Development of the
Electric Hubcap Motor Family
BLDC Motor Controller
95% Peak Efficiency!
Evolving Mechanical Design
The Electric Hubcap Motor Family: Electric Caik
- Electric Hubcap - Electric Weel - Bicycle Wheel Motor
The Turquoise Motor Controller
The Electric Hubcap
drive systems were born with
the concept that supermagnets had such strong magnetic fields that
surely it should be possible to make a simple, lightweight "pancake"
motor that could turn a car wheel directly to propel the car. This
would bypass the regular
inefficient automotive transmission and drive train with their typical
30-40% losses of power between the engine and the wheels, so it would
take 2/3 as much power to propel the car, 2/3 as much battery substance
to drive the same distance, and 2/3 of the energy from the electrical
grid to recharge the car.
Then I thought of mounting this motor on the
of the wheel, where it would merely be an "add-on" accessory, and the
still be run on its regular fuel. That way, there only had
to be enough battery power for "typical" driving, rather than for a
maximum range limit, "untypical" further distance being covered with
the original engine rather the electric motor. Thus the concept of
"hybridizing" a regular car came into being.
This was a great idea in theory as far as the above
reasoning went, but a critical part doesn't work. The supermagnet
fields act against the electromagnet fields, and the electromagnet
fields are the same in any motor, supermagnets or not. A pancake motor
with enough torque to turn a car wheel directly would be too big in
diameter to fit on the wheel. A motor of smaller diameter that wouldn't
hit the ground would have to be ten times more powerful than it would
otherwise need to be in order to get sufficient torque for direct
drive, and hence it would be too long and too heavy to
fit on the
wheel - and it would need more power to run.
But everything was rather vague and such details
weren't clear to me when I began. So I hopefully made a "motor" with
supermagnets mounted directly on a plate on the car wheel, thus using
the wheel and axle
as the motor's rotor and axle. The stator with the coils mounted in
front of that
to make a "BLDC" motor -- which term I hadn't run across yet, making
searches for information unfruitful. The motor stator simply bounced
around. I finally worked out that 12 alternating magnets with 9 coils
had zero net thrust: every forward force was matched by a backward
force. It couldn't be made the same as the generator! It turns out that
for a three-phase motor there must be two magnet poles for every three
coils. Period. I did some gluing and ungluing of magnets to rotors in
those times, soaking the rotors in a solution that eroded away magnets
as well as epoxy.
Once it had a working axle to couple the stator more
solidly to the wheel - a "lazy Susan" bearing, and the
magnets were rearranged to a workable configuration, it turned. But if
the load got too
high for the frequency drive - I had made the wrong type of motor
controller for this motor - it simply lost all power and stalled.
After creating a more suitable stator and inventing for
myself a workable BLDC motor controller system that turned out to be
the way everybody else already does it, I had a wheel motor with some
power behind it. But an
unexpected characteristic of the
motors was that they worked mch better with a gap of over 1/2 an inch
the coils and the supermagnets, which meant the powerful fields of the
supermagnets acting with a small gap weren't available, a major factor
decreasing the torque over what I had originally guestimated in my
mind. Later I
found other axial flux motors of similar configurations have similar
In October 2008 I actually
got the car to crawl across a parking area with who knows how many
hundred amps going into the coils. I soon burned out the power MOSFET
transistors in the motor controller. In fact, I went through dozens of
them. I tried improving the motor design, but at the same time I
started limiting the currents the controllers would supply to
non-destructive values, and the new
system wouldn't budge the car at all.
Car driven - barely - by 2nd prototype Electric HubcapTM
driving a wheel directly, October 20th 2008.
Third motor, with improved coils, was then tried.
However, torque from such directly connected motors proved insufficient
for practical driving.
