Build your own electric motor 9789163361722, 9163361728

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Build your own

Electric motor Axel Borg

Build your own electric motor Text and photo Axel Borg Layout Sara Borg

amazingDIYprojects

amazingDIYprojects.com Copyright © 2011, Axel Borg. All rights reserved. ISBN 978-91-633-6172-2

Introduction This is a practical handbook which, step by step, describes how to build a powerful electric motor the Do-It-Yourself-way.   The motor could be used to propel a light motorcycle, a smaller boat, an ultralight aircraft and many other exciting creations.   The motor is a “brushless double-sided axial flux permanent magnet 3-phase AC air core air cooled hall-effect sensor Delta connected-motor” One unique feature is that this motor can be built in a sensorless split stator version powered by 7 R/C hobby ESCs. This split stator version can, in some applications, be an economically attrac-

tive alternative to the hall sensor version, which is normally powered by a more expensive hall sensor dependant controller.   Although electric motors have been around for a long time, I have not yet found a building instruction that shows the Do-It-Yourself-minded person how to build a useful electric motor. This is why I decided to develop my own motor, constructed in such a way, using commonly available materials and tools, so that the technically interested person can build the motor in a wellequipped home workshop.

Contents Part 1: General information about DIY axial flux electric motors General information and outer boundaries

7

Air core axial flux motor characteristics

9

Two different ways of sensing rotor position

10

Split stator information

12

Power and efficiency

15

Electromagnetic coils and coil winding tools

16

Permanent magnets

20

Stator structure

21

Rotor structure

23

Part 2: Step-by-step building instructions Exploded view with named parts

27

Making a coil winding tool

28

Calculating length of copper wires

35

Coil winding

36

Building the stator and stator lamination tool



49

Building the rotors



93

Assembly and test running the motor

140

Part 3: Miscellaneous List of materials and tool requirements

147

Where to buy materials online

148

Inspirational pictures

149

Technical drawings

153

Part 1 General information about DIY axial flux electric motors

General information and outer boundaries Although the building instruction in this book is very specific, it is possible to build this motor in many different sizes and shapes and out of different materials. As long as you stick to the proportions of 3 copper wire coils for every 4 permanent magnets, scaling is simple!   A motor built according to these instructions weighs around 10 kg. The outer diameter is 366 mm, and width about 120 mm, the output shaft and threaded mounting rods/bolts not included. The maximum power input is not yet determind. The motor built in this book handles 7 kW continuously with bursts up to 18 kW without any visible damage.   The proposed motor has a stator with 21 (7x3) electromagnets and two rotor discs each carrying 28 (7x4) permanent magnets. This gives you the possibility to build it as a 7-split stator motor, powered by 7 R/C hobby ESCs.   Since I intend to use the motor in this build as a power source in a Yamaha TZR 125 motorcycle conversion I have chosen to couple the motor to a Kelly KBL 48601B (48 V 600 A peak) controller which uses hall effect sensors to sense rotor position. Therefore the motor in this book is built with hall effect sensors. The sensors give the motor more reliable starting characteristics when started from stand still under heavy load. There are also convenient throttle handles readily available, which you can plug into the Kelly controller.

However, it is always possible to power a hall sensor equipped motor like this one with a single (1) powerful hobby ESC. This is convenient during initial tests or if you wish to conduct experiments without spending the time it takes to connect the motor to a hall sensor dependent controller.   The magnets in this motor are 30 mm in diameter and 10 mm thick. I have found that 1/3 is a good relationship between a magnets diameter and thickness in axial flux air core motors.   For those interested in elevated power levels the best PM choice would be wedge shaped magnets rather than the simple non-optimal cylindrical ones, but these magnets are significantly more expensive. You would also need to re-design the coil shape if you change the number/size of the permanent magnets.   When it comes to magnetization grade N45 is good. A temperature resistance of 80 degrees C is, under normal circumstances, quite enough since the magnets are effectively cooled by air.   The following test values are intended to give you a “feel” for the differences that follow with the choice of magnet strength and whether you use iron on the back side of magnets or not.   With the same stator and air gap between stator surface and rotors magnets, but with the rotor equipped with different magnets I achieved the following results:

Part 1 - General information and outer boundaries    7

Rotor with 30x7 mm magnets N42 =75 rpm/V Rotor with 30x10 mm magnets N45 =59 rpm/V Rotor with 30x10 mm magnets N45 with 12 mm thick layer iron filings CA- glued at the backside of the magnets= 52 rpm/V.   The stator thickness is 7-8 mm plus the thickness of two layers of glass fiber reinforced epoxy, one layer on each side adding approximately 2 mm to the stator thickness, resulting in a total stator thickness of about 9-10 mm.   For practical structural strength reasons I recommend a stator thickness in the 6-10 mm region with a permanent magnet clearance, air gap, less than 2 mm on each side.   If you plan to build motors with smaller magnet diameters or thinner stators the air gap should also be smaller.   The maximum copper wire diameter I recommend is 0.2 mm. Thicker wires results in unreasonable high eddy current losses which generates unwanted and potentially destructive heating of the coils when the motor is spinning at high rpm. My personal choice is 0.1 mm copper wire, which also gives you the possibility to create coils where the relationship between the wire length and total wire cross section area are precisely right for your application.   The wire length in a motor with a stator thickness of 4-10 mm will probably be in the 1-10 m range with as many strands of copper wire you can fit within in the coil.   The proposed coil carries approximately 966 m 0.1 mm wire each. This includes both wire ends sticking out 0.35 m from the ready-made coil. To achieve a Kv of about 85 rpm/V the 966 m 0.1 mm copper wire should be divided into 210 separate pieces of wire of 4.6 m in length.   Longer and fewer strands results in a motor

8    Part 1 - General information and outer boundaries

with a lower rpm/V and vice versa. For example; if you cut the wire length in half to 2.3 m and double the number of strands to 420, the rpm/V is roughly increased to 170 rpm/V, and resistance decreases the into ¼.   All the coils in this motor should always be wound in the same direction. CW or CCW, it does not matter, as long as you stick to your choice.   This motor is designed to be connected DELTA. If you make coils with larger center holes it could be possible to connect them in STAR. For example: if you make the drop shaped center hole in the coils I describe here 4.75 mm larger in all directions it should be suiteble to connect as STAR.   If you chose to make a denser coils with smaller holes like the ones described in this building instruction, DELTA connection is optimal. If you connect this motor in STAR configuration the motor will, to some extent, fight its own direction of rotation.   If you decide to connect this motor in STAR configuration you must find the proper position for the hall sensors yourself, since DELTA timing is not optimal for a STAR connected motor. If you power the motor with a sensorless controller you do not have to make any experimental changes.

Air core axial flux motor characteristics From a DIY point of view, the air core motor has several advantages over conventional iron core motors.   One of the most obvious advantages is that you do not have to deal with the high precision

fabricating of thin iron laminations usually found in conventional motor designs. Not to mention, finding and buying the steel lamination material in small quantities.

+  Lacks the cogging effect created by the interaction of permanent magnets and iron. + Air core axial flux motors can achieve a very high level of efficiency and high power density. -

 

-

     

Less torque, in the designs proposed in this book partly or completely remedied by the relative large diameter design. Less thermal conductive material (iron) to help soak up and dissipate the heat that builds up in the copper coils due to I2 R losses. In the design proposed in this book this is partly or completely remedied by low phase resistance, 4,5 mΩ for the proposed motor, and a significant airflow over and through the coils.

