Motor Building Manual
Notes: The original Electric Hubcap motor was
intended exclusively to be mounted on the outside of a car wheel. Some
of this documentation refers to this. Now the motors have been made
more general purpose. And they have been improved on an ongoing basis.
Parts of this manual were written at various times and some of the
information is badly outdated. I don't have time now to properly update
The improvements have been documented in various issues of
Turquoise Energy News. There are presently (2014/03/21) two sizes: the
original size 4.6 KW 'Electric Hubcap' (9 coils, 12 magnets, 10"
rotor), and the 3 KW 'Electric
Caik' motor (6 coils, 8 magnets, 7.5" rotor). The second size was rapidly developed from November 2012
to February 2013, when the first one was made and used in an electric
outboard motor. See TE News especially from that period. An issue with
flaking coil coatings was solved about that time as well.
Additional larger size motors using the same coil, magnet
and sensor arrangements, are planned. For example, a very high torque
12 or 13 KW 'Electric Weel' motor with 24 or 27 coils and a 26"
diameter rotor, and a bicycle rim motor with 6 coils.
(Other than this note, the last update to this manual was
Skip to step-by-step instructions
The 'standard' Electric Hubcap Motor configuration.
shown without stator air filter
...5 KW at about 30
Second latest version in cross section: shaft, rotor compartment,
The disk brake rotor has now been replaced by a custom flat plate rotor,
saving an inch, and the motor body is now 11.25" diameter by just 3.5"
An old version prototype with prototype torque converter
As this project has not yet created a successful product,
a planetary gear, probably with nylon 'planets'
to ease lubrication requirements, is to be used instead.
by Craig Carmichael
Inventor and Developer of the Electric Hubcap Motor and Motor Controller
Started: Sept 22, 2008 - Last Rev: 2010 Dec. 7 (Interim version)
New "version 3" incorporating the many motor improvements of
fall/winter 2010 to early spring 2011.
Started: 2011/April/10th. Interrim version posted April 26th.
( Does this 5 KW motor seem too small for your needs? Check out the new
"triple" motor, the 15 KW, 28" diameter, 10x torque Electric Weel
- coming soon! )
This motor needs speed reduction to the car wheel. Only a
very oversize motor would have enough torque if directly connected. A a
efficient, mechanical torque converter is currently being designed.
"Clock escapement" design looks promising 2010/09/29. (A workable
version hasn't been created yet - I've had little time to work on it -
Other options are planetary gears, chain drive, etc. A two motors with
planetary gears system is being used as an interim measure
for city driving, approx. 0-55 Km/Hr, with motor de-couplers to
highway driving on gas.
This publication is free information about a new
whose potential hazards are significant but not yet well known, and the
author will accept no liability for anything that happens to anyone as
a result of any use made of it. You are on your own. You have been
Introduction to the third version
In the previous versions of this manual, various ways of
putting together Electric Hubcap type motors "from scratch" from
disks and trailer axle parts were examined. In this third edition, the
motor, while retaining the essential axial flux form and
electromechanical operation, was substantially redesigned over six
months from October 2010 to March 2011, and
these instructions have been substantially revised to match.
A "standard" motor configuration has been adopted for
production, with an enclosed main body of 12" diameter by 3.5" thick.
This main body is made of two compartments, rotor and stator, formed by
three big polypropylene-epoxy composite rings - at the ends and middle.
The rotor compartment perimeter has a thick outer cover for protection.
The shaft sticks out one end, like most motors.
The main housing and structural parts - the three rings
and the rotor edge cover - are better made, of non-conductive composite
materials instead of
metals for both weight reduction and electromagnetic reasons. The
iron powder coil cores have much lower losses than the previous
laminate core coils. With the additional novel technique of painting a
layer of ilmenite on the coils, a new standard in electric motor
peak efficiency has been achieved, about 95%.
As well as operational improvements, the motors have
become far simpler to make. No more fitting laminate core strips into a
coil. Disk brake rotors and trailer axles have been replaced with a
custom premade flat plate rotor that bolts to an "SDS" bushing set
on any length of one inch machine shaft. The body and stator parts have
molded as three rings of tough, light, strong polypropylene-epoxy
The magnet sensors are mounted on a single circuit board, available
This manual exclusively covers making this new 'production
version' Hubcap motor. It's so much better than the previous versions
that there seems little reason to make the older types. The
parts are now available premade. It's probably most practical now just
to buy the motor kit or at least some of the pre-made parts, all in the
Electric Hubcap products catalog. Instructions will continue to be
given for all aspects of construction for those who prefer to do it
Thus section 1 is still theory, only somewhat revised as
the motor still works the same way, but section 2 has been changed from
"Mechanical Components Selection" to "Motor Assembly". Here it is
assumed the parts are made or purchased and ready to assemble into a
motor. Subsequent sections deal with the details of individual parts
and their production or purchase.
1. Motor Workings ___finished initial
edit. check for duplications and inappropriate material.___
Electric Hubcap Overview
What does it cost?
Vehicle Mechanical Connections
Mechanical Torque Converter (MTC)
or Planetary Gear and Car Wheel Installations
Construction Principles: Safety
Battery Power Supply
2. Motor Assembly ___rewritten section___
3. Axle/Shaft, Bearings, Bearing Races & Hubs
Motors need an axle & bearings
3-2 Bearings and bearing races
Trailer wheel bearings prove to be ideal - and available
3-3 Bearing Race Hubs
The axle is the inside. A hub attaching the part that doesn't turn with
the spinning axle is on the outside.
4. The Stator
4-1 ELECTROMAGNET COILS
Cores & wire
Winding the Coils
Coating the coils with ilmenite
4-2 MAGNET/ROTATION SENSING
Hall Effect magnetic pole sensors
5. The Magnet Rotor
SUPERMAGNETS ARE VERY
HAZARDOUS! so READ this part and follow
Magnet Placement, handling the magnets, magnet placing jig(s)
Epoxying polypropylene strapping over the magnets
6. Mounting the Motor on a Vehicle and Testing
Brake Drum Housing Attachments
Fitting and vehicle suspension considerations
(up-down travel of wheels with weight, bumps and potholes)
Nyloc Nuts & things that fall off while driving
How long does it take to build?
Electric Hubcap Motor Specs
Section 1. Motor
Electric Hubcap Overview
The Electric Hubcap
(or "Hubcap Motor" or "EH") is a 'cake' shaped three phase, brushless,
motor. It can be purchased as a kit, made from pre-made parts plus
homemade parts, or made entirely 'from scratch'. It is
the easiest multi-horsepower motor to build, even at home, and its
performance is the best attainable, in a
package that's light in weight for its power (about 30 pounds;
It is probably about the most
electric motor out there, being an "ideal" version of the most
efficient layout (axial flux) of the most efficient family
(supermagnet) of electric motors, with very low loss iron powder coil
cores. A fabulous new feature gives it a good edge over other motors:
an ilmenite paramagnetic coating creates a low magnetic resistance
bending much of the normally wasted field that radiates
outwards into the air back around and into the core. I lack the time at
moment to chart the peak efficiency of about 95% (my estimate based on
the low no-load
currents), though I hope to within the
coming year (ie in 2011).
The Electric Hubcap motor was originally designed for
mounting on the wheel
of a motor vehicle. In that application, a versatile, efficient
mechanical torque converter on the same axle is planned to couple it
the wheel. Its unique features
combine to make it an ultra-efficient drive system, delivering an
estimated 1.5 times or greater thrust to the wheel than a typical
electric vehicle drive (operating through the vehicle's transmission)
for the same energy input. So little energy goes
to waste that it doesnÕt need a liquid cooling system. The motor's
magnets act as fan blades to cool the coils.
A successful mechanical torque converter for the system
hasn't been made yet, so planetary gears are employed to reduce the
higher speed of the motor to the lower speed of the car wheel, allowing
city driving speeds up to 60 Km/Hr (35 MPH) with two motors, on left
and right wheels. If and when the torque converter becomes available,
the gears may be replaced, improving performance at most speeds and
allowing highway speed electric travel.
This motor can be used most anywhere a high
performance multi-horsepower motor is required: lawnmowers, outboards,
motorcycles, sawmills... It is especially intended for battery powered
and as such has so far been configured for 36 to 42 volt DC operation,
solid state 3-phase brushless motor controller such as the Turquoise
Motor Controller, plans for which are also available at
ElectricHubcap.com . Low
voltages minimize shock and electrocution
hazards, but require heavier wires for greater currents, since power =
volts * amps. Low voltage is very suitable for powering with nearby
not where long runs of cable would be required.
In the brushless motor, magnet sensors and a solid state
motor controller replace
commutator and carbon brushes, allowing much higher power 3-phase AC
permanent supermagnet motors, with low power controls that can be very
sophisticated, low friction, low wear, and no sparking. The Turquoise
Motor Controller is located near the motor, with 3
feet or less of 3-phase cable between them.
Turquoise Energy offers the Electric Hubcap motor in kit
form, as well as various individual components for making them, plus
the Turquoise (Brushless) Motor Controller, created for our motors
though broadly applicable. (See Parts
The Hubcap Motor can be
made mostly with home tools.
In automotive use, it is easier to
simply add a motor to the wheel of a car than to rip out the gasoline
engine and all the associated parts and fit a (bigger) electric motor
inefficient drive train, and it leaves gasoline
operation available "as usual", eliminating worries about running out
of battery charge at an inopportune time or place. Only 2/3 as much
power is required for the same driving range, and the driving range can
be reduced to the normal daily requirement rather than the "worst case
requirement. This makes using lead-acid batteries (with sodium sulfate
added to triple their cycle life) much more practical even if no better
economical alternative is found.
Of course, the Electric Hubcap type of motor can
anywhere a motor of its characteristics -- high efficiency, a few
horsepower, high torque, lowish RPM range -- is needed. (It could for
example make a great washing machine motor, perhaps eliminating much
mechanism, a variable speed lathe motor (eliminating V-belts and
pulleys), a marine, outboard, or submarine propeller driving motor, and
Larger versions (the Electric Weel motor is the first larger
model) could power ships, locomotives, busses, and even
aircraft if lightweight batteries become available.)
This type of motor is run in a
six-state power sequence by a solid state electronic control system. At
any given time, one phase is driven high (eg, battery +36 to 42 volts),
low (Battery -ground), and the third is idle, with the three drive
wires switching continually based on the rotary position of the
supermagnets on the wheel. The basic control contains only a small
number of commonly available electronic parts, and a dozen high current
MOSFETs (= metallic oxide semiconductor field effect transistors) that
drive the motor coils.
effect magnetic switches, one per phase, synchronize the six-state
timing sequence with the
rotation of the supermagnets on the car wheel.
A potentiometer (for vehicle use it's connected to the
determines the amount of thrust the motor provides via a pulse width
modulation (PWM) or current limit switching circuit in the controller.
A current limiting circuit prevents overdriving the motor
controller, eliminating the potential for burnout under adverse
load conditions. (In the A3938/A3932 controllers, variable current
limiting is the normal operating mode.)
Detailed descriptions and schematics are given in the
for making the controller, the Turquoise
Motor Controller Making Manual. Another manual is planned for
making the mechanical torque converter, and Installing
Hubcap Drive Systems is to be detailed in yet another manual.
