# Building an Electric Motor



## Bugzuki (Jan 15, 2008)

I found this book to be a pretty good starting place.

Electric Motors & Drives

It does not really go into the how many turns of wire and stuff like that, but it will get you very familier with the ideas behind the different types of motors and drives. I thought it was well worth the time. And it is much less expensive then the ones you have listed. It's main focus is to give you enough information that you can make a very informed descission when desciding on a type of motor. I think it goes well beyond that thou, and almost gives you enough to design a motor. If I was going to look for a starter book again I would definitely pick this one again.

Hope that helps.
Paul


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## SirisC (Feb 8, 2008)

Looking through the preview of that book on Amazon, it looks very promising. I will probably get that book first.


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## mattyd (Jan 8, 2008)

I've been meaning to do this for the last 6 months as well, but I've always been in limbo since moving house, changing jobs, then moving house again.

My recommendations would be to build yourself a small permanent mag brushless motor for a radio controlled car or plane. And also build your own brushless speed controller for it.

That is my plan. From there I'll build a few slightly larger motors from old ceiling or pedestal fans, and from old scrapped power tools and vacuum cleaners. And design controllers, with monitoring, for each.

Then hopefully in 12 months i should have a little more understanding of the concept, and have my own pushbike running around with my own electric motor and control system. If i can make it work well, I'll look into making a full-size motor for a small vehicle.

The in-wheel motor that CSIRO in Australia designed for Solar cars is incredibly light, yet very powerful. I plan on sandwiching a few of those (that i would like to make myself) together. They use 2 rotors of Halbach magnet arrays made with precision cut magnets to focus the magnetic flux at the stator in between them. The stator is made with overlapping loops of Litz wire, squashed flat, and then cemented together with resin. The stator is mounted to the vehicle, and the rotors are mounted to the rim of the tyre. This is an axial flux style motor. The more common style of motor is a radial flux motor. This style of axial flux motor can reach efficiencies in normal operation and acceleration of 97%, and has very high torque for its weight. Being an AC motor, they also give fabulous regenerative breaking.

But even with all my planning and desires, this is just sandbox dreaming at the moment.

Having said all this, I'm hunting around for a used local version of "Permanent Magnet Motor Technology: Design and Applications"

http://books.google.com.au/books?id...f-page-link&cad=one-book-with-thumbnail&hl=en


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## John (Sep 11, 2007)

I remember reading about that motor. It's quite remarkable the efficiency they achieved. Maximum power was what was desirable for a solar car. 1.8kW if I remember correctly. It's not strictly speaking an AC motor but a brushless DC motor or an electrically commutated DC motor.


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## mattyd (Jan 8, 2008)

http://www.nano.csiro.au/resources/pf11g.html

Above is the link to the CSIRO webpage with some information on these wheels. You can download all sorts of things in that "Download" link. Just for starters though, and on rereading it all, the power output of the wheel was limited to 1.8kw due to that being the Max power set in the Solar Car race rules. Obviously this motor was made with a cost-no-object design approach, to get the maximum efficiency with the lowest weight (just 10kg) and some good torque (50.2Nm at zero revs and climbing a hill). All this from something about 5cm at its widest!

40 poles, 3 phases, apparently works best when each phase is a sinusoidal wave... used to be able to be bought for ........ $13000 as a kit.


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## Mike D EV (Sep 11, 2007)

I just acquired a Honda Insight IMA electric motor.
It is a pretty simple 14kw 3 phase brushless design, and it made me think that this would be a good design to use as an example for a home built motor.
http://www.99mpg.com/workshops/mikessaturdayhybri/
An interesting thing about it, the rotor could fit on one of the Insight rear wheel spindles, and the coil assembly easily fits within the stock wheels inner clearance, so it could be used as a rear wheel motor.
Since the car IMA controller is designed for the motor, I was thinking that one could electrically switch from the engine mounted IMA motor to the wheel IMA motor.
Mike


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## SirisC (Feb 8, 2008)

That CSIRO site got me thinking, what would happen with a motor based around a ring of helmholtz coils with a gear with permanent magnets attaced in the opposite direction of the magnetic field of the coil, you would have to use a motorcycle chain to connect the rotor to the driveshaft.

I have also considered the brushless design, even know a good supplier of neodynium magnets.

The attached image is a basic drawing of the helmholtz based idea.


