# Do-it-yourself hub motor?



## tylerwatts (Feb 9, 2012)

Paul

Sounds VERY interesting sir! I'm sure ill have a good few 2c to input...

Thinking on materials, what are power goals? I was thinking about the Enertrac hub motors with Al stator and rotor and 10kW cont and 30kW peak so here goes: I believe a rotor/wheel and a stator made of reinforced advanced acrylic would be plenty strong enough up to this sort of rating. There are glass, carbon and metal fibre reinforced plastics that are really strong, should handle a reasonable amount of heat also, and will be really light compared to metal versions. Worth looking into.

On a more costly scale, the world is your oyster with ceramics, and if designed right you can get light and very strong structures that can be electrically insulating and handle high heat and vibration, but will cost a lot to develop and manufacture...


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## PaulS (Sep 11, 2012)

I haven't calculated the ultimate goal yet but I am pretty sure it will have to move an 1800 lb car at close to 100 - 150 mph and have enough power to go 0 - 60 mph in under 4 seconds. That will allow it to compete with ICE and hybrids. The expensive part will be the battery pack - I would like to see at least a 300 mile range on the finished vehicle. The GVW will be 2300 - 2400 lbs. and use at least two of my hub motors.
The prototype will be built in my shop so we are limited in materials that I can turn on my lathe. I am thinking that metal - any metal that has an electro-mechanical linkage - is out of the question because it could cause stray paths for the magnetic fields. My first thought was poly-carbonate but I don't think it would withstand the heat. A high temp acrylic may work and maybe even a glass re-inforced acrylic. Carbon and metal fiber reinforced plastics I would have to check into but most are conductive and will react to running in a magnetic field by generating current - that robs power from the motor with induced drag.

It may help if you can visualize the rotor like a disc brake rotor but made of "plastic" with a close fit to the field poles that are electromagnetic "horse-shoe" magnets that would look like the caliper on the disc brake - only there are 15 of them. The rotor has 24 opposing poles / 12 on each side.
Ceramics would be an excellent fit but only in mass production. It doesn't hold heat, it is thermally stable in size and shape, and strong enough to take the forces of tourque and speed based centrifugal, centripital and gyroscopic effects.
How much heat is the key and I think it will be between 180 and 200 F unless I can find a way to cool it without a sink. A fan may work but air filtration to keep out particulates may hamper the air flow and be an additional maintenance factor. Tolerances are going to be very close - I am thinking less than normal machining tolerance of +/- .001". I am expecting half that at +/-.0005". 
Again, the first step will be a prototype and then working out a controller for the 15 field coils so we can vary the speed (frequency) and current sequencially. That is the part where I am lost - but I think a basic flip/flop running the processor timed by a hall effect on the rotor shaft may be the easy way out. (not ignorant just not well versed).
The other side is that I would like it to be able to be made by anyone, at home or with the aid of a local shop. I don't want to make any money off this, I would just like to make it available as an option that won't cost an arm and a leg to the home builder. The plans and schematics will be free to anyone so long as no profit is made. I am not sure yet how to license it for commercial use but it is a conversation I will be having with my attorney. For now I will hold the patents but it will be released as "open source" for unlimited personal use. Each contributor will be credited with his or her work on the project and named (if they want) on the paperwork, drawings and schematics. I can amend the patents to include partners and contributers alike.
Paul


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## major (Apr 4, 2008)

PaulS said:


> I can amend the patents to include partners and contributers alike.


That is incorrect. And the rest of the post....

Look at this thread. http://www.diyelectriccar.com/forums/showthread.php?t=14185&highlight=open+source+motor 
Like nearly 4 yrs, 471 posts and 170,664 views. And what do they have to show for it? And this thread. http://www.diyelectriccar.com/forum...conversion-42238p9.html?highlight=alaska+star He sounded a lot like you before he tried to delete himself out of frustration. And one of my favorites. http://www.diyelectriccar.com/forums/showthread.php?t=20591&highlight=wheelmotor 

Some folks get mad at me for throwing reality in their face. Sorry. In fact I like to see people experiment with motors. So go for it.

edit: Another one. http://members.shaw.ca/Craig-C/AboutEH.html 
And http://electrichubcap.creativesystemdesigns.com/
http://members.shaw.ca/Craig-C/AboutEH.html


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## Ivansgarage (Sep 3, 2011)

Gee Major why dont ya just poke em in the eye with a big stick.

But I do agree with you.

Check out this link.
http://www.pmlflightlink.com/#


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## toddshotrods (Feb 10, 2009)

Noble intent, but you're contradicting yourself all over the place. I won't touch the motor stuff, as I am mainly an industrial design type, and electric motor end-user. Here's one on the mechanical side:


PaulS said:


> ...Tolerances are going to be very close - I am thinking less than normal machining tolerance of +/- .001". I am expecting half that at +/-.0005"...
> 
> ...The other side is that I would like it to be able to be made by anyone, at home or with the aid of a local shop...