Part 1 - Air core axial flux motor characteristics    9

Two different ways of sensing rotor position This book provides information on how to build the motor with hall-effect sensors. However, this hall sensed motor can be connected to a single sensorless RC hobby ESC without any modifications. The motor can also be purpose built to be powered by 7 RC hobby ESC, one ESC for every 3-coil (phase). I call this the “split stator” version, since the stator is split into seven 3-coil segments. Each segment is functioning as a separate motor. The 7 ESC have a common power source and they should also be controlled by a throttle signal from one single servo tester or RC-receiver. Otherwise problems could occur if the 7 segmented motors were set at different throttle levels.   The hall sensor gives the controller information about the rotors position. This information is used to tell the controller which coils to energize to start the motor in the desired direction. The hallsensor motor can be fully throttled from stand still with a heavy load connected to the motors axel. This would be the case when the motor is used to power a motorcycle, especially when starting from a dead stop in an incline.   The sensorless controller, on the other hand, senses the voltage/current induced in the coils when the rotor magnets pass by.   The sensorless ESC does not know which position the rotor magnets are in when it is not moving. The controller simply has to take a chance and send out “random” current to the motor

10    Part 1 - Two different ways of sensing rotor position

Honeywell SS411A Bipolar hall effect switch.

coils. Once the rotor starts rotating the ESC can start to register the direction of rotation. If the direction is not the desired it will automatically change it. This can manifest itself by jerking action in the starting moment. The ESC procedure to find its correct rotation direction will be disturbed if the rotor is blocked or under significant load.   The sensorless version is best used in applications which have a very low demand for high starting torque, such as aircraft or boat propellers, or applications where the motor is not throttled until the motor is set in a rotating motion by an outside force.

One typical sensorless controller is a Radio Controlled Electronic Speed Controller, RC-ESC, which you, in other than remote control applications, can manually control by connecting it to a “servo tester”. The servo tester provides the ESC with the signal it needs to function.

The more rigid and programmable Kelly controller uses hall effect sensors in order to control motors in more demanding traction applications.

Hobby City´s Super Simple 100A 30V ESC.

Kelly Controllers KBL 600 A 48 V Controller.

Part 1 - Two different ways of sensing rotor position    11

Split stator information Connecting the coils in a split stator configuration gives you the possibility to build a high power motor controlled by several low cost speed controllers originally designed for use in RC-hobby. The use of several cheap RC ESCs can save you a lot of money. You can connect the battery side of several RC ESC in parallel so that they can be powered from one power source, one battery. The signal from one servo tester is strong enough to control an entire cluster of ESC using readily available split connectors. The idea is that one ESC only has to provide power to 3 coils, connected DELTA.

7x Hobby city´s “Super Simple” 100A 30V ESC.

12    Part 1 - Split stator information

The section of 3 coils is then arrayed in a circle, in this case multiplied 7 times. Each section connects to its own ESC, not shown in the drawing.

In the other motor version, like the one shown in this step by step building instruction, where all the 7x3 coils are powered by a single three phase brushless hall sensor dependant controller, the coils are wired like this. Hall sensors and controller are not shown in this drawing. The controllers 3 phase wires connects to the points1, 2 and 3.

In the split stator setup each speed controller powers only 3 coils. The motor can run at low speeds with only one speed controller connected to the battery. At higher rpm the voltage and current induced in the coils connected to speed controllers not connected to the battery will harm these inactive controllers and bring the motor to sudden stops. Make sure all controllers are connected to the battery before attempting full throttle runs. The ESC “brake” function must be disabled before running the motor. The hobby ESC cannot handle the currents involved in rapidly stopping the relative heavy rotor in a motor of this size. The ESC will burn before you will be able to react if the rotor is spinning fast when the brake function is activated.   The upside of the hobby ESC system is cost,

simplicity in the sensorless design, and that the motor will work well with two large 12V lead acid batteries in a series, neat and simple, if the intended ESC can handle 30V.   Another positive thing when using RC ESC is the high rpm limit of hobby ESC, which is usually very high, sometimes over 200 000 electric rpm. The Kelly controller handles max 40 000 electric rpm. This limits our 28 permanent magnet pole motor to 40 000/14 =2 857 rpm. (14=magnetic polepairs)   The downside of the RC ESC approach is that you are limited to a low voltage system, usually around 24 V nominal. Higher voltage ESCs are available but are currently so expensive that you might as well buy a “real” electric vehicle controller. Furthermore you probably want to rebuild the servo tester you use to control speed, turning it into a more ergonomic, rigid and safe throttle handle/pedal.

Original servotester.

Part 1 - Split stator information    13

Rebuilt servo tester.

14    Part 1 - Split stator information

Rebuilt servo tester, close up picture.

Power and efficiency No professional power or efficiency measurements have been made.   However, the measured motor temperature values suggest a fairly high level of efficiency. For instance, the air cooled motor can power a 125 cm diameter paraglide motor propeller 2 400 rpm consuming 7 000 W while producing 38 kg thrust. This is done @ 20 V 350 A with the coil temperature settling at about 50 degrees C at an ambient temperature of 23 degrees C.   The motors coils were built out of 82 strands of 0.2 mm wire 2.4 meter each which includes wire ends sticking out approx 0.25 m at each end. The rotor had magnets sized 30x10 and N45 in strength with a 12 mm thick layer of iron filings on the back side of the magnets. The motor was powered by 2 large 12 V lead acid batteries in a series feeding 7 “Super Simple”100 A ESC.   Another example is the motor shown in the building instructions in this book which I have put to use in my Yamaha TZR conversion. Each one of the coils in this motor consists of 966 m of 0.1 mm wire, 210 strands 4.6 m each.   This motor consumes 17 700 W peak with a 48601 Kelly controller powered by 11 prismatic

90 Ah Thunder Sky cells, during acceleration. Depending on how you ride the motorcycle the Wh/ km comes in between 50-60 Wh/km. The typical coil temperature while running is 30-40 degrees C above ambient temperature.   I have had small axial flux motors run up to about 80 degree C, more than 60 degrees over ambient temperature without any visible damage. So there is a good chance that more power can be put through the motor discribed in this book, without damaging the motor. Since the maximum power output for a given motor is often limited by heat it is important to mount a temperature probe in-between a pair of the motors coils. However, heat is not the only limiting factor. At a high rotational speed the structure itself might brake. If you intend to explore the full potential of this motor you must reinforce the motor further.   One last word for the experimental-minded person: do not underestimate the eddy current problem. Even though 0.1 mm wires has a relatively high percentage of isolation compared to thicker wires, the lost copper fill is a well spent waste of space, according to my own experience.

Part 1 - Power and efficiency     15

Electromagnetic coils and coil winding tools When current flows through the copper wire in the coils, they become magnetic.   Energized coils have a north and a south pole. By changing the direction of the current flow through the coils the magnetic polarity also changes. When the current is turned on, each coil attracts and repels four of the rotors permanent magnets, two on each side of the coil. By cleverly sequenced polarity changes the permanent magnet rotor is forced to spin with great force.   The coils are made up of several loops of thin isolated copper wire.   In order to wind these coils you will need to construct a special coil winding tool, which you can use together with a cordless screwdriver. This

way you will be able to make coils of a consistent quality.    The thickness of the coils in the motor described in this book is 7 mm. The coil thickness is not critical. I have built stators with coils having a thickness in the 4-20 mm range. The 4 mm stator was laminated with carbon fiber fabric to make it rigid enough. This stator makes it possible to have a very intense magnetic flux since the distance between the permanent magnets is fairly small. In theory, thin stators are a good thing. However, my experience so far and from a DIY perspective, building thin stators and coils does not seem to result in better motors.

Simple circular coil winding tool.

4 mm and 8 mm stators.

16    Part 1 - Electromagnetic coils and coil winding tools

The shape of the coil tool is determined by your choice of coil shape.   The simplest coil to make is a circular coil. All you need to produce circular coils is a cylindrical object of an appropriate size, 12 mm would be a good choice in his case, an adjustable stop ring and two plywood rings that have a sliding fit on the cylindrical object. The cylindrical object could be a bolt with a smooth section, a drill you can do without will also work fine or a custom made part turned down to dimensions in a lathe. The outer diameter of the plywood rings should be the same as the outer diameter of the final coil.

Finished coils of different shapes and sizes.

In order to achieve the full potential of this motor design you should make drop shaped coils. To be able to make drop shaped coils you will have to create a coil winding tool with two axels rather than one. Again I use two plywood pieces as end plates. One of the plywood pieces and one of the axels, preferably the smaller one, must be removable in order to loosen the finished coil from the tool. The T-shaped plywood piece is a tool I use to push down the copper wires in the winding tool. This tool will help you achieve good copper fill. Coil winding tools and 2 T-shaped wire compression tools.

