MODEL RADIO CONTROL ELECTRONICS 
This is a continuation page of the
norcim web site covering still more ideas and info.
Return to
norcim 1 home page.
Forward to norcim 3 more Tx circuitry, electric
glider and an idea from NASA!
norcim 4
electronic circuits of interest for radio control
norcim 5
commercial receiver testing by Radio Guru Dave McQue
norcim 6
historical info on PPM radio control inc Mathers/Spreng system
40MHz Dual
Conversion Receiver notes covering possible use on this band.
Micron
transmitters and the 40 MHz band
type and availability of crystals.
Micron
transmitters on the 35 MHz band, general notes and observations.
An electric
flight item an alternative motor for 400 models.
Another electric flight item miniature speed controller based on a Mike Norton design.
Glow plug heater
circuit for four stroke motors
Simple battery
monitor for receivers
Exciting PCM transmitter
and receiver notes from Alan Pratt
Tony’s Website simply loads of
electronic R/C gadgets and circuit stuff! If you
find interest in any of the items on this web site, then Tony’s place will blow
your head off!!
Possible use of the Micron FET7 receiver on 40 MHz.
This is a ‘Dual Conversion’ receiver and several
enquiries have come in about its possible use on the 40 MHZ band for model
boats and cars. Providing you can get hold 
of 40 MHz receiver crystals
(preferably Futaba manufacture) then the changes to the FET 7 receiver are not
too drastic! All of the changes are at the front end and involve the change of
the 33uH inductor, (fig 2 on microns drawing) to a 22uH value available from
Farnell Components* part number 513-477. The 27p capacitor and 4u7 inductor is simply
snipped out as not needed on the 40MHz band. The front 159DZ antenna coil will
need re-setting for maximum range using a 40MHz transmitter and you will find
that this will involve almost exactly one turn of the core further down,
clockwise, than the setting for 35MHz. Ideally the 27p capacitor across the
coil would be changed for a 22p but as its under the coil, this is not
practical. If starting from scratch then fit a 22p! The setting of the ‘L2’
coil (several type numbers were used for this coil) should not need any
alteration.
If you’r posh! and have an oscilloscope to use when setting up home built receivers,
then it is worth realising that the scope lead and scope, when connected to the
receiver, adds to the antenna circuit of the receiver! When removed the antenna
coil may not be perfectly set! To counteract this effect, a special scope lead
can be made using a scope input DIN connector with two half metre, or so, flex
wires terminating with mini crock clips or similar, with a 1K resistor in each lead at the crock clip. The resistors filter the RF antenna
effect while still allowing the receiver output signal to show on the
oscilloscope. The ‘scope output’ on all the Micron receivers is from pin 9 of
the 3361 IC after the 4k7 resistor.
If you’r not so posh! and don’t have an oscilloscope, then I have found that reliable tuning
of R/C receivers can be done with a ‘crystal earpiece’ costing little more than
a Euro (or less than a pound!). They usually come with thin flex wiring,
terminating with a jack-plug. If the tip is held on the resistor from pin 9
(micron receivers) with the ‘other metal bit’ resting against the metal can of
the coil (or owt that’s negative), then you can plainly hear the transmitter
signal as a ‘buzzing’ sound! The discriminator coil, L2 can then be set for
maximum ‘loudness’. For setting the antenna coil….put the receiver and battery
in a card box and move away from the transmitter until the ‘buzzing’ diminishes
slightly. Now adjust the front antenna coil L1 for maximum loudness or
reception of the buzzing sound. (note that a ‘hiss’ can be clearly heard either
side of the Tx signal buzz). That’s it! And it can be very accurate.
It’s probably worth mentioning that the L2 coil on
micron receivers can also be set using a multimeter. With the meter pos’ lead
to the pin 9 resistor, and neg’ lead to battery negative, simply adjust L2 to
achieve a reading of 2 volts, (with the transmitter switched on!).
A Word about Micron transmitters and 40 MHz.