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## 3dplane (Feb 27, 2008)

SirisC! Please don't think im negative about your idea on that motor but unless you provide a rotating (electro)magnetic field there is nothing going to force the gear with the magnets (rotor) to turn.(unless i'm missing something)
I agree with mattyd on looking into building your self a few small bldc(brushless dc)motors so you get the hang of it while it does not cost much.(Magnet wire and neos are not cheap on large scale) A few years back gobrushless.com was the kick butt diy motor site,have not visited lately.Also rcgroups.com has two places "electric motor design" and "power systems" full of good motor learning info.


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## 3dplane (Feb 27, 2008)

To Mike D EV! I think your switching motor idea using one controller is brilliant.One thing i would make sure is testing the assembled (new)motor on the same lenght of wires as it would be when its mounted in its intended location on the car.Just to make sure the longer wiring not going to confuse the controller.It may not even be a factor just thought i'll throw it out there.Btw congrats on the fifth wheel! You are still using it wright?(and i know its a few years late).That is the simplest electrifying method ever(brilliant)I'm vandalizing an ancient golf cart to experiment with similar setup. 
Barna


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## ecvs (Mar 4, 2008)

I am also interested in possibly building an electric motor. I have found an interesting group on yahoo called Irk-torquemax.. they build electric motors inside out. This seems to have a few advantages as compared to regular motors. I have a query into the guy who looks after the group asking how large a motor could be built. I'm guessing any hp could be made. The only concern I have is would it be too big or take up too much space to get approx a 20kw motor or in and around 30 hp. It looks like it wouldn't be all that hard to make compared to the regular motors.
Tom


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## Dennis (Feb 25, 2008)

This idea that a "regular motor" is different in handling peak horespower it can dish out versus a DC brushless motor has no factual basis. ALL motors follow the same guidelines rather they are brushless (AC induction, DC brushless permanent magnet) or brushed DC motors.

What you must ask yourself is how often will the motor be required to dish out X amount of horespower under the following: *ambient temperature*, *brushed (DC)*, *brushless (AC or DC) *, *efficiency under various load conditions*, *frame type*, *frame size*, *cooling methods and insulation class*. 

For example if you wish to have a motor develop 300 peak HP for 30 seconds and its specs are: 

Class H insulation
Blower cooled
DC motor brushed
Open non-drip proof frame 
9" inch diameter by 16" long
Ambient Temp 30 C summer day

Then it could meet those demands. Now lets say the same motor is used but with no cooling devices, then it will not be wise to push that much horsepower since motor life expectancy will be reduced.

It it were brushless then it could meet higher horespower peaks if all else is equal since the stator windings are all that need to be cooled rather than having to cool armature windings, brushes and field pole windings for a pure electromagnet DC motor, as well as higher efficiency of not using brushes contacting a moving surface. However, lets include the other factors for this next example:

Lets take a brushless DC motor with class A insulation and and run it at ten peak horespower for 30 seconds versus a brushed DC motor with class H insulation with all other factors not being changed. In this example the brushless DC motor WILL FAIL before the brushed motor from the simple fact that class A insulation cannot take near the temperature abuse of class H insulation. 

So now you realize it's not so much the type of motor design versus as it is the factors than govern what it is capable of.


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## veperformance (Aug 17, 2007)

The biggest problem i found in making an electric motor is cost of machine shop work.Brushless design being much more efficient will not require high temperature insulation since it will not produce as much waste heat and most rare earth magnets are rated max 80celcius anyway.as for exceding designed output of an electric motor consider that raising temperature of copper raises the resistance and reduce your magnetic field so you gain less than you give.


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## Dennis (Feb 25, 2008)

> The biggest problem i found in making an electric motor is cost of machine shop work.Brushless design being much more efficient will not require high temperature insulation since it will not produce as much waste heat and most rare earth magnets are rated max 80celcius anyway.as for exceding designed output of an electric motor consider that raising temperature of copper raises the resistance and reduce your magnetic field so you gain less than you give.



Motors are only efficient if its not under such severe load. It can be any motor you want, it still can overheat. Insulation class is important as the motor with the higher insulation class can take overload for longer periods than one with a lower insulation class. Take a brushless motor whether its permanent magnet or induction AC motor and lock down its shaft and I promise you it will smoke unless some form of protection circuits kicks in such as breakers or stall detectors.


