Electric Hubcaptm
Motor Building Manual


Latest version, 'standard' configuration
(without stator air screen)
...5 KW at about 30 pounds.


Second latest version in cross section: shaft, rotor compartment, stator 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The disk brake rotor has now been replaced by a custom flat plate rotor,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" thick.


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! )

Note:

This motor needs speed reduction to the car wheel. Only a very oversize motor would have enough torque if directly connected. A a versatile, 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 - 2011/04/10.)

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 allow highway driving on gas.

Disclaimer:

This publication is free information about a new invention 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 warned!


Introduction to the third version

   In the previous versions of this manual, various ways of putting together Electric Hubcap type motors "from scratch" from automotive brake 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 new 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 anywhere on any length of one inch machine shaft. The body and stator parts have been molded as three rings of tough, light, strong polypropylene-epoxy composite material. The magnet sensors are mounted on a single circuit board, available pre-wired.

   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 'from scratch'.

   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?
Electromechanical Basis
Electronic Workings
Electromagnetic Workings
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___

What Motors

3. Axle/Shaft, Bearings, Bearing Races & Hubs

3-1 Axle/Shaft
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
SUPERMAGNETS ARE VERY HAZARDOUS! so READ this part and follow instructions!
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)
Around-the-wheel Arms
Stator Arms
Nyloc Nuts & things that fall off while driving

7. Appendices

How long does it take to build?
Electric Hubcap Motor Specs

Section 1. Motor Workings

Electric Hubcap Overview

   The Electric Hubcap (or "Hubcap Motor" or "EH") is a 'cake' shaped three phase, brushless, axial flux, supermagnet motor. It can be purchased as a kit, made from pre-made parts plus other and 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; 5 kilowatts).
   It is probably about the most efficient 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 path, bending much of the normally wasted field that radiates outwards into the air back around and into the core. I lack the time at the 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 optimally to 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 applications, and as such has so far been configured for 36 to 42 volt DC operation, with a 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 batteries, though not where long runs of cable would be required.

   In the brushless motor, magnet sensors and a solid state motor controller replace the 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 Catalog)

   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 to the 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 battery 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 maximum" 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 be used 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 complex mechanism, a variable speed lathe motor (eliminating V-belts and pulleys), a marine, outboard, or submarine propeller driving motor, and so on. 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), another 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 (120 amps) MOSFETs (= metallic oxide semiconductor field effect transistors) that drive the motor coils.

   Three Hall effect magnetic switches, one per phase, synchronize the six-state motor coil timing sequence with the rotation of the supermagnets on the car wheel.
   A potentiometer (for vehicle use it's connected to the accelerator pedal) 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 and 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 separate manual for making the controller, the Turquoise Motor Controller Making Manual. Another manual is planned for making the mechanical torque converter, and Installing Electric 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 of the supplied voltage.

   The three phase "Y" motor wiring configuration is used, and the 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 are still 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 operation.

   The motor type is variously called a "permanent magnet synchronous 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.

Electromechanical Basis

   The Hubcap Motor's stator has nine cylindrical toroid 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, usually a length of one inch diameter machine shaft, with about a .55-.60 inch gap between the stator electromagnets and the rotor supermagnets. A unique part called an "SDS Taper Lock Bushing" attaches the rotor solidly to the 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 energize in 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 nothing useful.

   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 works in conjunction with three magnet polarity sensors, one per phase, input to a solid state motor controller. The controller not only 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 width modulation ("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 mosfet 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.

The Supermagnets

   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 from.
   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 somewhat varying torque ripple characteristics, but it won't much affect motor efficiency or maximum power.

    Unlike electromagnets, the supermagnets are always at full strength, and the permanent magnet supermagnet motor has much more torque at 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 the stator 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 electric conversions, generally mounted under the hood and coupled to a CV front wheel drive shaft.

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 would 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 pieces, 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 the current.
   To further digress into the subject of wires, thereÕs a reason copper 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, but 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 energy.
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, squashed,...) is 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 force radius.
   Increasing the diameter without adding more coils and magnets (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 a high 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, current lags 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.)
Electronic Workings

   Electronics are an important part of any modern car motor design. In the case of the Electric Hubcap, they energize the coils in synchrony with the rotation 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 consecutive coils.
   The three magnet outputs can directly feed the motor controller chip to actuate the correct coil drives, to generate the 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.
Electromagnetic Workings

   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, create magnetism north, off and south in the coils. Here is the sequence:

¿ A
---------------N--------------
  
--------------S--------------
  
¿ B S-----------  
--------------N--------------
   -------------S
¿ C  
--------------S--------------
  
--------------N--------------
  0¼ 60¼ (20¼) 120¼ (40¼) 180¼ (60¼) 240¼ (80¼) 300¼ (100¼)

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:
State Phase A
coils (0¼) 		Phase B
coils (40¼) 		Phase C
coils (80¼) 		North Rotor Magnets South Rotor Magnets
0 36v (N) 0v (S) - 10¼ to 30¼ 70¼ to 90¼
1
36v (N) - 0v (S) 30¼ to 50¼ 90¼ to 110¼
2 - 36v (N) 0v (S) 50¼ to 70¼ 110¼ to 10¼
3 0v (S) 36v (N) - 70¼ to 90¼ 10¼ to 30¼
4 0v (S) - 36v (N) 90¼ to 110¼ 30¼ to 50¼
5 - 0v (S) 36v (N) 110¼ to 10¼ 50¼ to 70¼


   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 rotor magnet 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.

