing by Radio
Guru Dave McQue UK.RCC
norcim 6 historical info on PPM radio control inc
Mathers/Spreng system
A 35MHz AND 40MHz TRANSMITTER CIRCUIT
Commercial transmitters for use with
model aircraft have a range of around a mile. This is provided by an RF section
of usually three or four transistors with the use of plug-in crystals to change
the frequency channel. The 35 MHz R/C band is now used for model aircraft in
many countries, so the following circuit is shown with component values 
for the 35 MHz band. The basic transmit
circuit is very simple and involves just the middle section of the diagram
shown. This consists of a crystal oscillator stage T2 that runs at half the
output frequency, followed by a frequency doubling stage T3.
All the circuitry to the right of T3 is
simply there to filter harmonics and spurious signals. (and
it does this particularly well by suppressing all but the 35 Meg signal by more
than 56 dB! This is an excellent figure for EMC, ‘electro magnetic
compatibility’ and non-contamination of the radio spectrum).
The circuitry to the left of T2 is there to give a small (0.75 KHz)
‘controlled’ shift the oscillator frequency, with each servo position pulse
that comes from the transmitter coder circuitry. The resistor capacitor input
to T1, slows the switching of T1, so that the shifting of the transmitter
output frequency, with each pulse, is smooth. This keeps the transmitted signal
‘narrow band’. The output of this circuit has been independently tested by the
ERA (Electrical Research Association) and is perfectly suitable for use on the
35 and 40 MHz bands.
It never ceases to amaze me that just
two transistors and a few components together with a 9-volt battery can
potentially transmit up to a mile radius! The circuit is based around ‘Fuaba’ spec plug-in crystals (available from most model
shops). All resistors are 0.25 Watt 5%. Capacitors are disk ceramic except C12
which is a 16v electrolytic. All coils are Toko 7mm
type.
A
The
Sun electric motor was mentioned in ‘circuit notes2’. Well the guy who was in
on testing this motor actually designed a model to go with it! It’s called ‘Whisper’(there are still some of these naturally talented
people out there! Makes you sick!). The 
model
however, turned out to be one of the most enjoyable electric planes I’ve ever
flown and I still fly it whenever I can. It’s basically a V tail glider with
wing area and overall dimensions that were dreamt up to suit the first examples
we had of the Sun motor. The fuselage was made wide enough to just take two
standard size servos side by side and deep enough (6 cm) below the wing to
allow the 7 cell AA battery pack just foreword of the servos. The speed
controller and receiver are positioned under a removable hatch just foreword of
the wing. The Graupner 9x5 folder prop gives really
good performance, producing thermal height two or three times using NH cells.
Fuselage is of conventional balsa construction with foam wing. (built up wing
could even be better). The motor was arranged to give a full 10 degrees downthrust to prevent too much ‘nose-up’ on full power. We
found that very slow landings were achievable by applying up elevator, without
the model dropping a wing. Think it’s the effect of the V tail cutting into the
airflow when the tail is low, but I’m sure there are more qualified nuts out
there who can explain this finding.
IT’S THAT MAN AGAIN! Alan Pratt.
Alan has been developing a simple 
speed controller for model boats and
cars. Unlike the model aircraft units, which only drive the motor in one
direction (for obvious reasons!!) Alan’s controller gives proportional reverse
too. Prototypes have already been seen on the water and the circuit is just
simplicity itself, but ‘good’ design is so often simple! Alan has produced a
very detailed overview of his controller together with the PIC 16F84
programming details. INTERESTED? Then don’t hesitate to contact him
using alan@pratta.freeserve.co.uk cos he is more than
willing to share the development details with you.
ALSO! Alan has much more info now on
his PCM Radio Control System covered in ‘Terry’s radio notes2’. Too much to print on the site But If you are interested in more
details of this ‘next generation R/C system’ then do contact ALAN direct on the
Email address above.
(P.S. Alan does not appear to have
finished yet, with his different projects ….So watch this space!)
IDEAS FROM NASA! When
a little web site like ours, popped up in the NASA Research
Re: Simple
first order-check on a dead receiver.
Dear Terry,
I happened on this quite by accident, but it is a very useful tool. If you have
a relatively sensitive general coverage receiver, you never have to open a
receiver to determine if the Local oscillator is non-functional.