I'd bet that the average machine shop would fail a majority of the time at meeting "+/- .0005" tolerance. "A couple thousands (.*00*2") is serious precision work for the average machinist. I know this because I design stuff that needs more precision, and often have a hard time finding people who can live up to it...

That means you're going to have a lot of people spending a lot of money for unobtainable (for the available resources they have) results. Regular production has to design a reasonable amount of "slop" into the process, DIY intended products need much more. That's part of the reason things we buy seem like they have so much more potential than we get for the money - goals and potential are commonly scaled back for production and long-term reliability. To even achieve .0005" is one thing, to have materials that can "live" there, on a budget the average person can afford - ain't gonna happen... 

Not trying to be a downer, just noting the inescapable reality of wants vs needs vs money vs physical reality. The world would be a much nicer place for people like me if those weren't concerns, but nearly a half century of trying to push the limits says they are.


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## major (Apr 4, 2008)

Ivansgarage said:


> Check out this link.
> http://www.pmlflightlink.com/#


How many more times do they need to go bankrupt? Somebody should poke them with a stick


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## PaulS (Sep 11, 2012)

Well, I can always just do it for myself....


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## PStechPaul (May 1, 2012)

I'd be happy to help, mostly with the controller design, but I think the basic premise of this project may have some fatal flaws. A hub motor is subject to a lot of mechanical stress and impact from the road environment, with sand, gravel, salt water, potholes, and other nasty hazards. If the tolerances are so tight, it sounds like you may be trying to reduce the air gap for higher efficiency, but it also means that the housing, bearings, rotor, and stator will need to be very strong and precise. You will also need to consider thermal expansion which will affect the air gap. And as mentioned by others, 0.0005" tolerance is beyond the capability of most machine shops, much less DIYers with Harbor Freight lathes and milling machines.

I think the only design concept that has not been fully explored is the SRM, and that may be the way to go. Permanent magnet designs have been popular among DIYers, but they tend to be costly and fragile. Hub motors may be practical in some applications where torque and speed range are limited, but for the design target you have proposed, with race car acceleration and top end speeds far exceeding legal limits on public highways, along with a range that is limited by battery technology, there are just too many pitfalls.

For the non-conductive high-temperature material, you may look into various grades of Garolite or Glastic, which are reasonably priced and machineable with carbide tools. Here is a chart of properties, and the materials can be obtained from www.mcmaster.com. They also have easy-to-machine glass-mica ceramics: http://www.mcmaster.com/#8477kac/=k0tshp.

Let me know if you have any more specifics about your design and what you may need. I am more experienced with electrical and electronic engineering and microcontroller programming, but I have a friend who is a mechanical genius who may be able to help with that part. You can see some of the things he has invented on his websites:
http://www.patcoinc.com/
http://patcoinc.net/


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## mizlplix (May 1, 2011)

Paul: Build yourself a first generation motor. There is a whole education in just that. Your second one will be a much clever design....By the time you get to the third prototype, you will have a good idea of what is required material wise and who can do the precise work you will need. 

If it was easy, they would be all over the place.

Miz


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## PaulS (Sep 11, 2012)

Miz,
You have no way of knowing what my background is so I should tell you that I have been working with electric drive and control systems for over 40 years. I have built DC motors before, I have repaired DC motors - lots of them in the 40 years working in the material handling industry. I have installed and repaird drive and pump contollers from the oldest manual contactor reistor type through the scr controllers, the transistor controllers and into the first and second generation AC controllers. I have worked with sieries would, series-shunt, parallel would and independent field excitation motors. I have a pretty good idea of what I am doing as far as the mechanics of it go. I have a lot of learning about how much tollerance and what light weight materials I can adapt because, frankly the material handling field cares little about weight (or rather getting rid of it), an when adapting stuff from that field into an EV car it is just a poor fit for any serious use.
Like I said, I can build the motor for myself and go from there. I may be older than most of the folks here but I have some advantages too. I have my own lathe and although it is a hobbyist lathe (10 x 40") I can hold tollerances to under .001" with it. All the machine shops I ever dealt with in the greater Puget sound area had no problems holding tollerances under .001". Some of those shops could hold tolerances to .0005" or less.


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## PaulS (Sep 11, 2012)

PStechPaul,
I could use some help with the controller but until I finalize the particulars you wont be able to do much. I can say that the motor will use pulse DC with polarity inversion and amplitude modulation to control torque and speed. The present concept could use AC tech but the frequency and amplitude would still need to be controlled independantly. 
The frequency will control the speed while the amplitude will control the torque. Using the DC will require swapping polarity many times per revolution because of the configuration.
I am hoping for 95% efficiency from the motor which will make it at least competetive with the top end hub motors with less weight and at a lower cost - for me if for no one else.