I started to realize there had to be some sort of gearing
between the motor and the wheel, and I conceived that a variable torque
converter would be the thing to keep the motor operating in its most
efficient range from stopped to highway speeds. Here the gap between
knowing what I wanted and and knowing how to get there was much
larger. I had
electronics and motor theory, and had wound and even made a motor or
two before ever tackling this project. I had never been a student of
mechanics... and except for some types which seemed unworkable for an
automotive on-wheel configuration, nobody else appeared to have done it
After spending a couple of years trying various futile
things, I diverted to something less frustrating and put the stator
that had moved the car into an
outboard motor, along with its 9" magnet rotor. They just fit in in an
open arrangement under the hood. Working on the motors again led to
their further evolution.
First Electric Outboard Motor Project, October 2010
Testing the 'Electric Hubcap' outboard, Nov. 6 2010
95% PEAK EFFICIENCY!
Soon I started testing the motors and found they weren't
efficient - in fact only around 50%. At first I wondered about losses
in the bearings, but it turned out the trailer wheel bearings had in
fact been an excellent choice. Then I noticed that a lot of the energy
went into heating up
the steel stator plate disk, even though it was over 1.5 inches from
the spinning magnets. Even the mounting bolts got warm. And the nail
gun finishing nail strips I was making into motor laminates were thick
compared to manufactured die cut laminates and so would have extra iron
eddy current losses.
I made a composite plastic plate of polypropylene
and epoxy with a bearing
moulded into it, and remounted
the original stator #1 on it. The difference was unbelievable! It soon
spun up to a dangerous RPM with very little power applied.
At almost the same
time, someone posted up a link to 'micrometals.com', who made iron
cores, mostly used for electronic switching devices. In their catalog I
found some iron powder toroid cores 2"
diameter by 1" tall. Wow - exactly my size! They sent me 9 samples and
wound the best motor yet.
I had been trying to create a better 'nanocrystalline'
core that would have very low losses, and found some interesting
materials (as well as creating an ewn glaze for solar collector cover
glass). I tried painting the coils with
paramagnetic rutile (titanium dioxide mineral) in sodium silicate
("water glass") to improve the magnetic circuit. The no load currents
dropped a further 15-25% or so. Then I
tried ilmenite (titanium-iron oxide mineral, again in sodium silicate)
on a second motor and it
was even better - 25-40% lower currents.
With these improvements, I now had a motor that was
perhaps 95% efficient! Yet it couldn't be said it was mechanically
EVOLVING MECHANICAL DESIGN
Occasional magnets flying off rotors at higher speeds
convinced me (a) to adopt a better system for attaching them and (b)
that the motors had to have a solid rim around the rotor compartment
for safety. Covering the magnets with polypropylene strapping allows
the motors to spin up to a couple of thousand RPM fine. They'll still
self-destruct if permitted to go up to somewhere between perhaps 3500
and 5000 RPM, or maybe even less. The original thin solid composite rim
(image below) still proved inadequate when such a speed was attained
and magnets broke off, and other deficiencies were shown from the same
failure, so I really beefed it up to 1/2" thick and otherwise improved
First closed body Electric Hubcap motor with polypropylene-epoxy body,
ilmenite painted donut coils with toroidal iron powder cores. (2011)
Paint is polyurethane with left side here still unpainted.
I then conceived that the coils with their hollow center
cores could be mounted held securely centered on "buttons" moulded into
the polypropylene-epoxy body rings, and improving molds continued the
process of mechanically
improving the design of the motor with each new one I made. By 2012 I
had good, efficient, safe motors.
2012 version Electric Hubcap
The ilmenite coil coatings didn't stick well and flaked
off, and it wasn't until late in 2013, as I developed the Electric
Caik size motor, that I found a rubberized primer it would stick to
I'd still like to improve on the magnet mounting on the
rotors. The motors could handle higher
RPMs if not for the possibility of having the magnets fly off the rotor
from centrifugal force, which (for the Hubcap size) seems to occur at
perhaps around 3500-4500 RPM or less,
which leads me to limit RPM to about 2000. (My basic BLDC motor
controller has no "smarts" to set a definite speed limit.) On the other
hand, at higher
speeds vibration can get pretty intense and energy is being wasted. In
practice, such magnet mounting improvement will probably consist simply
of a beefier
layup of PP strapping with more epoxy.