If you choose to make circular coils in this motor build, I would recomend you to make coils with an outer diameter in the 38-38.5 mm range. Circular coils will work but are less efficient than drop shaped ones in this specific application.   Making coils with smaller holes in the middle will lower efficiency since the motor, to some extent, will start to work against its own direction of rotation.

These are the coil winding tools I used for my motorcycle motor build.

Part 1 - Electromagnetic coils and coil winding tools    17

The motorcycle motor coil winding tool, assembled. Experimental CA glue tests.

The coils in these instructions are made up of many 0.1 mm copper wires in parallel.   The reason for using several parallel 0.1 mm wires rather than using a single thicker copper wire is to avoid losses due to the eddy current phenomena which tends to heat up the thicker wire quite noticeably when the motor is spinning at higher speeds. After testing different diameters of wire I have settled for the 0.1 mm wire. As a bonus you will find it easier to solder these thin wires. The winding procedure is the same regardless of the coil shape you chose.   Glue is applied in small quantities during the winding to make the coils rigid enough to hold together throughout the building process.   Spray glue is used in this build. The spray glue is flexible and allows the coil to be compressed during the stator lamination process. The picture shows experimental tests using CA glue. It works, but it takes a long time before it has cured completely and the coil will become extremely stiff. This means that it has to fit into the drop shaped hole in the stator as is, there is no possibility of squeezing it in.

18    Part 1 - Electromagnetic coils and coil winding tools

To avoid the copper wires getting stuck onto the plywood you should rub the wooden pieces with some sort of wax, I use a piece of ordinary candle to wax the surfaces.

Inexpensive non-stick preparation.

As mentioned earlier to achieve a Kv of 85 pm/V the 966 m 0.1 mm copper wire that a single coil consists of you should divided the wire into 210 separate pieces of wire, each of 4.6 m length. If you would like half the rpm/V all you have to do is to double the single wire length from 4.6 to 9.2 m and at the same time naturally cut the number of wires down from 210 to 105. Half the original cross section area and double length results in a rise in resistance by a factor of 4.   A simple jig and a hand held tally counter is used to simplify the process of measuring up the right number of wires in the desired lengths.   Soldering the multi strand copper wire coils demands a lot of heat to melt the thin but rugged wire insulation. I use a 200 W soldering iron and the soldering grease shown in picture to achieve clean soldering result. The soldering grease is applied on the multi strand copper wires before you start heating them up with the soldering iron.

A simple measurement jig.

Hand held tally counter and a bobbin holding 0.2 mm copper wire.

Soldering grease helps a little, but is not necessary.

Part 1 - Electromagnetic coils and coil winding tools    19

Permanent magnets I have been experimenting with NdFe permanent magnets in sizes ranging from 10 mm to 30 mm in diameter and 2-10 mm thickness. Building efficient motors using magnets smaller than 12-15 mm in diameter is hard work. When it comes to magnet thickness, I have found that it is good to have thicker magnets up to a certain level. Using magnets with a thickness greater than half the magnets diameter have proven to be a waste of money and weight.

If you are interested in elevated power levels the best PM choice would be the arc segment (wedge) shaped magnets rather than the simple non-optimal disc shaped one, but these magnets usually comes at a significant higher price. You will also be very limited in size since the arc shaped magnets are hard to find in a large variety of sizes.

The picture shows a simple 3-phase motor with 10x2 mm permanent magnets in the rotor.

15x8 mm N45 magnets works fine. Centrifugal cooling holes in the center, carbon fiber reinforced.

20    Part 1 - Permanent magnets

Stator structure The purpose of the stator structure is to provide a firm support for the 21 copper coils and support the motors 2 ball bearings which are fastened with thin CA glue in the stator center hub.   The stator center hub is made out of several pieces of 7 mm thick plywood. The large plywood disc carrying the coils is partly covered with glass fiber reinforced epoxy or polyester.   5 threaded rods hold the stator hub and the coil carrying disc together making it possible to align the structure under the building phase before they are finally glued together. The 5 threaded rods sticking out from the center stator hub provides a secure way of bolting on the motor to your vehicle or other application.

The part of the coil carrier disc is constructed from a 7 mm piece of plywood.

Split stator coil carrier disc.

The stator could also be made of 2 thin plastic sheets making the stator hollow and therefore possible to water cool after sealing it along the outer edges.

Experimental motor in pieces.

Part 1 - Stator structure    21

Water cooled stator structure.

Rigid stator lamination tool.

The decision as to whether you build the motor as a split stator one or not depends on your intended use. If your application demands high starting torque the hall sensor version is preferred.

Sealed water cooled stator.

Some wooden jigs have to be made before the lamination is made to ensure that the stator comes out as flat as possible after the lamination has cured.

22    Part 1 - Stator structure

Three hall sensors.

Rotor structure The purpose of the rotor structure is to carry the permanent magnets and transfer the force from the permanent magnet ring, to the motors centrally located shaft.   Creating a cooling airflow over and through the coils is another important job done by the rotor. The 2 rotor parts are cut out with a router, helping you to produce true circular rotors.

The shaft is a piece of steel. If you build a small motor with steel rotors you can soft solder a stop-ring in the center of the rotor, using ordinary electronic soldering tin/lead, and use it to secure the axel.   The picture shows a small rotor, about 120 mm diameter, with a 8 mm steel axel. In the build in this book the steel axel is fastened to the main wooden rotor using thick CA glue.

The router and the circular cutting jig.

Soft soldered stop ring.

Part 1 - Rotor structure    23

The permanent magnets are glued to the rotor using medium CA glue once their position is set. Carbon fiber is then applied 30 laps around the large circle of magnets to prevent the magnets from being thrown off the rotor due to the extreme centrifugal force acting on the magnets at higher rpm. Thin CA glue is used to soak and bond the carbon fibers.

Reinforced rotor.

30 laps of 10K carbon fiber.

This carbon fiber length is not enough!

Failure to apply enough carbon fiber will result in an exploding motor possibly killing or injuring persons standing in the way of the flying magnets!   If an inadequately reinforced rotor cracks, all magnets on that rotor will come loose. Be careful while testing the motor “naked” without protective shielding. Never stand in the radial circumference of the motor when running!

24    Part 1 - Rotor structure

The 2 rotor pairs are held in place using 18 M6 bolts with nuts.   The nuts are used to adjust the distance between the discs and used when you wish to separate the 2 discs from each other. This is very convenient since the force pulling the discs together is significant and it would simply be very difficult to pull

apart the discs in any other way without destroying the whole structure. Therefore, do not cut off the parts of the screws sticking out from the rotor.   I prefer stainless bolts, nuts and washers. The washers are important in their function of distributing the rotors magnetic pulling force over a slightly larger area compared to the nuts alone.

Adjusting axial clearance using a caliper and wrench.

This experimental motor only has 14 M6 bolts.

Part 1 - Rotor structure    25

Part 2 Step-by-step building instruction

Exploded view with named parts

1 Steel axel/shaft 2 M6 screws 3 Rotor hub 4 Primary rotor 5 M6 washers 6 M6 nuts 7 Permanent magnets 8 Carbon fiber reinforcement ring 9 Aluminum spacer tube 10 M10 nuts 11 Coils 12 Stator, Coil carrier disc

13 Spongy cloth 14 Ball bearing hub 15 Copper pipes 16 Ball bearings 17 M6 washer, oversize outer diameter 18 M6 screw 19 M10 threaded rods 20 M10 washers 21 M10 nuts 22 Carbon fiber reinforcement ring 23 Permanent magnets 24 Secondary rotor

Part 2 - Exploded view with named parts    27

Making a coil winding tool The first step is to build a coil winding tool. This tool can be made in several different ways. If you have access to a lathe it is really easy to make this part. It should also be possible to make a fairly accurate coil winding tool if you have a drill press.

