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Want a tiny, HIGH POW
Start with an old CD/
Did you know that you can convert the flea-power motors from old
CD or DVD-ROM drives to high-power operation – eg, for model
aircraft or other demanding uses? While it may seem improbable it is
relatively easy to do, the main change being to fit Neodymium ‘Rare
Earth’ magnets. Oh, you also need to find some suitable motors.
I
’ve been interested in aeromodelling for many years. When
I heard whispers a while ago that I
could make my own high-performance
brushless model aircraft motors using
parts salvaged from an old floppy disk
or CD-ROM/DVD drive, at first I was
sceptical.
But after doing a little research, I
found that it was indeed possible.
It seemed that all that was basically
required was to place some so-called
“super magnets” inside the motor
and to replace the windings to enable
higher current flow.
However, as with many projects,
when I looked further into it I discovered it wasn’t going to be as straightforward as I’d imagined.
I would need to find a good source
of old drives, locate the required type
of neodymium ‘rare earth’ magnets,
suitable ball-bearings and would need
access to a lathe.
The lathe wouldn’t be a problem
because my dad recently gave me his
old Emco on permanent loan. Finding
the right bearings also wasn’t much of
an issue; the types required are used
extensively in the likes of model helicopters and cars and are sold in most
model shops (and are also widely
available online).
The magnet hurdle also proved easy
enough to overcome since I soon found
a source on the web prepared to ship
as many as I wanted and so I promptly
sent away for a couple of sets. The
next big problem was impatience; the
magnets would take a couple of weeks
and I wanted be up and running today!
Sourcing parts
Since I own a computer repair company, finding old drives is not a problem; most workshops like ours have
a healthy stack of them until periodic
clean-outs mean we get to start on a
new stack. It is worth ringing around
to see what repair shops have available – and avoid those who’ll want
to charge you for taking away what is
essentially rubbish.
One of the bigger problems you’ll
face is that many optical drives don’t
use what has become the standardsized motor; a roughly 25-27mm diameter can/bell with an overall thickness
or bell depth of around 6mm. While
you can theoretically make your brushless motor from any old drive motor
you salvage, many are not particularly
suitable for the job, nor are they physically compatible with the standard
sizes of available magnets, the majority of which have been designed to fit
the 25-27mm motor mentioned above.
I stripped half a dozen old drives
to get a couple of decent bells. So get
Here’s a typical (if a little ancient these days!) CD-ROM drive, shown in its
“as-removed-from-old-PC” state at left. The centre photo shows the controller
board removed, revealing the motor in the centre (circled). Finally, the photo at
right shows what we are after: the motor removed from the CD-ROM drive (via
those three Phillips screws on the bracket in the centre photo) and held in the
hand to show just how small the motor actually is. Despite its tiny size, it’s quite
a powerful little beast and, just as importantly, is very reliable (when CD-ROM
drives fail, it’s very seldom the motor that has given up the ghost). But even
more importantly, this motor can be modified to give significantly more power
output – enough, in fact, to power an electric model aircraft. And that’s what we
are doing in this feature.
76 Silicon Chip
siliconchip.com.au
WER brushless motor?
/DVD-ROM drive!
By
Dave Thompson
At right: an assortment of motors
pulled from various surplus drives.
Note the variety of styles and sizes;
while you can fashion your motor
using any sized ‘donor’ motor,
most builders use the 26mm model
because the majority of available jigs
and magnets are designed for this
‘standard-sized’ body.
as many old drives as you can while
you’re on the scrounge.
If you’re wondering why I didn’t
simply work out which make and
models of drive contain the right motors and look for them, rather than
go through all this rigmarole, it isn’t
that simple.
You can take two outwardly-indistinguishable models and find they
have significantly different mechanisms. The chipset and firmware might
be the same but the cradle, motor and
laser assemblies vary greatly from
drive to drive, even within supposedly
“identical” models.
Useful bits and pieces
Regarding other parts in your optical
drive, there are several parts which
could come in useful.
Retain the chromed shafts the laser
assembly runs on, as you can use these
for prop shafts. They are usually highquality chromed steel and well worth
saving, though as they are often coated
with grease, you’ll probably have to
clean them before use.