Most good quality general coverage receivers (such as most amateurs and short
wave listeners have) will be able to detect and pick up the un-modulated local
oscillator. So you either set your short-wave radio to the known
oscillator frequency or offset the receive frequency by +/- 455 kHz to detect
the local oscillator. Since the
oscillator is un-modulated, you will need to turn on the BFO (Beat Frequency
Oscillator) in the receiver to be able to hear the squeal when you plug in or
turn on the receiver.
So why doesn't a good frequency counter pick this up? If it did, you
would never get a good frequency indication, as it would be chasing every weak
signal for many miles. So the threshold is set to some reasonable level to
squelch the micro-Amp level signals.
This technique is great when you are checking old equipment, crash checking the
receiver, and in handy checking for oscillator drift as the tone will change by
the frequency change, which you can see on an oscilloscope.
I think it would be very useful for a group such as yours, who might not have
thought about it, to have a good General coverage radio around.
Good to share, George B. Beeler.
Many thanks for that
George. I wish the ‘Beeler check’ had been around some years ago when I was
fixing R/C receivers for a living! Take care and do keep us in mind for the
future!
A reason for ‘soft uncompressed foam rubber’ packaging
of the receiver, is that when used in a power model, some of the electronic
components are ‘microphonic’. (probably not a dictionary word but means ‘act like a microphone’!).
High vibration levels caused by poor packaging, induces an unwanted electronic
ripple at the receive circuit output. This in turn can cause semi-erratic servo
control on PPM systems and possible complete signal lock-out of PCM systems.
The suspect ‘microphonic’ components in receivers
were found to be the electro-mechanical items like coils and filters. Filters
tended only to show a problem at certain resonant frequencies. NOW GO AND
CAREFULLY PACK YOUR RECEIVER IN NICE SOFT, UNCOMPRESSED, FOAM RUBBER! (And don’t give a damn what the model shop
people say!)
An experiment to prove the above point, can be done. (Sorry! The following info is aimed only at
the real hardened electronic crackpots out there!). A test
rig, can be built around a 120mm/150mm 8 OHM full range HI-FI speaker unit.
A 2mm Ply disc of maximum diameter is dropped into the speaker cone, with epoxy
around its edge. This gives a platform for the ‘test receiver’ to be strapped
to, using hooks and elastic bands. I used a simple square wave ‘555’ astable oscillator with a PNP/NPN power drive to the
speaker. The frequency of the drive unit was about 30 to 300 Hz. This reflected
tick-over speed, to full power, of a typical Glow-Motor used for model flying.
A 6v 0 6v nicad battery supply was used but this
could be increased (if you wish the receiver to revert back to kit form
within a few minutes!!) Flex wiring is needed for the receiver battery
input and the oscilloscope output of the audio test point on the receiver. Warning!
The resulting noise produced by the test rig will certainly wake the neighbours
if not the dead!
If you’re a Crackpot like me then…..HAPPY
RECEIVER DEMOLITION!
Only just found it!
But have a look at www.homepages.paradise.net.nz
as there are some interesting R/C circuits and development notes there. I
was only on for a few minutes and didn’t get the name of the guy who has shared
the info. Will add to this note for next time. Update
USE THE 459 MHz R/C BAND WITH YOUR YOUR
FAVOURITE PPM TRANSMITTER! Well Malcolm
Perry has come up with a device that simply plugs into the Buddy-Box socket of
your Tx and Hey Bingo! your transmitting on the UHF
band! Malcolm has even developed a UHF receiver capable of up to eight
channels!
EVER FANCIED A UNIQUE FREQUENCY?………then read on!
Why not UHF? By Malcolm
Perry
The
I have for several years experimented with systems
using this band with various degrees of success. I thought that your readers
might be interested in a recent attempt to develop a viable receiver using this
band. In the past I have built complete systems - from scratch! - a laborious
task if you consider all the mechanics as well as electronics that goes into a
system!
The system I am going to describe makes use of the
licence free (MPT) modules now available in this part of the spectrum. In fact
the UHF band is now shared, so modellers do not have exclusive use of all the
frequencies, which is a shame. The modules you can buy are in the lower part of
the band, but this sharing is not all bad news. A characteristic of UHF is that
it does not propagate far and to date I have not experienced any interference
on the frequency I have chosen. The modules are designed to a specification,
and the one chosen is a dual conversion superhet with
a low noise amplifier front end. In fact the modules are complete and will with
a little interfacing accept a TTL logic drive and at the receive end reproduce
the same.