The truth table for each phase of a typical MOSFET driver chip is:

Input for HIGH drive MOSFET
(phases A, B & C are alike) 		input for LOW drive MOSFET
(A, B & C are alike) 		MOSFET Outputs:
High side & Low side
1 ("off") 1 Both Off
1 0 Low On, High Off
0 ("on") 1 High On, Low Off
0 0 Both OFF (NOT both on!)

    If 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 controller manual.

   To visualize the workings, let us simplify by considering a rotor with only two magnets, N and S, 180¼ apart, 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 2).
    Then, with the second, oppostie, magnet 30¼ past the top coil, it goes "on" with 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.

   In the 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 by "B".

   The 9 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).
Air Circuit

   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.
Vehicle Mechanical Connections

   Two 1/2" x 1" rectangular steel tube "brackets", upper and lower, bend around 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 springy mounting 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.
Mechanical Torque Converter or Planetary Gear
and Car Wheel Installations

   For its 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 reduction.

   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 grease.
Construction Principles: Safety

   The 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 comes 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 disassembled 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 protected.
More on all this later.
Battery Power Supply

   The 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 batteries for 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 - 6 KWH) 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 trying to 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 Assembly

   This section covers main assembly of the whole motor from the components. It assumes all the components themselves have been created or assembled.

   The main components of the Electric Hubcap motor are:

* Stator: inner stator ring, coils, magnet sensor board, perimeter air intake screen.
* Wiring end: outer stator ring, with bearing outer race ("bearing cup") and bearing dust cap.
* Rotor: axle with SDS Taper-lock bushing and magnet rotor, trailer wheel roller bearings
* Shaft end: Rotor cover bell with bearing outer race ("bearing cup")
* Mounting Straps or Brackets

STATOR ASSEMBLY

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 bearing holder plates to 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 polarity.

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 other phases.

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 coils.

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 in.)

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.)

ROTOR COVER

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 on the 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 bushing.

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 good.)

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 motor.
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 Axle

   From this point on I'll focus on the specific "standard" configurations and implementations of the Electric Hubcap motor unless otherwise indicated.

   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 this to work.

   The axle has to be strong enough to withstand these same dynamic forces plus any external load that puts stress on it. The 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 twist it off even if it was held from bending. Car engines and transmissions use hardened steel parts and keep them cool in a bath of oil.
   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 that come 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.

3-3-A

   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 2010/11/25.)

* 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 deep.
   - 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 seal (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.

3-3-B

   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.

3-3-C

   Another option is a trailer wheel hub. With the '6129' rotor, a 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 drill).

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 welding rods.

   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 few spots.

   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.
   The high-power 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 works!)
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 come.
   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 connecting wires.

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 is somewhat 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 repair shop or web sources] OR 4m of #11 AWG magnet wire per coil.

* T200-26B iron powder toroid core (Mfr: micrometals.com)

* High temperature epoxy, pref. thermally conductive epoxy (150¼c+) .

* 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 while winding.)
   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 gradually set.

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 epoxy.

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.

   Pour some sodium silicate into a jar that has a good lid. Add as much ilmenite as it seems to want to absorb and still stay fluid. You can dip the coils in the jar or paint the liquid onto them.

Note: It doesn't adhere very well. Expect some to flake off.

   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.



Coil winding jig. The bearing spindle (left) can be had, eg, at a motor 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 with indents 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.

   The number of turns was derived empirically, 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.
   #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 diameter is 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" outer perimeter, 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 coil.

   Only the wide gap between rotor magnets and stator coils (ideally ~0.57"?), gives the clearance and leeway to permits the thick epoxy ring between the coils and the magnets on the rotor!

Wiring 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 the case using a trailer wheel hub). This both keeps lead lengths shorter and leaves more empty space for cooling airflow around the outside.
   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 connection. 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" coils ends 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 or sleeving... or electrical tape(?). Forget heat shrink as the wires may get 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 copper


   On the ends of the heavy leads, use Anderson Power Products 75 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 controller.


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)
Supermagnet Safety

   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: check axle, spacers, bearing and bearing cup and be sure the rotor can't slide down all the way to the stator.
   To avoid having your fingers potentially mashed, always hold the magnet rotor between the magnets, never with the fingers on the faces of the magnets, and keep them off the inner face of the stator during assembly.

   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 place.

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.

Magnet Placement, 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 views:




My original magnet placement template, top and underside views.
Adjacent magnets are covered to prevent magnets accidentally clamping together
(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.
(The pacific dogwood (oiled) was just too beautiful to put ugly screws into from the top!)

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.)

Section 6. 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 bottom.



Upper Bracket installation.
The protruding arms of the bracket were later cut shorter.
The stator straps were bent to meet these shorter ones.

First, the tire wall generally sticks inwards past the housing, so I 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.

Around-the-wheel Arms
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.


End of stator strap to connect it to the wheel bracket. [fix: Needs image]

Nyloc Nuts & avoiding things that fall off while driving
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!

Parts List
Axle parts
Shaft (4140 HTSR machine shaft, 1" x 6")
SDS Bushing
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

Rotor parts
5/16" Steel Plate Rotor
12 - Supermagnets
1m - 2" PP strapping
Epoxy Resin
Rotor Compartment Cover Bell, PP-epoxy

Stator Parts
9 - Coils
9 - Coils
    9 - T200-26B Iron Powder Toroid Cores
    36m - #11 AWG Wire
    Hi-temp, thermally conductive Epoxy
    Sodium Silicate
Magnet Sensor PCB
    3 - Hall Effect Sensors
    AD590 ¼ Sensor
    2 mach. screw
    epoxy
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

Electric 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 coil surfaces.
   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 onto.)

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 races.

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.

http://www.ElectricHubcap.com/

Electric Hubcap is a trademark of Turquoise Energy Limited.