Also take care with the laser. If your
donor unit is an 8X or faster DVD
drive, the laser diode is a sought-after
component for optics experimenters
who want them for match-lighting
and balloon-popping laser projects so
careful extraction is well worth-while.
I suppose you could even sell the
laser for a few dollars to cover any
costs you may have incurred obtaining the drive, or save it for your own
evil-genius laser projects.
Then again, anyone who wants one
of these has probably scrounged it
themselves (and possibly discarded
the motor!).
If you do decide to salvage it, take
great care as I’ve discovered these laser
diodes to be extremely static-sensitive
and physically easy to damage and
they are usually solidly fastened to
the head assembly.
While you are breaking the drive
down, there may also be many little
gears, switches, bearings, belts and
other bits and pieces that always come
in handy so get as much as you can
from each drive.
Even if the motor is not a suitable
donor there are plenty of other goodies worth salvaging or passing on to
someone who will use them.
Which motor type?
There are two basic configurations:
in-runners and out-runners. An example of an in-runner motor is your
typical DC brushed unit, in which the
A small selection of the thousands of commercial brushless motors available. They’re easily distinguishable from
standard (ie brushed) motors because invariaby they will have three wires – brushed motors have just two.
siliconchip.com.au
July 2012 77
Standard sized
bells ready for
modification. Note
the difference in
heights. As long as
you have enough
material to safely
glue the magnets to,
any sized bell can be
used. Also note the
lip on the inside of
the centre hole – this
must be removed as
described in the text.
body of the motor remains static and
the armature or rotor spins – your car’s
starter motor is a classic in-runner
type. An out-runner motor on the
other hand has a fixed stator and the
outside or motor body rotates instead,
typically with a drive shaft connected
to the rotating body to which gears or
in our case, propellers are connected.
Out-runners are very efficient,
which is why motors like these can
deliver a surprising amount of power
for their diminutive physical size. Our
motor will therefore be an out-runner.
The first thing to do is break down
your acquired motor. Sometimes the
two halves are only held together by
the existing magnet’s magnetic field
so pulling this type apart is very easy.
Some will have an ‘R’ clip, circlip or
similar device holding things together.
If you strike a clip version, easing the
clip free will allow the two motor
halves to be parted (if you get the clip
off in one piece, save it for optional
use later).
If in doubt, a good pull should separate the motor without breaking anything. If you find yourself reaching for
a screwdriver in order to lever things
apart, be very careful as it doesn’t take
much to ruin either component and
we need both bits completely intact.
Once the outer bell is removed,
you’ll see it contains a ceramic magnetic ring. Also note the exposed stator remaining attached to or pressed
onto the motor’s circuit board (unless
you’ve already stripped that part
away).
Put the stator part to one side for the
moment and let’s look at the bell. Your
bell may already have a shaft fixed
in place, running down the centre
through the stator. If so, count yourself
lucky because very few do these days,
however, this pretty much shoehorns
you in to what style of motor you will
78 Silicon Chip
be building; more on that later.
When the plastic disc holder, which
is typically mounted to the ‘top’ of the
bell assembly is removed (it should pry
or break away reasonably easily), you
should see a small-lipped hole in the
centre. This will later be utilised to
house our prop-shaft. Take the bell and
using a small jeweller’s screwdriver or
similar tool carefully pry the magnetic
ring out.
Take care not to distort the bell doing
this; they are reasonably strong but can
be easily bent out-of-round if you are
too vigorous. It doesn’t help that the
ring usually doesn’t come out easily;
though it may seem like it, most are not
actually glued in place, relying instead
on a very tight interference fit and they
sometimes take some removing.
The material the magnetic band is
made of is similar in consistency to
a ferrite rod, meaning they are very
strong but quite brittle.
I usually just break the ring in order
to remove it by using an automatic
centre-punch; the type you set by
turning the end to adjust the spring
tension/impact energy and then push
down on until it ‘hammers’.
Start with a lower tension setting
before cranking things up to 11 as
this method seems to shatter the ring
easily and a higher setting may end up
ruining the bell.