More completely, the power to the
motor is regulated (a) by the choice of battery voltage, (b) the
construction, wiring and connection configuration of the motor coils,
and (c) by the pulse width modulation (PWM) or current limit switching
the supplied voltage.
The three phase "Y" motor wiring configuration is used,
three coils of each phase are wired for a safe 36-42 volts DC. The only
disadvantage to low
voltage operation is that the current is inversely higher,
necessitating heavier power wiring. However at 36 volts the wire gauges
reasonable when the power wires are quite short, as in a battery
installation. (At 12 volts the wires
would be awfully fat.) And, the lower voltage
rated mosfets have better specs. A few dollars extra copper is cheap
life insurance, and fewer batteries are needed for tests and basic
The motor type is variously called a "permanent magnet
motor" or PMSM, "brushless
motor", or "PM"
(permanent magnet) motor. Driven
with a motor controller having magnet position feedback it is the drive
signals which are synchronized with the motor rotation rather than the
other way around.
What Does It Cost?
As of the near the end of 2010, it appears that if you
find economical retail sources for all the stock parts and raw
materials, and buy
only the amount required, the cost will be somewhere a little under
$300 in Canada.
With ready-made parts - stator rings, bearing plates,
coils, etc, the
cost will be higher, since someone has done some of the work for you.
The special parts are not at this point "mass-produced", though some
are done with machines.
The Hubcap Motor's stator has nine
electromagnet coils, individually bolted between two flat
polypropylene-epoxy composite rings.
These are electrically connected as three sets of three-phase coils. In
this axial flux motor layout, these face six
supermagnet permanent magnet poles similarly spread around the
face of the rotor (a flat plate steel rotor or a car disk brake
rotor), usually organized
as 12 equally spaced magnets that also act as air fan vanes to cool the
coils, thus: NNSSNNSSNNSS. The rotor is placed on an axle,
a length of one inch diameter machine shaft, with about a .55-.60 inch
between the stator electromagnets and the rotor supermagnets. A unique
part called an "SDS Taper Lock Bushing" attaches the rotor solidly to
axle. A trailer wheel tapered roller bearing
mounted at each end of the motor case allows the axle to turn.
As with any permanent magnet motor, the electromagnets
sequence as the motor turns so that the coil ahead of each supermagnet
on the rotor is
attracting it and and the coil behind is repelling it,
providing the turning force. Each coil is turned off while a magnet
passes directly over it, since attracting or repelling it there does
The electromagnet coil magnetizations must be synchronized
with the travel of the supermagnets around the rotor. In some motors,
this is accomplished with a commutator and brushes. For the Electric
Hubcap this would be impractical. Instead, the brushless motor
conjunction with three magnet polarity sensors, one per phase,
input to a solid state motor controller. The controller
activates the coils in proper sequence, but it increases or diminishes
their electromagnetic strength, depending on how much power
is being called for, by pulse
("PWM") or current limit switching, and it determines
whether the motor will run forward or reverse. Special features such as
regenerative braking may also be available.
A heavy but short (3 feet or less) three wire cable (3 x
#8 AWG) connects the high
power switching transistors in the controller to the motor coils.
In order to tell the solid state controller where the
magnets are, the motor contains three solid state magnet sensors called
Hall Effect Sensors (one per phase), and a separate light cable
connects these to the motor controller. The Allegro A1203 sensors used
in the motor are
of a specific variety, "bipolar switches", which produce a logic "1" if
activated by a north magnetic pole and a logic "0" when the rotor
transitions to a south pole.
Supermagnets have very powerful magnetic fields. In fact,
they are so strong with such a deep field that a large flux gap, about
.57-.75 of an inch, separates the supermagnets on the rotor from the
electromagnets on the stator. This large separation increases
efficiency over radial flux designs, whose flux gaps are typically
measured in hundredths of an inch, and prevents the gradual
demagnetization of the supermagnets that the radial flux designs suffer
The magnet poles are usually formed of two supermagnets
each, the twelve magnets each having dimensions 1/2" (thick) x 1" x 2".
These also act as 'fan blades' to cool the coils. But most any
organization of six equal magnet poles, eg, six 2" x 2" x 1/2" magnets,
or unequally spaced pairs of magnets, will work. Each setup may have
varying torque ripple characteristics, but it won't much affect motor
efficiency or maximum power.
Unlike electromagnets, the supermagnets are always
strength, and the permanent magnet supermagnet motor has much more
stopped and low speeds than any other electric motor family. (In fact,
supermagnets are so magnetic they are potentially hazardous to handle -
two coming together can crush.) Their
magnetic flux is so strong one would think a motor could be made to
drive car wheels directly with no speed reduction. However, the flux in
electromagnet coils that drive them is less powerful, and only a motor
that is very oversized in every other respect could accomplish this.
Such a motor would be too large and heavy to mount on a car wheel.
Hence the torque converter or planetary gear.
Note: in spring 2011, a large diameter, 15 KW version of
the Electric Hubcap motor for
directly driving vehicle wheels, the Electric Weel
motor was designed. This incorporates the components of three Hubcap
motors, spaced around the rim of a 26 inch rotor, still just 3-1/2
inches thick. Only in diameter is it "oversized", but that diameter
gives the Weel motor ten times the torque of the Hubcap motor. Since it
is nonetheless too large for wheel mounting, it is intended for fully
conversions, generally mounted under the hood and coupled to a CV front
The Electromagnet Coils
In the Electric Hubcap, The coils consist of 1" thick x 2"
diameter "hockey puck" toroidal iron powder cores (the "magnetic
size") with copper wire wound around them in a rectangular "donut",
making a total of about 2-1/2" to almost 3" diameter (the physical
size). The 'missing' iron in the hollow center of the toroid is in the
least useful place, and the core has 40% less iron powder to have 'iron
losses' in, though these losses are already much lower than with the
typical iron laminate core used in most motors.
If solid iron cores were used, the magnets spinning past
generate electricity into the iron. The electrons would run around
in circles inside the iron in one big short circuit,
causing heat, drag and very low efficiency. Today's usual practice
is to make the entire stator out of die-cut thin sheets of iron alloy
varnished to insulate them from each other and laminated together. You
can see these laminates in motors and transformers everywhere.
One might liken this to damming a stream with multiple dams, one after
another. They stop the stream from flowing. Putting the laminates the
wrong way is like putting dams parallel to the stream: the water will
run between them and keep flowing.
But the iron powder cores are like dividing the stream
into little cubes of water: there is almost no flow.
Up to the the point of magnetic saturation of the iron
in the core, the
magnetic flux is proportional to the electric current through
the coils, not to voltage or power. In fact, the voltage and power
required to push the required heavy current through the resistance of
the copper coils and overcome the residual magnetic retention
(hysteresis) of the coil iron is waste energy.
If we had room temperature
superconductors very little waste energy would be used to start the car
rolling. Copper, though the second best known conductor of all
materials at room temperature, has resistance, which wastes energy to
overcome in supplying
To further digress into the subject of wires, thereÕs a
is almost universal for motor use:
Silver is the best conductor. But it is only slightly better than
copper (about 10%) and very expensive. It might increase efficiency
from, eg, 90%
to 92%, and there may be situations where silver is a better choice,
car motors probably isnÕt one of them. Silver wire for the Electric
Hubcap would cost perhaps a couple of thousand dollars instead of
forty or fifty dollars for copper. (2009 prices)
Aluminum is the third best conductor. It is often used for electrical
wiring, and a larger gauge of this cheaper metal can compensate for its
somewhat lower conductivity. However, in motor coils there isnÕt much
room to put copper wire thatÕs as heavy as is desirable, let alone
wires occupying more space. This contributes to motors overheating
easily. Aluminum would make for less powerful coils that waste more
Also, aluminum is more prone to becoming brittle and failing with
vibration and in sometimes damp environments, the contacts corrode more
easily and work loose by expansion and contraction with temperature
changes. And it can't be soldered. Bad connections would not only make
the car run badly, they can
blow up motor controllers. So, though tempting for heavy cables, it may
be a poor choice of wire for any vehicle use.
Also of note, work hardened copper (hammered, bent back and forth,
up to 5% less conductive than annealed (soft) copper.
No known alloy has as good conductivity as these pure
elements. Copper is THE choice.
There is one more factor governing
torque: the large diameter of the Electric Hubcap locates the
magnetic forces farther from the axle, providing more leverage from the
same magnetic force. In effect, having the magnets and coils at 4
inches effective radius from the center provides a torque advantage of
two to one versus a similarly magnetized radial flux PMSM with a
two inch effective radius. This is also the principle behind the 10x
torque Electric Weel motor, which has an effective 12 inch
Increasing the diameter without adding more coils
(or increasing their size) will decrease the magneic flux concentration
over parts of
the rotation. I donÕt pretend IÕve worked out the optimum except by an
"eyeball" sense of proportions - I expect it's pretty close, though.
The increased diameter Weel motor adds magnets and coils to maintain
the same density of force components as the Hubcap motor.
Once the vehicle is moving, the low RPM motor still needs
torque, but power comes into play. E = 1/2 MV2, so power
of a given motor is closely related to the square of motor speed, the
RPM. Also the power, Watts, = Volts * Amps.
But as speed increases, a motor starts to act as a generator. If,
say, one is supplying 36 volts and the motor is generating 18 volts,
the maximum current to the motor drops by half. At the speed where the
motor is generating almost 36 volts, it wonÕt go any faster and has no
power to spare. This dictates the maximum RPM. Raising the voltage, eg
to 42, also raises the maximum RPM.
Another facet of coil operation is that in an inductor,
voltage. On measuring the inductance per phase as 0.60mH, it turned out
to be only a 3¼ lag at 1000 RPM, or 100 Km/hour with smaller 13 inch
wheels, which is within reasonable limits for efficient operation. Over
2000 RPM or so it might become significant, but that's about the EH's
maximum RPM. (A later version of the coils measured 410-430uH. The iron
powder coils haven't been measured yet - I have to borrow an inductance
meter to do so.)
Electronics are an important part of
any modern car motor design. In the case of the Electric Hubcap,
of the magnets.
Without that, a brushless motor canÕt be used as a car drive.
The control electronics, however, are simple, with simple Hall
switch 'commutator' signals
telling the motor controller which coils and polarities to activate
based on where the magnets are in their rotation. This feedback system
is an integral part the motor.
The three hall effect solid state magnet polarity sensor
switches are mounted on the stator, with the three sensors located
nearest the supermangets and in the gaps midway between three
The three magnet outputs can directly feed the
motor controller chip to actuate the correct coil drives, to generate
six-state drive sequence.
There are minor timing inaccuracies with
this system, first because they don't switch until slightly after the
midpoint between two opposite magnets, and second because the
inductance of the coils delays current flow through the coils, but it's
close enough that fine adjustments are academic in this motor.
To run the motor in reverse, the signals are simply
digitally inverted (inside the motor controller chip.) Of course,
'forward' and 'reverse' depend on
the order of the sensor wires and on whether the motor is on the
left or right side of the car.
