# In wheel hub electric motors??



## nucleus (May 18, 2012)

They don't exist (in a practical sense), or work for anything much larger than a bicycle.

Bad idea. 

Lack of gearing means you need big heavy motor, which means big heavy hub and high unsprung weight. 

Big heavy motor needs cooling, how is that dealt with?

Ditto brakes, regenerative braking is not enough, where do you put the brakes?

Recent thread:

http://www.diyelectriccar.com/forums/showthread.php?t=184329


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## MathisLaurant (Feb 21, 2017)

Yes, you will have poor ride quality with hub motors this is one company moving forward with it that i know of 

http://www.proteanelectric.com/


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## Karter2 (Nov 17, 2011)

MathisLaurant said:


> Yes, you will have poor ride quality with hub motors this is one company moving forward with it that i know of
> 
> http://www.proteanelectric.com/


 Dispite being one of the leaders in the field, even Protean dont appear to have "moved forward" with this concept in the last 4-5 years ?
I suspect one of the reasons is because the torque capability of these motors is a fraction of a conventional geared EV drive train (EG Tesla)
Their 1000Nm max is only similar (less infact) than Tesla cam produce at the motor,...before a 9.7:1 multiplication in the final drive gearing !
One other reason is of course the unmentioned cost of the (multiple) hub motors and the control systems required to drive them.


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## Prideisdead (May 18, 2017)

Alright thanks for the reply. So i guess nothibg at this point.

I guess a single motors full replacement would be the most economical and easyiest to do.

Im more intrested in the the acceleration EVs. 

Hopefully me and the wife will be attending pikes peak this year. A bunch of awesome EVs will be there.
Rimac.
Tesla.
Eo1
Faraday
And possibly a bonda nsx.


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## Karnaj (Sep 13, 2014)

Curious to know if anyone has heard about the YASA or Ecomove hub motors. Haven't been able to find much on the YASA but the numbers reported for the Ecomove don't look bad from my limited understanding. 40kw peak/24.5kw continuous, 361 ft/lb torque in a 46.5 lb package? Sounds good. Going by a formula I was given of ~7hp per 1000lbs of vehicle needed for decent performance (more if hilly terrain expected), these look like a possibility. Assuming this is all true what am I missing? Controllers and price not being factored for this question.

I'm truly curious. In hub motors would clear up SOOO much room for batteries for the project I would like to do, a 33-34 Ford Tudor Sedan. All I have to work with is the engine compartment, the old classics didn't have a trunk in those days.

I would really appreciate input from the more in the know.


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## brian_ (Feb 7, 2017)

Karnaj said:


> Going by a formula I was given of ~7hp per 1000lbs of vehicle needed for decent performance (more if hilly terrain expected), these look like a possibility.


7 continuous horsepower per thousand pounds of vehicle is okay to keep the vehicle moving at a constant and moderate speed on level ground. To accelerate well by current automotive standards, 70 horsepower per thousand pounds (for as long as it takes to get up to speed) is closer to a reasonable power budget.


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## Rustle731 (Sep 14, 2017)

You're referring to the MTSU project. There are videos and articles and they've had some limited success. Protean purchased a bike/scooter hub motor manufacturer in China, and struck a deal with FAW Volkswagen (China) a few years back, for Hybrid development. Protean also partnered recently, stateside with ConMed in Vancouver Wa, for development of Hybrid vehicle fleets. Here are a few links: 
http://www.proteanelectric.com/
https://cleantechnica.com/2012/07/26/mileage-boosting-drop-in-plug-in-hybrid-retrofit-kit/
And a pic:


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## brian_ (Feb 7, 2017)

The pictured thing from MTSU is an old dead-end project. An earlier discussion of this particular device can be found starting at post #473 of the _open source hub motor/wheel motor_ thread, but there are lots of wheel motor discussions in the forum.


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## izzzzzz6 (Oct 12, 2017)

Hi Guys. I found myself here after asking myself similar questions but for slightly different reasons and hence not exactly hub motors but two motors driving each drive shaft independently.
I'll try to list the reasons, the concept and the questions.
Ps. I have seen many hub motors for sale on Ali Baba but i'm not sure who is actually buying these and weather or not they are just a concept product or not.