Unless you really want to retain the
ring for other experiments, I suggest
you do the same; removal without
breakage is possible but usually difficult. Once broken, the bits fall out
easily.
Check the now-empty bell for any
remaining debris and if necessary
clean it out with some methylated
spirits on a rag; we will soon be gluing to this inner surface so it needs
to be as clean and contaminant-free
as possible.
If your bell is one of the rare types
that doesn’t already have a hole in the
centre of it, you’ll have to make it. The
hole can be drilled by hand with a
suitable drill press or hand-held drill,
though if you have access to a lathe,
this will make the job easier and far
more accurate.
If you drill by hand, be very careful
to get things perfectly centred. If you
don’t, even by the tiniest amount,
your motor will likely shake itself and
anything attached to it to bits.
The hole should be the size of the
intended prop-shaft and if you have
retained the chromed shafts the DVD
drive’s laser-head assembly was running on then you already have the best
item for the job. These are usually 3mm
in diameter, so use a suitably-sized
drill to make the hole in your bell a
tight fit for the chosen shaft.
Once the hole is made, clean it up
by using a counter-sink bit or a larger
drill to ensure there are is no swarf
left behind.
If the bell already has a hole,
chances are it has a lip on the inside
edge as shown in the picture . This lip
will need to be removed. Again, if you
have a lathe this is relatively simple,
though it can also be done by hand
using a larger drill bit, something in
the order of a 9mm (3/8th inch).
Proceed as if you were countersinking the hole and carefully take
the lip down until fully removed. The
bell material is not hardened so going
should be quite easy. I shouldn’t need
to stress that going too far will ruin
things, so take it slowly.
Motor styles
At this stage you’ll have to decide
on what style of motor you will build,
taking into account how you will ultimately mount it in your model and
how you fit the prop shaft to the bell.
One configuration has the bell at
the back with the prop shaft running
forward through the stator/body assembly. This configuration suits bells
with a built-in shaft, as mentioned
above.
The second configuration is more
common because more donor motors
come without embedded shafts and this
is the type of motor I built. This type
has the bell at the front and the prop
shaft runs forward through the bell to
the propeller as well as back through
the stator/body assembly and anchors
with a circlip at the rear bearing.
siliconchip.com.au
The bearings are tiny
– and they are also one
of the most important
parts of the motor,
given the high speed
at which it spins. It’s
always wise to replace
any bearings with
new ones – they’re not
particularly expensive
and are available at all
good model shops.
In either type of motor, the bell is
fixed to the prop shaft via either two
nuts or a brazed-on brass fitting and
grub-screw assembly – the latter is this
type I describe here.
You also have a choice of propeller
mounts. You can use two nuts on a
threaded portion of the shaft or you
can use any of the “propeller-saver”
fittings commonly used on electric
model motors (refer images).
Propeller savers have the advantage
that they mount using two opposing
screws, meaning you don’t have to
thread the shaft and the prop is held
on with an O-ring that loops over the
prop and around the mounting screws;
should you hit the ground, the prop
simply flexes out of the way and hopefully doesn’t break.
My advice is to avoid hitting the
ground!
Mounting the prop shaft
Methods of mounting the propeller
shaft requiring heat (brazing or soldering fittings onto the bell) must be done
before the magnets are fitted. Some
people might want to braze or solder
the prop shaft directly onto the bell
and this is fine, as long as it is centred
and straight.
However, we have a chicken and
egg scenario; fitting the shaft or shaft
holder now will make placing the magnets much more difficult, especially if
you don’t have a jig, whereas heating
the bell after the magnets are placed
will ruin all your hard work.
I suggest not fixing the shaft to the
bell permanently, instead using a removable system such as a brass shaft
retainer. This enables you to use the
same prop shaft on a variety of bells
and motor bodies.
If your shaft is to be cold-fitted, that
is, mounted with a couple of nuts either side of the bell, you can proceed
with placing the magnets. If you want
to braze a shaft-holder to the bell, you
can do that now.
Using a lathe, turn up a suitable
shaft holder from brass or steel and
drill and tap the retaining grub-screw
hole(s). Using the prop-shaft as a
guide, carefully position and braze the
shaft holder in place. Mount the whole
bell assembly in a lathe, drill-press or
even an electric drill and spin it up,
checking to see everything is nicely
aligned.
