Book 3

Model
Cars Bok3
MOTOR
TUNING
the complete story
U A f K PRESENTED FREE
WITH THE FEBRUARY 1970 ISSU E OF M O DEL C A R S

Hey baby; w e’re blow ing our own
trumpet.
Together we could m ake beautiful
m usic.
We will shortly be able to give you
the low down on a sm all su rprise
that narrowly e scaped publication in
th is issue.
B .I.C .O ., 2 L an caster Road, W.11
T elep h o n e No. 0 1 -2 2 9 1601
European Distributors for the products of
Cham pion o f Chamblee
3

s e lf flu xin g w ire
FOR ALL M O D E L C A R S
A N D T R A IN S, Etc.
on i oz. Reels
28-36 swg, 26-33 B /S
Reels 2/6d. each.
Packing and postage 6d.,
three or more 2/- post free.
Also High Temperature Wire.
4/6d. per reel.
Trade enquiries welcome.
N. J. E L E C T R IC , 1587 L O N D O N R O A D ,
L E IG H -O N -S E A . Telephone: Southend 73694
1 1 m a I C ? 373 H IG H ST. N O R T H . M A N O R P A R K
VYdll ILLUvlUld L O N D O N 1.12 01-472 2508
East London Model Car Centre
M A IL O R D E R O ver C2. p o st Ire*;
otherw ise odd 1/-.
C lu b * - w rite lo r deteile o l epeciel
term s on c lu b orders.
S p e c ia lists in C h a m p io n and M u ra
Products.
A rm atures and M o to rs to order.
H O U R S : 10-6 p.m. S u n d a y 10-1 p.m
M o n d a y s and Fridays. 7 -1 0 p.m.
C lo se d Th ursday.
R A C IN G : M o n d a y & Friday.
O otails o n Roquest.
DON'T FORGET!
Binders for this series of handbooks, in handsomo grocn card with
gold lettering and uniquo clip systom, aro still available, price
2/6d. inc. postage.
Cheques or P.O.s. please, to
M O DEL C A R S M A G A ZIN E,
13/35 Bridge St., Hemel Hempstead. Herts.
4

ELTHAM MODELS
Ian & Ray Skilling
MAIL ORDER CENTRE
M A IN A G E N T FO R M U R A M O T O R S
M EDIUM PRICED MOTORS
R iko w h ip 16D
1969 B /R accd M a b u c h i 29g
w in d (idoal lor be gin n e rs) 31/-
C ham pion 'B la c k P ow e r’
1969 B /Raced M a b u c h i 29g.
w ind, b lack caso. strong
s p rin g s and h / sin k s in ­
cluded 32/6
M u ra 5 % B lu o Print
M u ra thick case, unm oltablc
ondboll (idoal lor rew in d in g) 38/-
M u ra M in i-B ru te
Largo size arm ature. 160 case.
Sam e length a s short m a g ­
num . unm eltable endbell ... 50/-
C h am p ion 'H o ly S m o k e ’
55 x 28g. w ind, D Z M a gn o ts.
unm eltable o n d b o ll............ 55/-
M u ra Sto ck D
29g. w ind, thick case, b a l­
anced. epoxied. unm eltable
ondb oll ..........................65/-
Lenz Red Ball
Sam e a s S to c k O o n ly slightly
thicker c a so and opposito
rotation ...................... 70/-
M U R A
N E W . G roup 12 motor
M u ra Case, black endbell.
.007 stack 29g w in d 34/-
N E W . G ro u p 20 motor
M u ra Case, black endbell.
007 stack, epoxied balanced
27g. w in d ............ 50/-
Team C u k ra s M o tor
24g. w ind. .030" can. unm eltable
grey endbell and spare
m auve ondboll. (Sa m e o s
M u ra w hite ondboll) ... 75/-
MOTORS FOR M EN'
M U R A
’B ’ Production
The o n ly w ay to g o - low.
042 low profile can. bullot
proof endbell. Stand ard
m o t o r ................................ 100/-
S u p e r ’B ’
Sam e as ’B ’ above but w ith
C u k ra s .007 arm aturo. 23g.,
24g., 25g . 26g. 26/27.
27/27. 27/28. ............ 120/-
C u sto m 'B '
The m o st p ow erful m otor
M U R A have over producod.
H igh temp groen epoxy.
A vailab le. 23g.. 24g.. 25g.,
26g., 27/27, 28/28. 27/28. 135/-
Sbort M a g n u m
H a s all the features of tho
’H ot’ M o to rs oxcopt for tho
length (Idoal for 1/32 a/
w in d e rs). 27g.. 28g., 29g.
W in d s ...................... 100/-
C H A M P IO N
B ig Louie
24 on 25g w ind. Pow erful
D Z M a g n e ts Bullet proof.
O rango, unm eltable endbell 115/-
B ig Louie
26 or 27g. W in d . Pow erful
O Z M a g n o ts O rango u n ­
meltable endbell ............ 95/-
MOTOR KITS
C H A M P IO N
535 M o to r Kit
D Z M a g s 0 1 0 ' S ta c k F/G
Com m . Bullet proof w hite
endbell. Reel of 25g. W ire 60/-
C ozine Kit
A s above but w ith T B D.
black unm eltablo endbell ... 72/6
N o w you’ve read our im pressive stock o f m otors — com e and
see them along with our large sto ck o f other 'g o o d ie s’.
P O S T & P A C K IN G 1 / 6 - o v e r E3 FREE (UK. o n ly ) O v c rso a s 7/6 per p a r c e l-
all sent air mail. Ploaso w rite nam e and a d d re ss clearly.
54 WELL HALL ROAD, ELTHAM, S.E.9
Tel. 01-850 4324
5