Concept: Using two BLDC motors, one to drive each driveshaft.

Reason: 
1. Two motors are twice as powerful as one and BLDC can be wired in delta and Star configuration meaning that a virtual (electrical) gearing is available for low and high speed rpm.

2. Disposing of a gearbox will save space, weight and resistance.

Questions:
1. Will the torque be adequate to get a very small car rolling at a modest acceleration (not for racing along, just enough to be drivable).
2. If the motors are connected (wired) in parallel. Will this work as a differential.
Meaning that; When turning corners will the wheel that is moving faster transfer the extra electrical energy into the motor that is trying to turn slower or will the motors soak up the difference in energy and naturally let more energy go to the motor that is trying to spin faster through the corner.

Other possible problems:
1. Might be difficult to fit two motors between the driveshafts in a front wheel drive, might be easier on a rear wheel drive.
2. Switching from delta to Y or Star could be tricky at high current loads.
3. Finding a controller which can produce enough current and be able to over-volt the motors without surpassing their Max KW rating (for higher rolling speeds)


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## dcb (Dec 5, 2009)

fyi the need for delta/wye switching (like series parallel switching) is largely overcome with a better controller and battery. 

You *can* change the peak torque/peak rpm with pole changing motors (non linearly) in an induction motor at least, but with bldc/pmac I doubt it since the poles are fixed by the rotor.


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> Concept: Using two BLDC motors, one to drive each driveshaft.
> 
> Reason:
> 1. Two motors are twice as powerful as one and BLDC can be wired in delta and Star configuration meaning that a virtual (electrical) gearing is available for low and high speed rpm.
> ...


There seem to be two separate ideas being mixed up here.

Separate motors for each wheel
This eliminates the differential, not the transmission.​
Changing wiring configuration of whatever you consider to be a "BLDC" motor
This might help reduce the need for a multi-speed transmission, but has nothing to do with separate motors for each wheel.​

As already noted, this really isn't about in-wheel motors; the only connection is that in-wheel motors are inherently one-per-wheel.

What isn't clear is whether the intention is to use the motors to drive the wheels without any reduction gearing. Again, this is unrelated to in-wheel motors, which can be used with or without gearing. I don't any sense in using motors without gearing... and that's why essentially no one does it.

Two motors are obviously twice as powerful of one of the same motors, but more obvious solution to getting twice as much power is to simply use a bigger motor.


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> 2. If the motors are connected (wired) in parallel. Will this work as a differential.
> Meaning that; When turning corners will the wheel that is moving faster transfer the extra electrical energy into the motor that is trying to turn slower or will the motors soak up the difference in energy and naturally let more energy go to the motor that is trying to spin faster through the corner.


This depends on the motor type, but seems unlikely to me to work acceptably for any type of motor. At a first approximation motor torque output is dependent on current, so maintaining equal current between the motors would provide the equal torque split provided by a mechanical differential; however, parallel connection will provide equal voltage (not equal current) and if one wheel slips due to inadequate traction the result would not likely be good.

Managing the speed difference is a well-known issue. I noticed that Curtis Instruments has a standard solution: *Dual-Drive*. It is mentioned as a feature in many of their controllers, and a typical application is described in an article on their site.

The idea of Dual-Drive is:

each motor has its own controller
the controllers are connected to communicate with each other
one controller is designated as the master (and the other the slave), just so that the control logic runs in one place
an angle sensor provides steering position input to the master controller
control parameters are set appropriately for the wheelbase, track, and steering sensor calibration
the motors are driven to maintain the speed difference corresponding to the current steering angle
... or from the article:


> The standard Curtis dual-drive
> software allows the 1236 controllers (one master, one slave) to correctly control the dual-drive operation of the truck. This includes varying motor speed on inner and outer wheels during turns to provide true differential control.


Current production EVs generally use a single motor per axle and a conventional mechanical differential, so they resort to using the same methods for individual control of wheel torque for traction and stability control. A trend toward separate wheel motors is starting, to allow this control to be executed by the motors, without dissipating power in brakes. This makes sense, but implies an advanced level of control.


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> 1. Might be difficult to fit two motors between the driveshafts in a front wheel drive, might be easier on a rear wheel drive.