The three motor wires are driven in a
six state sequence. Since there are 9 coils and 6 magnet poles, they
line up the same every 120¼ and the sequence repeats itself 3 times per
revolution. (The 3:2 ratio of coils to magnets is universal for
three-phase PMSM operation.)
Each phase wire is driven for 2/3 of the time, and only two phases are
driven at a time. All three are never on at once. Each coil is "on" for
two states then "off" for one, and at the midpoint of its "on" state,
the other two coils swap over as the magnets rotate. The three states, high,
off and low, or 36 volts, undriven and ground,
north, off and south in the
coils. Here is the sequence:
| ¿ B
| ¿ C
When one line is driven to +36 volts
while another line is driven to 0 volts, the coils driven to +36 are
north at their top ends and south at the bottoms, while the coils
driven to 0 volts are the opposite magnetic polarity. Both sets of
coils provide the same magnetic strength. (DonÕt ask me which, "N" and
"S", is really which!) Two wires (and hence two phases) are driven at a
time, one high and the other low. The third phase coils are idle. Each
set of coils goes N, N, off, S, S, off, repeatedly. The intervening off
state, not going directly from high to low, reduces the inductive
spikes made by the coils, reducing the amount of filtering required.
The power is timed so that adjacent coils become north and south as a
magnet passes between them, one coil repelling the magnet and the other
attracting it to provide turning torque. As the magnets pass directly
over a coil, it is turned off. Energized coils here would simply repel
or attract the rotor magnets to the stator coils without providing
turning force. Note that right in the middle of one set of coils being
"north", the other two sets swap being "south", and vise versa.
With spread out magnets along the rotor, it is the position of the
center of force that is being considered.
At the risk of being repetitive, here is another representation of the
six state drive sequence:
Note that at all times (disregarding
the PWM or current limiting modulation that repeatedly turns all the
drives on and off during their
"on" times) one phase is driven high and another one phase is driven
low, providing continuous north-south magnetic thrust forces at all
points of rotation.
The maximum rotational force is generated when the
pole is directly between two energized coils, one attracting it and the
other repelling it.
Since the sequence repeats every 120¼, each coil is north
for 40¼ then
off for 20¼ (half the sequence), then south for 40¼ and off again for
20¼ (the other 60¼ half). That 120¼ also sees the two magnet poles,
north and south, 60¼ each, go by the three coils of phases A, B and C.
The astute student will notice that
with only three magnet sensing elements, the six states arenÕt entirely
decoded for the six inputs to the MOSFET driver. "A" would seemingly be
high for 60¼ and then low for 60¼ of the 120¼ cycle with no "off" time,
instead of only on for 40¼ and off for 20¼. Where is the translation?
For the answer we look to the digital logic and to the way the optics
connect to it.
truth table for each phase of a typical MOSFET
driver chip is:
for HIGH drive MOSFET
(phases A, B & C are alike)
for LOW drive MOSFET
(A, B & C are alike)
High side & Low side
On, High Off
On, Low Off
||Both OFF (NOT both
both high and low of a phase were
on at once, the high and low side MOSFETs would create a short circuit
from the 36 volt batteries to ground, and blow the fuses (after
burning up first themselves). The chips donÕt let that happen, and they
also insert a very short delay in any transition directly between high
and low drives being on to ensure the same. This is covered in more
detail in the motor
To visualize the workings, let us
simplify by considering a rotor with only two magnets, N and S, 180¼
and a stator with three coils 120¼ apart. The six states then occur
over one rotation, 360¼, with 60¼ per state.
The timing (turning clockwise) is then that the top coil
"A" is off until a
magnet pole is
30¼ past it. Then it turns on with the same polarity as that magnet for
the next 120¼ (to 150¼, states 0 and 1 of the table), repelling it.
It then turns off while the other magnet goes by it from -30 to +30¼
and the first magnet goes from 150 to 210¼ at the opposite side (state
Then, with the second, oppostie, magnet 30¼ past the top coil, it goes
the opposite polarity for the second half cycle (states 3 and 4 from
210¼ to 330¼, with state 5 again being "off" from -30 to +30¼).
While the first magnet moves away from the top coil from 30¼ to 150¼,
the opposite pole is approaching the top coil and is attracted, going
from -150¼ to -30¼ from our coil. More of the repulsion of the first
magnet is in the first 60¼ from 30¼ to 90¼, then that magnet becomes
more distant from the coil. More of the attraction of the second
magnet is in the second 60¼ as it approaches our coil.
The other two coils do exactly the same thing, but 120¼ and 240¼ out of
phase to the top one, between them providing continuous strong thrust
at all points of rotation.
first 60¼ of the 120¼ swing
(30¼ to 90¼), phase "B" has been on, the magnet going -90 to -30
degrees from it, attracting the magnet "A" has been repelling. Thus the
magnet is being strongly pushed by the coil just behind it and strongly
pulled by the one just in front. The opposite magnet is also being
weakly rotated by the same two coils, which are more distant as it is
crossing over the third, "off", coil.
In the second 60¼ of the swing (90¼ to 150¼), phase "B" goes off as the
magnet goes by it and "C" comes on. Now "C" is pushing and "A" is
pulling the opposite magnet immediately between them with the same
strong forces, while the first magnet is weakly propelled as it passes
coils, 6 magnet poles machine,
works exactly the same, but the six-state cycle repeats itself three
times over 360 degrees, ie every 120 degrees. All the angles are 1/3
and three identical sets of coils are pushing three sets of magnets. So
the timing is that the coil is off while a magnet pole passes over it
from -10¼ to 10¼ past it, a 20¼ span (state 5). Then it turns on with
the same polarity as the magnet for the next 40¼ (states 0 & 1).
This repeats with opposite polarities for the other magnet in the
second half of the cycle (states 2 (off) and 3 & 4).
Naturally an air cooled motor has to push cooling air through as it
spins. In this motor, the magnets act as fan blades to push air from
the center to the outside.
Air is drawn from the open outside edge of the stator,
across and between the coils, to the center. It is then drawn through
the larger center hole in the inner stator ring into the center of the
rotor compartment. From there it is expelled to the outside edges of
the compartment by the spinning magnets. It goes around the rotor and
out vent holes in the shaft side of the rotor.
In theory it should be slightly more effective to have the
exit holes on the outside of the rotor on the magnet side, but I
decided to keep that solid for safety in case anything should fly off
the rotor. I am specifically thinking not only of dirt, but of magnets
if the motor is considerably over-revved or if they haven't been
well glued on.
Two 1/2" x 1" rectangular steel tube "brackets", upper and lower, bend
from behind the wheel just
afront and behind the tire. They attach to the brake drum backing plate
behind the wheel. They must be custom bent and fitted to individual car
models. Two steel straps, upper and lower, extend left and right from
the outside end of the motor to attach to the brackets. This somewhat
holds the motor up right in front of the wheel. It allows the motor to
flex up and down as the wheels hits bumps, and it takes the torque and
prevents the motor from spinning instead of the wheel. If you are
wondering about the strength of the brake
drum backing plate for this purpose, recall that the brake shoes attach
here and it takes all the force of squealing the brakes!
To connect the
turning force to the wheel, a "thrust plate" is attached to the output
of the planetary gear. This protrudes from the motor and fits into the
space between the lug nuts on the wheel, and in fact the force of
turning is applied to the lug nuts and bolts on the wheel. Are they
strong enough? Yes: they have to take not only the engine torque, even
going up a hill, but also the torque of locking up the brakes with a
skidding tire. They can take the electric drive.
The brackets and straps are adjusted to hold the motor
straight and centered over the wheel with the "thrust plate" nicely
lined up when the vehicle is at rest. Pushing the motor up or down
should cause it to angle up or down a bit.
Torque Converter or Planetary Gear
and Car Wheel Installations
size, the Hubcap motor has a lot of torque, yet it barely moves a car
by turning the wheel directly. Its lower torque, higher speed must be
converter to higher torque, lower speed to start the vehicle moving.
The mechanical torque converter hasn't been successfully
created yet (Apr. 2011), so a planetary gear, which is actually a set
of several gears, is employed for the reduction.
The planetary gear has:
a) The central "sun" gear, on the motor shaft.
b) A set of four or five "planet" gears mounted on a sort of ring in a
square or pentagon formation around the sun gear. The inside of each
planet gear meshes with the sun gear.
c) An outer ring gear, forming a case with the teeth on the inside. The
outside of each planet gear meshes with the ring gear. (No astronomer
has seen one of these surrounding our solar system so far, nor do all
our planets follow the same orbit.)
There are a number of ways this set of gears can be used,
with three possible speed reductions, one of which turns backwards.
However, switching between them would be problematic and only one
configuration is used. In that configuration, the sun gear is mounted
on the motor axle and the outer case is held stationary.
The planets with their square or pentagonal middle turn at
a reduced speed from the motor shaft, generally between about 2.5 to
one and 5 to one, the torque increase being proportional to the
The higher the ratio, the faster the vehicle can
accelerate, but the lower the speed at which the motor's maximum RPM is
reached. At too low a ratio, the car may not accelerate sufficiently
for city traffic situations, or it may not climb hills. At too high a
ratio, even city street speeds may be unattainable, which may
necessitate two motors and gears to allow cutting the ratio in half.
About 80 Km/Hr is the most that can be hoped for with two motors at
fairly low ratios.
These limitations illustrate the desirability of a
variable reduction torque converter, to optimally achieve all
objectives - for smaller vehicles, probably with one motor.
For this "open air" gear, an assembly of nylon planet
gears is used in place of metal. With metal planet gears, the gear
drive would need oil dripping on it all the time instead of just some
motor is mounted on the wheel,
which is unsprung, and although it is somewhat sprung by the flexible
coupling and mountings, it is subject to levels
of vibration not felt inside the car. Furthermore, if, eg, a roofrack
loose, it is likely to be noticed and retightened, whereas the motor is
down at the wheel. Some parts inside canÕt be
seen, and the whole motor has to be
removed to inspect and retighten them. Even the brake drum has to be
if the innermost stator bracket bolts come loose.
And there is more possibility to cause harm if something
comes off the motor, wheel or brake assembly, or even comes loose, by
losing power while driving, by having a loose part jam the wheel or
cause a flat tire, or by dropping a chunk of metal on the road in front
of the next car.
It is therefore critical to have a robust design, to
install all the
parts very securely, and to have scheduled inspections, frequently in
the beginning stages. Fragile parts must be carefully situated and
More on all this later.
electric Hubcap runs on 36 to 42 volts
of batteries capable of supplying up to 100 amps continuous, situated
where convenient in the vehicle. Generally it is desirable to locate
them close to the motor controller(s) so the heavy leads are short,
minimizing voltage drop and cost.
As I write this, generally the most economical
electric cars are lead-acid. These are rarely an environmental problem
as they are normally recycled. With sodium sulfate added to the
electrolyte, they can last for 4 or 5 years in EV use.
They are, however, heavy and bulky. They are supposedly around 40
WH/Kg, but since they
shouldn't be discharged more than 60% (and will perform dismally beyond
that as well), effectively they're only 24 WH/Kg.
The Electric Hubcap hybrid helps out by needing many fewer of them.