Now the brilliant range
of Hi-Speedand
Clubman Special cars
All these cars and a complete price
list of other accessories are at your
normal Airiix stockist.
1/32*4 scale HI SPEEO'
READY TO RACE CARS
Porsche 5192
Vanwall 5103
Maserati 5104
MiatCeeper 5165
lotas Cortina S IM
F err an 2 SO IM S140
Porsche Carrera S 5 U I
Honda S142
Eagle Weslale 5143
Cooper 5150
Ferrari 5151
U r n
SI S3
E Type Jaguar S194
Price 74/1 Id each
Ford Malta S197
BRM
S19S
Ford Sports
Prototype S199
Price 29/ttdeach
1 /32nd scale CAR KITS WITH
SLIM LINE MOTOR
BRM Formula I S001
Aston Martin OBS 8004
Honda 8006
IndtNovi
Ferguson 8009
Ferrari 250 IM 8003
Porsche Carr era 6 8005
Eagle Weslake 8007
Felday Ford S 8008
Price 46/6d each
1/32 scale CAR KITS
WITH 4-W HEEl DRIVE
MercedesBeru 1S4 723 I ladr-Non Ftrgwsea727
Felday Ford 728 I Price S4/2d each
1 /32nd scale RE AOYTO-RACE CARS WITH
BALL RACE MOTORS (REAR WHEEL DRIVE)
8RM Formula 1 730
Aston Martin OBS 732
Honda 734
Felday Ford 736
lodiNo«vFerguson726
Ferrari 2S0LM 731
Porsche Carrera 733
Eagle Wetlake 73S
Price 54 lt d each
1 /2« scala READY-TO-RACE CARS
J Typo Ford 860 I Ferrari 330P 863
Lola T 70 862 Ford Sports G.T. 864
Chaparral 2C 861 I Price 70/6d each
r
AIRFIK?:MRRC < § 5 >
COMPLETE CAR RCAOY TO RACE
6

Model Cars
MOTOR
TUNING B ook 3
• 1 9 6 9 /7 0
Prepared by
Dan Glimne
for Mode! Cars
readers
C o n te n ts
15. Winding
16. Pointers
17. Epoxying
18. Balancing (static)
19. Balancing (dynamic)
20. Endbell
21. Brushes and Springs
22. Assembly
23. Service
Concluding a three part series
8
14
15
17
19
21
22
24
25
Model & Allied Publications Ltd.
13/35 Bridge Street Hemel Hempstead, Herts.
Publishers of
Aeromodeller, Model Boats, Model Cars, Model Engineer, Model
Railway News. Meccano Magazine. Radio Control Models & Electronics,
Scale Models. Plans, Technical Books, etc.
7

R ig h t, w hich arm h a s been
sim u lta n e o u sly w o u n d ! Y es, the
one o n the right. N o te that
o n the oth e r a rm , the tu rn s
o n the last-w ound pole has
flow ed out o n the o thers - not
good f o r the balance and
perform ance.
Y o u ca n learn a lot b y analyzing your blow n arm s. T h is M u ra 007 (far left) w a s
cut off right in the m iddle to check the w ire laying. Note that sp ace h a s not
really been u se d - the w ire h a s not gone o n in neat layers. The a rm ? Shortcircuit
d uring a 24-hour due to in su lation bre akdow n of the Poly-Therm alex.
Centre, the difference betw een a h a n d w ou n d arm (on left) and a m achine-w ound
arm. Note that the h and-w o u n d w ire h a s gone on in a not very neat fashion,
resulting in three b ig h ole s n e ce ssa ry for b a la n c in g it.
15 winding
Learning to wind competitively will take time and lots of practise.
Therefore, I suggest that you get any old armature you can lay your
hands on, buy a couple of miles of cheap winding wire and start
practising until you feel that you have really mastered the art. Experiment
with wires thick and thin, single, double and triple, put on
old Mabuchi coms and try the results. If you blow the arms, so what,
they were not made to be competitive armatures anyway. Just rip
off the old wind and try something else. The practise you get is
invaluable and will not cost you much more than time. Don't try your
hand on a serious tuning job until you can really wind.
The right equipment is important. For the serious tuner, a WINDING
MACHINE is indispensable. Winding can be done easier, faster and
with more precision, which will show up in performance. The wire can
be 'packed' tighter, meaning more turns in less space, which in turn
makes for more power and less unbalance. Many of the winds I have
mentioned are impossible when winding by hand alone. Just try to
cram on 60 of 28 that way! With a machine, however. 75 of 28 can be
done on a 16D-armature.
There are not many makes on the market. Teddington's Mini
Winder is the one we use, with good results, as some of you readers
may have noticed from last year's National Championships here in
Sweden. Price is only 19/11, so buy one for your club today. Other
good ones are LaGanke and Cobra, both American, but I'm not sure
these are manufactured any longer. You might try sending to the
U.S. for these. Price is six bucks.
First a few mods on the Teddington machine: the inside of the
adaptor should be ground out slightly and the adapter epoxied to
one of the halves -see figure.
Now, as for winding, I will reveal a special technique we invented
a long time ago. A s of writing this, we have hitherto kept it silent
and we believe we are the only team - at least hore in Sweden - to
use this.
8

When first embarking
on simul winds, our
Teddington gadget was
modified as shown
here: tape was wrapped
tightly around a
tile . . .
.. . and the file then inserted In
the hole on the machine. A few
pieces of thick copper wire helped
keep the file in place.
Next, transfer som e w ire to two em pty sp o o ls. M u ra 25 copper w ire w a s used
here. The insulatio n m ust be stripped off. U se fine em ery paper for this
If you take a look at a run-of-the-mill armature, you can easily tell
in which order the poles have been wound, since the last one will
have its turns flowing out on the two other poles. Those of you who
read and memorised the chapter on winding theory will at once
realise that this is not so good: the coils will generate unequal fields
and unequal back emf's. meaning parasite currents. The obvious
answer, therefore, is to make the coils equal by winding them at the
same time. Out of this thought, the technique of simultaneous winding
was born. Simultaneous winding will require a lot more work, but
once you have made your first successful armature, admired the
beautiful work and watched its performance, you will never want to
go back to the old pole-at-a-time method again. Of course, the technique
described here is not quite simultaneous winding, but the next
best thing, with a noticeable difference in performance when you
have mastered it.
The first thing is to further modify your Teddington machine. I will
here describe the mods we did for making our first simul-winds. but
you should think out a more elegant solution with time.
Get a long, round file, with a max. o.d. of about 1/4 in., and start
wrapping tape tightly around the middle. See photos. Wrap tape
until the file can barely be inserted in the big hole on the armature
holder. Insert the blank armature and tighten the screw. (We have
re-tapped the hole and changed to a more sturdy screw.)
For the next step, you should have two small, empty spools, the
kind that Mura- and Cobra wire come on. Now, get out your wire,
and on each of these two spools wrap on wire enough for one pole.
Figure 22: M o d ify in g the Teddington w in d in g m achine. Figure 23: T h is arm h a s
been w o u n d w ith the pole-at-a-tim e method: yo u can easily see in w h ich order
the p o les have been w ou n d . Figure 24: W h e n strip p in g insulation off the wire,
rem em ber to keep the 3/32 in. distance . . . for safety reasons.
9