These motors rev like you wouldn’t
believe and if your alignment is out,
the whole thing will vibrate badly and
cause problems so you’ll need to either
tap it into round or re-do it until you
are satisfied everything is perfectly
centred and running true.
Once the shaft holder is fitted, you
can now remove the prop shaft and
proceed to assemble the magnets.
There are many sources on the web
for the right-sized rare-earth magnets.
Most of these accept Paypal or similar
online payments and fire your magnets
out in a small envelope as soon as
payment clears.
I began buying my magnets from a
US source, though this worked out to
be quite expensive due to the hammering our NZ dollar was taking at
the time.
I ended up importing magnets made
to my own specifications and while
this was an expensive exercise, I have
since sold many sets to other enthusiasts at about half the price others were
charging and this has helped recoup
some of the costs.
There are two main types of magnets
used in our motors; flat and curved.
Flat magnets tend to be cheaper
and can be fitted into a wider variety
of bells; curved magnets are usually
designed to fit the more standard 1
inch/25-27mm diameter bell and
while slightly more expensive (due to
the manufacturing process), they are
also more efficient.
If you are aiming for maximum
performance from your motor, curved
magnets provide the best possible efficiency and power output.
Whatever magnets you use, you’ll
need twelve of them per motor and
since they are very small, things can
get a bit fiddly.
Refer to the images and note how
the twelve magnets are placed; they
are equally spaced around the circumference of the bell and their poles
are reversed in alternate order, so you
have, facing inward (or outwards) a
north-south-north-south-north-south
configuration.
It is vitally important you observe
this same configuration, otherwise
your motor will not run properly, if
at all.
When you buy a ‘set’ of 12 curved
magnets, you should receive six polarised one way and six the other.
(Left): they’re sometimes called
“scary magnets” because they
are so powerful (don’t get
your fingers caught!). In
fact, they are “rare earth”
(or Neodymium) types and
getting them apart can be
rather tricky!
(Right): here’s the little
plastic jig I made up to
allow accurate magnet
placement inside the motor bell.
siliconchip.com.au
July 2012 79
These two pics show how
the new magnets are glued
inside the motor bell.
At left, spacers hold the
magnets at the right
distance apart, immediately
before glueing in place.
They do have a tendency to
move of their own accord
without the spacer.
At right, this part of the job is
finished, with all the magnets
glued in position. Take care
not to get any glue on the face
of the magnets: clearances are
rather tight!
Whichever magnets you use, figuring
out which way they go is critical.
You don’t need to know north from
south, just that this side of the magnet
is one pole and the opposite side the
other pole, meaning the next magnet
in the bell must be the reverse of the
previous one.
I figure it all out during assembly by
putting two magnets together; if they
stick, then they are facing the same
way; if they try to push apart, that’s
how they should be placed in the bell.
I originally placed all my magnets
by hand and if you are adept at small,
somewhat fiddly tasks this will not
present a problem.
However I have since created a simple plastic jig which has made things
easier (see the photo overleaf). If you
are serious about making more than a
few motors or have fingers of butter
and fists of ham, I suggest a jig may be
the best way to go, although it is by no
means mandatory to have or use one.
I have also used spacers made from
either card or plastic to separate the
magnets before and during gluing,
however you need to be careful you
don’t glue the spacer in as well as
these can be difficult to remove without damaging the magnets and bell
assembly.
Those wanting a jig can also approach me for this item.
there are also gel-style cyanoacrylate
glues which are much thicker in consistency and take a few seconds longer
to cure then their water-like cousins.
It is this type of instant glue I use to
cement my magnets in place. Not only
does this give me a little more time to
ensure I have things in the right position before the glue sets, I also end up
wasting a lot less because it doesn’t
run everywhere or create problems.
Another very useful-but-optional
addition to my glue tool-kit is cyanoacrylate accelerator which is used
to decrease glue curing time. It usually
comes in a pump-type applicator or
small spray bottle and can be directed
onto the area, instantly curing any
cyano-based glue it touches.