Three large "size 27" "deep cycle" 12 volt batteries (50 pounds, $100
each) will run the car. Six of them (two parallel banks of three - 300
pounds), or (better) six or seven 6 volt "golf cart" batteries will do
it with some
driving range and longer life.
If more cost is accepted, much greater electric travel
range with less
weight can be had. Nickel-metal hydride AA cells (at least about 2000 -
can be soldered together, or lithium batteries purchased. My money's on
the NiMH dry cells (about 100 WH/Kg) as being better performers than
lithium ion, which have similar energy density. And they are dropping
in price each year. It's a lot of soldering though - 1/4 as many NiMH D
cells, though only 75 WH/Kg, are easier. Li-S seems like a promising
new contender with exceptional energy density. I myself have been
create economical, high energy density 2 volt salt solution cells with
Ni/Mn-Mn. So far, the self discharge and the internal resistance are
much too high to be practical. (But I think I've just figured out the
cause of the self discharge: the oxygen overvoltage needs to be raised.)
On any batteries, the Electric
Hubcap will go farther than any other car drive. And because the
car becomes a "hybrid" instead of an "electric car", whenever the
batteries are considered "low", the driver will simply switch to
gasoline driving until it is convenient to recharge them (or use
"charge while driving" (on gas), with an advanced motor controller) and
switch back when theyÕre recharged.
Section 2. Motor Fabrication and Assembly:
This section covers:
Step by Step Instructions
1. Fabrication of the Motor Body
2. Fabrication of the Rotor with Magnets
3. Assembly of the whole motor from the components.
The main components of the Electric
Hubcap motor are:
* Body - 3 PP-Epoxy castings:
- Central body
- Stator end bell & bearing
- Rotor end bell & bearing, with optional steel face
- coils with wiring and connector
- magnet sensor board & connector
- perimeter air
intake filter "furnace filter"
- type a: steel rotor with NIB Supermagnets
- type b (projected): lexan double rotor with ceramic cup magnets
1. Fabrication of
the Motor Body
The three ring
plates are the two end "bells", and the
rotor-stator dividing plate. Plastic composite material is used because
the spinning supermagnets would drag electromagnetically on metal
parts, and heat them up. (Even 1/4" coil attachment bolts got warm, and
so a smaller size, #10-24, was chosen.) The rotor rim is formed around
dividing plate. It is made very thick in case magnets fly off a rotor
from substantial overspeed or from weak epoxy results or poor
construction/workmanship: they can break through
a thin cover and become potentially lethal projectiles. The dividing
plate prevents moving parts from from potentially contacting the coils
and the magnet
sensor circuit board. The magnetic flux gap between coil cores and
rotor magnets is sufficiently wide to accommodate this construction.
The stator end ring is held in place by the coil clamping bolts and
coils. The rotor end ring is held by 2.5" to 3" #10-24 bolts fitting
through the rotor rim, with tee nuts at the stator side of the dividing
Electric Hubcap body parts, painted with yellow urethane,
holes not yet drilled, plus painted magnet rotor without magnets (top
1.a. The Three Body Ring Plate pieces
A "Mini Electric Hubcap" body ring piece, with
mounts for 6 coils.
The rough patch at the left wasn't sufficiently wetted with epoxy,
and was touched up with some more epoxy later.
The body parts, of polypropylene-epoxy composite, may be
purchased or fabricated. The bulk of the volume of this composite is
the polypropylene (PP) cloth; the bulk of the weight is the resin. PP
is stronger, lighter, cheaper and nicer to work with than fiberglass.
The composite body pieces are painted with polyurethane to protect it
and raise the temperatures it can withstand.
Energy makes molds and jigs for fabricating the motors, on demand. By
having the molds, one can produce the bodies for any number of motors
instead of just buying an individual motor kit(s). A single body ring
will suffice for all three ring plates. A second mold for rotor end
bells permits making rotor bells without superfluous coil mounting
buttons, but it's not vital.
A new stator/body plate mold routed from 1" thick UHMW polyethylene.
Epoxy doesn't bond to polyethylene.
- Polyethylene plastic to protect workbench from epoxy resin
- Organic vapor filter mask to protect lungs from epoxy resin
- Vinyl disposable gloves
(Latex ones will soften and rip in the epoxy)
- Container(s), stir
stick(s) to mix resin
- Grams resolution Kg+ scale
- Ring plate mold(s): 3/4" plywood bottom stiffener, bottom,
top, center, top stiffener, fabric containment ring. (These are
specifically with a CNC router made for casting Electric Hubcap or
Electric Hubcap Mini motor body ring plates by
Turquoise Energy Ltd.)
- Five or six - 4" C-clamps (four for mini motor)
- Blade screwdriver, small putty knife, or other thin pushing
- Warming oven
- Scrap pizza pan or other drip catcher
- Lexan Drill Template (by Turquoise Energy Ltd. - CNC drilled
template to exactly line up all the holes in the ring plates.)
- Polypropylene cloth (Roll of "Landscaping fabric", "cloth
grocery bags" or other sources)
- Epoxy resin (at least 1 Kg for mini size. Many brands will
work fine. I've been using "West System")
1. Cut strips of PP cloth from the roll,
and rip them into small pieces
(eg from 2" x 4" up to 4" x 6" or 6" x 8" or...???). Rip some very
pieces to stuff
into the coil mounting button recesses. I stuff the pieces into plastic
for weighing and carrying. For the mini motor, use about 75 g of fabric
ring. For the large, about 175g (IIRC).
The body parts mold and C-clamps (Mini Electric Hubcap)
2. Lay PE plastic on work surface. Resin doesn't bind to polyethylene.
mold is also made of polyethylene, but waxing it eases removal of
3. Set down the bottom plywood (waxed), and the mold bottom on it. Lay
the small pieces of cloth and the other pieces nearby. Insert the mold
center post onto the center bump.
4. Don gloves and mask and mix about 3.5 to 4 times as much epoxy by
weight as PP cloth - say 250g for the mini motors and 550 for the
large. In the large motor, the dividing ring can be a little thinner,
say 125g of cloth and 400g of epoxy. (In the mini, all the rings are
5. Pour a little epoxy around the mold base and into the holes, then
work the small pieces of PP cloth into the coil button recesses,
wetting them well.
6. Place the containment ring over the mold. Add some bigger pieces of
PP, and pour a little more epoxy over them. Repeat in layers until all
and epoxy are in the mold.
7. Knead, turn and twist the fabric by hand to get a more even
distribution of epoxy through the cloth. The jumbled ripped cloth will
make a stronger part than neat, separated layers. Try to get an even
distribution of material throughout the mold.
8. Slip the mold top over the center post and
inside the containment ring, and push it down. When it won't easily go
any farther, slip on the top stiffener and remove the containment ring.
9. Use the C-clamps to push the top down. When the gap nears closure,
use a tool such as a screwdriver to push in the cloth
that's sticking out. Work the top down until the gap is closed and all
the material is within.
10. Tighten the C-clamps. If one side clamps notably thinner, open it
up and redistribute some material. It is surprisingly easy to end up
with a considerably lop sided part. A certain amount of uneven
thickness seems almost unavoidable and can be tolerated. Indeed, even
the center often turns out a little thicker than the edges.
11. Resin will ooze out around the rim and the center hub. I usually
scoop it up with the mixing stick (or brush if I have one already
wetted) and scrape it back into the container
for touch-ups on the finished ring or to start the next job. I save the
container in the freezer
to prevent the epoxy from setting. (It lasts a day or so in the
12. At room temperature, the resin takes 8 to 24 hours to set. Put the
C-clamped mold on the drip pan and put it in the warming oven. Set it
to 65¼C/150¼F. About 70 minutes sets the resin. Put a note on the oven
reminding not to turn the temperature up higher.
13. Remove the ring from the mold. It is still somewhat soft for some
time - it will gradually change shape for even a day or two. Place it
on a level surface, and put a weight on it if it seems to start warping.
Repeat the process for the other two ring plates.
1. Fabrication of
the Motor Body - step b) The Rotor Rim
To make the rotor rim the
same way as the plates from cloth scraps requires an elaborate mold
using quite a lot of UHMW or other polyethylene, and getting good
results is somewhat harder. Instead we use commonly available PP
(or nylon) strapping as a material that will pretty much hold the
without being compacted into a mold, and a piece of the body mold and a
couple of formed rings to stiffen things up while the epoxy sets. The
operation is best done in two parts: a thin skin (eg, two layers) of
wide strapping wrapped around the outside, then a thick shell (~8
layers, 1/2") of narrower strapping wound to fit inside the 'canister'
resulting from the first step.
- mold top from body rings mold
- rim spacer ring
- paper clips, thin wire
- cheap 3/4" or 1" paint brush
- inner spacer ring
- 3" polypropylene strapping (comes in rolls - try a tent and
- 1.5" PP strapping
The "mold" used consists of the top of the plate mold, and
the rim spacer ring.
1. Set the round plate mold top on the plastic on the workbench. Set
the divider plate-ring on the with the coil buttons down. Set the rim
spacer ring on top. (If there are two body molds, use a shorter rim
spacer ring with the second body mold top on top of it.)
2. Wrap two full layers of the 3" strapping around with a small overlap
to 3 layers, and cut it to length. The strapping should extend to the
table below, leaving about 2" above the ring plate.
3. Mix some epoxy resin (somewhere under 100g). Thickly paint one side
of the strapping and wind it back around the plate, painted side in.
Don't wrap it very tightly - it tends to shink around the plate in the
oven, and the pressure can cause the plate to warp.
4. Use a paper clip or wrap some thin solid core wire around as a giant
'twist tie' to keep it from unravelling.
5. Warm it in the oven for an hour. Put the remaining resin and
paintbrush in the freezer.
6. Remove the spacer ring from the top and extract the mold top piece
from underneath. (Sometimes easier said than done.)
7. Ensure that the mold top piece fits into the top end. It is to be
placed there during the next phase of fabrication. Sometimes a knife
helps to open a gap if it's tight. If it won't go, some sanding or
scraping may be required.
8. Mix some more resin.
9. The 1.5" PP strapping is wrapped pressing outward against the outer
strapping now completed. Wind it in, determine how much is needed for a
1/2" thickness, and cut it to length. The rotor bell bolt holes go
through this material, and it is the safety catcher should any magnets
unhappily fly off the rotor like lethal bullets, so don't skimp the
10. Using plenty of epoxy, paint a few feet of the strapping, then
start wrapping in the painted portions. Push the strapping lengthwise
to get it to push firmly against the outer shell without notable gaps.
Repeat until it's all wrapped.
11. Insert the inner spacing ring, which pushes the material outward
and prevents the mold top piece from pushing down on the fabric.
12. Insert the mold top piece (as if it were the rotor end bell) to
hold the exactly round shape and full diameter of the bell piece as the
13. Put any remaining epoxy and the brush in the freezer. Warm the part
in the oven for 70 minutes.
14. Touch up: fill any gaps with epoxy, making sure the rim parts are
well bonded to the plate, and set the part aside for a day or return it
to the oven.
1. Fabrication of
the Motor Body - step c) Hole Drilling
1. Fabrication of
the Motor Body - step d) Painting
2. Fabrication of
the Rotor with Magnets
3. Assembly of
the whole motor from the components.