Transmitter
My idea as you can see from the attached
picture is to use the 'buddy box' trainer facility to take the output from a
standard transmitter and interface it into the UHF TX module. Simple really and
the advantage is that there is no modification to the transmitter that might
invalidate its approval standard. The unit can be removed and the transmitter
operated normally just by removing the DIN plug. In fact a simple adaptation of
the interface means that when the UHF module is plugged in the normal internal
transmitter is disabled - an important additional
safety feature.
Receiver
Perhaps the most difficult part of the exercise was to
develop a practical receiver, given that today's modellers expect small size and
lightweight as standard. You can tell from the attached picture that this
receiver is reasonably small; its actual dimensions are Length 60mm, width
42mm, and depth 34mm. Weight 70grams. For this you get 8 channels, only 7 used
with my transmitter combination and the exclusivity of the UHF band, It would
be fair to add that the receiver is slightly more complicated, because I found
that the recovered data from the UHF module was prone to noise bursts (glitching in modeller's terms) This was considerably
reduced by the use of a Phase Locked Loop discriminator in place of the
internal quadrature detector. The decoder board is
fed by the receivers second IF frequency at 455kHz.
Conclusion
I think the answer to my question "Why not UHF" is pretty simple and it is not necessarily a
technological one. The particular '459mhz' band is only available in the
Finally I would add a health warning - developing
systems that perform safely requires careful design and analysis or the old
adage that your "model might come crashing out of the sky" could
become true! Still as I said at the start, it is a shame that more use is not
made of this band or, as I noticed, one of your writers has already said we
will loose it.
Interested? Then you can
bend Malcolm’s ear at Malcolm.c.perry@btinternet.com
JOYSTICKS AND THINGS!
several Emails have arrived recently asking how to
wire-in transmitter joysticks, that have a separate potentiometer for
‘in-flight 
trim’. The circuit shows one of the ways
to do this and was actually used by Micron in many of their transmitter kits.
The circuit used, terminates with a three-pin socket. If the socket is reversed
when at the Tx coder, then the servo in the model
works in the opposite direction (an added bonus!), giving what is called
‘servo-reverse’. Micron’s older ‘5044’ coder used this set-up without problem
but the later ‘4017’ coder can give some problems owing to the restricted
current drive capabilities of the standard Cmos 4017
chip. The trouble is, that available joysticks use a 5K main pot with an
in-flight trim pot of also 5K. This results in a 2K5R load for the 4017 chip.
Unfortunately this is borderline current output for the chip! A solution to
this problem could be found by replacing the 5K ‘in-flight trimpot’
with a pot of higher value, say 22K, which would reduce the load on the 4017
chip. The HEF4017BT was found to give the best drive current some time ago but
there may be 4017 devices with better drive capability now, which would
alleviate the problem. However try this circuit first!
FANCY TAKING PICTURES FROM 500 FEET UP!!
Well give a ‘lateral
thinking exercise’ to the adventures the kite-man on www.gentles.milestoneet.co.uk/KAP/Pencam.htm This guy shows how
to fit a small inexpensive webcam to a kite! Taking wonderful photos from 500
feet up! I already have a similar super-light webcam and intend using his
detailed electronic circuitry and ideas, to ‘Velcro’ my webcam to the underside
of the wing of my ‘AA’ battery powered electric glider. This would show that
even a dinky plane can be used for aerial photography! James’s complete web
site has a much wider content too and for these reasons is well worth a visit.
I had an Email from James recently outlining his latest adventure of fitting a
miniature video camera to his kites, with instant relay to ground via a UHF
link! More on this one later.
GOT
ONE OF THE THOUSANDS OF PPM RADIO CONTROL SYSTEMS OUT THERE?? Then
read on again, because this Multi Servo Failsafe unit from Alan Pratt
will transform the safety of your system and add to your flying,
sailing, or driving confidence! The picture shows one of the DIY prototypes
that I managed to 
snaffle
for testing. With only five components, it can be assembled in around fifteen
minutes! (Wow, have things changed since
I was a lad!).
The
commercial possibilities of a Surface Mount version of this unit, in my
opinion, are big by modelling standards. It is estimated that 10s of
thousands of eligible model radio control systems exist in the
The unit
simply plugs in-line from the receiver to the servos. Under heavy radio
interference or loss of signal, it will automatically drive the servos
to a position, pre-set by the pilot! This is magic for the
average flyer and a must for quarter scale. Initial bench testing has
also revealed other technical benefits of the AntiFerence
program that Alan has developed for use in his microcomputer device. I am
convinced that this is not the last we are going to hear of this exciting
development! Me?…well I’m off to fly with the snaffled unit installed and
just itching to switch the transmitter off at 500 feet!