Left to right. W rap the wire end around the shaft and start winding, slowly and
evenly I m ust point out that I never wind with the com on, since this will only
beinthewaywhenweto lay the wire neatly. The first ten turns are com
(wind is 25 of 25). Put the spool pleted on the file and lock with a strong alligator
clip. The arm is turned and the second pole wrapped with ten turns from the
next spool. Put this spool at the other end of the file and lock
About 1.65 to 1.70 inches per winding turn is the figure to calculate
with for an average arm, but if you have got a long or a short stack
armature, this should be considered. When in doubt, though, take a
little extra. That 3d. or so of wire is a cheap insurance against having
to rip it off and starting over again because one of the wire lengths
was too short.
Now, pick one of the spools and start stripping the wire insulation
at the end. This stripping should be done with a piece of fine emery
paper. X-acto or chemical strippers are not recommended, since
knives will easily scrape off too much and chemicals are highly
corrosive and therefore dangerous. With the emery paper, sand off
the insulation all around the wire, but see to it that the border-line
between insulated and stripped wire is a well-defined circle around
the wire.
Place this wire end at one of the poles, with the insulated part
sticking out about 3/32 in. from the pole. See figure. The wire end
is twisted tightly around the shaft. Then start winding, turning the
handle slowly with one hand and letting the wire run out between the
fingers of the other. The first two turns can be wound a shade
loosely, but after that you start pulling hard, and I mean hard. I've had
26-gauge wire snap right-off while winding.
Wind on 10 turns, making sure that the wire comes on tight and
even. A hard pull is essential for this. With these 10 turns on, put the
spool on the file and lock it with an alligator clip. The advantage of
the file here is the rough surface, which will make the clip stay in
position. Note that wire should be tightly stretched. See photosl
Loosen the locking screw and turn the armature so that the next
pole is available for winding. Don't forget to keep the wire on the
first pole tight! It is advisable to be two persons whenever doing this,
so that one person can keep the wires tight while the other handles
the locking screw and changes armature position. Now repeat the
process of insulation stripping and wind until you have your 10 turns
on this pole also. Put this spool at the other end of the file, locking it
as before.
The armature is again turned - tricky business, since the wire on
the poles must be kept tightly stretched - and the third pole started
upon as before. Mind the insulation business and wind on 10 tight
turns.
10

Left to right. Take the third spool and start w inding the third pole. W h en this
pole has its ten turns, turn the armature so that the first pole is again available
and then change the spools on the file. Really, two persons should work with
keeping the wire stretched. Now just continue in this fashion, changing poles and
winding until all the poles have been done. Remember to strip the insulation
off at this end of the wire, too.
Here comes the worst part. Recommended succession: (1) unlock
screw, turn armature, lock screw; (2) Remove the clip and lift off the
spool belonging to the next pole (i.e. here the first wound); (3) Put
on spool from the last (third) pole. Remember, the wires of all poles
must be kept tight, so this is really work for two persons.
Now we are back on the first pole, so wind on another 10 turns,
repeat the exchange process above, wind 10 turns on the next pole,
and so on.
This, then, is the method of near-simultaneous winding. W e do not
always wind on 10 turns at a time; nearing the end we can go
down to 5 or even less turns in order to get a symmetric arm.
This is dependent on wire size and the number of turns used For
example, a 65 of 28 might be wound 10-20-30-40-45-50-55-60-65, a 35
of 26 in 10-20-25-30-35 steps, and a 25 of 25 in 8-15-20-23-25. This
is up to you to decide yourself.
Mind you, I said it was going to be work, and it needs considerable
practise to master. You will curse me loud and long when you first
embark on this venture, but after 20 armatures or so this will be
Now take a careful look at the arm and be honest with yourself: is this wind really well
made or should I do it over? I must take the opportunity of saying that I consider this
wind below my usual standard, due to having to get up every few minutes to take photos,
arrange lights and so on. So had it not been that this was a ‘how-to' job, I would have
done it over if it turned out like this. You should be able to do better. If the wind is
considered O K , put a few turns of tape around it and insert in a vice. Use extra pieces of
thick paper so as not to mar the
shaft. Carefully untwist the wires,
sort out the pairs and check that
insulation stripping is OK. Twist the
wire pairs together - not too tightly,
or a wire might snap off.
11

Left to right. A close-up of what the joints should
look like. Note that only a small amount of solder
is needed, and that this m ust flow out evenly on
wire and com ear. If you are not pleased with your
first attempts, let the com cool off and do it over.
D o not solder all three joints
in a row: the com m ust be
allowed to cool off in between
Then, adjust the com in position, wrap some copper wire around it to act as a
heat sink, and solder. Remember to work quickly, as the extreme temps necessary
for this kind of solder can easily damage the com. However, don't cut time short
and fake the job: of all the solder joints in a race car, these three are probably
the ones subjected to m ost abuse. W hen the joints are O K . lightly brush off the
com with a soft toothbrush.
routine (the winding, not the cursing, I hope). Practice makes perfect.
So just keep on winding the poles as described here. Paper and pen
might be useful so you won't lose track of the turns.
When you have wound the last turn on a pole, the insulation
must be stripped off again. As before, work with fine emery paper
and see to it that the bare copper stops (or starts, depending on
how you see it) those 3/32 in. from the pole. Then just cut off the
wire with a few inches of bare copper sticking out, and twist the
wire end around the shaft. Turn the armature and put on the last
turns on the next pole, then repeat the process above. The third and
last pole is again treated the same way.
Now you should have the armature looking like the photo. Good.
Remove it from the winding machine and put it in a vice like in photo.
Insert pieces of thick paper so that the vice jaws will not mar the
shaft. Then wrap the same tape around the stack and the wire, so
that the latter will stay in place during the next steps.
Untwist the wire ends on the shaft and sort them out, so that they
two and two come out from between the poles. Don't miss here . . .
when you are sure that you have the right wires in the right places,
check that the insulation really is stripped off all round, twist them
together two and two and cut off to about an inch length.
Now put on the commutator and adjust it into position. The twisted
wire ends are bent tightly around the commutator tabs and soldered.
When the solder joints are finished and perfect, snip off the loose wire
ends with a sharp pair of cutting pliers.
NOTE: those solder joints are critical. Use a well cleaned soldering
iron with enough watts and point temperature, heat the com tab and
the wire thoroughly while applying cleaning fluid, preferably of the
non-acid type, and then apply a small amount of the com solder and
make sure it flows out into an even joint. To prevent damaging the
com from heat. I suggest winding it with bare copper wire acting as a
heat sink. See photos.
If you instead wish a cross delta connection, the wires should not
be twisted together but instead crossed in front of the pole and
joined to their respective com tabs. Note risk of short circuiting, so
make sure the wires do not touch. Soldering is as before.
12