A tube of thin instant glue, one of
gel-style instant glue and a bottle of
accelerator will suffice for all our motor gluing needs.
The magnets stick to the metal side
of the bell quite well by themselves
(duh) so it is relatively easy to place
the first one, hit it with a spot of instant
glue and when set, carefully place the
next one, spot glue it and so on until
all are placed.
Trying to put all the magnets in
and align them before gluing usually
ends up like a comedy skit, with your
magnets suddenly jumping about before clicking together to form a single
column stuck to the bell and all facing
the same way.
Keep in mind that these magnets are
unbelievably strong for their size and
given any chance at all will move just
where you don’t want them to. If you
do happen to end up with a magnet
“stick”, pulling them apart is virtually
impossible – they need to be “slid”
sideways off each other.
Just be careful that you don’t get
any flesh between them if they snap
together or you might be tempted to say
some very naughty words (like bother,
crummies, oh dear, etc).
I found that carefully placing and
securing each magnet before moving on to the next is the best way to
proceed as it keeps everything under
control and also allows me to get my
magnet positioning right.
Once you’ve done this a few times,
it gets a lot easier and having a jig to
hold things in place as well is a definite
advantage. Keep in mind that while
magnet spacing is not hyper-critical,
(it really doesn’t matter if you are off a
half a millimetre here or there), performance can suffer if the magnets are too
far out of line so try to be as accurate
as you can. Again, a jig helps here.
Super glue
At this point we should have a quick
look at the types of glues used in our
motors.
Hobbyists would know about socalled ‘Instant’ or ‘Super’ glues, which
are thin, fast-setting cyanoacrylatebased adhesives, marketed under a
wide variety of names.
However, many people are unaware
80 Silicon Chip
Here’s another view of
the completed motor
bell and magnets sitting
on the author’s fingers
. . . giving a good idea
of just how small these
motors are!
siliconchip.com.au
All of the old wire has been removed and the
stator given a bit of
a clean-up,
ready for the
new wire to
be wound
on . . .
When you have all twelve magnets
tacked in place, go around and if necessary add another spot of glue under
and between each one to be sure everything is well-anchored in.
Flat magnets will usually have a
slight gap under their middle, with
only the ends touching the bell and
this gap should be filled with a drop
of gel glue as well.
Once done, run the thin glue all
around to fill in any gaps and hit the
whole thing with your glue accelerator. This should set things nicely and
result in a solid mass holding the
magnets in place.
Just make sure you put all the glue
drops in before giving it a spray as the
accelerator will instantly cure any liquid glue it touches, even that coming
out of the tube or on your fingers! (You
can also buy cyanoacrylate solvent if
the worst comes to the worst).
Also make sure no glue encroaches
past the inside-facing surface of the
magnets as things run very close and
the rotor binding on the stator is one
sure way to damage your motor and
potentially burn out your speed controller. By now your bell should have
all the magnets glued in place and be
ready for the shaft to be assembled.
Mounting the prop-shaft is one of
the critical parts of the job because it
must be centred and dead straight. If
you brazed a shaft holder as described
earlier, yours is already done, however
if your bell has room and you are taking the locking nuts route, then you’ve
a bit more to do.
Find some appropriate low-profile
nuts and thread the back end of the
prop shaft you are going to be using
to suit.
Mount the bell using one nut on the
inside and one (preferably a “Nylock”
or similar locking nut) on the outside.
Tighten fully and spin up the assembly
as described above.
It should be nice and balanced
with no wobbling or wandering out
of round. If it is out, tap the high side
gently with a light (rubber) hammer
and try again, repeating the process
until it runs true. Once done, put it
to one side as you are now ready to
wind the stator.
Important note
The prop shaft will be exposed to
And here are the new windings. If you
look closely, you can see that the coils
are in series with each other, spaced 3
apart (see the wiring diagram below).
some very high stresses and possibly
temperatures as well. Do not just glue
it in place because this can only end
in tears – very likely your own – when
it flies off and hits you.
As mentioned, these motors are
surprisingly fast so whichever method
you use, the prop shaft must be mechanically very well secured to the
bell.
The motor body
Now is the time to decide on the
body style and mounting configuration
you will use.