The ‘MICRON 35/40 1996’ transmit sections always made
use of ‘Fleet Control Systems’ crystals for use of the 40 MHZ band. These were
manufactured by the ‘IQD’ crystal company in 
Micron transmitter kit perfectly
without any circuit change at all! However these crystals have been obsolete
for some years now. In an attempt to find an alternative, I have found that the
standard Micron transmit section will work with Futaba 40 MHz crystals
providing a capacitor value is changed. The capacitor in question is the 56p
across the base/emitter of the BF450 transistor. If this is raised to a value
of 150p, then Futaba 40 MHz crystals can be used. The transmit section has to
be tuned to the new band using the LED tuning device that comes with the Micron
transmitter kit. A small reduction in range may result from using these
crystals, (as the Tx crystal is one third of the output frequency unlike the
Fleet crystals which were half frequency) but this can be corrected if
necessary by reducing the 100R output transistor, input resistor to 68R. This
is probably unnecessary however, as the range required with model boats, is
lower than that required for model aircraft. Remember, Micron transmitters must
use the special micron loaded antenna and the 40 MHz version must be used
for this mod. UPDATE
Another Word about Micron transmitters on the 35 MHz band.
A few constructors of recent Micron transmitter kits
have expressed grave doubts about the ‘range’ or ‘power output’ of their latest
version of Microns offering, as the current consumption of the whole
transmitter is less than 80 milliamps! In my opinion this is totally
understandable as their latest 
however point out that this is
simply not the case and despite the small battery power needed, the range, even
with their mini loaded antenna is still comparable with the ‘commercial
counterpart’ and the answer is simply the use of their loaded antenna system.
To prove the point, R/C Model World magazine March 2000, in their ‘electronics
project series’, covered a ‘Transmitter Output Tester’ that measures the field
strength (power) of any Tx at a distance of 10 metres. I have used this smart
device now many times and conclude, I wouldn’t be without it. Not only does it
show that the Micron Tx output is comparable with other transmitters but its
occasional use with any transmitter gives great confidence of correct output.
All of this becomes more interesting really, when you consider that the Micron
transmitter can work for up to twice as long as other transmitters, between
charges. Good for a day (or two) on the slope!
Yet another Word! on Micron transmitters
a couple of recent enquiries, ask if the latest
Micron transmit section could be used 
in earlier Micron transmitters. A
quick consultation with Roger Keately at Micron and a search through the
mountains of drawings and sketches he had, suggested that this had been thought
about and indeed possible. The only thing needed is a special connecting
flylead to connect the older (excellent but now obsolete!) NE5044 encoder to
the new transmit section. This lead is shown and can be made up using parts
available from most electronic stores or Micron. The odd thing about this lead
is that it can be fitted any way round! ie there is no specific end which must
go to the coder or RF section, the wiring appears to sort itself out, whichever
way round the lead is fitted.
A quick mention about a possible alternative electric flight motor for ‘400 size’ gliders. This is a ‘general
purpose, heavy duty, 6 to 12 volt, 3 pole motor’ made by the Sun Electric
Company (which I believe is in 
motors are available from
electronics stores and school technology suppliers for about a ‘fiver’. I’ve
now used several of these motors in ‘400 size’ 1.5 metre span gliders with
great success and offer the following notes for what they are worth! Armed with
a typical 400 motor and some kitchen scales, I did a simple comparison test.
Both The Sun and the ‘400’ motor run fine on 7 or 8 AA packs, both giving
around 5 minutes duration with NC cells (in the air) and 10 minutes using NH
cells. The 400 motor liked a ‘Gunther’ 5 x 4.3 prop and gave a static thrust
reading of 9.5oz. On the other hand, the Sun motor liked a chunky 8 x 5.5 prop
and gave a thrust of 12.5 oz. This is a 30% thrust increase for the Sun motor!
As with all good things, there’s a downside! The Sun motor is a big motor, weighing in at a full 2 oz heavier than a typical ‘400’.