28    Part 2 - Making a coil winding tool

1

Cut out and glue the coil winding tool templates to a piece of 7 mm plywood using spray glue.

2

Drill the 3.5, 7, 10 and 15 mm holes.

Part 2 - Making a coil winding tool    29

3

4

30    Part 2 - Making a coil winding tool

Use the 3,5 mm drill to mill a path between the 3.5 mm hole and the 7 mm hole.

Cut and sand the 2 end plate pieces to their final shape.

5

Cut out a piece of 15 mm steel rod and drill an 8.5 mm hole in the center. This can be done without a lathe, the center hole need not be absolutely centered.

6

Then you taper the hole to a M10 thread.

Part 2 - Making a coil winding tool    31

7

Insert an M10 threaded rod of appropriate length in the hole. De-grease and sand the 15 mm section of the shaft.

8

Temporarily fasten the end plate pieces with the 10 mm hole on the 10 mm rod pushing it as close to the 15 mm part as possible using a nut to hold it in place. Mount the other end plate on the 15 mm section of the coil winding shaft. Clamp the coil winding tool around the wooden stator structure to achieve the right distance between the coil winding tools end plates.

32    Part 2 - Making a coil winding tool

9

Now secure the end plate on the 15 mm part of the shaft with thin CA glue.

10

The coil winding tool is now ready.

Part 2 - Making a coil winding tool    33

11

Use the 7 mm drill as the axel through the 7 mm holes. A piece of duct tape prevents you from getting sore fingers.

12

Before you start winding up strands of copper wire it is a good idea to apply some sort of slippery, anti-adhesive, substance on the wooden parts. I have melted/rubbed candle wax on the surfaces facing inwards making it easier to extract the coil from the tool. The melting/rubbing procedure has to be done several times during the process of winding 21 coils. I use a hot air gun to melt the candle and heat up the wooden surface.

34    Part 2 - Making a coil winding tool

Calculating length of copper wires All data presented here are results from real life experience and actual tests. Since you are building this motor by hand from scratch, there will be variations in the final result. Using my simple math will, however, keep you in the ballpark. If one coil happens to carry a few strands more or less will not affect the performance in a noticeable way. I have yet to build a flawless example myself. First you have to decide what rpm/V value you want. This will depend on what battery voltage you have at hand and what controller you will use. The need for low speed torque is also an important factor. If your application demands high torque at low rpm you will have to go with longer and fewer wires. This is a result of the way the Kelly Controller works. This controller will not deliver peak amps at low rpm or stalled rotor. Instead it will deliver max ampere at a higher rpm while accelerating the motor from a certain rpm, perhaps 30–50 % of no load rpm.   To get a rough estimation of the individual wire length divide 390 with the desired rpm/V and you have the wire length in meters. In this example

I want a motor that turns 85 rpm for each volt applied.   390/85 = about 4.6 m. The total wire length in one coil is about 966 m if you build the motor with 0.1 mm wire and a 7 mm thick stator. To calculate the number of wires in a coil simply divide 966 by the individual wire length, in this example 4.6 m. 966/4.6 = 210 single strands of 0.1 mm wire 4.6 m each. Wire length includes 0.35 m wire sticking out from the coil in both ends.   This rough math is valid when using 30x10 mm permanent magnets with an N45 magnetization grade. The magnets are mounted without iron on the backside of the magnets.

Part 2 - Calculating length of copper wires    35

Coil winding You will most probably have to make a couple of practice coils before you get to know the technique well enough. Make sure that the coils fit in their place in the stator before you start mass-producing them. If they do not fit you will have to use fewer strands of copper wire or shorter strands. Sometimes it is a matter of using the compression tool more frequently during the winding of a coil making it denser. In my experience the easiest way to achieve a good repeatable result in measuring up length and number of wires is to screw two wood screws with the desired distance between them on to a plank of sufficient length. You might have to join a couple of planks to achieve the desired length.   When working with 0.2 mm strands building coils with 30–60 indivibual strands in the winding it is OK to do the measurement job rolling copper

36    Part 2 - Coil winding

wire from a single bobbin.   When working with 0.1 mm wire preparing to make coils with more than 200 individual strands you must use several smaller bobins fastened on a shaft in parallel.   I use 10 smaller bobbins on one shaft which means I only have to walk the measuring distance of 4.6 m 21 times for each coil instead of 210.

1

Wood screw holding multiple loops of copper wire.

2

This is the plank I used when I was building a high rpm/V motor, about 150 rpm/V, 2.4 m wire length. In this build I extended the plank in order to measure up the 4.6 m strands.

Part 2 - Coil winding    37

3

This 10 roll setup makes it a lot easier to mesure up the 210 pcs of 0.1 mm strands. A tally counter is simply taped onto the handle which helps me keep track of the number of strands I have measured up.

4

Use a pair of scissors to cut the copper wires and twist them together. Repeat procedure at the other end.

38    Part 2 - Coil winding

5

6

Fasten one end in a solid object.

There should be approximately 0.35 m wire sticking out at each end of a finished coil.

Part 2 - Coil winding    39

7

Draw 50 cm long lines 8 mm apart on the protective paper back side of the aluminum tape. Divide the 50 cm 8 mm wide lengths into 35 cm and 15 cm long sections. It is also possible to use other tapes such as duct tape.

8

Cut along the lines. You need at least 21 pieces of each length. But since you will probably need to make a couple of test coils it is a good idea to cut out a few extra tape strips.

40    Part 2 - Coil winding

9

This is a useful device if you are working indoors and want to avoid excess glue being sprayed all around.

10

The spray pattern should be absorbed by the cardboard.

Part 2 - Coil winding    41

11

12

Wind a layer of tape with the adhesive side facing out.

Fasten the end plate with a nut by hand or gently using a tool. Use a washer to distribute the pressure against the wooden endplate.

42    Part 2 - Coil winding

13

Start winding up the wire. Chose the winding direction and stick to it during the winding of all 21 coils!

14

Spray on spots of glue every 20-40 cm preventing the coil from falling apart during the motor build.

Part 2 - Coil winding    43

15

Make a simple winding compression tool and use it 6-10 times during the winding of a coil. Without this simple tool it will be harder to achieve good copper fill.

16

44    Part 2 - Coil winding

Use a 35 cm tape strip to secure the wire when you are done winding.

17

18

Twist the lose ends together.

Twist the other ends as well, and loosen the tool from the screwdriver.

Part 2 - Coil winding    45

19

20

46    Part 2 - Coil winding

Unscrew the nut.

Twist and pull out the 7 mm drill.

21

Gently twist the endplates apart. If the coil windings get stuck to the endplates you will need to re-wax them before next coil winding session.

22

This is how it is supposed to look when you have separated the coil winding tool successfully.

Part 2 - Coil winding    47

23

48    Part 2 - Coil winding

Completed coil, ready to mount in the stator.

Building the stator and stator lamination tool The stator consists of two parts, the ball bearing hub, which holds the ballbearings, and the coil carrier disc, which holds the coils in place. I have chosen to build these parts of plywood simply because it is readily available, light weight, bonds well with adhesives and is easy to machine using nothing but simple tools. Other materials are of course possible as long as you stay away from electrically conducting materials due to the eddy current phenomena.

Part 2 - Building the stator and stator lamination tool    49

1

We start out by making the ball bearing hub. Cut out 8 circular pieces of 7 mm plywood 160 mm in diameter.

2

50    Part 2 - Building the stator and stator lamination tool

Glue them together with glue suitable for wood.

3

Mount the template using spray glue.

4

Drill the holes 7, 10, 12 and 42 mm in diameter. I use an adjustable drill when I make the 42 mm center hole. You should be able to slide in the ball bearings in the hole without applying excessive force. Make a couple of test holes before attempting to drill the actual center hole.

Part 2 - Building the stator and stator lamination tool    51

5

Drill a 20 mm hole in a scrap piece of board. Cut a piece of 20 mm shaft to a lenght of approximatley 100 mm.

6

Temporarily place the two bearings inside the center hole and slide the 20 mm shaft through the hub down into the 20 mm hole in the scrap board. Sand the outer radius of the ball bearing hub.