Both use the same simple turned
aluminium body, though the Top Hat/
bulkhead mounting method requires
more lathe work than the other clampstyle mounting system so it is up to
you which one you use.
Both methods require an aluminium
cylinder, turned from 10mm or similar
aluminium stock, which will become
the motor body.
The body must be fabricated so that
it press-fits into the hole in the centre
of your stator. Make it about 30-35mm
long and if you use a standard stator,
it should be about 8mm in diameter to
Here’s how to re-wire the motor – there are nine identical coils, each connected as
shown here with three in series. The dots indicate the “start” of the coil while its
end connects to the start of the next coil and so on. The “starts” of each of the three
sets of three coils then connect to the motor controller, while the “ends” of the
three sets all connect together, as
shown here. Always wind the coils
in the same direction,
TO
starting at the outside
CONTROLLER
and working
towards the middle
TO
MOTOR
of the stator. Wind
SPEED
as tightly and as
CONTROLLER
neatly as possible
for maximum power.
JOIN AND
INSULATE
siliconchip.com.au
July 2012 81
ensure a perfect interference fit.
Each end of the shaft then needs to
be turned to fit your choice of bearing. If you retained the chromed shaft
from your donor CD/DVD drive, the
bearings should have a 3mm inside
diameter to accommodate the shaft
and about a 6mm outside diameter.
As mentioned, these are standardsized bearings as sold for replacement
parts for model cars and helicopters
and as such are easily sourced and
inexpensive.
If you chose something different for
your prop shaft you’ll need to source
bearings that will suit it.
This is where engineers can have
a lot of fun making their motor bodies from whatever material and parts
they may have lying around in their
bits boxes.
The only considerations are strength
and weight – we want to make the motor strong enough while keeping it as
light as possible.
Winding the stator
Now take the stator an push out
any centre and strip any PCB or other
mounting material from it along with
the existing wire until you are left with
a naked unit.
It is best to start with known working configurations and if you want to
experiment from there, fine.
I recommend starting with 10 to
13 turns of 0.4mm enamelled copper
wire, wound as neatly as possible. You
can use more turns of a lighter wire or
less of a heavier wire (anywhere from
0.25 to 0.5mm or larger).
It is essential you follow the winding directions exactly and wind the
same number of turns in the same
direction on the correct arms of the
stator; any discrepancies here are as
potentially damaging as mechanical
imbalances.
Once wound, you’ll need to connect the stator windings to your speed
Suggested methods
for propeller shaft
mounting and motor
body construction.
You make the body
whatever shape and
size you like, as
long as it fits your
stator, bearings and
prop shaft.
controller. There should be three free
‘ends’ that will need connecting and
the easiest way to do this is with a
strip of Veroboard with the appropriate
tracks drilled.
Simply cut a piece wide enough for
your motor body with a track to spare
each side and make sure the strips run
length-wise. Drill a hole closer to one
end big enough to fit your motor’s body
and break the tracks where required
with a 3mm drill bit to create three
separate connections near the other
end of the board.
Make the hole a reasonably tight
fit for your motor body; while there
are usually no significant stresses or
strains on the connector board, gluing
should not be necessary but if you do
encounter movement, a spot of instant
glue should suffice.
Carefully cut your windings wires to
length and scrape the insulation using
a hobby knife or similar. Tin the bare
leads well before soldering to your
connector; high-resistance joints here
will cause problems.
Brushless
motor speed
controllers – on top
is a commercial model
and at bottom is a
home-made
‘analog’
speed
controller.
82 Silicon Chip
Setting it all up
By now your motor body should
be complete; the windings wound,
connector board fixed and the leads
nicely soldered. All that remains is for
the magnet/bell/prop shaft assembly
to be sized and fitted.
This is how I set mine up:
• I fit the prop shaft loosely through
the brass shaft holder and feed
enough of the shaft through the
bearings in the motor body until it
clears the end of the back bearing.
• I have already turned a groove into
the end of the prop shaft in order
to accept the circlip and I then fit
the circlip.
• I push the shaft toward the front
of the motor, (the prop end) until
the circlip is flush with the back
bearing.