1. The stator outer ring is the large flat composite plastic ring with
the smaller center hole. Attach the smaller set of inner and outer
this center hole via the five bolts, sandwiching the stator ring. A
bearing cup (outer race) should
fit in from the inside and stop against the outside plate. If it falls
in between the plates, a center spacer/stopper is needed.
2. Put the eighteen #10-24 coil
mounting bolts through the holes in the outer stator ring from the
outside (bolts sticking in to the inside), with washers. Set it down
with the bolts sticking up and put the nine
coils into place around the
bolts (on the inside side), with the leeds towards the center.
3. The three coils of each phase are wired together, in series or in
parallel. The coils of each phase are at 120¼ intervals from each other
- equidistant - with two other-phase coils between each pair. The motor
is wired in "Y" (AKA 'wye') configuration rather than Delta. As the "Y"
shape indicates, one leed of each phase connects together at a central
point. The wiring instructions are different depending on whether the
coils of each phase are to be wired in parallel (go to 5) or in series
(go to 4).
Use the wire sleeving to suppliment the thin insulation of the magnet
wire wherever it might contact another wire or anything else. Solder
joints if certain they're right; put marette connectors ("wire nuts")
over bare joins.
The terms "clockwise" and "counterclockwise" below are
reversible as long as all are done the same way. A coil wired backwards
to the others will try to turn the motor the other way (the north and
south magnetic poles will be
reversed) and the motor will draw very high current and
won't run well. All three coils of all three phases must observe this
4. series coils: If the coils have 20-21 turns of #11 AWG wire
(two layers of very fat wire), they are wired in series for 36-42 volt
operation. The correct leeds must be chosen so that the current going
through flows around all three coils in the same direction - all
clockwise, or all counterclockwise.
a. Take a leed that starts onto its coil counterclockwise and push it
aside as the start leed. This goes to the plug. If it is too short,
attach a 10 inch length (or shorter) of #8 or #10 stranded wire to it.
b. Take the other (clockwise) leed and pull it to the right. Connect it
to the counterclockwise leed of the next coil of the phase, which is
the third coil to the right.
c. Take the clockwise leed of this second coil and route it to the
right. It goes to the counterclockwise leed of the third coil of the
phase, three more coils to the right.
d. The clockwise leed of this third coil goes to the center or "Y"
point, along with the matching leed of each of the other two phases.
e. Wire the other two phases the same way.
5. parallel coils: If the coils have 60-63 turns of #14 AWG
wire (5 layers of medium wire), they are wired in parallel for 36-42
volt operation. The 21 turn, #11 AWG wired coils may be wired in
parallel if 12-14 volt operation is desired.
a. Tie the clockwise side of all nine coils together. This is the
center or "Y" point.
b. Take the three coils of one phase, each third coil, and tie the
three counterclockwise ends together. Preferrably, pig-tail them to a
#8 or #10 leed about 10 inches long to go to the plug. Same with the
6. Connect the three pins for the APP coil power plug to the three coil
wires. If you don't have the
correct crimping tool (who does?), solder the wire into the pin. It
needs lots of heat, and if your soldering iron won't do it, you may
need to use a propane torch. (I may supply 10 inch wires with the pins
already on one end.)
7. Snap the three plastic housing pieces onto the three pins from the
8. Insert 6 "flush nuts" into 6 of the 9 outer holes in the inner
stator ring, symmetrically spaced, from the stator side. (These hold
the rotor compartment cover bolts, which line the rotor up when screwed
9. Screw the magnet sensor board onto the inner stator ring via the two
screw holes in the ring that match it, on the stator side. The center
of the board overlaps
the four inch center hole in the ring.
9. Align the inner ring with the magnet sensor on the outer ring with
the coils. Make sure the coils and circuit board (and its components)
line up without
hitting and that no coil wires
will hit the magnet sensor board. The coils can be moved a bit.
10. Screw in the 18 coil bolts to secure the stator pieces together.
11. Wind a 40 inch x 2 inch piece of plastic window screen around the
open outside edge to keep mosquitos out. Staple, tack, tape or glue it
in place. ...wait, no, not glue! (Air will be sucked through this
screen towards the large center hole in the inner ring.)
1. Attach the larger inner and an outer
bearing holder plates to
the center hole in the rotor cover "pan" via the five bolts,
sandwiching the flat ring. The plate with the larger center hole goes
inside. (You couldn't get the stator side wrong because it could be
reversed until the coils were bolted on. This end has to be right.)
ROTOR & AXLE ASSEMBLY
(Assumes supermagnets have been mounted on rotor.)
1. Put the protective cover over the magnet side of the rotor. Hold it
with a couple of C-clamps.
2. Fit the SDS bushing into the center hole of the rotor from the
magnet side. (Watch out for magnets grabbing it!) Hand tighten the
three bolts to hold them together.
3. Slide the 1" round machine shaft axle through the center of the SDS
4. Slide the spacer over the magnet end of the axle.
5. Slide a bearing over each end of the axle, both with fat side facing
in towards the rotor.
6. Place a bearing cup (outer race) into each end plate center,
oriented to match the bearings. THE MAGNET ROTOR WILL STRONGLY PULL
ITSELF TOWARDS THE STATOR.
7. Take the protector off the magnet rotor and insert the magnet end of
the axle into the stator. Observe the caution above. I put wooden
wedges in and pull them out a bit at a time to ease the rotor into
place. The rotor should stop with the desired gap between the magnets
and the coil cores, but some adjustments are usually required. Add
washers or decrease the length of the spacer.
9. Pull the axle out or push it in to get it flush with of a little bit
past the end of the stator-end bearing.
10. Do up the three bolts that hold the rotor, bushing and axle
together. When they are tight enough, the axle won't slide. They must
be evenly done up for the rotor to be aligned - to turn with no wobble
- and they must be quite tightly done up to prevent anything from
slipping, including when there's a heavy load on the motor.
FINISH and TESTING
1. Put the rotor cover on over the rotor and do up the bolts, with one
angle iron foot and a reinforcing bar. The two bottom bolts are also
used to hold the foot on, with a third bolt attaching the reinforcing
bar. It isn't really necessary to put bolts in all nine hole positions,
tho they are all drilled. I use four or five bolts.
2. Put the other angle iron foot and reinforcing bar on the outside
side of the stator.
3. Try turning the axle and make sure nothing is jammed. It won't start
turning easily owing to the magnetic cogging. But nothing should grind
when it does!
4. Fasten the motor safely to a workbench or whatever. (C-clamps are
5. Connect the motor controller to batteries with two .5 ohm, 5+ watt
resistors in parallel, connected by skinny alligator clip leeds. These
will limit the current and perhaps save the motor controller if there's
some problem. Connect to 15-20 volts if possible (in which case
dispense with the resistors), or 24. The more you limit the power and
voltage, the more likely you'll be not to lose the controller if
there's a problem. But the controller won't work right if it has less
than about 15 volts going in.
6. Connect some controls to the motor controller. And connect the
magnet sensor board plug. (The motor won't run with it unplugged - I've
tried more than once.)
7. Connect the motor coils to the motor controller plug with skinny
little alligator clip wires (again to limit current), and determine
which power wire pin goes to which one on the controller. There are 6
possible ways to put them and only one is right. About three ways, the
motor won't run - it may start to turn and then suddenly stop and
perhaps jitter back and forth. A couple of ways, the motor will seem to
run fine in one direction but will run badly in the other, drawing a
lot of current. Then on about the 6th try it will run well both ways.
Don't turn the control up very far. Bad connections and high powers can
blow the motor controller or components on it.
8. About the time things are going well and the motor is humming away,
you will smell your resistors and skinny alligator clip wires burning
up. Stop and snap the plastic power plug pieces together in the order
carefully figured out. Remove the resistors from the power supply.
9. Now look over everything, pray, and try running the motor without
the 'cautions', perhaps at 24 volts, perhaps with a single 20 amp fuse
in the controller power line. (It will blow rather easily, of course.)
Then try full voltage (usually 36 to 42). If by some miracle everything
is still working okay (...should happen...), you can put in the
regular four - 40 amp fuses, 160 amps. (Those shouldn't blow while your
car is 'floored', climbing a long hill: four - 30s (120 amps) just
might, so we pick the 160.)
INSTALLING PLANETARY GEAR
For vehicle drive, a planetary gear is attached. For a
small car with 13" wheels/tires, a ratio of about 2.8 to one is ideal.
With larger wheels (the outer diameter of the tire is the critical
thing) or heavier vehicles, higher gear ratios will be needed.
1. Put the central "sun" gear on the motor shaft. put in the two bolts
to hold it in place.
2. Place the outer ring of the gear on the bearing holder plate on the
3. Insert and tighten the seven bolts in the seven outer holes in the
plate, locking in the outer ring.
4. Bolt the thrust plate to the nylon planet gear carrier.
5. Put some grease on the planet gears.
6. Slip the carrier onto the gears on the motor.
If you have metal planet gears, oil must continually drip on the gear
unit while it is in use, or it'll be damaged in relatively short order.
The nylon gears are really the only way to go.
Section 3: the
From this point on I'll focus on the specific "standard"
configurations and implementations of the Electric Hubcap motor unless
Motors need an axle between the stator and the
rotor to keep them lined up.
Normally it would seem obvious that an axle is required,
but originally I thought perhaps just mounting the stator in front of
the car wheel with the magnets fixed on the car wheel could work, since
the car wheel had its own axle, and the stator would be stationary. The
stator jumped and shimmied in every direction when the power was turned
on instead of simply turning the wheel. With no axle they would have
had to have been held in alignment by very solid steel castings for
The axle has to be strong enough to withstand
these same dynamic forces plus any external load that puts stress on
greater the torque of the motor, the stronger the metal of the axle or
the larger its diameter must be. The high torque of the Electric
Hubcap, for example, would quickly bend a typical 1/2 inch threaded
mild steel rod. A gear or V-belt pulley attaching a heavy load would
off even if it was held from bending. Car engines and
transmissions use hardened steel parts and keep them cool in a bath of
The thinnest axle for the EH motor should be about about 1
inch diameter hard steel. Luckily, there are trailer wheel "stub axles"
from one inch size up, which are not only suitable and available but
have commonly available standard sized tapered roller bearings to
match, which are virtually ideal for these motor rotors. A one inch (or
larger) hard steel bolt would also work, and doubtless they come in
many lengths to suit the fit for the application. Whatever the
assembly, be sure the retaining system can't come unscrewed or loose
and let a spinning rotor loose - put a cotter pin on the nut, tighten a
set screw in a hollow, or whatever it takes.
Sealed ball and roller bearings come complete with an
inner and outer bearing race, the smooth, hardened steel rings
that the balls or rollers roll on, and contain sufficient trapped
grease internally for many years.
The trailer bearings have a built-in
inner race, but a separate outer race. They should be well greased when
installed and occasionally afterwards. One type of outer race is used
for both 1" and 1-1/16" trailer wheel bearings, so a single type of bearing
hub can be used with either size axle, and this is the size
selected for the 'standard' Electric Hubcap motor.