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## Ioku (Sep 27, 2007)

I've also been thinking of building a motor, what I'd really like to build would be a wheel motor because for one there very expensive and most of the wheel motor company's don't seem interested in dealing with small time hobbyists like us. And something I've noticed about the wheel motors is they all seem be permanent magnet motors, so is this type of motor just more powerful or more efficient then say an ac motor.


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## Dennis (Feb 25, 2008)

You know come to think of it, I have never seen an inside out 3-phase induction motor before. It would be rather unique to have the rotor be the outside piece while the stator is the inside piece. I have seen single phase ceiling fan motors configured like this and brushless DC motors.

The way to get lots of torque for this direct drive application is to increase the number of poles to say like 48 for the AC motor. With a switching frequency of 400 Hertz max, the RPMs will be approximately 1000 RPM which is plenty for tires. The tire will be the gear ratio so to speak. The torque would probably be about 12,000 FT*Lbs or more from zero to clamp point set by the controller I would guess....


The only downside is how to get the controller to properly control torque of the independent wheel motors and get regen to work properly without out of phase issues which can be catastrophic.


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## aeroscott (Jan 5, 2008)

how er this works out ,halback , neodymium, induction, etc . this will become self evident . the major step forward is , us developing the skills to build and not to be mindless consumers buying hopeless black boxes put forth buy people who care only about profit , are dead to the passion of these endeavors . what I and 2 buck chuck ( merlo )think , john


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## Bugzuki (Jan 15, 2008)

What is the equation for RPM/poles/hertz? I know the more poles the slower the speed, so you have to have a higher input frequency, but can not remember the exact equation.

With an inside out hub motor you could probably integrate the brake rotor into the motor, and you probably could get a lot of torque due to the larger diameter rotor. 

The downside would be more rotating mass. So, more power would be used in acceleration. 

I just can not get over being a fan of internal motors with axles. Call me old fashion.


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## aeroscott (Jan 5, 2008)

Dennis could better answer about higher frequency operation . but at 60 cycles / sec. 2 poles = 3600 rpm, 4 poles = 1800 rpm , 6 poles = 1200 rpm , 8 poles = 900 rpm , 12 poles = 600 rpm , 16 poles = 450 rpm , 24 poles =300 rpm , 32 poles = 225 rpm , 48 poles = 150 rpm , then say 400 cycles or 6.6 times faster then 60 cycles . so 6.6 times 150 rpm (48 pole )= 1000 rpm . I remember some air craft generators ran at 400 cycles to 800 cycles , some had cvt's and stayed at 400 cycles or c.p. s.


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## ecvs (Mar 4, 2008)

Dennis,

You can see a picture of an inside out motor on the yahoo group called Irk-torquemax. There is one good advantage to building a permanent magnet motor inside out, and that is the magnets will have no problem at high rpms because they are held in place by centrifical force.
As for controlling the motors, electronically would be no problem for one two or even 4. Just means more ciruitry.
Tom


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## 3dplane (Feb 27, 2008)

Tom! I wish i knew more about controllers but i've built a few of those motors you are referring to. Ranging from less then an ounce to 8+ pounds.Their biggest advantage is that they have an "elecrtonic gear reduction" so model planes can swing large props without a gear box.The bell(rotor with the mags)does not follow the rotating electromagnatic field one to one.As the phases are fired off the bell instead of following, it just steps to the closest magnet pole(s).And the way it happends to work out is the number of magnetpoles divided by two is the reduction.example 12 pole rotor=6:1, 14 pole=7:1.meaning the magnetic field will have to make 6 or 7 revolutions(respectively) to one bell(motor shaft)revolution.DIY it and you have a huge range of torque or rpm game to play(good thing)rpm/volt will be affected by number of stator arms to number of winds to number of magnet poles to air gap,mag.strenght stator lenght,diameter so on.My biggest concern in our application is start up under load.Starting props is no big deal cause there is no load untill rpm kicks in.I've seen controllers for them up to 300 amp but not the kind of voltage we could use.(yet) Barna


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## ecvs (Mar 4, 2008)

The motor I think could be made for any voltage. How much voltage are you thinking we would need. IGBT's handle 1400 volts at 1000 amps. Would that be enough?
Tom


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## 3dplane (Feb 27, 2008)

What I meant with the voltage is that the "hobby" controllers dont really go above 50 v i guess due to safety reasons.I've seen castle creations show their SHV (super high voltage) unit but as far as i know its not available.We can make the motors any(within reason)voltage.(more turns of skinnier wire etc).With your knowledge maybe you could look into the working of these BLDC controllers as some people have made some.I tried looking into it but but its greek to meBarna


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## 3dplane (Feb 27, 2008)

Sorry forgot to say the SHV was 98V if i remember correctly.