However the fact still remains that if you can shave a couple of ounces off the
typical 35/40 oz flying weight of a ‘400’ 1.5 Metre span glider, then there is
an appreciable increase in thrust from somewhere, using the Sun motor. UPDATE!
TRANSMITTER ANTENNAS (telescopic aerials in old money!)
I know you’ve read it before but it is a fact that
telescopic aerials were never designed for model use! The caster base fuel gets
into these things, dries out into a gum, almost making it impossible to
collapse the aerial down without bending or breaking it! If this is not bad
enough the ‘grunge’ that’s living in the aerial, sadly
reduces the range of the Tx. (simply because of poor electrical contact of each
telescopic section). Occasionally, unscrew the antenna, extend it and
squirt ‘WD40’ into the bottom screw hole. A few collapses and extensions, using
a kitchen towel to clean the antenna will prolong its active life! (Aahhh!). A
word of warning though! If the aerial has been left in the ‘grunge’ condition
for too long, then after the above servicing, you may find that the top section
is so slack that it slides back under its own weight! The only consolation is
that the only thing keeping it extended before cleaning, was grunge and this prevented the aerial working correctly anyway. Should this
happen, the antenna needs replacing.
An electronic modeller contacted me with an idea of
using a speed controller circuit to keep the glow-plug of a four-stroke motor,
‘hot’ at low revs and tick-over. Unfortunately the detail of the mail involved,
has disappeared and I now can’t give credit to the guy who was originally
involved. However his idea is shown in the circuit alongside and involves the
modification of 
his Micron speed controller to
achieve the above. It is well accepted that 4stroke motors often ‘cut out’ at
low revs or tick-over, particularly when using low nitro fuels. Some 2strokes
can also suffer from this when using less expensive ‘straight’ fuel and could
also benefit from this device! The Micron speed controller is very easy to
modify, as it’s a kit! The only mods involved are the changing of the original
0.22 uF capacitors to a value of 0.47uF (see circuit) and the addition of a 5v
‘resistorLED’ which shows the glow state of the Glow-plug. The finished unit
plugs into the throttle output of the receiver (together with the throttle
servo, so you will need a two way plug!). The resulting ‘Glow-plug controller’,
heats the glow-plug, (Using an on board nicad battery) from about quarter
throttle, with very little heat, down to full heat at tick-over. The ‘on board’
nickel cadmium single cell battery needs to be about 2000 mAH or more to last
the flying session. Setting up the controller involves adjusting the 22K
trim-pot to just give maximum brightness to the LED, when the motor
is set at ‘tick-over’. You should then notice that as the throttle is slowly
increased, the LED looses intensity until around a quarter throttle, when the
LED (and therefore plug) is not glowing at all. 2% petrol added to a basic mix
of glow fuel often helps with general performance and tick-over. (more than 2%
does not work well) The use of a ‘synthetic oil’ based fuel compared with
castor-based type, ‘in itself’, helps with both throttling and a reliable
tick-over. The petrol mix idea, mixes with both types of fuel.
SORRY MODELERS! But I’ve just come across a web site that’s more for
the ‘real hardened electronic drinkers’. Don’t visit this site if you are
weak willed, as there is some real weird electronics there! If your game, then
have a stiff drink and visit www.electronicstuff.co.uk !
RECEIVER
this is about the simplest circuit you can get using
a simple zener voltage diode (BZX79C3V9 Farnell order code 369-378). The
circuit is shown alongside and simply plugs into a spare servo output of the
receiver. The idea is that, providing the receiver battery is well charged (4v8
plus), then the transistor TR1 remains conducting at all times and the red LED
shows no warning. However as the battery begins to sag, the demands of the
servos pull the voltage down below TR1 conduction and the LED flashes. It is important that use of this circuit involves ‘stirring’ two or three
servos before and after each flight. If the LED flashes, then it’s time to go
home and charge the battery!