This is an issue at front or rear, since

the width of the motor assembly (across the outputs) must fit between the shortest acceptable axle shafts, and
the width of the motor assembly (across the housing) must fit between the suspension mounting points.
The most common drivetrain configuration in modern cars is a transverse engine with the transmission on the end of the engine, and despite the combined length this all fits in the front of the car. The popularity of McPherson strut front suspensions is largely due the amount of space this design leaves for the engine. To address the shaft length issue, the differential is always arranged to be near the engine/transmission connection. Rear suspensions typically leave less space for a wide motor assembly, because they are designed to fit under a floor (rather than around an engine) and only need to accommodate a small final drive unit (differential).

The packaging is particularly difficult - due to the first dimensional limitation - if the motors are placed end-to-end with outputs (including reduction gearboxes) on the outboard ends. Despite the width, this configuration is used in a few cases, such as the Rimac Concept One (which is a wide car) and the front of the new Acura NSX (which has very small front motors). The normal solution is to face the motor outputs inboard, with the gearboxes between them, placing the gearbox outputs very close together near the centre; this requires that the gearbox shift the shaft centreline far enough to clear the motor cases... such as in this Xtrac:


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## izzzzzz6 (Oct 12, 2017)

Sorry. I know it is not exactly relevant to in wheel motors but it is a similar system that is up against similar obstacles. It was more of a question that i was throwing out there. 
The thing with 3 phase motors and i believe it included brushless is that you can change the wiring from Delta to Star mid rev. This acts like an electronic gear to some extent thus potentially helping to eliminate the transmission, perhaps it is enough to have these two modes rather than gears, assuming that the direct drive was geared up correctly and that the motor had lots of overhead and also assuming that you don't need tonnes of torque at low speeds. If your motor(s) is/are well overrated then as long as you don't exceed it's rated power level you can push it a bit at low speeds or over volt it a bit at high speeds (potentially risking premature damage to the bearings or speed wobble from parts not being balanced at those speeds + timing issues etc).
With the gains from less weight and less friction plus more space for bigger motors and batteries it might suit some people to go single speed as far as gears go.
The question about differential was just to see what people think or if anybody knows if there would be enough forgiveness between the two motors if they were connected in parallel or would such a simple setup potentially cause damage to AC and BLDC 3 phase motors ? 
Perhaps it would work well with other types of brushed DC motors or perhaps the motor turning fastest would start to act like a generator and try to power the slower turning wheel causing tyre ware etc.?
It just might be an easier or cheaper option than buying what appears to be not easily available in wheel motors. If you can fit them in. 
But I'm sure there is an easy way to correct the wheel speeds electronically if going diff-less. I just don't know the answers sorry.


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## izzzzzz6 (Oct 12, 2017)

Good answer. Might also help to go this route if you can get 2 fairly large controllers with this feature. To double the power by doubling your controller count and motor count etc..


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## izzzzzz6 (Oct 12, 2017)

That photo looks like a sweet setup, which OEM makes that one? Have you seen the guy with the dual motor 4x4? He has a chain link between the two. 
I'm guessing that a motor won't always have the same performance in reverse? actually i don't think it's a problem with 3phase BLDC as you can usually reverse any 2 of the 3 windings to change direction. that way you could stack motors and just reverse the direction of the one that is powering the other wheel. Or perhaps there is enough play in the driveshafts to off set the two motors?
In wheel sounds like a great idea though. I like the idea of the electric skateboard which has it's motors built into the wheels. I would lie to get my hands on some of those motor wheels.


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## dcb (Dec 5, 2009)

izzzzzz6 said:


> can change the wiring from Delta to Star mid rev. This acts like an electronic gear to some extent thus potentially helping to eliminate the transmission,



I don't think it does actually, that was more of a hack for controllers that couldn't deliver a lot of current or voltage.

however pole changing does have potential, as you are changing the circumferential distance between the poles on the fixed vs rotating bits, and the attraction isn't linear with distance.


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## WolfTronix (Feb 8, 2016)

The old Brusa AMC motor controllers (circa 1993), have a Delta / Wye input...