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## ecvs (Mar 4, 2008)

Well at the moment I am the guy who is designing a motor controller that is open source on yahoo as a group called evcs. There are about 40 guys who have joined recently from here, some just watching and waiting and others who are also involved in the design. We have a 300 hp controller that is unproven at the moment that could drive just about anything you want to. We will eventually have a proven design that will be well documented that anyone with a little electronic knowledge could build.
Tom


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## Dennis (Feb 25, 2008)

> What is the equation for RPM/poles/hertz? I know the more poles the slower the speed, so you have to have a higher input frequency, but can not remember the exact equation.


Formula is (120*HERTZ)/# poles = synchronous speed which assumes no slip. It's only an approximate equation that does not account for the slip as more load is applied to an asynchronous. For synchronous motors it is exact, even under load.




> Dennis,
> 
> You can see a picture of an inside out motor on the yahoo group called Irk-torquemax. There is one good advantage to building a permanent magnet motor inside out, and that is the magnets will have no problem at high rpms because they are held in place by centrifical force.



I'm not really a big fan of permanent magnet type motors. I rather have a outside rotor bar squirrel cage type iron rotor using copper rotor bars embedded into the iron slots of the rotor. Imagine this being inside out:


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## John (Sep 11, 2007)

Bugzuki, I wouldn't worry too much about rotating mass. At 60 mph your hub motors might be doing about 900 rpm. Running a single motor through a gearbox and final drive at 60 mph it might be doing about 4500 rpm. So your zero to 60 mph for a hub motor arrangement is zero to 900 rpm as opposed to zero to 4500 rpm for a single motor arrangement assuming no gear changes are required. So your angular acceleration is going to be 5 times as great for the single motor over the hub motors. The rotational inertia of the an outrunner is going to be disproportionately larger per unit mass than say a conventional motor due to the larger radius of gyration of the outrunners rotating parts. This and there being four motors instead of one could bring you back to a similar rotational inertia for both arrangements if your hub motors were of similar weight. Hub motors need to be very light to prevent them destroying the cars handling by increasing the unsprung to sprung weight ratio too much. So they need to adopt the most power dense arrangement. Use of a halbach array PM outrunner should also prevent the outside of the motor having a strong magnetic field to attract metal debris from the road. I'm not sure how you could avoid this with an induction motor.


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## Madmac (Mar 14, 2008)

For those thinking of motor building this paper

http://www.ansoft.com/news/articles/Induction_Motor_Design_for_Electric_Vehicles.pdf

gives a few interesting things on AC motors, although the target size is a bit small.

Madmac


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## aeroscott (Jan 5, 2008)

very good , learned a lot . thanks , john


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## aeroscott (Jan 5, 2008)

if I used a larger ac motor then necessary how would it effect cruising range . I was thinking that the controller could be tuned for lower power . the motor i had in mind is a 6 pole 1200 rpm @ 60 cps running at 2400 rpm @120 cps. this motor is 200 lbs and 7.5 hp rating . I hear that low rpm motors have a lot of copper in them . its 91.5% eff. at rating. The idea is to run a 2.23 rear end no trans. 1200 rpm would 35 mph and 2400 would be 70 mph . oil and water cooling will be added.


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## aeroscott (Jan 5, 2008)

saw a motor today 400 cycles armature was about 3.5 " in dia. 8 poles(stator) runs at about 5500 rpm . I was told it is 25 hp ,wow .I think it was water cooled .If internal oil cooling was added the hp should be 2.5 times higher (62 hp ). the armature had bars about 1/4" apart . is this the big secret of high performance ac motors


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## Dennis (Feb 25, 2008)

aeroscott said:


> saw a motor today 400 cycles armature was about 3.5 " in dia. 8 poles(stator) runs at about 5500 rpm . I was told it is 25 hp ,wow .I think it was water cooled .If internal oil cooling was added the hp should be 2.5 times higher (62 hp ). the armature had bars about 1/4" apart . is this the big secret of high performance ac motors



Usually if it's an AC motor, the rotating member is called a rotor rather than an armature. The big secret of torque performance is not really secret, but the rotor bars shape, depth and thickness determine what type of torque characteristic the AC motor will have when hooked up to mains frequency (no flux vector controller). In fact the rotor bar's design determines the four types of AC induction motors called NEMA designs A, B, C, and D torque curves. 