The next step is tying the com. Got some strong thread and wrap it around the
com ears in a criss-cro ss fashion as show n here. A little thread around the w ires
behind the com is also useful.
The electrical connections of the armature are now finished, so
theoretically it should be functional. Before we epoxy the armature,
this should also be checked. We can as yet correct a fault by taking
off the wind and do it over, should we have bombed' the job, but
with the epoxy on we will be beyond the point of no return. There are
chemical softeners and strippers for epoxy, but these are dangerous
and highly corrosive. Besides, I consider it a waste of time to try
and save an epoxied arm.
So wrap the armature with one turn of thin, sticky tape, preferably
something like Scotch Strapping tape Put on the washers in each end
and insert the armature in a case with magnets, screw on the endbell
and install brushes and springs.
NOTE: we use an unshimmed Champion 507 case assembly for
this, since it has an air gap big enough to enable running the armature
with tape on. This tape, of course, is a safeguard against the
unepoxied wire coming off. I suggest that you, too, have a 'trial' case
with endbell for this purpose of checking armatures. The endbell can
well be a stock Mabuchi or similar, since the short trial runs will
cause no heat problem. Brush springs, too. can be the standard 'soft'
variety.
Then plug in your controller to the track, hold the endbell wire on
the lane braid and give the controller a few light squeezes.
WARNING: do not fall for the temptation of giving it a punch or
two' and see that revs are good. As long as the epoxy is not in place,
the arm will all too easily blow, tape or not. Just give it light bursts
of current, 15-20 times, to see that the arm will start easily and from
any position.
If the wind was not OK, face it like a man and start the job over
again. If the arm seems to work good, we can proceed to epoxying.
NOTE: if you are just practising your winding hand, do not bother
about epoxying. Instead, wrap the stack with an extra turn of tape
and give it those full 12 volts to see if you succeeded When the arm
blows, just rip off the old wire and start on another wind.
★ ★ ★ ★
13

16 pointers
Stripping: making a good job here is important. If any spot of insulation
still remains on the wire, it can foul the whole com solder joint.
Also, I suggest stripping even wires with 'solderable' insulation for a
less messy job.
Packing: the tighter you can pack the wire, the less weight and space
that will be required, and the more performance added. A trick is
using a popsicle or ice cream stick (of wood), suitably shaped, for
packing the wire. Usually the wire is packed after each layer is
finished, but if you can arrange it, have a friend turn the handle on the
winding machine while you 'steer' the wire with one hand and pack
it in with the other. Caution: do not use pieces of hard plastic or
metal for this packing, since this will inevitably scar the insulation
Soft wood is best.
Wire: if you for some reason rip off the old wire and start on a new
wind, you must also use new wire. Winding while pulling hard will
really strain the insulation, so it might break and short circuit the arm
if you try using it again. Don't try to pinch your pennies here, wire
is only used once.
Sorting: Sometimes (clumsy winding, natch) sorting out and pairing
the right wires can be a nuisance. The trick here is tying one knot on
every wire end extending from one of the hollows between the
poles, two knots on all wire ends from the next hollow, and three
on the wires belonging to the third. Then, when sorting out the wires,
just take all those with one knot and twist together, then take these
with two knots and do the same, and so on. The knots, of course,
should be tied far enough out on the wire as not to interfere with the
com solder joints.
Left to right: W hen double winding, w ind with both w ires (or all three in a triple)
at the same time Be careful when packing the wire, so that wire insulation is
not scarred. Star winding. The three 'lo o se ' ends of wire are twisted together . . .
and then soldered and cut short. This is just a 'demonstration w ind', so no great
care has been taken in w inding the arm evenly.
1 4

W ith the arm h o t, hold it in pliers and ap ply the epoxy all around - rem em ber
n o w , sm all am o u n ts are needed. D o N O T cover the sold er joints w ith epoxy, but
give tying thread a light im pregnation. C h eck com p osition! Before epoxyin g the
arm , both epoxy and arm m u st be thoroughly heated. T h is can be a c co m p lish e d
as show n, by h avin g the arm stand upright in a hole and the epoxy nearby. The
arm m u st be turned around often, to heat evenly. D o not heat the epoxy for too
long: it m u st still flow evenly w hen applied. The finished job. Rem em ber to keep
heating the arm, s o that the epoxy w ill flow in and im pregnate the wire.
U nepoxied tu rn s of w ire 'd o w n in sid e ' can shift and u p s et the balance.
Double winds: These should be wound with the two wires simultaneously,
even though it will be more work. Layering’ the wind
(winding one coil at a time) should be avoided, for the reasons given
earlier. Keeping track of two wires instead of one will require practise,
not to mention triple winds. I strongly advise using the knot trick
here, as sorting out 12 wire ends on the double wind (and 18 on a
triple!) will easily make your blood pressure rise.
Star winds: Wind and curse as usual, but now the finishing ends of
the wire should not be drawn up to the com but instead be twisted
together and cut off at the other end of the stack. See photo! This
"pigtail" (the twisted wires) should be soldered, cut off to the
shortest possible length and tucked in. The disadvantage of the star
wind is that the armature will obviously be out of balance due to the
pig-tail and therefore require that bigger holes be bored to compensate
for this. However, we are projecting starting with the pig-tail,
wound symmetrically around the shaft close to the stack and epoxied,
and then proceed to wind as usual. At the com end the usual solder
work is done, with the difference that now only one wire end will be
connected to each com tab (for a single star wind). Commutator
advancing is the same as for delta connected winds.
★ ★ ★ ★
17 epoxying
The armature must always be epoxied, to prevent the wire flying
off at high R P M ’s. In addition to this epoxying, we also tie the com
wires as an extra safeguard. Use a thin line or wire for this, nonmetallic
of course. Personally, I use thin stretchable nylon wire,
the kind that can usually be purchased in a haberdashery shop.
Common sewing thread will work fine, too. Just wind it on crisscross
between the com tabs as the photo shows.
For epoxying the armature, I do not recommend Araldite, though
this statement will probably get me a few enemies. Araldite, if subjected
to very high temperatures, will crack and break the wire. We
have had this happen on several armatures. Instead, I recommend
15