52    Part 2 - Building the stator and stator lamination tool

7

Use a hot air gun to remove the template.

8

Now is a good time to give the hub a protective layer of spray paint. Do not bother to paint the side of the hub that will be facing the coil carrying disc.

Part 2 - Building the stator and stator lamination tool    53

9

Degrease and sand the ball bearings outside ring.

10

54    Part 2 - Building the stator and stator lamination tool

This is what the outer surface should look like when you are done.

11

Place the hub on a smooth surface with a piece of plastic film underneath the hub. Slide down one of the bearings and gently press it down until the bearing rests on the underlying smooth surface.

12

Carefully turn the hub upside down and fix the bearing using thin CA

glue.

Part 2 - Building the stator and stator lamination tool    55

13

Turn over the hub once again and slide in a piece of 20 mm axel and put the second bearing in place.

14

Glue the second bearing with thin CA glue. Make sure the axel can spin easily resting in the two bearings. Otherwise you must adjust the bearing alignment.

56    Part 2 - Building the stator and stator lamination tool

15

Leave the axel in this position until the glue has cured completely.

16

Now we carry on by constructing the coil carrying disc. Temporarily adhere the coil carrying disc template using ordinary office tape.

Part 2 - Building the stator and stator lamination tool    57

17

Perforate the lines in the template with a sharp tool in order to make visible dotted lines on the plywood surface. Do not forget to mark the center hole and the outer radius of the entire coil carrier disc.

18

If you wish to make the lines more distinct you can use an ordinary pencil combining the dots with a line.

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19

Use an electric hack saw with a narrow blade to saw out the drop shaped holes. Work slow and carefully not to break the thin wedges between the coils. It is not a problem if you break one or two though.

20

Grind the holes to their final shape using a rotary sanding tool.

Part 2 - Building the stator and stator lamination tool    59

21

The holes are ready when you are able to slide in the coil winding tool. If this proves to be impossible you will have to sand the outer edge of the coil winding tool slightly so that it does fit.

22

60    Part 2 - Building the stator and stator lamination tool

Drill a 20 mm hole in the center.

23

24

Place the piece of 20 mm axel in the hole.

Slide the hub onto the axel.

Part 2 - Building the stator and stator lamination tool    61

25

Drill the 10, 12 and 7 mm holes through the coil carrying disc. Secure the disc with a couple of steel rods as you continue drilling holes to hold the disc in position.

26

Make a mark on the side of the disc that is facing the hub to avoid misalignment later on.

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27

Enlarge the 20 mm center hole to 25-26 mm.

28

Divide the disc into sectors of 3 drop shaped holes in each sector. Mark the holes 1-2-3.

Part 2 - Building the stator and stator lamination tool    63

29

Mark the path for 3 hall sensor wires and one path for a temperature sensor. The temperature sensors path is the one ending between holes 2 and 3. The lines should go to the stators one 7 mm hole.

30

Mill out the paths for the 4 leads ending in the 7 mm hole. Write numbers 1-2-3 close to the three 12 mm holes.

64    Part 2 - Building the stator and stator lamination tool

31

Now it is time to build the stator lamination tool. Cut out 2 pieces of board 400x400 mm, 20-25 mm thick. Use an electric hack saw to saw a 190 mm in diameter hole in one of the boards. Mount 4 short legs on this board. Saw a 205 mm diameter hole in the other board.

32

First use one of the lamination tools as template when you mark a piece of fiberglass cloth. I use 290 g/m2 woven fiberglass cloth.

Part 2 - Building the stator and stator lamination tool    65

33

Then use the other lamination tool as template when you mark another piece of fiberglass cloth. Cut out both parts with a pair of scissors.

34

You should now have two pieces of fiberglass cloth with same outer dimensions, 400x400 mm, but with different size holes, 190 and 205 mm diameter.

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35

36

Cover the lamination tool with thin plastic film.

Place the fiberglass cloth with the 190 mm hole on top.

Part 2 - Building the stator and stator lamination tool    67

37

Place the coil carrier on the fiberglass cloth as shown in the picture. The milled path for the sensors should be facing up.

1

2

68    Part 2 - Building the stator and stator lamination tool

38

In the following description the wire coming out from the coil center marked with 1 will be called the “inner wire” and the wire coming out at the coil periphery marked with 2 will be called the “outer wire”.

39

Place 3 coils in a row marked 1-2-3.

40

The wiring starts by sticking the no1 coils inner wire into hole no1. Then take the inner wire of coil no2 and stick it through hole no2. Finally take the no3 coils inner wire and stick it through hole no3.

Part 2 - Building the stator and stator lamination tool    69

70    Part 2 - Building the stator and stator lamination tool

41

Next step is to take no1 coils outer wire and stick it into hole no3.

42

Proceed by sticking no2 coils outer wire into hole no1.

43

44

Finally stick coil no3 outer wire into hole no2.

Repeat this procedure for all 7 sections of 3-coils.

Part 2 - Building the stator and stator lamination tool    71

45

46

All inner wires put in place.

All outer coil wires in place. Make sure that there is sufficient clearance in the center and for the 5 mounting rods that will later on go through the 5 holes, which are 10 mm in diameter. You might want to fix the wires temporarily with a glue gun.

72    Part 2 - Building the stator and stator lamination tool

47

Mount a temperature sensor of your choice. I have used a digital thermometer intended for computer use with a slightly modified probe, thinner wire and a smaller sensor. The temperature sensor leads should go through the 7 mm hole in the stator.

48

The hall sensors used in this build are Honeywell SS411A bipolar Hall Effect switch sensors. The left pin is Vin (+), the middle pin is ground (-) and the right pin is signal out.

Part 2 - Building the stator and stator lamination tool    73

49

I use a thin model railway signal cable for the + and – wire. You can identify the polarity through the color of the leads. One is plain copper (left) and the other one is silver colored, tin coated (right).

50

Solder the + and – leads and a signal wire, in this build I have chosen a yellow wire for the hall signal out. Use crimp tubes to insulate the leads.

74    Part 2 - Building the stator and stator lamination tool

51

Label the signal wires 1-3 when you are done soldering the three sensors.

52

Mount the sensor labeled no1 in coil no1. Use medium CA glue.

Part 2 - Building the stator and stator lamination tool    75

53

Continue by mounting sensor 2 in coil no2 and then sensor 3 in coil no3. All the sensor leads should go through the 7 mm hole in the stator.

54

Laminating the stator. You need the tools shown in picture. I use a roller with an aluminum roller. In this example I use epoxy as a bonding agent. It is also possible to use other bonding agents such as polyester or large amounts of thick CA glue, although that would be quite expensive and very unhealthy if done indoors.

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55

No matter of what glue you use I strongly recommend you to laminate the stator outdoors for health and safety reasons. There should be one layer of plastic film and one layer of woven fiberglass fabric with a 180 mm hole in the middle on top of the tool, underneath the stator. I use fiberglass fabric that weighs 290 g/ m2. Place the other fiberglass fabric with the 205 mm hole on top of the stator.

56

Mix epoxy and use the roller to spread it out evenly on the stator. When the fabric gets properly impregnated with epoxy it becomes transparent. Place a layer of thin plastic film on the fiberglass fabric.

Part 2 - Building the stator and stator lamination tool    77

57



58

Place the other lamination tool with the 205 mm hole on top of the stator.

Flip the stator and lamination tool over and remove the bottom stator tool, the one with legs, make sure the thin plastic stays on the lamination tool and not on the stator. Continue lamination by rolling out epoxy on this side of the stator as well.

78    Part 2 - Building the stator and stator lamination tool

59

Reposition the stator tools with legs on the stator.

60

Flip over the entire package once again and apply several clamping tools to press the two lamination tools together.

Part 2 - Building the stator and stator lamination tool    79

61

In order to secure the wires coming out of the coils I would recommend you to do the following: Cut away the thin plastic material as shown in picture. Be careful, you do not want to cut any copper wires.