Delta is about twice the RPM, and about half the torque of Wye.
Wye is about twice the torque, and about half the RPM of Delta.

An external contactor is used to switch the ACgtx20 motor between the two wiring configurations (all coils are in the junction box):

Delta:








Wye:








Note: you would bring all the coils out to your Delta/Wye contactor.

The Delta / Wye input tells the AMC motor controller which parameter set to use (resistance, inductance, back EMF, etc... changes between the two modes).

My test box even supports this feature:








My truck in Delta has a max speed of 70MPH.
My truck in Wye has a max speed of 35MPH (but acceleration is twice that of Delta).


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## dcb (Dec 5, 2009)

WolfTronix said:


> Delta is about twice the RPM, and about half the torque of Wye.
> Wye is about twice the torque, and about half the RPM of Delta.


The thing is (and I assume you are aware of this) that it is probably current limited by the controller (and/or rpm limited by bus voltage).

So that a better controller/battery will negate any benefit from delta/wye switching, and is much simpler conceptually. In delta each phase is seeing 1.73 times less current unless you dial up the current from the controller. In wye it takes 1.73 times more voltage to cancel out the back emf at a given rpm.

This isn't the case with pole changing (i.e. dahlander) motors I don't believe. You can change the toque/rpm capabilities of the machine. So while delta and wye (as a machine with its own limits, independent of controller limitations) operate in the same torque/rpm modes, pole changing can indeed act like a gearbox, kinda, within limits.

I did an armchair analysis of ABB motors here:
http://www.diyelectriccar.com/forums/showthread.php/number-poles-revisited-again-164921.html


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> That photo looks like a sweet setup, which OEM makes that one?


The transmission is the P1227 from Xtrac, shown with YASA motors. It probably isn't available directly to a retail customer; the target is vehicle manufacturers. This is a "torque vectoring" configuration (two separate motors and transmissions, mounted together). YASA shows some additional configurations of this series of Xtrac transmissions: YASA P400 Series Motors with lightweight gearboxes


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> I'm guessing that a motor won't always have the same performance in reverse? actually i don't think it's a problem with 3phase BLDC as you can usually reverse any 2 of the 3 windings to change direction. that way you could stack motors and just reverse the direction of the one that is powering the other wheel.


Brushed DC motors routinely have the position of the brushes adjusted slightly for optimal performance in a specific direction. With one motor per wheel, you would just adjust each motor to suit its forward rotation direction... but performance in reverse is still limited.

I agree - it appears that this is a non-issue for AC motors.



izzzzzz6 said:


> ... Or perhaps there is enough play in the driveshafts to off set the two motors?


Not likely - if you place two motors transversely, one ahead of the other, the shaft angle required to make up half the motor case diameter over the length of the shaft (between inboard and outboard joints) seems excessive.


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## izzzzzz6 (Oct 12, 2017)

Nice to hear about some real life results. So it could really be worth trying a double BLDC drive without transmission?
Does your truck also have a tranny or is it direct drive from the motor? 
Is that with a three phase AC or DC motor?
I'll have to check it out. Do you have some posts on the forum with some more info?


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## izzzzzz6 (Oct 12, 2017)

Controllers will always have a nominal efficiency at some point of their power curve.
I'm thinking for example, if we were talking about Brushed DC, then beyond a certain speed (when trying to reach top speed). It might be better to just eliminate the controller and have a direct connection to the batteries (assuming the setup is well balanced and the motor won't burn out).
By doing this you can eliminate any losses in the controller.
if the speed becomes too great you just power off from the pedal and roll until you need to boost again. (could be annoying if your not just holding top speed). Then perhaps there is reason to switch in a different type of controller solely for top speeds. By designing one that is more efficient at those high rpm high current demands there may be a little leeway as far as tweaking for speed or economy gained. 
If we are talking in wheel motors then that is potentially 4 controllers worth of lost economy when operating outside of the nominal range for efficiency.
I'm getting carried away. I really don't know enough about efficiency of brushless motors and their controllers. I'm guessing a computer can control a variable frequency type drive and tune for efficiency continually. Although everything does have a nominal range at the end of the day depending on what it was designed for.
I doubt that there exists much of a solution for brushless apart from changing the timing perhaps.
It would be interesting to see the difference in top speeds with and without the controller in a brushed setup.
I remember my 1st RC car's speed controller. It was manual and controlled by a servo. at full speed it was just a straight connection to the battery, otherwise it had to pass through a high power resistor or two.
As far as the controller limiting rpm or speed, that may be the case but there is often a way around that by re-programming, over-volting or modification.
Once you have unlocked the full potential of the system, you would just need to be aware of your motors limitations in the respective wiring configurations. 
You would need a watt meter or perhaps even an ammeter for each mode and just treat it like a rev counter. Don't red line for too long! Or just ask the controller to do this for you.
Perhaps have one controller for Delta and one for Wye. Each one setup differently to work best at those speeds. The switching relay could switch controllers at the same time as switching the wiring configuration.