HAD AN EMAIL RECENTLY from Mohamed Shiraz Kaleel
and well worth a mention! Mohamed pointed me in the direction of a real
interesting group web site. These people actually build their own electric
flight motors from CDROM drive motors! The site is extremely detailed
and professional. A massive amount of technical info is available there
showing how to convert CDROM motors into powerful brushless type flight motors
capable from slow flight to 2kW! There is even details of the necessary
electronic drive unit including, even a kit of parts! Well worth a
visit if you are a mechanical and electronic nut, wishing to see the cutting
edge of brushless technology…. http://www.yahoogroups.com/group/lrk-torquemax/
IN 1950 (WHEN
BEER WAS TUPENCE A PINT!) there was just one transmitting frequency for model
control! At the flying field you simply waited for the existing model in the
air to ‘fly away’ then it was your turn to entertain the masses of kids that
would materialise from absolutely everywhere! It was probably as far back as
this, that the ‘initial seeds’ were sown, that slowly germinated into what is
now called the ‘Radio Control Council’ of the UK. This is a body of
representatives, experts and Gurus from all walks of the radio control model
world. They descend upon the Boardroom at Bletchley Park MOD establishment
around twice a year and with coffee and sandwiches, discuss the future of ‘model
radio control’. Liaison with the government ‘Radio Agency’ is
continual and on occasions Radio Agency officials attend these meetings.
One of the staggering achievements of
the RCC is that
Other technical inputs of the RCC include the introduction of FM radio in
1978, Narrow Band 10KHz FM radio 1980, A new 35 MHz band for models 1981,
Development of transmitter ‘Type Approval’ testing procedure, A special surface
model (boats/cars) band on 40 MHz, (leaving the 35 MHz band for aircraft only),
European Harmonisation of model frequencies and specs, Discussion of receiver
‘Type Approval’, R/C System EMC testing……..and the list goes on!…… (Not a lot of people know that!!!).
So! The next time you get
back from flying with a smile on you face! Just you point yourself in the
direction of ‘
A ‘FACTORY BOOT’ FOR RADIO CONTROL
HARDWARE! Do any of you
budding electronic entrepreneurs or existing manufacturers out there fancy a
ready available injection tooled battery box? Or a receiver case? Or a
transmitter joystick assembly? Or a commercial, large, metal gear, servo,
(quarter scale delight!)? Or ready available transmitter case mouldings? Or
multi finger precision control pots? Or servo grommets? Or a multitude of self
tap screws? Or other interesting items? (remember that initial tooling for these things can cost £thousands)
Or perhaps you fancy a machine or
two that can manufacture some of the above R/C items? Well, simply log-on to
the SLM Model Engineers web site
and have a good old rummage around the bits that Martin has available. I
know that they want to shift quantities of this stock but they are also very
helpful with smaller orders.
Want to know
of an electronic kit supplier with things like!!! Speed
controllers, servo testers, 
Micro
FM receivers, Micro AM receivers, chargers for nicads and NiMH batteries,
chargers for 6v and 12v Gel cell batteries, Big range of electric motors for
models, Servo slowdown kit, Servo failsafe, Big range of Sound Simulators for
model boats,
Photo shows actionkit’s DUAL SWITCHER KIT but there are many more!
SOME
INTERESTING GROUNDWORK…RECEIVING VIDEO FROM A MODEL?
James Gentles, the ‘Kite-Man’, mentioned above in radio.3, has been
progressing real well with photography from a kite flying at up to 500 feet
altitude! His findings will be of interest to modellers attempting to use one
of the recently available, miniature video cameras, with a miniature UHF
downlink transmitter module. Just one of the many web-site pages from James,
covers the problems found in having a UHF transmitter sitting very close to the
receiver in the ‘model’ (kite!). He covers this complex world of EMC (electro
magnetic compatibility) in a simlple hands on way
with plenty of practical advice, suggestions and findings. www.gentles.milestonenet.co.uk/KAP/rig02/emc.htm
also see www.gentles.milestonenet.co.uk/Gallery/2003/index2003.htm
Can just
imagine sitting down in the evening, after a good day’s flying, glass of
wine….. watching a replay of events from the cockpit…Wow!
NOW WITH THE
ABOVE IN MIND…..TAKE A LOOK AT http://www.kapshop.com/Full/ and click on the
instruction at the bottom of the page to take you around an almost impossible
journey!! But a quite wonderful experience!!
………Radio2