62

Pour small amounts of epoxy in the outer parts of the circle. Make sure not to glue the stator tool and stator together. Use your fingers to spread the glue to the copper leads coming out from the coils.

80    Part 2 - Building the stator and stator lamination tool

63

Make sure that the five 10 mm holes and the center hole are free from wiring. Let the stator cure properly before you attempt loosening the lamination tools from the stator.

64

Once the stator has cured you can open up the lamination tool and remove the thin plastic film.

Part 2 - Building the stator and stator lamination tool    81

65

66

Cut off all excess material.

Use a Dremel tool and/ or a hobby knife to cut out triangular air cooling holes in the center of every coil. Be careful not to damage the copper wire or hall sensors! Start by cutting away material in the coils where the hall sensors are positioned.

82    Part 2 - Building the stator and stator lamination tool

67

If you wish to give the stator a coat of protective paint then this is the time to do that.

68

Soldering the coils/phase wires. The procedure is not the same when working with 0.1 and 0.2 mm wires. Please note the differences. Soldering 0.1 mm wires are much more straight forward. If you are using 0.2 mm wire it is harder. Practice your soldering skills on scrap pieces of multiple strand wires until you feel confident about how to do it. Cut off the phase wires, leaving 5 cm sticking up from the stator. Spread the separate coil wires. This goes for both 0.1 and 0.2 mm wires.

Part 2 - Building the stator and stator lamination tool    83

69

Burn off all insulation on small clusters of the 0.2 mm coil wire, using a small torch. Do not do this on 0.1 mm wires.

70

Use a file cleansing tool or similar to sort out the individual strands and brush off the carbonized insulation. Do not do this on 0.1 mm wires.

84    Part 2 - Building the stator and stator lamination tool

71

Apply soldering fluid on the bare copper strands. Preparing the soldering with soldering fluid is also valid for the 0.1 mm wire.

72

Immediately solder the wet wires. Repeat the procedure until all wires are tinned. This goes for both 0.1 and 0.2 mm wires. Use a powerful soldering iron, minimum 80 W.

Part 2 - Building the stator and stator lamination tool    85

73

Cut of 3 pieces of 12 mm outer diameter copper tubing 50 mm length. This goes for both 0.1 and 0.2 mm wires.

74

Thread the copper tube over the pre soldered coil wires. This goes for both 0.1 and 0.2 mm wires.

86    Part 2 - Building the stator and stator lamination tool

75

Make a temporary seal at the bottom of the tube to prevent soldering tin from leaking during soldering. I use aluminum foil and a scrap copper wire. This goes for both 0.1 and 0.2 mm wires.

76

Heat up the copper tube with a small torch and apply a significant amount of soldering tin inside the copper tube. This goes for both 0.1 and 0.2 mm wires.

Part 2 - Building the stator and stator lamination tool    87

77

Now it is time for the final stator assembly and alignment. Use the ball bearing hub as a template and cut out at least two layers of spongy cloth.

78

88    Part 2 - Building the stator and stator lamination tool

The result should look like this.

79

80

Place the 2 spongy cloth discs on the coil carrier disc.

Place the hub on the coil carrier disc.

Part 2 - Building the stator and stator lamination tool    89

81

Mount the hub on the coil carrier disc using 5 bolts washers and nuts. Tighten the nuts on each one of the five bolts sticking out of the hub using only your fingers. You might have to extend the threaded part of your bolts (middle). Another alternative is to use a threaded rod and cut it to appropriate length (right).

82

Secure the bolts and all wiring with CA glue. All wires should be stiff once the glue has cured.

90    Part 2 - Building the stator and stator lamination tool

83

Adjusting the stator. Now it is time to adjust the stator so that it becomes perpendicular to the axel. Fasten a 20 mm steel axel on one side of a table. Put the stator on the axel. Fasten a ruler or other object with a distinct end. The end of the ruler should be close to the face of the stator, starting with a distance of 1-3 mm.

84

Rotate the stator and watch the distance between the ruler and stator as it changes during a revolution. Tighten the bolts, this time with a wrench, in such a way that the fluctuation in distance between stator and ruler during a revolution is minimized. Hopefully you are able to achieve a fluctuation of less than approximately 0.5 mm. Tighten the bolts firmly, but not excessively.

Part 2 - Building the stator and stator lamination tool    91

85

When you are satisfied truing up the stator, remove the axel and place the stator on a horizontal surface. Apply rich amounts of thin CA glue to the spongy cloth so that it gets totally soaked. Let it cure overnight.

86

92    Part 2 - Building the stator and stator lamination tool

Lock the nuts with CA glue as well.

Building the rotors In this build I have chosen to use a router to cut out the pieces that will become the rotors. This building method often results in rotors that spin fairly true even before balancing them. If you have a large drill press it will be of great value, and will make the center hole drilling easy. Since my drill press does not accommodate a plywood piece of this dimension I had to drill the center hole with a hand held electric drill, which is not optimal. Nevertheless, this motor turned out just fine.

Part 2 - Building the rotors    93

1

2

To build the 2 rotor discs you need 2x4 pieces of 4 mm plywood board 400x400 mm.

In order to perform this massive gluing task you will need to prepare the operation. I usually mix the glue with small a small amount of water, 5-10 percent, to make it more fluid.

94    Part 2 - Building the rotors

3

Glue 4 plywood sheets into a single piece.

4

Place a thicker board on top of the pile of 4 plywood sheets. You can use the stator lamination tool you made earlier in this build.

Part 2 - Building the rotors    95

5

Then place some heavy objects on top and let the glue cure overnight. Repeat again for the next set of 4 plywood sheets.

6

96    Part 2 - Building the rotors

Mark out the center of one of the plywood pieces.

7

Screw the 2 plywood pieces together using 8 screws, 4 in the outer parts and 4 screws close to the center hole.

8

Make a mark where the outer radius of the rotor is, radius 183 mm and the inner rotor radius, radius 103 mm.

Part 2 - Building the rotors    97

9

Use a template to mark out where the eighteen 6mm holes will be.

10

98    Part 2 - Building the rotors

Use a sharp object and mark the spots to drill.

11

Drill a 20 mm diameter hole in the center of both plywood boards. If you have a drill press that can handle a piece of this size, use it! Try to drill the hole precisely vertical.

12

Drill all of the 6mm holes.

Part 2 - Building the rotors    99

13

Drill an extra 2 mm hole for alignment purpose. The exact location of this hole is not critical.

14

Make a center tool that fits your router of a 20 mm steel axel. A metal spinning lathe makes this job much easier. The centricity of this piece is important.

100    Part 2 - Building the rotors

15

Mount the center tool in the center hole with CA glue. Use a set square for correct alignment.

16

Fasten the router in the center tool.

Part 2 - Building the rotors    101

17

Adjust the position so that the radius will be correct, outside your 183 mm radius mark.

18

Start milling. Do this step by step, milling away a couple of mm for each completed revolution.

102    Part 2 - Building the rotors

19

This is how it should look when you are done with the first milling part.

20

Now place the milling tool on the inside of the radius 103 mm mark.

Part 2 - Building the rotors    103

21

22

Mill a path, no deeper than 10 mm.

Make a cross mark in the side for correct alignment later on. This is very important!

104    Part 2 - Building the rotors

23

Heat up and remove the center tool. The CA glue will be soften and let go at high temperature. Watch out for hazardous smoke fumes.

24

Unscrew the screws and separate the two discs.

Part 2 - Building the rotors    105

25

Re-mount the center tool in one of the discs as shown. Note the cross mark on the side.

26

106    Part 2 - Building the rotors

Adjust the center tool and glue it into place once again using CA glue.

27

In order to place the magnets in a perfect circular shape you will need to make a circular magnet spacer tool. This can be made of some scrap board material. Make a mark of a circle with the radius as close as you can to 118.75 mm. Saw it out leaving it a couple of mm oversize.

28

Drill two 20 mm diameter holes, one in the circular piece and one in a scrap piece of board. Put a piece of shaft into the scrap piece of board and clamp it to the work surface of your belt sander.