THE ELECTRIC HUBCAP MOTOR FAMILY: Electric
Caik - Electric Hubcap - Electric Weel - Electric Cycle Wheel
The original size Electric Hubcap Motor has 9 coils and 6
magnet poles. The magnets are doubled-up and hence there are 12
supermagnets on the rotor.
But the coils and the magnets are separate units which may be employed
in various configurations. The coils can be wound as 63 turns of #14
wire for 36 volts, or 21 turns of #11 wire, for 12 volts. If the 12V
coils are placed in series, three coils per phase makes 36 volts, so it
can be done either way.
The potential list of practical choices reads:
6 coils and 8 magnets, 24 or 36 volts, OD 9.25", torque '2/3'. This is
the Electric Caik.
9 coils and 12 magnets, 36 volts, OD 11.25", torque '1'. This is the
12 coils and 16 magnets, 36 or 48 volts. This would be a 'large
Electric Hubcap' and isn't in present plans.
18 coils and 24 magnets, 36 volts (72v is possible) This would be a
'double Electric Hubcap', not in present plans.
24 coils and 32 magnets, 36 or 48 volts, OD 28", torque '8'. This is
the Electric Weel, now under development.
In addition, one can envision magnets arranged around a
bicycle wheel and attached to the rim or to the spokes near the rim,
only an arc of coils instead of a complete circle stator, eg 6 coils,
driving some of the magnets in turn as they pass by the coils. This is
'incomplete' utilization of the magnets, but it would have the same
power as the Electric Caik, and should have sufficient torque to
direct-drive a bicycle to good effect with no gears. It would be a
silent direct drive motor with 'extra' magnets -- instead of gears. (If
you can't direct-drive a car, you can still use the concept!) At age
motivation for building this one is limited compared to when I was an
avid cyclist in my teens and 20s, but it's in my mind to do if I find
The torque of an Electric Hubcap motor at low speed is
around 1.5 foot-pounds per 10 amps of DC current from the batteries. As
the number of driving elements increases, so must the motor diameter to
fit them. The torque increases both with the diameter and the number of
elements, so almost as the square of the size. Hence the Weel motor,
with 2.66 times the driving elements and triple the effective driven
diameter, is to have about 8 times the torque of the Hubcap motor. That
might actually drive a vehicle wheel directly with no gearing. Two of
them for double torque on left and right wheels, certainly should.
The Caik motor was developed at the end of 2012. has
somewhat more torque per amp than I
This is probably a result of using 3/8" thick magnets
instead of 1/2" thick. Contrary to simple logic that says they're
weaker magnets so the torque will be lower, this results in a smaller
flux gap so the motor coils may be better coupled to the magnets. I'll
be trying the 3/8" magnet thickness on all the motors, and probably
Also three thin magnets (3/16" to 1/4") per pole in place of two
thicker ones to even out the flux, would be a good experiment. More
even flux may result in still thinner gaps. And that still leaves the
possibility of using larger and thicker but less powerful ceramic
magnets instead of the more costly supermagnets.
One concern of thin gaps is that I took advantage of the
thick gaps to put a wall between the "stator compartment" and the
"rotor compartment" so that trouble in one (eg, magnets flying off from
over-revving, or burned coils from excess power) will leave the other
undamaged. If I actually get thin enough gaps, there won't be room for
the wall and the whole design would have to change. I don't expect this
to happen with supermagnets, tho I may have to thin this inner wall and
reinforce the coil mountings via the outer wall if results are really
good with thin magnets.
Electric Caik Magnet Rotor
On another note, motors have to have air flow to cool the
coils. In the Electric Hubcap family, the magnets themselves act as the
blades of a surprisingly effective centrifugal fan. Air is drawn in all
around the rim of the stator compartment through a 'furnace filter'
strip across the coils to the center, where it goes through the central
hole into the rotor compartment, is flung to the outside by the magnets
on the rotor, goes around the outer edge of the rotor, and exits
through holes on the rotor end.