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> Does your truck also have a tranny or is it direct drive from the motor?
> Is that with a three phase AC or DC motor?
> I'll have to check it out. Do you have some posts on the forum with some more info?


I assume that this is directed to Wolftronix...

He has a Solectria E-10:
Solectria E-10 Restoration

The E-10 uses two induction (3-phase AC) motors (each with its own controller), both driving through toothed belts to the same gear wheel on the shaft to the truck's rear axle, so it has a two-stage speed reduction system - a first stage by belt and a second stage by the pinion and ring gears in the axle - with a single ratio.


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> ...
> If we are talking in wheel motors then that is potentially 4 controllers worth of lost economy when operating outside of the nominal range for efficiency.


Four controllers don't mean any more loss than one four-times-larger controller handling the same total power.


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## izzzzzz6 (Oct 12, 2017)

Well Weather or not 4 controllers have more or less loss than one 4x their size is hard to say. But i guess my point was that there is always some loss in a speed controller and that they are probably made to be more efficient at nominal speeds (depending on the application).
I really think there could be a significant amount of power saved by eliminating the controller at top speeds which could work with a brushed motor especially if you were maxed out on a freeway for example.
I was just wondering if there might be a way to do something similar with three phase in order to get the best efficiency possible at top speeds. Since you need some sort of controller for three phase the only other option i could think of is to have multiple controllers that are designed to give better efficiency at different speeds. So for town driving the car would switch to the controller that was made to be most efficient at lower rpm. And when of the freeway the controller best suited to high speeds would kick in and the other/s would switch out and turn off.
The difference might not be much but who knows it might be as much as a 5% increase in range or it could potentially decrease the battery size by 5% which could result in a saving of weight (depending on the weight of the extra/modified controller).


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## brian_ (Feb 7, 2017)

izzzzzz6 said:


> I was just wondering if there might be a way to do something similar with three phase in order to get the best efficiency possible at top speeds. Since you need some sort of controller for three phase the only other option i could think of is to have multiple controllers that are designed to give better efficiency at different speeds.
> ...
> The difference might not be much but who knows it might be as much as a 5% increase in range or it could potentially decrease the battery size by 5% which could result in a saving of weight (depending on the weight of the extra/modified controller).


I doubt that even a perfect inverter or controller would be 5% more efficient than an inverter or controller at a typical operating condition. Even if it were, that would only correspond to 5% more range if the motor were operating at this alternate operating point all of the time. So if there is perhaps 1% more efficiency to be gained (from running at this specific condition 20% of the time), wouldn't that likely be lost in the extra wiring and contactors needed to run in two different configurations?


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## izzzzzz6 (Oct 12, 2017)

Great point but perhaps 1% is not being generous enough 
If i told you that there were two battery types available for your project and that one of them had 1% or 2% more stored energy available then you might decide to buy the better battery no?

If enough other tweaks could be made in other areas then might it be possible to see an even higher overall gain in efficiency?
If in the future electric cars start to cover longer distances as standard then this concept might prove worth while.

Cars could be covering many more motorway miles and thus the advantage may be realised more than 20% of the overall driving time, which is the ratio that you had suggested that we might be benefiting from if high speed economies were achieved if we changed the controller at different rpm (or by redesigning the controller to have a wider efficiency characteristics whilst still providing adequate output power across the rev range).