A 12 VOLT GLOW-PLUG DRIVER Please note that this circuit has not been assembled
or tested
but it is offered for experiment by those electronic nuts who
may wish to assemble it and modify if necessary. Needless to say that if you do
dabble and get results (or don’t), then do let the web site know! The circuit
is based on a standard text book ‘multivibrator’ and it’s voltage supply is the
starter battery used by modellers. It fires a stream of thin 12 volt pulses to
the standard 2 volt motor glow-plug, simulating a 2 volt supply. The 47K pot
allows adjustment of the width of the pulses to suit the type of glow-plug used
(simply adjust the pot to obtain a rich orange glow with the glow-plug used) A
zener diode allows automatic fattening of the pulses when the starter motor
load abruptly pulls the battery voltage down. Q1 and Q2 are BC184LC or similar
transistors with Q3 being a BUZ11A or similar power mosfet. The LED will
illuminate when the plug lead is connected to the glow-plug, providing the plug
element is intact. The LED should be a high brightness type. Q1 and Q2 must be
high gain type, preferably better than 400 at around 2 mA. Worth a mention is
that the glow-plug connector type should be of the ‘box-spanner’ type. The ‘clip
on’ type can so easily clip on to the motor body and head causing a short
circuit which would not be good news for the BUZ11.
SOME EXCITING STUFF has just come in from long lost flying friend, Alan
Pratt. We first met when Alan was a student at
Reviving an interest in R/C
modelling after a 16 year break I decided to give my old Micron radio gear a
technical facelift. I had used PIC
microcontrollers prior to my retirement from industry and being mindful of the
attractions of pulse code modulation this seemed a logical approach. The coder and decoder boards are built and
tested and work fine. An electronic
speed controller is bread-boarded and this also works fine. I have standardised on the PIC 16C84 (16F84)
microcontroller because it can be repeatedly re-programmed making it ideal for
development work. It also has non
volatile eeprom data memory which enables the system user to store operational
data eg. failsafe settings.
Photo 1 shows the coder board
driving a standard Micron RF board (27 MHz early 80's vintage). The 
main components are
the PIC, a low cost 8 bit serial A/D converter and an HC4051 analogue switch. A
maximum of 8 channels is possible with this configuration although I have
provided for 6 on this board and am currently only using 4. The two
potentiometers set the +ve and -ve reference voltages for the A/D converter and
hence the servo pulse width range. The
small sockets at the bottom of the board will accept one of the proprietary FM
Tx modules (418 or 433 MHz) which are widely available. I have a notion to
download data from air to ground and this provides a development route for
bench testing. I have written the PIC program to generate either pcm or ppm
code.
With my version of pcm the
control information for each channel contains an address element and a data
element. The data is variable to effect the control but the address is fixed
for each channel and can be used to check for valid data. In this way it is
easy to detect invalid signals (eg. due to interference or out of range) and
invoke failsafe settings.
Photo 2 shows the Rx decoder
board with a Micron Rx. Apart from the +ve and -ve supply it needs 
only one connection to
the Micron Rx - the pulse output. The other Rx output used to reset the 4015 chip
on the Micron decoder is not required. To aid development and range checks I
have included a miniature LED which lights when valid data is being
received. I have fitted two DIL switches
on the board. Only one is currently
used. It selects either control or
program mode. In program mode, with the
model's controls adjusted to suitable failsafe settings the data can be stored
in the PIC's memory. The second switch is connected to a spare PIC input pin
for an as yet undefined purpose. (pcm or ppm?). An attraction of
microcontrollers is that additional functionality can often be added later
simply by re-programming.
I don't claim that this is ground
breaking technology nor that it represents the only approach to the subject. The
project serves to satisfy a personal interest in hobby electronics and provides
a technical challenge. As with most of my projects development/modification is
on-going without any planned timetable so its status could be classed as
'fluid'. I would be happy to share these ideas with like minded hobbyists so if
anyone has any questions or comments feel free to send me an E-mail. I will be
preparing a more detailed technical overview of the system in due course
(mainly to record details for my own benefit) with circuit diagrams and PIC
program listings (assembly language). UPDATE
Alan Pratt alan@pratta.freeserve.co.uk
A GREAT BOOK to have to
hand, is the RSGB (Radio Society of Great Britain) ‘RADIO & ELECTRONICS COOKBOOK’.