Dexter is a popular brand of trailer axle
components. Many others can be found on the web.
Seemingly "standard" part numbers for the bearing parts are:
Bearing Outer Race: L44610
1" I.D. Bearing: L44643
1-1/16" I.D. Bearing: L44E5453 (if I've read the tiny, splotchy,
engraved print right.)
3-3 Bearing Hubs, Turning Bearing Hubs
The hubs are made from cast 1-1/2" I.D. pipe couplings
threaded on the inside at both ends, whose inside diameters are over
1-3/4" in order to fit over the steel pipes, and whose outside
diameters are consequently well over two inches. The length of the ones
I'm getting are about 2.2". These are turned on the lathe to fit. They
are as ideal as a non-custom part could be, but unfortunately I can't
vouch for the dimensions being in any way standard. Another batch from
another company may be somewhat different, eg a different length, or
may not even be suitable.
There are two ways to turn the hubs. In all the turning,
be careful: the size goes from "nope, still too small" to "oops, now
it's too big!" with a surprisingly small amount of turning.
The first way is utilized if the lathe is too small to
hold the rotor with the welded hub. In this case, the hub is welded by
itself, and welded to the rotor afterwards. The alignment is bound to
be poorer than if the tenons are turned after it's welded into place.
First the hub is centered on the lathe as best it may be, and one tenon
("socket") is turned to accept a bearing race, then it is turned around
and the other tenon is turned. Then, the outside and end of one face is
turned to fit in the center hole of the rotor disk as well as possible.
it should fit through just flush or a bit more. The outer face of the
other side is turned flat so some sort of seal can be fit in. At
the moment, a very short length of 2" ABS plumbing pipe is being used
as a seal between two differently rotating hubs. I suggest also turning
the outside diameter of that end so that an ABS outside coupling for 2"
pipe is a smooth sliding fit. (The seals are the most vaguely defined
remaining aspect of the entire 'standard' construction as of
* The outside of one end is turned to fit
squarely in the center hole of the rotor.
* A tenon is made on the inside of that end to fit a 1" / 1-1/16"
trailer bearing outer race, extending in about [try] 24mm.
- A bearing seal or cap, as well as the bearing race, goes
in that tenon.
* A similar tenon is made on the other end, but only [try] 7mm
- Only the bearing race goes in this tenon, and it sticks
out a bit.
- These tenons determine the spacing between the rotor
and the stator, which should be about 2", and the length of axle left
over to put the end nut on, plus allow for bearing seals.
* a simple greased rubber or plastic sleeve fitting closely over the
protruding bearing races might make a good bearing seal.
* or: The outer face of that side is turned smooth to accept an axle
(one side) or a pipe or tube to hold the seal piece (the other one)
There's a really tricky part to this: The welded end of
the hub actually shrinks a bit during welding, so the tenon needs to be
turned a bit oversize: the ring has to fit quite loosely. Otherwise, it
won't go in at all after the welding. This is another reason for
turning the tenons after the hub is welde if possible.
Finally weld the hub onto the rotor, following
instructions in 3-4.
It the lathe is big enough to turn the rotor with the hub
welded to it, things are easier. (I had to chop 1/4" off my lathe's bed
with a zip disk, to make the 5" radius gap just that vital little bit
wider. Then it was big enough.)
In this case, center the hub in the 3-jaw chuck as best it
goes, and turn the outside of one end to fit in the rotor. Then weld
the hub onto the rotor, following instructions in 3-4.
Bolt the assembly onto the large lathe plate and get it
turning true and square. Turn the bearing race tenons as above.
Another option is a trailer wheel hub. With the '6129'
problem arises that the hub's wheel flange won't fit into the hollow of
the rotor. If a good fit of rotor and stator can't be arranged, another
rotor should be considered, such as a Honda
brake rotor (which is 10" diameter and has an exactly big enough center
hollow but unfortunately has fins, making it heavier and harder to
3-4 Welding Bearing Hubs
I made a clamp from a piece of angle iron and two bolts to
hold the hub square in the hole for welding. Drill holes for bolts in
the angle iron (or whatever) 100mm apart to match the lug bolt holes in
the rotor. put the angle iron over the hub end and put the bolts
through the holes in the angle iron and the rotor. Do up the nuts.
(Threaded holes in the angle iron might be an improvement.)
If the (turned flat) end of the hub sticks through the
rotor by just a bit, you can check for square with a straightedge. But
beware that it usually moves when the first weld or two are tacked on -
adjustment may be necessary. This creates the worst alignment problems
if the bearing race tenons are already turned.
This is a bit of a tricky welding job. Both the hub and
the rotor disk are made of cast steel. Some even say "You can't weld to
cast metal." I'm not an experienced or knowledgeable welder and I had
problems initially with cracked welds and very weak joins or no joins
at all, but I asked my neighbor and at welding supplies and got
valuable advice. It can be done well with specific techniques and
First, there is special welding rod for cast metal, or
some stainless steel rod types work well. Ask, and take whatever they
have that they recommend, or take welding rod "for stainless steel
tubing". I've been using 3/32" stainless rod, which disappears rapidly
into the joins.
A second thing is to pre-heat the metal. I used a
'swirljet' propane torch (with which one can even braze small parts)
and didn't even get all that metal glowing. I would have liked to get
it still hotter (dull red hot), but even so it was far more than 'warm'
and it seemed to help make the joins stronger.
None of the joins to the hubs seemed to have a problem at any time.
Without the pre heating, some of the welds seemed to crack, probably
while they were cooling, and the joins were weak between the weld and
the rotor metal.
The third thing is to crank the welder's heat way up near
or to the max. Otherwise, or without the preheating, the join from the
weld metal to the rotor metal will be weak. Get the weld bead melting
into the rotor, then attach it to the hub, which is easier.
Finally, weld all the way around the circle, not just a
With my first unsuspecting hub welding jobs, trying to
hammer a bearing race into a tenon that was too tight caused the welds
to break off where the weld met the rotor, and the hub came off. When I
did all these things, I tried pounding the next two rotors quite
heavily with a hammer to no effect. Being somewhat timid, I stopped
short of using 'ultimate' force that might crack the hub or rotor metal
itself regardless of welds. It seemed strong enough. Perhaps another
time on a 'discard' rotor and hub, I'll try that and see whether the
weld or the metal itself gives way first.
Section 4: The Stator
The stator compartment is a big "hockey puck" disk formed
from the nine electromagnet coils, sandwiched between two polypropylene
rings. Also enclosed is a circuit board with the three magnet position
sensors and a temperature sensor.
The circuit board is mounted on the inner ring such that
the magnet sensors are in the spaces exactly between four adjacent
coils and thus near the spinning rotor magnets, and the temperature
sensor is in close proximity to the side of a coil.
electromagnet coils are energized by the
power mosfet transistors in the motor controller, to drive the
supermagnets on the rotor around the rim. The magnet sensors indicate
to the motor controller which polarity of magnets is currently where,
to continuously co-ordinate the coil switching with the rotor rotation.
The sections of this
chapter outline the making of each of
the individual stator components.
Stator outer ring with coils ready for wiring.
(Used very old #11 magnet wire with cotton insulation: bulky but it
Shaft bearing cup holder is installed at center.
4-1 The Stator Rings
The rings that sandwich the stator coils are cast from
polypropylene fabric ("landscaping fabric"), which is lighter and
stronger than fiberglass, in epoxy resin, which (I believe) takes heat
better than polyester resin and is less brittle. The rings are then
spray painted with polyurethane higher temperature insulating spray
paint. They are very tough. With enough pressure they will flex a bit,
but they are not prone to cracking.
The inner ring has a 4" hole in the center. The SDS
coupling of the rotor will protrude slightly into this hole, and the
remaining gap around it allows cooling air flow.
The usual stator is the '6129' disk brake rotor disk. The
side cast with the raised hub is considered to be the "outside", while
the hollow-centered "inner" face, or just "the face", faces the magnet
rotor. The design size is 10.125" diameter, and this rotor is about
9.975", so the coil cores on the face stick over the edge about 1/8",
as (theoretically) do the magnets on the rotor. Except for this slight
deviation, and for the fact that the machined flat face surface is only
1.5" wide instead of 2", the 6129 rotor is as close to "perfect" as an
off the shelf part made for something else entirely is ever likely to
There are 18 holes of 1/4" diameter to mount the 9 coils.
There are also threaded holes for 1/4" bolts (drilled about 7/32"
diameter and tapped 1/4"-20): 6 for mounting the magnet sensors, two of
which double as motor mounting holes, and two or four on the opposite
side also for mounting the motor. One extra 'mounting hole' is drilled
to allow inserting bolts or threaded rods in three holes 120¼ apart to
screw in and push the stator and magnet rotor apart, as the magnet
rotor is powerfully attracted to the stator when they are in proximity.
The mounting holes are positioned in the gaps between the coils, which
occupy most of the surface except in near the center. Three of the
holes for mouting the magnet sensors are under coil wires, and care
must be taken to put only very short bolts into these holes (3/8", or
1/2" with lock washers, plus the magnet clamp thickness) to avoid
damaging the coils.
There are also (at least) four large holes in the 100mm
lug bolt pattern in the raised center hub of the disk, which may be
used for mounting or for cooling air intakes. Another large hole
(optionally two on opposite sides), at least 5/8" diameter, is usually
drilled in the side of the central hub for the three heavy coil
4-2 The Bearing Hub
The bearing hub is covered in Chapter 3: The Axle.
If, as is usual, one is attached to the stator, it must be welded on,
or a trailer wheel hub must be bolted on. These subjects are also
covered in earlier chapters about putting together a matching set of
rotor, stator. axle and bearings.
4-3 The Coils
It's not difficult to wind good coils, but it
time consuming. Turquoise Energy sells them finished, or resells the
iron powder cores alone.
Supplies required for each coil:
* about 220 grams/8 oz/12m of #14 AWG magnet wire (pref. 150¼c+
insulation) [total for nine coils: 2Kg or 4-1/2 pounds -- local motor
shop or web sources] OR 4m of #11 AWG magnet wire per
* T200-26B iron powder toroid core (Mfr: micrometals.com)
* High temperature epoxy, pref. thermally conductive epoxy
* Also required is a coil winder jig (see picture) and a
spool(s) to wind
the cores in on. [bearing axle for coil winder: motor shop?]
Winding the coils
The coil cores go on a 3/8" threaded rod with two shaped
plastic side washers (that epoxy won't stick to) and a nut on each end,
that together form a spool an inch
wide to wind the coils on. I thread a handle onto the bolt to turn it
with, which goes up against the outer end nut. To speed production, I
have several sets of spools, since the coils must stay on the spools
until the epoxy has set.
The spool goes into a "drill chuck" on a mandrel with
bearings, which is C-clamped to a table. It's fast, easy and does a
neat job. In lieu of a chuck, probably a coupling nut from the mandrel
axle to a threaded rod would work - or maybe just put the spool and a
nut and the handle right on the mandrel.
When the spool is assembled and mounted, I mix a little
hi-temperature epoxy and start.
I've been using "thermally conductive"
epoxy from MG Chemicals (electronics supply store) to conduct the heat
quickly to the surface where cooling air reaches it and prevent
internal heat build up.