Part 2 - Building the rotors    107

29

Sand the magnet spacer tool into the correct dimensions, as close you can to the radius 118.75 mm.

30

Place four washers as spacers on the rotor disc. Use tape to hold them in their position. They will prevent you from accidentally permanently bonding the magnet spacer tool to the rotor disc.

108    Part 2 - Building the rotors

31

32

Place the magnet spacer tool on the rotor disc.

Now it is time to actually mount the magnets on the rotor discs.

Part 2 - Building the rotors    109

33

The magnets should be placed alternating north and south pole facing up. An easy way to check polarity is to make a feeler wand. Simply glue a small magnet to a stick and you can feel if the magnet is repelling or attracting the stick. It is, however, difficult to mount the magnets the wrong way since they will then repel each other sideways. The feeler wand is still a convenient way to determine which side of the magnet to sand. Sand the magnet on the flat side that will later on be glued down on to the rotor surface.

34

110    Part 2 - Building the rotors

Sand the outer radial surface as well.

35

Remove magnetic dust using adhesive tape.

36

Place the magnets on the rotor disc and check that the polarity alternates between the magnets. This picture shows repelling action.

Part 2 - Building the rotors    111

37

38

This picture shows attracting action.

Completed permanent magnet circle. If there are gaps between the magnets and circle tool you will have to increase the magnet spacer tool diameter by adding one or more layers of tape around it just as I had to in this example. If the circle tool is too large there will be gaps between magnets and then you will have to sand off more material from the magnet spacer tool in order to decrease its diameter to the appropriate size.

112    Part 2 - Building the rotors

39

Once you have the magnets in place in a perfect circle it is time to glue them into place. This is done by gently prying the magnets up one by one and carefully squirting in some medium thick CA glue in under each magnet. You will have to make a tool for the prying action.

40

Pry up one magnet at a time and apply CA glue and make sure it makes its way in under the magnet. Use eye protection and gloves.

Part 2 - Building the rotors    113

41

42

All magnets glued in place.

In order to keep the magnets firmly pressed down during the time it takes for the glue to cure, I usually place a few magnets on the opposite side of the rotor, attracting the magnets being glued.

114    Part 2 - Building the rotors

43

It is now time to repeat the magnet fastening procedure on the second rotor disc. Once the glue has cured, gently pry up the magnet spacer tool.

44

Heat and remove the center axel. Re-glue it into the center of the other rotor disc. Once again, create a space between the magnet spacer tool and the rotor using a couple of washers. This is to minimize the risk of the magnet spacer tool becoming glued onto the rotor.

Part 2 - Building the rotors    115

45

Following procedure is necessary to make the magnet placement and polarity match the outer 6 mm holes. Place a sanded magnet on one of the magnets on the previously glued rotor close to the cross mark. Apply a portion of glue on the single magnet.

46

Place the rotors as shown in the picture with several 6 mm screws in place lining up the structure correctly using the cross mark as reference and let the glue cure.

116    Part 2 - Building the rotors

47

Once the glue has cured, use nuts and washers to pull the rotor pieces

apart.

48

Repeat the sanding and gluing procedure in the same way as with the previous rotor. Once again pry off the magnet spacer tool and heat up and remove the center tool.

Part 2 - Building the rotors    117

118    Part 2 - Building the rotors

49

Flip over the rotor and re-fasten the center tool using CA glue.

50

Re-align the router and mill through the remaining mm of plywood.

51

This is how the wooden structure of the secondary rotor looks after milling.

52

Heat and remove the center tool in the remaining plywood hub. This piece will soon be a part of the rotor hub.

Part 2 - Building the rotors    119

53

Building the rotor hub. Cut out a 3 discs of 4 mm thick plywood. They should be slightly oversize compared to the plywood hub.

54

120    Part 2 - Building the rotors

Glue the thin discs together and then glue them onto the hub.

55

Drill a 20 mm hole through the plywood piece starting in the exist-

ing hole.

56

Use the belt sander to smooth the outer radius in the same way you sanded other pieces earlier in this build.

Part 2 - Building the rotors    121

57

58

122    Part 2 - Building the rotors

These pieces should now be glued together.

Apply a rich amount of glue.

59

Use the center tool to correctly align the two pieces.

60

Apply pressure. You are now done with the wooden part of the primary rotor.

Part 2 - Building the rotors    123

61

If you wish to protect the motor with a layer of paint, then now is a good time to do that. It is not necessary to cover the magnets but I think the result is worth the extra effort.

62

The shaft. Cut a piece of 20 mm steel axel about 250 mm in a length or whatever suits your future plans.

124    Part 2 - Building the rotors

63

Drill a hole in one end, approximately 30 mm deep, and taper it to M6 thread. It is not crucial that the hole is centerd but if you have a lathe, use it!

64

Place 7-10 washers, 1-1.5 mm thick on the rotors magnets evenly spaced. These washers represent the air gap between the rotor and stator. The more precise the parts you previously made, the thinner the washers can now be used.

Part 2 - Building the rotors    125

65

Push the axel through the stator and the rotor, just as in the picture. The axel end with the threaded hole should be level with the face of the stator bearing shown in picture.

66

126    Part 2 - Building the rotors

Make a mark on the shaft using a permanent marker.

67

Remove the stator leaving the axel in the rotor. Make a new mark on the axel on the other side of the rotor.

68

Within these marks you should make deep groves with a file or an angle grinder. This will help the glue bond to the axel in the next step.

Part 2 - Building the rotors    127

69

I use medium and thick CA glue when adhering the shaft. Apply thick CA glue directly on the shaft.

70

128    Part 2 - Building the rotors

Apply a little extra CA glue while placing the shaft in the rotor.

71

Check that the air gap created by the washers is even and correct.

72

Make sure the shaft end is not sticking out from the bearing.

Part 2 - Building the rotors    129

73

Make a spacer out of a piece of 20 mm inner diameter tubing. You will have to figure out the exact lenght yourself. It will probably be somewhere in the 21–23 mm range This spacer determines the air gap between the magnets on the primary rotor and the stator.

74

The spacer tube is placed on the axel resting on the inner bearing ring in one end and, in the other, resting against the rotor closest to the axel. It is supposedly cut to a length resulting in an air gap between the rotor and stator of 1-2 mm. The bolts and washer located close to the center are related to the forthcoming use of this particular motor as a motorcycle motor. The bolts will later on hold a chain sprocket in place.

130    Part 2 - Building the rotors

75

The next step is to reinforce the rotors. I built a test stand, which comes in handy during this process.

76

The rotor is supposed to rotate freely in this setup.

Part 2 - Building the rotors    131

77

Cut out a circular piece of board, 310 mm in diameter, with a 20 mm center hole and cover it with thin plastic.

78

132    Part 2 - Building the rotors

Place it next to the rotor.

78

Finally, place the remaining rotor as the picture shows. Be careful, there is a very strong magnetic field present!

80

Apply 30 laps, about 30 m of 10K carbon fiber tow carefully glued using thin CA glue. A large bobbin is visible in the background. Carbon fiber tow is available in much smaller quantities in local hobby shops.

Part 2 - Building the rotors    133

81

82

134    Part 2 - Building the rotors

Close up picture. The white tape helps me count the revolutions.

Repeat the procedure on the outer rotor.

83

To balance the rotors you need the jigs in the photo and epoxy putty. Build the two following pieces of wood and two hobby knife blades, with the sharp side facing down into the wood. If the sharp side is facing up you will create grooves in your motors axel.

84

Balance the main rotor first.

Part 2 - Building the rotors    135

85

Balance the rotor by adding non-mixed epoxy putty to the part of the rotor which always ends up pointing up when you roll the rotor.

86

in place.

136    Part 2 - Building the rotors

When you are satisfied with the balance weight mix the epoxy and put it

87

Fasten the screws, nuts and washers as shown in picture.

88

Place the other rotor on top making sure they line up correctly with aid of your cross mark.

Part 2 - Building the rotors    137

89

The secondary rotor is placed at the same distance from the main rotor as you expect it to be when running the motor. The distance between the rotors is the sum of the stators thickness and the air gaps on each side.