NEMA design A motors develop max torque in the upper RPM range then they suddenly lose torque if load is greater than the upper torque. This highest torque value is called breakdown torque. NEMA design B is the most widely used motor in the industry. Its max torque is also in the upper RPM range (or breakdown torque), but much less than NEMA design A. This motor though has less starting current than Design A does so it will not tax the power distribution nearly as bad as a Design A would. NEMA design C motors develop max torque at around zero RPM, then the torque curve will fall slightly and then rise to another peak. It looks almost flat. Finally NEMA design D motors are used in special applications that require high starting torque which this motor can produce that exceeds all other NEMA designs, including C. The down side is this motor has poor speed regulation compared to other designs.

Here is a picture of the different torque curves of the NEMA designs:


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## 3dplane (Feb 27, 2008)

Dennis!
That's good info! I've got an AC motor question for you. As I understand, in the rotor the connecting bars act like big "coils" so when they receive a "pulse" from the stator there is current flow INDUCED in them wich constitutes in a magnetic field that becomes focused or concentrated by the silicon steel fillings back toward the stator.But due to reactance(or impedance?or reluctance?or discodance?) there is practically a delay so the interaction occurs at an angle wich provides the torque.Correct me if thats wrong. Here comes the question!(or questions) What would happen to the stator windings,or more like the voltage and current in them if the rotor was not present? (or partially pulled out but allowed to rotate)And why? I'm guessing there would be crazy voltage spikes and other bad things going on.I'm not about to try this, I'm just trying to get a better grasp on this AC stuff.Playing with transformers(cut one open and rewound to make a golf cart charger) I noticed the presence (or lack)of even small amounts of iron laminations in a closed magnetic circuit made a huge difference in the induced voltage. Thanks for your input! Barna.


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## Dennis (Feb 25, 2008)

If the rotor was not present then the stator windings will go up in smoke because the rotor's moving magnetic field (rotor turning) is not present to induce an AC voltage against the AC supply voltage. So the full AC supply voltage is applied to the stator windings. Now this voltage difference is angle dependent so you will need to convert from the time domain to polar form then to rectangular form to subtract the real parts and imaginary parts of the back EMF of the motor from the supply voltage and then convert back to polar form, then finally to the time domain to find the actual AC voltage in the stator windings.

FYI, DC motors also make AC, but the commutator is a "mechanical rectifier" so that is why its output voltage is DC.


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## aeroscott (Jan 5, 2008)

rotor got it , so what would be the best motor for controller running. ? im thinking d . how do the a,b, c,d, rotors look . do d's have the most bars like the the small 400 cps motor or Tesla motor . the Tesla guys said it was all in the rotor .


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## Dennis (Feb 25, 2008)

> rotor got it , so what would be the best motor for controller running. ? im thinking d . how do the a,b, c,d, rotors look . do d's have the most bars like the the small 400 cps motor or Tesla motor . the Tesla guys said it was all in the rotor .


I hope you realize that those torque curves are only valid when the motors are connected to a fixed frequency AC mains like 60 hertz. If these motors where hooked up to flux vector controllers then they all will have the same torque curves. With that said a NEMA design D motor is a poor choice to use with a flux vector drive because this type of motor is only 80% efficient and has poor speed regulation characteristics. The best motor would be an inverter duty rated NEMA design B motor. You could use a regular NEMA design B motor although don't expect it to last long from the high switching transients of the controller.

The rotor bars will be smaller or larger and will be embedded a certain depth into the rotor slots depending on the design as well as the shapes of the rotor bars will effect the torque performance.


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## aeroscott (Jan 5, 2008)

thank you Dennis , that clears things up alot


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## Mike D EV (Sep 11, 2007)

Lets not forget that there are lots of Prius synergy drives in recycling yards. The MG2 BLDC motor has enough torque to push a 2800 lb prius around.
I bought two of the units, and have hacked one so both motors will turn as a unit. MAx speed would be in the 90 MPH range with the stock tires.
The drive with inverter can be had for under 1K.

It has forced oil lube with built in oil pump, parking pawl, and the final drive with differential built in. The drive weighs only 220lbs, and is designed for automotive use.

http://www.99mpg.com/Projectcars/evinsight/

It would be difficult to make anything that even comes close for that money.


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