Some epoxy is
painted onto the core with a small flux/glue brush, then the first
layer of #11 AWG magnet wire, 11 turns, is neatly wound starting at the
hole in the left side washer. (Leave a sufficient leed length sticking
out the hole. The leed has to be bent around so it doesn't tangle up
Holding the wire so it doesn't unravel (I put my hip
against the handle so the spool can't turn), paint epoxy over the first
layer. Holding and painting here is the trickiest part, but I haven't
come up with a setup to hold the spool and wire.
Then wind the second layer, 10 turns, ending back at the
start. Since there are only 21 turns in two layers, you're already
finished winding. Hook the wire around the slot so it won't unravel,
and cut it with sufficient length for the second leed.
Paint epoxy over the second layer. I put the coils in a
warm oven (65¼C) for a couple of hours for the epoxy to set. Otherwise
it can take a whole day. Once it's hard, the spool can be removed,
leaving the core with the solid mass of wire wrapped around it.
Left over epoxy and the brush can generally be saved
overnight in a freezer for use the next day, though it will very
Note: The coils can't be dipped in motor varnish and baked in an oven
(common motor process) because they are only rated for 70¼C - hence the
Coating the coils
A coating of ilmenite in sodium silicate (pottery/ceramics
supply) creates a path of lowered magnetic resistance from the wires
into the core. Magnetic flux that usually radiates into the outside air
and is wasted, is bent around and into the core.
Ilmenite (TiFeO3 mineral) combines paramagnetic properties
of titanium with ferromagnetic properties of ferrous oxide.
- small paint brushes (eg, 1/2" or 3/4" width)
- Two small jars with lids (for mixed plasti dip and mixed ilmenite in
- large plastic jar with lid (to shake primed coil in ilemite powder)
- Organic vapor filter mask and or good ventilation
- newspaper or plastic sheet (for spills/slop)
- Performix PLASTI DIP (primer)
- Toluene (methyl benzene) solvent to thin plasti dip
- Sodium Silicate, AKA "Water Glass" (liquid or add water)
1. Put down spill sheet. Put on mask or open windows or...
2. Pour some ilmenite powder into the large jar
3. Pour some PLASTI DIP into a small jar. (Try to re-seal the original
container in a plastic bag or airtight container so it doesn't dry out.)
4. Thin it a little with toluene
5. Add some ilmenite. Mix.
6. Bend the coil wires around to hold coil off ground (This is also to
'center' it in the big jar later).
7. Paint a coil with the mix.
8. Put the coil in the in the large jar of ilmenite powder, put the lid
on, and shake it or tumble it around.
9. Shake and brush off any excess ilmenite powder (back into the jar is
good). Set it aside for paint to dry.
10. Repeat 7, 8, 9 for each coil. Then close the mixed paint jar for
next time, and clean the brush with toluene, seal it in a plastic bag
to keep it soft for next time, or discard it.
11. Let the paint dry on the coils.
12. In the other small jar, pour in some sodium silicate.
13. Mix as much ilmenite as seems to want to go in to make a creamy
chocolate sauce. (It gradually
separates and becomes harder to re-mix, so don't make a bigger batch
14. Paint the primed coils with it.
15. Heat a cooking oven to 240¼F/115¼C.
16. Put the coils on a baking tray and heat them for 20 minutes or so.
The sodium silicate dries and becomes insoluble above about 95 to
105¼C. (Repeatedly heating the coil cores above 65¼C will gradually
degrade them, but a tec person at micrometals.com said a single short
heating to 110¼C should be fine.)
17. Close the jar, clean the brush in water.
Once the coating is dry, it's baked in an oven for 10-15
minutes at 110¼C. (Although this is above the 70¼C temperature rating
of the cores, a tech person at the core manufacturer says it's okay for
the short duration.) The reason for this is a peculiar quality of
sodium sulfate: It's initially hydrated and water soluble, but at
95-105¼C, it loses its water of hydration and becomes insoluble.
The number of turns was
by making motors and measuring the currents.
The maximum coil currents were to be 30 amps, the maximum value for a
coil of #14 wire of this description according to a "rule of thumb"
calculator on the web. That's 90 amps per phase. It's all approximate,
based on heat and how fast it is dissipated. The heat increases with
the square of the current though, so it rises fairly rapidly above the
maximum current density. If the currents are too high, the coils will
overheat and burn out. (You've probably burned out an electric tool or
two by overloading it?) 60 to 63
turns is in range for 36 volts - don't start a sixth layer of windings
to get an
extra turn or two.
winding jig. The bearing spindle (left) can be had, eg, at a
shop. The drill chuck with the same threads was a separate purchase.
The spool is a short piece of cheap plastic rod (turned on a wood lathe
for the big washers) on a 3/8" threaded rod. A nut holds the inner end
while the threaded handle holds the outer. Turning backwards winds the
handle off, and the outer washers are removed to release the coil of
wire. Later, the rear washer was faced by a Ôwasher' of metal cut to
fit on the spool, which is pulled to push the coil off the winder from
behind - that works better.
#15 wire is too light for
the motor currents. #13 wire would reduce copper losses and heat, but
the coils probably won't fit on unless the nominal stator
increased, eg to 10.5". (If you have trouble getting #14 wire, each
three AWG gauge sizes is half the cross section, so you can try two
strands of #17, soldered together at each end. That gives the same
cross section of wire. But it's almost bound to be a bit
bulkier when it's wound -- I hope it will fit. Going the other way, you
could wind the three coils of each phase in series instead of in
parallel, each with 21 turns of about "#9-1/2 AWG". But #13 magnet wire
and heavier is less available than thinner gauges.)
Coil Bolt Holes & Template
The nine coils are attached at 40¼ angle
intervals around the rotor.
The bolt holes are all in-line about 0.9 inches in from the 10"
at 8.1" diameter. Select one lug bolt hole as "north" and center one
coil on it. The bolts are #10-24, so drill 3/16" holes in the outer
plate and 1/8" holes in the inner. The bolts thread into the inner
ring. The distance between holes for each coil is .75" .
Use 1-3/4" long bolts. Put flat washers under each
Only the wide gap between rotor magnets and stator coils
the clearance and leeway to permits the thick epoxy ring between the
coils and the magnets on the rotor!
up the coils
It is preferable to face the leads inwards and do the
wiring in the
center unless your hub arrangement leaves insufficient room (as may be
using a trailer wheel hub). This both keeps lead lengths
shorter and leaves more empty space for cooling airflow around the
The coils of each phase are wired in parallel and the
phases are "Y"
connected, therefore one side of all nine coils is connected together.
On the other side, the three coils of each phase, 120¼ apart from each
other, are connected together and to a heavy lead (#6 or
#8) that will connect to the cable from the motor controller.
There are a number of ways to bare the end of the wire for
The insulation can simply be sanded off, but that's usually pretty
tedious. One popular wind plant maker prefers to burn it off the ends
of the coil wires with a propane torch and then clean them off with
sandpaper. That works well. I prefer to scrape it off with a small
sharp knife (eg: pen knife, paring knife, not exacto knife), and clean
it up with sandpaper. (Somewhat more tedious, but I've never burned
myself at it!)
Make a ring of about #10 wire to attach the "center point"
to. This should be soldered to all the wire ends going clockwise into
the coils (or the opposite, as long as they're all the same). It must
not connect to ground. I strip
some insulation off the end, then I cut the insulation the spacing for
of each coil and slide it down until there are nine bare spots the
right distance apart. Wrap with electrical tape - the awkward shape
leaves few options but tape unless you can manage to slip some sleeving
on to cover each join.
A piece of small diameter soft copper pipe (eg 3/16" I.D.,
used for oil
or propane tank connections) is about right to stuff in three coil
wires in one side and the heavy lead (#8) in the other. These are then
crimped and insulated. (pieces of large diameter wire/cable insulation
sleeving... or electrical tape(?). Forget heat shrink as the wires may
quite warm - heat shrink isn't generally used in motors.)
Crimping the leads:
The three coils on one side, the lead on the
other, using a piece of copper propane pipe as a large crimp connector.
(Two wires are the #14 coil leads; the third is a #10 wire - the coil's
lead was too short.) A piece of sleeving is then slipped over the bare
On the ends of the heavy leads, use Anderson Power
amp Power Pole connectors. These are the only physically
compact suitable plugs I've found. You can buy single connector units
and stack three to get a three position plug and socket. The plugs and
sockets of the single units are identical - you just turn
one over and they mate. There are supposedly different colored plastic
bodies (eg, to
identify the three phase wires), but I could only get black and red.
I found the Power Pole connectors at an electronics store,
not at any
electrical supply. Big marette connectors ("wire nuts") can of course
be used, but they make more chances of shorts, bad connections,
and crossed wires, some of which which can blow the motor
Hall Sensor Circuit Board & Cable
The hall/magnet sensor circuit board (which also has a
motor temperature sensor at one of the coils) is held with two machine
screws threaded into the inner stator plate/ring.
Section 5. The Magnet Rotor
First magnet rotor with polypropylene strapping and epoxy composite to
retain the magnets.
A PROTOTYPE Magnet Rotor with a unique "skip tooth" configuration
for sharp transitions between norht and south:
yellow is south poles up, black is north poles up.
What this really does for torque ripple is untested.
However, the magnets were simply glued with epoxy glue to the rotor:
GLUING ISN'T GOOD ENOUGH - the magnets can fly off like bullets at high
RPMs! (and some have done so)
The neodymium, iron and boron supermagnets (Nd:Fe:B, NIB
or 'rare earth' magnets)
are very powerful. It is easy to get nonchalant, but one or two magnets
can do serious injury. Never get your finger between two of them! A
rotor with a dozen could be deadly. If two magnets get stuck together,
there is a special jig to get them apart safely. One of the reasons I
chose the 1/2" x 1" x 2" magnet size for hand-made motors is that I
would want a machine to handle supermagnets any bigger than that. Also
they're the most common and cheapest large size to buy... perhaps for
the same reason.
Be sure before you go to assemble the rotor and stator:
sure the rotor
can't slide down all the way to the stator.
To avoid having your fingers potentially mashed, always hold
magnets, never with the fingers on the
faces of the magnets, and keep them off the inner face of the stator
I usually put 3 wooden one+ inch thick wedges on the
stator, which I pull
out in steps once the rotor is resting on them. I pry up with a 4th
wedge to get each one loose, and lower it a bit at a time until it's in
When the magnet rotor is assembled, place a couple of
layers of thin (flexible) sheet steel over the magnets as a safety
measure, and put it in a box with some styrofoam over it as well.
1" thick foam safety cutout.
The pieces of sheet metal
magnetically clamp it to the magnets.
That this seemingly innocuous rotor is a very dangerous piece of
equipment can hardly be overstressed. The magnet rotor may be thought
of as something of the nature of a loaded rat trap: Working with it is
a case when simply moving
slowly and deliberately won't protect you from sudden and perhaps
serious violence from a slight misstep.
handling the magnets, magnet placing jig
Up to six magnets can be placed without too much danger, but as more
are added between, things get very scary without a safety and placement
guide. Here is the latest magnet placement template, top and bottom
My original magnet placement
template, top and underside views.