90

138    Part 2 - Building the rotors

Start the balancing procedure again.

91

Put the epoxy in place once you are satisfied.

Part 2 - Building the rotors    139

Assembly and test running the motor

Now it is finally time to run your motor for the first time. It is always exciting to collect the first batch of data, such as rpm/V, no-load current and temperature at different speeds/ loads etc.

140    Part 2 - Assembly and test running the motor

1

2

Mount the main rotor and secure it using a bolt with a large washer and a lock ring.

Screw on nuts and put washers in place on the M6 bolts.

Part 2 - Assembly and test running the motor    141

3

Place the other rotor on top, again noticing the cross mark for correct lining up. Lower the rotor bit by bit by screwing down the nuts.

4

142    Part 2 - Assembly and test running the motor

When you have lowered the rotor close to its final position it should look like this.

5

Final adjustment can be carried out by mounting the motor on a test stand. A piece of metal wire taped to the stand like the picture shows can be of great help. Rotate the rotor by hand and adjust the spacer nuts until the rotor discs are parallel and running true. Aim for a magnet to stator disc clearance of 1-2 mm on each side of the stator.

6

The first test run is easiest carried out using a RC hobby ESC with a servo tester unit to provide a throttle signal. Use a power source in the lower part of the ESC accepted voltage range to minimize risk both to you and the motor during the first test.   Simply Connect the ESC to the motor; any phase wire configuration should work. You will probably want to check the voltage, current and rpm. No-load amperage and rpm will vary with your design. At 12 V it might be somewhere in the 4-6 A range.   I use a laser tachometer, not shown in picture, to measure rpm. Depending on which controller you use and what settings you programmed into it, the start might be jerky.   Always disable the ESCs “brake” function before running the motor!

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7

Connecting the motor to the controller is straightforward work. The risk of ruining something is, according to my own experience, very small. Although mixing up the hall sensor or motor phase wires does not normally fry your controller I do recommend you to be very careful during the first run. I use low capacity batteries for the first experiments, just in case.   The drawings show how to connect the hall sensor signal cables to a brushless Kelly controller. All other connections are done as described in the user manual, which you can download from Kelly Controllers homepage.   The 3 hall sensor Vcc pins (+5 V) should be connected together as well as the 3 ground pins (-). The paralleled cables are then connected to the Kelly Controllers (+) 5 V respectively (-) ground.

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8

The paralleled positive and negative hall sensor cables to the left, temperature cable in the middle and finally the 3 hall sensor signal cables to the right.

9

If you wish to change the direction of rotation without flipping a reverse switch on the controller itself you simply rewire the hall signal cables as the picture shows.

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Part 3 Miscellaneous

List of materials and tool requirements Complete list of material

Tool requirements

Plywood 1.7 m2, 4 mm thickness Plywood 0.3 m2, 7 mm thickness Fiberglass cloth approx. 300 g/m2 with epoxy Carbon fiber tow 10k (10.000 individual fibers), 60 m Neodymium Magnets 30x10 mm, 56 pcs Copper wire 0.2 mm diameter, 5000 m or Copper wire 0.1 mm diameter, 20 000 m Copper pipes 12 mm diameter 50 mm length, 3 pcs Steel axel 20 mm diameter 400 mm length Spongy cloth 160x160 mm 2 pcs Bolts M6, 80 mm length 18 pcs Nuts M6, 36 pcs Washers M6, 36 pcs Treaded rods or bolts M10 120 mm long, 5 pcs Nuts M10, 10 pcs Washers M10, 5 pcs Ball bearing 20x42x12 mm, 2 pcs Bolt M6, 20 mm Washer M6 oversize outer diameter, 22-25 mm Aluminium tube 20 mm inner diameter, 25 mm length Cyanoacrylate glue (CA glue), thin, medium and thick White glue for gluing the wooden parts

Cordless screwdriver Electric drill with a stand or a drill press Electric hack saw or a small band saw Router Belt sander Dremel or equivalent hand held rotary multi tool Screwdrivers, various sizes Wrenches, various sizes Side cut pliers Set square Center punch tool Ruler Clamping tools, 8 pcs Sandpaper Metal file Metal saw Paintbrush Small butane gas torch Large (minimum 80 W) soldering iron Small (approximately 30 W) soldering iron Tread cutting tool M6 and M10 HSS drills, 1-10 mm Wood working drills, 15 and 20 mm diameter Adjustable drill capable of drilling 42 mm holes

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Where to buy materials online The following websites are available in english.

Magnets: supermagnete.de Truly great service and good price. They will also arrange to produce customized magnets upon request. Enameled copper wire and hall effect sensors: elfa.se Although it is a Swedish supplier they do deliver worldwide. Elfa is a very large and rather expensive store with high quality products. R/C electronic speed controllers, servo testers and CA glue: hobbycity.com They have a great low price profile and world wide shipping. Speed controllers with sensors: newkellycontroller.com Very fast response and shipping. They have a lot of other electric vehicle equipment as well, such as contactors, high amp fuses and throttle handles. Carbon fiber tow: search e-bay.com for carbon fiber tow. Look for a 10-12K tow. You should also be able to buy carbon fiber material from your local R/C hobby shop. Iron filings: search e-bay.com for iron filings In EU you can order from sagitta.se. Search for “järnfilspån”. Plywood, steel rods, bearings nuts and bolts: check out local hardware store.

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Inspirational pictures This is a 1989 Yamaha TZR 125 motorcycle. The weight is 131 kg, ready to run.

Same view now with the electric motor in place. The total weight ready to run is 140 kg with 3 kWh of LiFePo4 batteries.

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The picture shows the Kelly controller and a support bearing just behind it. The support bearing is necessary in any application where significant radial loads on the motor shaft will occur.

7 ThunderSky LiFePo cells 90Ah each. The low voltage setup results in easier battery management. No BMS is used. The cells are normally charged in series and only occasionally separately if a single cells voltage has fallen to a lower level than expected.

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A custom seat is built which contains 4 ThunderSky 90Ah cells.

A digital PC-temperature gauge and a cycle analyst replaces the original temperature and rpm meters respectively. The cycle analyst is a great little device giving the driver various important information.

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4 mm thick plastic sheets, spray painted black, covers the cooling air inlets behind the front wheel protecting the motor and controller from water splash etc.   The gearing is 45/14, approximately 3.2:1. I have kept the original 45T rear sprocket in this build.

Top speed is 95 km/h, 60 mp/h. 50-60 wh/km, 80-100 wh/mile. Range 40-50 km, 25-30 miles at 80 % Depth Of Discharge, DOD.   Due to specific laws in Sweden this motorcycle type is limited to 11 kW maximum power. Therefore the Kelly controllers max battery current setting is lowered to 46 %. If the controller is run unrestricted the peak power is just under 18 kW. Please note that this motorcycles battery pack is not well suited to repeatedly leave 18 kW bursts.

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Technical drawings Using templates is an easy way of making 2–D ideas into 3–D artifacts. You can either make the templates by hand from the technical drawings shown in this chapter or via a computer program such as Auto Cad and print them out on paper. There is also the possibility of drawing the pattern directly on the various pieces you want to form.

If you wish to glue the templates onto the pieces that you will cut, drill etc. it is important to use a glue that does not contain any water since that will make the paper swell and lose its proportions, giving you a false geometry. Personally I use spray glue which has the excellent property of being removable after heat treatment with a hot air gun.

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Coil carrier disc, hall sensor version

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Ball bearing hub, hall sensor version

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Coil carrier disc, 7-split stator version

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Ball bearing hub, 7-split stator version

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Primary rotor and shaft

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Secondary rotor

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Coil winding tool

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Magnet spacer tool

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Build your own electric motor This is a practical handbook which, step by step, describes how to build a powerful “brushless double-sided axial flux permanent magnet 3-phase AC air core air cooled hall-effect sensor Delta connected-motor” the Do-It-Yourselfway. The motor could be used to propel a light motorcycle, a smaller boat, an ultralight aircraft and many other exciting creations.