Mini-Wheels' epoxy, which will stay together during racing - at least
we have never had this epoxy crack in our tests. (In a 24-hour, for
example, we ran an arm that was epoxied half with Araldite and
half with Mini-Wheels. The Araldite cracked.) If you cannot find this
epoxy in Britain. I suggest sending for it from some American mailorder
firm.
The Mini-Wheels stuff is a 24-hour epoxy, but by heating we can
make it both cure quicker and flow out more evenly. Therefore, place
a small amount of mixed-out epoxy and your armature in close vicinity
to your hot solder iron. Use a piece of wood - not balsa - with a
shallow 5/64 in. hole in it to have the arm stand upright. Heat for
15 minutes or so, especially the arm should be thoroughly hot. Then
grab the armature shaft in a pair of no-knurl pliers and apply a thin
coat of epoxy with the help of a match or a toothpick. No great slabs
are needed, just a thin coat that will flow out and impregnate the
wire. Smear a little on the com tying thread, just enough to cover it.
but leave the solder joints free!
Too much epoxy is dangerous, it will act as a dead weight and a
heat trap, with consequent less performance and more heat. I assure
you that very small amounts are needed - see photos.
I am no fan of put-it-in-the-oven school, instead I recommend that
you place the armature near your hot solder iron where you can
easily keep a check on it all the time. The hot epoxy must not flow
out on the shaft or into the com segment slots. However, if you only
have put on that small amount of epoxy, it will usually stay in place
while curing. But check often, and turn the armature upside down
every two minutes or so for the first half hour. Then you can shut off
the solder iron and let it cool slowly while keeping the arm nearby.
Changes in temperature should be performed slowly - the trick of
directly taking the arm from oven to refrigerator can cause dangerous
temp stresses on epoxy and insulation
Now the epoxy should be rather stiff, so put the arm away and let
it cure the rest overnight. Of course, should the need arise (like
working all night trying to meet the sign-up deadline at 8.30 a.m.).
you can always keep on heating the arm with the iron. I have once
prepared, wound and balanced an arm in 5 1/2hours, but I would rather
not do it again, even though I managed to win that race.
NOTE: do not forget to check that the com sits in the position you
want. Finally, getting the epoxy to cure and then discovering that the
com is all wrong, as I have seen happen, is not very funny ... for
yourself.
it it it it
16

Ways of balancing. The worst method is this one
(top), from a Champ 507. with long slashes
ground in the pole surface. The Dyna method,
filing up notches (next down). The best method
of removing weight, drilling holes in the pole
surface (bottom). The arm here turned out
fairly well balanced after winding, so only two
small holes were needed
Now for balancing, with the method that at least 99% of the readers m ust be
familiar with - the Razor Blade Method. Check that edges of blades really are
parallel. Heating the lead epoxy on the arm. Shift between placing the arm with
the lead epoxy top and bottom, so that it will not flow out too much.
18 balancing (static)
Now the armature is wound and epoxied. but we are not out of
the woods yet: it has to be balanced first.
Why balance? Well, when doing the armature, we have usually not
quite managed to get the wire and the epoxy on evenly, with the result
that the armature will be heavier on one side. Only once in my
nine years as a racer have I seen an arm that turned out perfectly
balanced (static), but unfortunately, it was not mine. Anyway, you
can see that happens very seldom, so chances are your armature will
need a little work.
If we put our unbalanced arm in a motor and have it run. centrifugal
forces will try to force the heavy side away from the shaft,
causing vibrations, friction and heat. Friction and heat have already
been discussed in general and it should be obvious that these are bad
for performance, but let us consider vibrations. Vibrations - any
vibrations - in a car are detrimental, since they will spread everywhere
in the frame. And you can easily imagine what kind of roadholding
you will have with the rear axle trying to jump up and
down . . .
(You should watch worn gears, bent axles and out-of-round
wheels, too, since these can cause serious vibrations. Ideally, gears
and wheels should also be balanced for maximum performance.)
So it is clear that the armature should be balanced, and the obvious
way is to either remove weight from the heavy side or add weight to
the light side.
For static balancing (we will discuss dynamic in a moment), the
tried and true method is to place the armature on a pair of razor
blades stuck into a piece of balsa. Blade edges must be parallel and
horizontal. When the arm is placed on the blades, it will turn until it
17

ests with its heavy side down. Note, however, that a nick on the
edges or wear damage on the shaft can also cause the arm to stop in
certain positions and fool you. To avoid this, try the armature several
times in different positions in different places on the blades. If the
same pole (mark them A, B and C for easy identification) always
'hangs down', your arm is obviously out of balance.
NOTE: an even better method, especially with small amounts of
unbalance, is to lean the wood piece with the razor blades slightly
and have the armature roll down them slowly. If the arm rolls with
the same speed, the static balance is OK. But if it rolls in a 'calypso
rhythm', work is needed. Let us start with method A , removing
weight from the heavy side.
There are different ways of doing this, as the photos will show.
The old Champion balancing, grinding off big slices, is the worst. It
will short circuit many plates and make for higher core losses due to
eddy currents, as explained earlier.
The Dyna method of filing notches will short circuit less plates, but
still leave a rather long scar in the pole face.
The best way of removing weight is by drilling holes, since the
least pole area will be disturbed. All motors of quality (Champion has
switched to this method on its new series) have this kind of
balancing.
However, drilling holes in the hard pole surface without slipping
accidentally into the wires is not easy. Experience speaks. Therefore.
I recommend the beginner to use the notching method instead, by all
means use holes.
Having determined which of the poles is the heaviest, the armature
is clamped in a vice with this pole up. Use inserted pieces of thick
paper or similar, so that the arm will not be marred by the jaws or
the vice. Now grab a thin round file and start working away, holding
it as in the photo (less risk of driving the file into the wires). Please
note that the notch must not necessarily start on the middle of the
pole face (cross-wise), but rather on the exact part of the pole that
is pointing down.
NOTE: always, however, file on the middle of the pole face, lengthwise,
or you might risk further damaging the dynamic unbalance.
Should the notch threaten to grow too big, it will be better to make
two smaller notches beside each other. But don't forget to check the
balance often, so you won't remove too much!
If you use holes, these should be about .05 to .10 in. in diameter
This will depend on the amount of unbalance. If the hole is somewhat
to the side of the pole, don't drill it too deep or you might cut a few
wires.
If you consider it for a second, employing method B and adding
weight to the light side is really much smarter. Notching or drilling in
the poles means less magnetic mass, and though the armature will
run faster when balanced, we have actually lowered torque. Method
B means more (dead) mass, but provided the unbalance, and thus
the mass needed is not too great, we have made an overall gain by
retaining torque.
The method has its limitations; it cannot be used on 'fullhouse'
winds, as there must be space for the weight we are going to add.
Otherwise the method is a simple one.
For best results, we should start while epoxying the armature.
Mix up some epoxy, same as the one used on the armature, and put
it beside the solder iron for quick curing. Then get out some lead
sheet and start filing on it, until you have a nice collection of lead
18