The overall concept is for a car with the hub motors mounted inboard, disc brakes attached to the inboard shaft and the outboard shaft connected to axles to the wheels. Independent suspension and less unsprung weight. Most of the mass - batteries, controller and cooling will be near the center of the car - either under the passengers or behind them. The double wish-bone suspension will give better handling and the light weight will help the acceleration and handling.

Although the motors are being purpose built for my application they could be fit into many conversions with little need for transmissions and other power robbing accesories. Its a good situation for all the experimenters.

Paul


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## PStechPaul (May 1, 2012)

OK, I'll wait for you to contact me about anything I might be able to help with. When you supply more details I can let you know what I think and whether or not I can help. It would be mostly in the area of microcontroller design and power drivers and PCB design. You might contact my friend Tony at www.patcoinc.com to discuss mechanical details.

Good luck!


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## mizlplix (May 1, 2011)

> Miz,
> I have built DC motors before, I have repaired DC motors - lots of them in the 40 years working in the material handling industry. I have installed and repaird drive and pump contollers from the oldest manual contactor reistor type through the scr controllers, the transistor controllers and into the first and second generation AC controllers. I have worked with sieries would, series-shunt, parallel would and independent field excitation motors. I have a pretty good idea of what I am doing as far as the mechanics of it go. I have a lot of learning about how much tollerance and what light weight materials I can adapt because, frankly the material handling field cares little about weight (or rather getting rid of it), an when adapting stuff from that field into an EV car it is just a poor fit for any serious use.
> Like I said, I can build the motor for myself and go from there. I may be older than most of the folks here but I have some advantages too. I have my own lathe and although it is a hobbyist lathe (10 x 40") I can hold tollerances to under .001" with it. All the machine shops I ever dealt with in the greater Puget sound area had no problems holding tollerances under .001". Some of those shops could hold tolerances to .0005" or less.


Uh...Sorry if my post set you off. *It was a supportive statement.* No need to respond. I will not reply to yours again.


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## PaulS (Sep 11, 2012)

mizlplix said:


> Uh...Sorry if my post set you off. *It was a supportive statement.* No need to respond. I will not reply to yours again.


I wasn't set off. I rarely get upset on the internet. I was just letting you know that I had some experience in the field. I always assume that people have good intentions unless it is blatently clear that the opposite is true.
I appologize if it seemed like I was attacking you for your suggestions. Nothing could be farther from the truth.


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## Apex-xt (Jun 27, 2008)

I'm interested in this too!

Long-time lurker. About two years ago I thought about a concept that instead of using one honking big motor, use multiple small ones. 

So, starting with a design for a small pancake motor along the lines of a Fisher & Paykel that might be light enough for an individual to wrestle around by themselves, cheap enough and simple enough to machine out at a local shop, hobbyist, etc. It would be far too small/underpowered to use alone. But mount 2 per wheel on an inside axle - Subaru AWD donor, using the existing articulating axles, shortened to accommodate 2 motors per wheel, inboard so as not to load the suspension. I know it would need creative controlling to synchronize the 8 motors. Maybe a Raspberry Pi synchronizing two motors on each wheel and another one synchronizing two Raspberry Pi's per axle and another one synchronizing the two axles! They're cheap and powerful. 

But it would add some interesting capabilities to use only front or rear axles depending on load, all axles for snow, even selecting 1 motor per wheel as each wheel would be independent. Or, dropping to only 2 motors as load decreased. And, if one or two motors fail, you could limp home and replace it at home with a standby or two.

Yea, I know, too far fetched. Let the hammer of reality strike!

So, I'll watch this thread with interest. Your motor and controller design might be just the ticket for what I'm looking for. Keep it up!!


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## PStechPaul (May 1, 2012)

I had a similar idea, but mostly for tractors, which would use three motors per wheel: http://www.mytractorforum.com/showthread.php?t=249420


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## Ivansgarage (Sep 3, 2011)

Tell me Paul, why would you want three motors, three times the trouble.

Why not just one motor and right angle gear reduction, like wheel chair.

------------------


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## PStechPaul (May 1, 2012)

There are a few reasons to consider multiple motors, although none of them are really compelling.


Multiple motors offer redundancy, if one or more fail.
The design I show allows the motors to be shifted in or out, for freewheeling. That was for use as an auxiliary drive for extra traction at low speeds.
It may be cheaper to purchase six small custom motors than one or two larger ones, at least for a prototype.
The form factor of three motors allows a greater ground clearance, which is important for a tractor or other off-road vehicle.
Having three drive gears can provide more torque than a single drive, and distributes the force equally on the large wheel gear.
Spur gears may be less expensive and more efficient than a right-angle reduction drive.
The motors could be equipped with two different size gears and used as a high/low shift.


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