The high efficiency not only gives a bit more drive, but
it reduces heat generated and hence cooling requiements. For example,
95% efficiency has just a bit more thrust than 90%, but it has just
half the internal heat generation.
The Electric Hubcap and Electric Caik motors have been
created. The molds and jigs exist and they can be produced in small
quantities. Furthermore, the designs for the molds and jigs exist as
CNC files and more molds and jigs can easily be made. It is intended
that they are available to anyone who wants to build these motors, and
I'm willing to teach motor making.
Pieces for Electric Hubcap Motor Kit - 2011
(Case items have been improved)
The Hubcap motor is still intended for vehicle transport,
but still, after 5 years, awaits a successful torque converter to
enable turning cars into plug-in hybrids. The Caik motor was originally
intended for electric motorbikes and boats. The first one is in use as
a converted electric outboard motor.
Electric Caik motor mounted in Honda 7.5 HP outboard motor body
...reinventing the Weel
It is intended
that the Electric Weel molds and jigs be created next. The bike rim
motor is planned but if I'll have time for it I'm not sure.
In designing motors for electric transport, I had the
thought that we
all, even axial
flux and brushless motor designers, have been thinking inside a very
box about what a motor is or should be, selecting dimensions and
proportions that aren't appropriate for vehicle drives, and then having
to gear them down to get sufficient torque to budge a car, incurring
the efficiency losses and additional expenses and problems inherent in
gear and transmission systems.
This motor bursts that box in a 15 KW pancake package
inches in diameter and only about five inches thick, with the force
arrayed only around the outside rim. This configuration gives it nine
the torque of a typical high-torque axial flux supermagnet motor made
for vehicles, but with only three times the power. I expect it has the
speed range to directly match a vehicle
wheel. I intend to connect it directly via a CV drive
shaft to a front wheel (or to a differential attached to the
though other couplings might also prove
The design of the Weel calls for the unmodified motive
three Electric Hubcap motors would use: 24 coils, 32 supermagnets, and
controllers. Each controller, fed from the same control signals, drives
1/2 of the coils, at 48 volts. The Electric Hubcap motor and matching
Brushless Motor Controller have undergone three years of development
and these components should impart the same 95% efficiency and
to the Weel.
It was originally to have had 27 coils and 36 magnets, the
"Triple Electric Hubcap", driven by three 36 volt motor controllers and
having 9 times the torque of the Electric Hubcap. But since it's so
large, I decided to build the stator as 8 separate octagonal sections
that bolt togetther. Since these would have had to have 3.33 coils on
each equal section, a 24 coil configuration was decided on, 3 per
section with magnets adjusted to suit and (hopefully) using only two
motor controllers, at 48 volts.
The steel parts for the prototype Electric Weel
motor, cut by
The rotor is made in two parts: a thinner (1/8") plate for lightness
with a ring (3/16": total 5/16") for sufficient magnetic
conduction thickness at the rim. The original 36 magnet positions
are marked around the rim. (Now there are to be 32 magnets.)
The stator will be composite plastic outside in the vicinity of the
center plate is 3/16" steel for strength and stiffness.
The eight Polypropylene-epoxy rings will attach to this metal center
forming an octagonal body.
The heavy axle and bearings will handle the high torque and loads.
[Thinking back to large sawmill blades of yesteryear, it may be that
rotor would best be "cupped", hammered to a slight bowl shape.
As it spins, it stretches slightly around the outside edge and becomes
flat. But blades are cupped to specific RPMs, and for a variable
speed motor it may be necessary use a thicker rotor plate, or to weld
ribs onto it. (I wonder if there's anyone still around who knows
how to cup big sawmill blades! Anyway, this rotor is 26", not 48" or
larger.) But I digress.]
Owing to all the other
concurrent projects, the first weel motor is still not
completed and running, and now the prototype has been sold as a
'kit' to be used as a generator for a hydro power project.