Below. If using brass plate
thicker than .015 inches, a
notch will usually have to be
cut so that the brush holder
will not be seated too high.
At left. Bend clip to fit
and solder it in position.
It must be soldered both
to brush holder and plate
for maximum heat conduction.
The brush holder m ust be filed down in bottom and then soldered exactly in
position. Use square tubing for a jig. Note that this step really is important, or
timing can be seriously out of whack. Lastly, solder the post protector in p o sition.
You can easily w hip up your ow n from brass or steel tube. For bullet-proofing,
the endbell m ust bo modded: the ring around the bearing (thin arrow) must
be removed for bullet-proofing the bearing, and the ridges that originally held the
brush holder (thick arrow) m ust also be removed. U se sharp X-acto knife and
flat file.
dust, which is added to the newly-mixed epoxy and thoroughly
diluted. Use plenty of lead dust; the epoxy should be thick with it.
In the meantime, the epoxy on the armature has started to stiffen, so
now we hastily get out the razor blades and check unbalance. This
time, however, we add our lead epoxy to the area between the poles
that is up' when the arm has come to rest.
NOTE: this balancing method will take a few hours, since the added
weighted epoxy will flow out and continually change the balance
For best results, the lead epoxy should always have cured enough so
that it will barely flow out on the epoxied wires. Patience!
NOTE: the reason for starting to balance like this while the armature
epoxy is still wet, is to ensure that the lead epoxy really will
stay in place. In all fairness. I must point out that there have been a
few cases when the lead epoxy came off at high R P M 's, but these
have been cases when the balancing epoxy was added long after the
armature epoxy had dried.
NOTE: very seldom, actually, will the unbalance be so neat that
only one pole has to be notched or lead epoxy applied in one spot.
Usually, two poles will have to be notched or epoxy applied in two
spots, and then also usually in unequal amounts. Care!
NOTE: of course, you can combine the methods. This is up to you,
though.
★ ★ ★ ★
19 balancing (dynamic)
As yet, we have discussed static balance - the armature is in
balance while resting on the razor blades or in the motor. If we run
it, though, we will in all probability still experience vibrations from
dynamic unbalance.
19

I mentioned that after winding and epoxying, the poles are not
equally heavy. Static balancing, as discussed in the preceding chapter,
will correct this. What it will not correct, however, is the weight
distribution of the poles. One pole might be heavier on the com side,
another towards the opposite side. Obviously, we again have some
kind of unbalance, and this is called dynamic unbalance. Everything
is OK as long as the arm is motionless, but when it starts to turn, it
will try to whirl, as the term is. The whirling will again cause vibrations
and friction with subsequent slowing down and heating up.
NOTE: total unbalance can be seen as the sum of two unbalances,
static and dynamic. We can remove the static unbalance, but this
still leaves the dynamic kind.
As for ourselves, we cannot do anything about this with our
primitive equipment. To detect and correct dynamic unbalance, it
takes an experienced operator and a machine worth hundreds or
thousands of pounds. Luckily, there are a few balancing firms that
will do the job for us - against payment, of course.
The nearest firm for British readers would be Model Racing Car
Centre at 390 Brockley Road. London, S E 4. Their price for a balancing
job (using holes) is 10s.
Across the Atlantic, we have the famous Thorp of Pomona, who
does all the balancing for the U S. pro teams. The address is John
Thorp, 143 West Commercial, Pomona. California 91766. They charge
you $2.50 but will make an absolute perfect job and in addition true
up the com for you.
If you decide to send your armatures for dynamic balancing, don't
forget to include a cheque or money order for the correct amount plus
postage back to you, and your name and address. Make sure your
armatures are carefully packed up, so that they will survive the trip
without damage.
NOTE: dynamic balancing is, of course, superior to static, so I
strongly recommend it for your racing arms. A good knowledge of
static balancing is always an asset, though, if you are faced with
the problem of quickly fixing an armature overnight.
A few last words on balance, before we leave the subject. A
balanced arm might become unbalanced with time, because of centrifugal
forces, thermal expansion or shocks - like from hitting the floor.
Therefore, it might be necessary to rebalance the armature when it
starts losing its zing. And if your armature is dynamically balanced,
solder your pinion, don't hammer it on!
4r * ★ *
20