Adjacent magnets are covered to prevent magnets accidentally clamping
(woe to any flesh in between!), and this has come in handy occasionally.
With opposite adjacent magnets, it takes a strong grip to prevent them
from flipping, jumping sideways, etc.
dogwood (oiled) was just too beautiful to put ugly screws into from the
It's shown as originally set up for the 10.5" diameter rotor size
with 18 magnet
positions. (NNNSSSNNNSSSNNNSSS) However, 18 magnets is more than are
needed (and brutally magnetic). I later made a new base part for 12
magnets at 10" outer diameter.
The black mark at the entrance to the slot is some epoxy glue. As you
can imagine, it's impossible at some point in the
insertion to keep the magnet from snapping down onto the rotor.
(*Somewhere*, I had pictures of actually putting the magnets on the
rotor with this jig. Now I can't find them!)
Once the magnets are
in place on the rotor and the epoxy has set, 2" side polypropylene
strapping is cut into lengths with angled ends. This is epoxied onto
the rotor and magnets to from a continuous ring around the rotor and
secure the magnets into place. This is vital, not an option - the
magnets will fly off eventually without it, and they fly like bullets.
Installing the epoxy coverings on a magnet rotor.
(this prototype with disk brake rotor and left-over + used magnets.
The epoxy protects the magnets from further oxidation.)
Mounting the Motor
(I plan to write another whole manual about electrifying a car with the
Electric Hubcap system. This section, which obviously needs a major
update, will stay with the motor making instructions until that's done.)
Brake Drum Housing Attachments
The mounting arms attach to the back of the brake drum housing behind
the wheel. At its center, the stator is firmly attached to the wheel by
its axle, but the arms are needed to prevent the stator from turning.
They absorb the rotational torque of the motor's thrust and braking.
The brake drum housing is strong enough to handle this force. Consider:
the brake cylinder mounts on it and it must be able to absorb the
torque of screeching tires.
There are two pairs of arms, upper and lower. The trickiest and most
"customized" part of the whole installation is securely mounting and
placing these arms so they are out of the way of all moving parts as
the suspension rides up and down from the top of its travel to the
The protruding arms of
the bracket were later cut shorter.
The stator straps were bent to meet these
First, the tire wall generally sticks inwards past the housing, so
bolted two thick steel plates to the brake drum housing to extend it
beyond the tires. Alternatively, the stand-off blocks could be welded
to the rectangular tubing, or the tubing could be bent to fit. (I had
to cut the rear block and do some bending of the lower arm anyway, to
get it past the shock absorber.)
For mounting, the brakes must be disassembled and holes drilled through
the housing Care must be taken to ensure the heads of the bolts are
clear of the brake shoes and mechanism, and don't interfere with
operation of the brakes in any way.
(In fact, the front mounting block here pushed on the parking brake
cable and the right side parking brake didn't work well, if at all.)
1" x 2" tubing wouldn't have fit in. I wanted 0.5" x 1.5" tubing, but
local stores only had the 0.5" x 1". I used that. It probably flexes a
bit more than is desirable.
To bend the elbows, first I bashed in the flat center section with a
hammer along the area to be bent, from both sides. Then I C-clamped
them to something roundish. I can't remember what it was, except that
it had a straight section and I used two big C-clamps, clamping the
short arm end, which left the longer center portion to push on.
I did it out at my "anvil": a flat solid rock sticking out of the
ground in the garden, with a 24 oz hammer. It was tough going with
nothing to really hold that short end, and I'm sure a very big vice
would have been most handy, or a really skukum work table that would
have held those C-clamps solid while I pounded.
Fitting and vehicle suspension considerations
(up-down travel of wheels with weight, bumps and potholes)
The bracket should be tested to make sure it doesn't hit the car at any
point in the travel of the suspension.
Jacking up the car on the body near the wheel will cause the wheel to
drop down relative to the car until the suspension "tops out". But that
usually moves the bracket into more open space. It's the other
direction where things usually get tight.
To push the car down one must add weight, and perhaps "jump" up and
down on the bumper. It should be ascertained that even when the
suspension "bottoms out" the brackets don't hit anything.
Once the arms have been attached,
they must be fine-adjusted - again
bent - to meet up with the stator arms for easy attachment. The best
way to do this is with a piece of rectangular steel that fits inside
the tubing, eg a 1/2" x 3/4" x 3' long steel rod. Stick it in the end
and move it around until the arm ends where you want it.
Stator Arms - Strapping
The stator is held on by strapping, eg, 1/8" x 3/4" mild
steel bars. These wrap around the outer end of the motor stator and the
ends insert into the wheel bracket arms coming around the wheels. They
are held by bolts. I drilled 1/4" holes in the arms, and matching
7/32" holes in the strapping, threading them
for 1/4" bolts. The bolts go through the outer hole, thread into the
strapping, and come out the other hole. Then a nylock nut goes over the
End of stator strap to connect it to the wheel bracket. [fix: Needs
& avoiding things that fall off while
Just a final safety reminder that the motor should be solid. "Nyloc"
nuts can be valuable for keeping bolts from falling out even if they
come loose. So can lock washers and "loc-tite".
Check everything carefully before enclosing it, and before taking the
car on the road. Listen for anything unusual as you start to drive and
for the first while.
Check again after 1, 5, 25, 100 and 500 Km.
The one-piece coil casting on my first prototype fell partway off after
some tens of kilometers, when some of the bolts came loose. (The design
was quite different from later versions.) Amazingly, it did it in a
parking lot. I stopped at once and removed it. No harm was done.
Potentially, it could have been on a busy highway with nowhere to pull
over. It would probably have broken right off and been a serious hazard
for cars behind!
Shaft (4140 HTSR machine shaft, 1" x 6")
Bearing Cups (outer races)
2 - Bearings
2 - Inner Bearing Race Mounting Plates
2 - Outer Bearing Race Mounting Plates
10 - 1/4" 20-TPI x 3/4" s/s bolts
5/16" Steel Plate Rotor
12 - Supermagnets
1m - 2" PP strapping
Rotor Compartment Cover Bell, PP-epoxy
9 - Coils
9 - Coils
9 - T200-26B Iron Powder Toroid
36m - #11 AWG Wire
Hi-temp, thermally conductive
Magnet Sensor PCB
3 - Hall Effect Sensors
AD590 ¼ Sensor
2 mach. screw
5-pin Trailer Plug
2-pin Trailer Plug
3 - APP 70A Power Connector Pins
3 - APP 70A Power Connector Housings
5 feet - Wire Sleeveing
Inner Stator Plate, PP-epoxy
Outer Stator Plate, PP-epoxy
18 - #10-24 x 1.75" Bolts
18 - #10 Washers
Polyurethane Spray Paint
Hubcap Specs. - NOT YET UPDATED
approximate nominal specs
Volts: 36-42 (nominal battery voltage)
Amps: around 127 (~90 amps max in each phase * sqrt of 2 = 127)
Watts (in): around 4570-5334 (V*A)
HP (out): around 5.3
Note: HP at estimated 75% efficiency at max powerout.
Efficiency will be
higher when operating below max. power, eg, 25% power in might be about
90% eff, yielding 1.6 HP.
RPM: 0 - 2000
Cooling: Fan (magnet 'fins') - moving air & convection; exposed
Air is drawn in at central vent holes near axle, is blown
outwards across the coils by the magnets - "cooling fins" - and is
expelled through air gap at stator rim.
Note: permanent magnet rotors don't get warm. Only the
stator needs cooling.
Overall diameter (with 12" I.D. "culvert pipe" PVC plastic cover): 13"
Rotor & Stator nominal Outer Diameter: 10" (The outer sides of the
coil wires protrude beyond 10".)
Overall Motor Length: Varies by spindle & rotors chosen.
Practical minimum length: 8 + 13 + 14 + 25 + 8 mm = 68mm or 2.7"
(Magnet rotor thickness + magnet width + air gap + coil width + stator
"rotor" plate thickness) -- excluding protruding nuts and bolts
Note: this excludes the thickness of the torque converter.
Coil Size: 1" thick circular disc, 2.65" outer diameter
Coil Wires: 60-63 turns of #14 AWG magnet wire wound on 2" diameter
cylindrical former, about .95" across.
Coil Cores: Strips of 1" long nail gun finishing nails, spray painted
(insulated) on one
or both sides and broken to length to create a laminated cylinder, 1"
tall x 2"
diameter. Two voids, centered on 1.5" apart left and right, are left
for 1/4" diameter mounting bolts.
Coil Iron Characteristics: The nails should not become magnetized when
rubbed with a
supermagnet. (ie, they should not be able to pick up other metal
objects. All brands I tried passed this test.)
Inductance: The individual 61 turn coils apart from the rotor measured
410 to 430 microhenries. A full
stator measured 396-397 uH between any two phases, and 176-179 uH
between any phase and the "Y" common point. (Coils in proximity, eg on
a rotor, interact magnetically to increase the inductance over a lone
coil, so simple math for series or parallel components doesn't work.)
"Glue": Finished coils are cast in high temperature epoxy or dipped in
motor varnish and baked. Then they are dipped in high-temperature flat
black enamel (stove paint) and the (accessable) excess is brushed off.
Stator: nine coils around rim facing magnet rotor magnets, spaced 40¼
apart. three phases. Each set of three coils 120¼ apart is wired in
parallel. Motor is wired in "Y" configuration, so one side of each coil
(eg the CCW lead in) goes to the center point while the other ends (eg
the CW ends) tie to the three supply wires, #8 or #6 AWG.
Gap, stator coils to rotor magnets: 1/2"-5/8" (13-16mm) nominal.
(There is an
optimum somewhere around here... a gap that is too small makes
excessive vibration and WORSE motor performance instead of better. A
gap that's too large provides less torque/power.)
Rotor Magnets: twelve - 2" x 1" x 0.5" Nd-Fe-B ("NIB") or other
supermagnets, nominal strength 35 - 45. They should be magnetized
through the thickness; ie, the large (2" x 1") faces should be the
poles. (Other sizes to make a similar magnetic field would also work
fine.) Note that these magnets double as the cooling fan fins.
Bare Motor Weight: 31-33 pounds
(with 6129r disks, two machined & welded-on 1-1/2" pipe coupling
bearing hubs, no mountings or covers, ready to fit torque converter
Some Mechanical Specs (applies to standard configurations)
Axle: Dexter 6" trailer stub axle with flange, 1" or 1-1/16" diameter.
Bearings: Trailer axle bearings, 1" or 1-1/16" I.D., O.D. per matching
Bearing Hubs: 1-1/2" threaded cast steel pipe couplings. Tenon depths:
7mm (inner shaft side), 21mm (outer, disk, side). Tenon diameters:
sized to trailer bearing races. Bearing hubs are machined, and welded
to brake disk rotor centers.
Motor Rotor & Stator: rear wheel disk brake rotor per Ford Escort
1991-2003, Mazda Miata 1993-2005, AS6129, Raybestos 6129R. 9.8"
diameter, hub rise ~1", 4 bolts, 100mm bolt circle.
Electric Hubcap is a trademark of Turquoise Energy Limited.