• I then push the bell/magnet assembly down the prop shaft until it sits
nicely over the stator but doesn’t
rub against it.
• I nip up the grub screws holding the
prop shaft and give the bell a turn. It
This commercial ‘propeller saver’
mounts onto the propeller shaft by
tightening the two Allen screws.
The propeller locates onto on the
saver’s centre boss and is held
in place by a suitable O-ring
looped around it and the two
Allen screws. In a crash,
the O-ring flexes or lets
go altogether, releasing
the propeller and hopefully
saving it from damage.
siliconchip.com.au
and then round the
end of the shaft using a file or sander.
You can now
mount the propeller. Your motor is
finished and ready
to mount and test.
When testing, it’s absolutely
vital that the motor/prop is very
securely fixed to an immovable
object. A loose, fast-spinning
prop can do a lot of damage before
it reaches the end of its power
cables! I use this large piece of
timber and make sure it
is held very tight
in a bench vise.
should feel totally free but magnetically ‘lumpy’, the lumpier the better.
Any rubbing must be investigated
and dealt with before applying
power. Fine tune the bell position
on the shaft if necessary. The bell
should definitely NOT rub on the
windings.
• I then measure how long I want the
prop shaft to be and mark it – you
can make it any length to suit your
models and mounting methods
(within reason of course). I remove
the shaft from the motor, cut it to
length and then thread it for fitting
the prop nuts.
If you are using a propeller saver
device, simply cut the shaft to length
Testing
If you are using a metal clamp
style arrangement
to hold your motor,
take care you don’t
squeeze too hard or
short the connector
board. If you are
using a ‘top hat’
bulkhead mounting
system, make sure
the grub screws are
tight and evenly
clamping the motor
body.
Over-tightening
either mounting
system may damage the aluminium
motor body so take
care not to overdo it.
Wire up your
speed controller, R/C receiver (or
servo simulator) and LiPo battery as
you normally would.
For safety, I always mount a 15A
miniature car fuse in one of the speed
controller’s lines to the motor. LiPo
batteries as used in models like this
can pump out some astonishing currents and a simple 50c fuse can save
a lot of grief!
Mount the motor solidly in a vise,
test rig or your model and switch on
all your R/C gear.
Plug in the motor’s LiPo battery,
making sure you keep well clear of
the propeller.
Most modern speed controllers have
a protection feature built-in which
won’t allow the motor to run at all
until the throttle is set to absolute
zero, (check your trims as well) but
some older speed controllers do not
have this facility.
If all looks good, slowly apply some
throttle and your brand new motor
should leap into life. If you want to get
serious about experimentation, a full
test rig with a tachometer, voltmeter
and ammeter installed is the only
way to really fine tune your propeller, wire gauges and number of turns
combinations.
Typically, though, you’ll just want to
get the motor into a plane and go flying
and trim it out from there. Whichever
way you do it, you have just created
a well-performing brushless motor
out of junk and that is a satisfying
achievement!
Propellers
Propeller size depends greatly on
the size of the motor you’ve made, the
number of windings and the gauge of
the wire used.
If the prop is too small, the motor
may rev too high; too big and it might
not rev enough and a heavy prop
may cause electrical overloading and
overheating.
Either condition may damage the
motor, especially if you run it at high
speed in a test rig without adequate
cooling.
Note that the prop blast is not usually sufficient to keep things cool when
the motor is static at higher revs so
take care when giving it the beans on
the bench.
I started with a couple of props, one
a 6 x 3 (6 inches diameter and 3-inch
pitch) and the other a 7 x 4. On my
motors, the smaller prop allowed for
very high revs but not a lot of performance in my model. The 7 x 4 suited
it much better and the model flew very
well with it while keeping the revs and
temperature down.
SC
And here’s the completed assembly,
ready to go flying . . . oh yeah, you
might also need a plane, a controller,
a battery, a radio control unit and a
nice large field . . .
These stainless
steel shafts (which
make superb prop axles!)
were pulled from a DVD
player at the same time as I
was recycling the motor. I also got
the laser and various other bits and
pieces for good measure!
siliconchip.com.au
July 2012 83
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