Also since motorway driving is done at higher speeds this also means that it is most likely going to be the time we see the highest current draw from the batteries. Which means that just a few percentage gained in efficiency will go a longer way at 300A per say when compared to the saving of a few percent at 80A for example whilst poodling around town or when driving at medium speeds around the suburbs.
If battery exchange / charging stations or perhaps even super fast charging stations are to be implemented in the future then perhaps these small gains will not be worth it, perhaps such technology would only be implemented in the higher end cars. 
But at least for anyone out there who might be running brushed DC motors, it might be worth considering. 
I doubt even the best controllers are actually more than 90% efficient in real life conditions. So imagine gaining 10% efficiency when running at full speed. 
A pain in the ass when the only speed control becomes pedal on pedal off but perhaps there is still something to be gained here for someone reading this.


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## SteveWrightNZ (Nov 3, 2017)

Hi everyone, first post!

https://www.aliexpress.com/wholesale?SearchText=electric+car+hub+conversion+kit

I found this thread with google, and I don't see the chinese conversion kits mentioned anywhere. I don't know whether US$2K is cheap, but it seems to include everything including the wheels and brakes.. Battery separate.

Anyone tried these?


Steve


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## Duncan (Dec 8, 2008)

Hi Steve
Could make a good boat anchor - or go kart possibly 

Kelly controllers don't have a good reputation!

And Hub motors are no use to man or beast


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## SteveWrightNZ (Nov 3, 2017)

Thanks, Duncan.

Can you direct me to reading material on the points you've made? I've had a google around, but I don't really know what I'm looking for.

cheers mate,
Steve


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## dcb (Dec 5, 2009)

well you can start with this very thread
http://www.diyelectriccar.com/forums/showthread.php/wheel-hub-electric-motorsii-184393.html

and expand your search to the entire site with some googlefu
https://www.google.com/search?q=hub...m/forums&oq=hub+motor+site:diyelectriccar.com

But basically:

lots of unsprung weight, poor handling.

low torque (lack of gearing, otherwise 350nm isn't too shabby), might get stuck on a hill etc.

low power, comparatively. If you geared these down so you could climb a hill, you would have a top speed of like 10mph.

electrical bits splashing in puddles.

bouncing your motors off of curbs and ruts.

more rotating mass, more energy consumption.

less room for things like brakes.

motor cables flexing and work hardening, and generally being more exposed.

Virtually nobody does it, and those that do don't share all the relevant details, success is measured by if it backs out of the garage with little to no assistance.

etc. etc.

they are fairly practical on a commuter bicycle fyi, and with various mods you can push them hard enough to actually be good. But those are simple no suspension and already lightweight machines.


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## SteveWrightNZ (Nov 3, 2017)

I see. Good for a very large skateboard, but oops nowhere to put the batteries... 

Thank you!


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## DrEVILish (Nov 8, 2017)

My stupid idea is to take an already perfectly good gas guzzler and add a pair of hub motors to the rear wheels of a 4x4.

Why has no one created a design like this: 
You pull off the rear brake discs and mount a bunch of permanent magnets in a ring bolted to the wheels.
Then mounting a ring of windings to the brake calliper mounts.

This adds a small amount of extra weight, over what you've already removed.

You still have your front brakes which should be strong enough to stop the vehicle anyway. Using the rears now as regen.

Giving your car ability to increase its acceleration by only applying current from the batteries under acceleration (<30mph depending on throttle position) and under extreme acceleration (throttle >50% open). 
If throttle position 0% enable regen.

Should be generic enough to work on any car, for a number of rear wheel sizes. Creating ones to replace the rear discs.


Please poke holes in this idea.


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## Duncan (Dec 8, 2008)

Hi Doc
The problem with that comes with the numbers - this is roughly like putting a hamster wheel under your bonnet and expecting the poor beastie to propel your car


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## brian_ (Feb 7, 2017)

DrEVILish said:


> ... You pull off the rear brake discs and mount a bunch of permanent magnets in a ring bolted to the wheels.
> Then mounting a ring of windings to the brake calliper mounts.
> ...
> Please poke holes in this idea.


The general idea is a parallel hybrid, and that's sound... due to the benefits of regenerative braking and making power available for greater brief acceleration without a larger engine.