20 endbell
And now we have reached the third and last main unit in the
motor, the endbell.
A good endbell must meet three requirements: it must provide a
stiff bearing area for the armature, it must not break down from heat,
and it must provide a good current conduction. I may be fastidious
when it comes to this, but my choice is either a white Mura or a
Champion endbell. The grey Mura is good and will stand up to most
E C.R A. racing, but for the fast commercial crowd, the white version
will give added security.
The heat is the worst problem in motor building today, as any
24-hour racer will testify. (Lars has still got scars from our last
enduro.) The usual breakdown of an unprepared endbell will be that
the material melts so that the brush holder and the spring will sink
down forever in the plastic. To avoid this, bullet proofing' was
invented by soldering the brush holders to a metal plate, and a few
other refinements. This has the advantage of distributing the heat over
a greater area for quicker heat dissipation
All endbells should be bullet proofed for maximum security. If
you're the lazy type, you can buy ready-made parts from Mini-Wheels
or Champion. However, knocking up your own bullet plates is not
difficult.
Get brass sheet of a suitable thickness, anything between .015 and
.040 in. are used. Cut out two plates that will fit exactly on the
endbell and drill holes for the spring post and the screw. See photos.
If you are using brass thicker than .015, you must also file a notch
across the plates, or the brushes will ride too high.
Next step is to file down the brush holders as per figure. Then
comes the tough part, soldering this modified brush holder to the
plate in exactly the right position. This will need patience and many
resolderings, in all likelihood. The brush holder must be exactly
centred, or you will have difficulty controlling the timing, as I pointed
out earlier. Also make sure that the brush holder will be close to the
com, for maximum brush stability. About .012 in. between the com
and the brush holder is the ideal.
The next step is the clip, which must fit tight against plate and
brush holder. If necessary, reshape to fit, then solder it in place. The
clip should be soldered to both the plate and the brush holder.
Lastly, solder the post protector over the hole for the spring post,
and clean up the job.
NOTE: use high-temp solder for the bullet plates. The endbell
assembly can actually get so hot that common solder will melt.
The endbell must be modified to accept these plates. Get an X-acto
knife for cutting down the edges around the brush holder, and afterwards
file the area flat.
21

Figure 25: M o d d in g the b ru sh holder. File
d o w n (sh a d e d area) until only 1/64 in.
rem ains below bru sh hole.
Check that the brush will easily slide through the brush holder,
otherwise deburr the edges with a square file. With the complete
bullet plates on, check for alignment by sticking in a piece of 3/32 in
square tubing through the whole assembly.
Variations on a theme: if you wish, skip filing down the brush holder
and instead cut a slot in the plate so that the unmodified brush
holder can protrude down into the Vee. Solder as before.
To have even more efficient heat dissipation, your bullet proofing
plates can be done 'elephant ear' size, sticking out a good bit from
the endbell. This is dependent on how much space you have in the
chassis. It won't look pretty, but it's efficient.
A rather primitive form we invented about a year before 'real'
bullet proofing became the vogue, was to solder a piece of braid to
clip and brush holder. This piece is allowed to stick out a good bit
and will dissipate heat surprisingly efficiently.
Concerning the bearing, use either a Mura or a Champion bearing,
according to the endbell make. A Mabuchi bearing will quickly develop
an oval hole, so I cannot recommend it.
Bullet proofing the bearing is frequently done. Either remove the
outside edges around the bearing hole screw on the plate and apply a
few quick dabs of solder, or reverse the bearing and solder it to the
plate from the outside. See photos. As with the case bearing, polishing
the inner surface to a high gloss is advisable. Bullet proofing the
bearing is usually only done on can drive' motors.
★ ★ ★ ★
21 brushes & springs
With that, we have completed the requirements for the first two
items, bearing and heat proofing. Remains securing the current
conduction.
On a stock endbell. the current will go via the spring and via
contact between brush and brush holder. The latter is rather erratic
when the brush is vibrating during running, and the increased current
through the spring will heat it up and make it lose pressure.
What to use here is shunted brushes, meaning that the current will
go directly from lead wire joint via the shunt to the brush. Shunted
22

Bulletproofing, elephant ear size. These are made from silver-painted plastic, just to show
you how it can look. Just about any shape is acceptable, as long as It won’t short-circuit via
the chassis. Holes (should be many and small) are drilled for lightness and quicker cooling
The first bullet proofings simply consisted of soldering a piece of braid to the clip and brush
holder. Even today this trick could be used to further increase heat dissipation on a
bulleted endbell.
brushes can be bought ready-made, both Champion and Titan are
good ones. Using these, just tuck in the shunt ‘tail' and solder.
Otherwise, shunting your own brushes is easily done. Got some
flexible lead wire and strip off the plastic sleeve insulation. Insert the
brush and jam the shunt wire between brush and spring. See photo.
Then just solder the other end of the shunt wire directly to the lead
wire clip. Simple, wasn't it?
NOTE: try sanding the brush slightly where the shunt wire will lie
against it. Careful . . . that carbon is brittle.
NOTE, lately, using double shunt wires to each brush is becoming
popular. Another trick is to insulate the spring with a piece of plastic
sleeve on it (not the brush end of the spring).
NOTE: unless your black Mura case will turn pink from this, I can
recommend good ol' Mabuchi brushes. Correctly shunted, they are
superb. Pay attention to the springs, and make sure you use strong
ones. Champion's are my favourites. If you are looking for really
strong springs, I can recommend those from Model Racing Car
Centre. Warning, though, as they will eat the brushes in a very short
time.
As for springs, shape them like in figure 26 and make sure they
have an arc of at least 120 degrees
NOTE: springs and brushes should be changed between every
race, to keep performance up. Some people will even change springs
A very good job can be done with square tube for brush holder and home-made clip.
Champion's bullet plates are instead given a Vee to fit an unmodded brush holder. Unfortunately,
these will only fit Champion's own endbells as standard. With a little modding of,
say, a Mura endbell, though, they can be used. The usual way of bulleting a bearing.
Bearing it knocked out, turned around and soldered in the plate. This will allow the
bearing to run cooler
- high temps can cause
a ’break-down' of oil
or grease. Don’t forget
to polish the inside
surface.
23

The other end of the shunt wire soldered either on top of the dip or around the pickup
wire tab. By all means, do make a better solder joint than the one here. Remember to use
a long enough piece of shunt wire, so that it will not stretch when the brush is wearing
short. The other method of bulleting the bearing. The plastic ring is cut away, as in photo
and the bearing soldered in the plate. Only a few quick spots of solder are necessary
Shunting the brush: the shunt wire is jammed between the brush slot and the spring . , .
between practice and race, but this is up to you. If you are going to
put away the car for a few days. I advise you to unhook the springs
★ ★ ★ ★
22 assembly
At long last, we are now ready to assemble the motor. Check
everything for absolute cleanliness, no metal dust on the magnets,
nothing in the com slots, etc. Take the armature and put on the
washers - don't forget the fibre washer on the com side - and care ­
fully put the arm in the case. Check that there is a slight clearance
between armature and magnets. Then put on the endbell and screw
it on tight. Spin the armature a couple of times to check that nothing
is binding. Now install brushes, shunts and springs.
Solder the lead wires on each side and connect the motor to a
power source. Have it spin a 'fast idle' (R P M about 15,000). Run the
motor like this for about 20 seconds and then put a drop of oil in
each bearing. Increase revs slightly and run the motor like this for
1-minute periods. Total running-in time is usually about 15 minutes.
WARNING: do not let the motor run free at anywhere near max
R P M 's. since burrs at the com segment edges can easily crack the
brushes.
24
Figure 26: The s p r in g s should
be b ent a s show n. B y the
w ay, m ake sure that the
s p rin g w ill never stick in
the slo t o n the b ru sh holder,
a s th is w ill le sse n b ru sh
p ressure and th u s perform ­
ance. The s p rin g end m ust
m ove freely here.