The motor controller, as mentioned, started out as the
wrong type for the job: a variable frequency drive. Starting at low
frequency, the motor spins up synchronously with the frequency. For
this reason, three phase motors with permanent magnets were called
synchronous motors, or "permanent magnet synchronous motors" (PMSM)
when I was in school in the 1970s, and I hadn't heard the now usual
term "brushless DC" motor (BLDC). This caused most of my trouble in
looking for information about them. The main trouble with operating
them with a frequency drive is that if the load is too high they get
out of sync, lose power, and suddenly stall. Used on 60Hz AC power as
three phase motors, they need a starter motor to get them up to speed.
The integrated circuit I stumbled on for this controller,
the IR2130, proved to be a very good 3-phase MOSFET driver chip family
for the sort of motor power I'm running, but I didn't recognize it
until I had taken some
unproductive diversions along the way. One of the 'diversions',
however, led to a major advance. But I'm outrunning the story line.
I created a method with three optical sensors so that the
frequency of the 'frequency drive' became synced to the motor rotation
instead of the motor to the frequency, and the power and hence speed
was regulated by pulse width modulation. This is what moved the car
(barely) in 2008.
Then I found out that my fine sensor system 'invention' is
the way everyone does it, except using Hall (magnetic) sensors to pick
up the actual magnet positions instead of optics adjusted to align to
them. And finally somewhere I picked up the term "BLDC" off a couple of
web sites, and - now that I had already done everything wrong and
finally gravitated through trial and error to the right techniques -
info became much easier to find.
Another 'diversion' I took was to think in terms of the
sort of high voltages everybody seemed to be using for electric
vehicles, 144 volts being common for hybrid cars. I started thinking of
120 volts from 10 batteries. The day I carefully wired up 60 volts of
batteries in sequence and tested things... and then casually grabbed
the 60 volt wire to disconnect the batteries... I started thinking
about electrical safety. Nothing happened, but what if that had been
120 volts? What if it had been damp out? That careless grab could have
ended my career.
I decided that after all, power equals volts times amps,
and to run at a safe voltage just needed more amps. I took the three
coils in series on each phase of the motor, and rewired them in
parallel instead. That made the motors 40 volts instead of 120, at
three times the current. Each coil has exactly the same voltage and
current, so the motor is really exactly the same. Since it's hard to
get 40 nominal volts from 12 volt batteries, it became 36 volts.
I put away the high voltage MOSFETs and found lower
voltage ones. To my surprise, they could be had rated for
commensurately higher currents, like 120 amps continuous and much
higher for brief periods. It seems MOSFETs are also the same power
whether configured for high or low voltage.
The chief differences then between high and low voltages
are electrical safety and the thickness of the wires needed. In a
building, long runs of very heavy wires would be prohibitively
expensive. In a car, the longest run is if the batteries are in the
trunk and the motor up front.
I started to wonder why we didn't hear of more
electrocutions of amateurs converting cars to high voltage electric.
For all the discussions I had on the subject, no one enlightened me and
I didn't find out until I got a converted car myself, that the entire
high voltage system is ungrounded, floating. In theory, this means that
any point of high voltage wiring touched by a grounded person becomes
the ground point... as long as only one person touches only one point
a time, and nothing else grounds the circuit somewhere else. In
practice, dust and moisture on the batteries usually cause enough
conduction to give the worker a tingle or a shock. But it's enough to
prevent a count of bodies of DIY - and factory - electric car workers
from piling up.
Having never considered the floating system idea,
conscientiously grounding the negative to the car body, I could easily
have been killed by high voltage had I continued in that direction. I
still consider lower voltages to be the way to go. If the power needed
can be kept down by 'ultra efficient' motors and transmissions, the
wiring isn't too heavy. But I also plan to
adopt the floating system idea. My larger transport motors such as the
Electric Weel will then go up to 48 volts with little worry about
[Last update: 2014/05/14]