(ISBN 0 7506 52144) Edited by Dr George brown. This is an excellent book
covering the radio side of electronics from the ground up. Topics
starting with ‘What is a resistor?’ ‘What is a capacitor?’ and ‘Radio waves
explained’ introduce more than eighty excellent constructional projects and
gadgets including, ‘A radio that is powered by three lemons!’, ‘A solar powered
radio’, ‘Christmas tree lights’ and more. Amateur band receiver and transmitter
projects are there too! This is a real easy book to understand and I recon
would be an excellent book for school use that could span from mid GCSE level
right through to A level and beyond! I can’t think of any another book that
could do that with the radio side of electronics.
‘Alan’s Hobby Web Links’ A brilliant site listing thousands of Hobby
links, in carefully prepared sections, on an A to Z basis! Provides a
stepping-stone directly to the topic of interest! Simple to use, and saves the
time and frustration of searching. Click
Here (use the Back arrow to return to Terry’s radio notes!)
‘Tony’s Website!’… For those of us who have an interest in both
electronics and modelling, then this site is an absolute must to visit! Tony
covers dozens of electronic R/C projects with superb graphics, circuits,
layouts, parts lists and technical notes. For us like-minded people, it is
simply a joy to browse. Visit and Enjoy!! Click here (use the Back arrow to return
to Terry’s radio notes!)
circuit design
by Mike Norton http://home.hiwaay.net/~mjn/
with SMD modifications
by John Chambers Helen_john1@hotmail.com
John Chambers recently mailed me details of his ‘mini version’ of Mike Norton’s excellent speed controller. With Mikes blessing, we
can give the following details for those of you who would like to have a go!
The finished unit is real small and fits directly to the back of most 400
‘size’ motors. The controller can handle up to 20 amps continuous with battery
packs between 7 and 12 cells. (it may even be possible to use a higher cell
count if necessary but best to email first)
A single input lead provides the 5 volt supply for the receiver and
servos. The controller can also be used with 540/600 size motors providing the
20 amps is not exceeded. It is also possible to use the ‘large 400’ motor mentioned earlier (from JPR Electronics at around
£2.90 inc VAT!) Incidentally, if you wanted to use the controller with this
motor then one of the FDS7760 output devices can be safely left out, reducing
the necessary pocket money for the project!
For those who want to have a bash! John can supply super quality double-sided fibreglass printed circuit boards (I’ve seen some!) and also the ready
programmed microcontroller IC! Simply contact him at his Email address above. I
hope the three pictures are self 
explanatory but do take a look at Mike Norton’s excellent web
site, as much of the
detail info is there. John is also doing some notes about the circuit and
layout, which will be included here as soon as available.
Although I have not done it yet!! John has convinced me that it is possible for home
constructors to assemble surface mount devices, using just a pair of tweezers
and a solder iron bit of around 1mm tip diameter. The knack is to hold the SM
device in place with the tweezers, while spot ‘heating’ one pin of the device
to the board. The quality of this solder joint is not important at this stage
as long as it holds the device in place. Next use a spot of top quality flux
cored solder, with the iron, on the other pins of the device to give good
solder joints. Now go back to the initial solder joint that held the device in
place and use a spot of solder to ensure this joint is as good as the others.
The sample speed controller on loan from John performs
real smooth and the motor braking, (with no prop fitted) is ‘wow!’. It’s nice
also to see that the On/Off switch (PS1/PS2) is completely safe and will not
burst the motor into life until a definite Low/Off motor signal is first
received from the transmitter. I now have a PCB and one of John’s programmed
controller chips and intend ‘cloning’ a speed controller for the ‘Sun’ motor
powered glider I’m flying at the moment. UPDATE
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