A trick from U S . racer Dave Grant: polish the com with a hard eraser, for seating
and a better surface. Note how shiny the com turned out. This w orks wonders
for the brush track. For cleaning com slots, use a piece of filed-to-shape ice
lolly or ice cream stick - never metal.
Putting on the pinion: sand the shaft end lightly and cut up a few
small notches in it. If you have a drill blank, this can only be done
with a motorised tool and a carbide disc. Heat the shaft with the
solder iron and apply a thin coat of solder at the shaft end. Then
give the pinion hole a few quick takes with a round file and put it
on the shaft end. Now apply the cleaned end of the iron against the
pinion and start pushing. After a few seconds, the solder will melt
and the pinion slide into position. Heat for a few more seconds and
then let it cool, and you have your pinion soldered on.
At a recent race, I saw another method: put Araldite inside the
pinion and slide it on to the shaft, then heat with a match and you are
ready to race. When you want to remove the pinion, heat with another
match while using a pinion puller. However, I am not sure that
I would use this method myself.
* ★ * *
23 service
Your motor will need constant care, supervision and service for
maintaining top performance. Brushes and springs must be changed
between every race, also springs between practice and race for max
power. Never use excess o il! This is a common fault, but excess oil
will just dirty up the case and the com with subsequent slowing
down.
Every now and then, you will have to disassemble the motor and
clean it. Use liberal amounts of kerosene, pipecleancrs and rags on
the case and endbell. wipe carefully afterwards and make sure no fluff
from the pipecleaners is left. Check com solder joints and resolder
25

these if necessary. If you have access to a low-R P M . power drill,
insert the arm with the com end in the chuck and true the com
with a pencil eraser. Clean with a fine cloth and make sure the com
slots are free from dirt by running a toothpick along them.
Every time you disassemble the motor, the shaft must be carefully
sanded so that no solder will remain and mar the bearing. The endbell
bearing must be changed every 3 or 4 races (sprints), since it will
wear out quickly. Never remove the magnets unless absolutely necessary.
If possible, try to remagnetise before every race, for maximum
zap in your motor.
And with that, my article on motor tuning draws to a close. (At last,
you must be saying.) Give your motor lots of maintenance and
tender, loving care, and it will be faithful to you and win many races.
If anyone has any problems or simply wants to know more, just
send a letter to Model Cars. I will try to answer those questions of
most general interest in the magazine.
Good luck !
* * ★ A
26

Now you have all three b o o kle ts in
the ‘M otor T u n in g’ Series, d o n ’t
forget author Dan G lim n e ’s offer to
help with m ore inform ation or a s s is t
with problem s a s you go on to hot
up your own power units.
A d d r e s s any co rresp ondence to
Dan, care of ‘M odel C a r s ’ o ffice s at
13-35 B R ID G E S T R E E T
H E M E L H E M P S T E A D
H E R T F O R D S H IR E
W e’ll be only too pleased to p a s s
them on.
27

Tell your friends about
Model
Cars
... the hobby and our magazine.
The hobby because it embraces such a wide range
of miniature car topics from fast, slick slot racing
through die cast collecting and radio control racing to
plastic kits and breathtaking display models. Whatever
your vehicle interest, you'll find enthusiasts with
similar ideas.
The magazine because Model Cars caters in depth
for all types of car modellers and publishes a host of
exciting features every month. That's what we do
for you. All we ask you to do is
TELL YOUR FRIENDS ABOUT MODEL CARS
28

inc. post & packing
A s you collect this series of Motor Tuning
books. Model Cars can offer this attractive
green binder with 'Motor Tuning' in gold block
titling on the cover, in which to keep your
books safe and sound for bookshelf or workshop.
There are, unfortunately, a limited number
available so you should order early.
Cheques or Postal Orders to:
MODEL CARS M AGAZINE
13-35 BRID G E STREET
HEM EL H EM PST EA D , HERTS.
29

ai
WANT:
| slot car 'bits'.
fast mail order (free
| service) racing, (we
believe the best in the
5 country) and 'statics'
or home raceway sets
YOUNEED
1
c
2
00
30
O
>
V)
o >
H
m
O
I 367-9 HIGH ROAD, TOTTENHAM , LONDON, N.17
Telephone 01-808 5668
§ for details see our latest ad.
5 in Model Cars
>
c H
o
§ o00
30

E
IT's
W ITH A
MINI-WINDER
u
i
c
K
E
R
THE MINIATURE ARMATURE WINDING TOOL
Basic Mini-Winder for -J" dia. armatures.......... 17/6
De-Luxe Mini-Winder
for |", i", 9/16" & t" armatures.................. 22/6
24 AW G
29 AWG
28 SW G
33 SW G
SELF-FLUXING REWINDING WIRE
B. & S. American Gauges. 2/6 per reel
25 AW G 25 A W 6 27 AW G 28 AW G
30 AW G 31 AW G 32 AW G 33 AWG
Standard W ire Gauges. 2/6 per reel
29 SW G 30 SW G 31 SW G 32 SW G
34 SW G 35 SW G 38 SW G 37 SWG
P IM M not*: Each raal contain* 4 oz. of wira
wound on plastic spools of a siza to avoid kinking.
PO STAG E and PA C K IN G
Up to 10/-. 1/-; £1, 2/-; £2. 3/-; £3. 4/-;
£4, 6/-; £5. 6/-; over £6. post free.
Teddington Model Supplies
LIMITED
84-86 Broad S treet Teddington, Middlesex
Tel. 01-977 4349

Prlmod by Graphic Art Services (Brighton) Ltd.. Burgas* Hill, Sussex