The electromagnetic reality is that with these in-wheel non-geared motors running at wheel speed, they will have very low braking torque (too low to be effective) and low driving power (too low to be very useful). There is a reason that every practical traction motor is geared to run at much higher speed than the vehicle's wheels (and so the torque delivered to the wheels is much higher than the motor output torque).

A practical issue of construction is sealing these large-diameter rotating assemblies. A gap large enough to tolerate road dirt would not be efficient.

But the problem which kills the idea is that the motor/generators would be insufficient as rear brakes, because they would be neither sufficiently reliable not be sufficiently effective to be the primary braking system. The assumption that front brakes by themselves are adequate is false.

This sort of scheme has been proposed as an add-on to the brakes, rather than replacing them. That still has most of the same problems, and is less desirable than a conventional parallel hybrid (with the motor/generator mounted between engine and transmission) because it would be more expensive, heavier, and less effective.


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## WolfTronix (Feb 8, 2016)

The brake disk its self could be the rotor in an axial topology AC induction motor. No magnets needed.

You could still have your brake pads and caliper for hydraulic brakes.

Then the rest of the circle is taken up with the stator coils.

If you could manage 5HP continuous per wheel, and perhaps 10-25HP peak, it could work as a bolt on hybrid conversion.

I did no math on this, just speculation.


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## brian_ (Feb 7, 2017)

WolfTronix said:


> The brake disk its self could be the rotor in an axial topology AC induction motor. No magnets needed.
> 
> You could still have your brake pads and caliper for hydraulic brakes.
> 
> Then the rest of the circle is taken up with the stator coils.


I'm sure this has occurred to many of us while daydreaming about future possibilities, but I usually imagine the rotor as PM. Induction helps both cost and temperature tolerance (needed because of the friction brake), but adds a challenge for regenerative braking at very low speed (because there is no torque without slip).

The rotor ends up completely encircled, which is a serious cooling challenge, so it would need to be vented (which is normal for front brake rotors, but not rears on production cars), with airflow radially through the stator.

Windings would normally be a major issue for a rotor which needs to withstand being used as a friction surface for braking; however, the intention would presumably to use the normal squirrel-cage design (rather than the relatively rare wound induction rotor); due to the axial flux the conductors would run nearly radially and be shorted by rings at the rim and inside of the stator face area. To my surprise - although in hindsight it makes sense - these rotors do not have insulation between the conductors and the laminations, so the brake pads could actually slide across the conductors and wear down their surface. Still, I wonder about the compatibility of a mix of iron and whatever the conductor material might be (aluminum or copper).

It may even be practical to use a solid aluminum rotor, although this would presumably be less efficient than a design with conductors across iron laminations, and would be problematic as a brake rotor. Aluminum brake rotors do exist - they're even a regular production item from Wilwood - but they are not ideal (for multiple reasons); they require an anodized, ceramic, or plasma-coated surface, and I don't know how that would affect induction motor performance. Solid aluminum would be simple.


There are two major issues with the motor-instead-of-brake idea: the loss of the brake, and the effectiveness of the motor. WolfTronix's dual-purpose rotor idea addresses the first, but still leaves the second.


WolfTronix said:


> If you could manage 5HP continuous per wheel, and perhaps 10-25HP peak, it could work as a bolt on hybrid conversion.


Even if the brake issues are manageable, as a motor the interrupted stator is interesting. With a PM design I can see how this could work, but with induction it is not so clear. Even if three-quarters of a stator is three-quarters as effective as a full stator, this is still a motor running at wheel speed, and not an optimal one at that.

The combination implies (in practical terms) that the motor gap would be open, rather than enclosed.

It might be a "bolt on" conversion, but it would not be a simple one, because the vehicle will have a mounting bracket for a brake caliper... not for a stator assembly. Vehicles designed for drum brakes but available with disks would probably be easiest, because they would accommodate a stator mounting plate similar to a drum brake backing plate. It also looks like a workable stator would be bulky compared to a typical disk brake caliper, so fit may be a challenge.


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## Duncan (Dec 8, 2008)

To add to Brian's comment

Even when you got all of that done - it would add about the same amount of useful power as couple of hamsters


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