The key material in the SIM-WIL's in-wheel motors, DuPont's Zytel HTN polyphthalamide (PPA), is used in the motor bobbins shown here. The material is stronger, lighter, and more cost-effective than what it replaces. (Source: DuPont Performance Polymers)
This seems like a great example of engineers thinking out of the box. Maybe I dont' know enough about the space, but putting motors in wheels as a means of increasing mobility on a single charge seems pretty unique--and compelling. Is any one aware of others using this as a mainstream approach?
Beth, acutally this is the way electric cars should be designed. Having one big electric motor is really a legacy of the ICE design philosophy. Of course, it made sense there. I always assumed that this is how electric cars would be designed, and I believe that over the years there have been such prototypes or design studies. Locomotives, for example, the real model for how we should be designing electric and hybrid vehicles, use a motor for each driven axle. Of course, becuase they run on rails they don't need one for each wheel. In the conventional vehicle world, companies like Audi have long touted all wheel drive, where power is feed to each wheel in an optimum way. With modern control systems and, of course, innovations in the motors themselves, this should be a no brainer for the modern electric or hybrid vehicle.
I have to say, that I have heard of this design approach before (motors in wheels) but not sure if it was ever on a vehicle intended for production. Makes perfect sense, though. No more drive shaft tunnel or heavy gearbox and differential. I'll bet it's low maintenance as well. Total cost of ownership/operation is probably pretty good when compared to gasoline and hybrid models.
While I would agree that there is indeed some ICE legacy to the single motor design direction there are other considerations.
Placing the motors in the wheels increases the unsprung mass of the vehicle and this has an adverse effect on the performance of the suspension. Typically both ride and handling charateristics deteriorate when the ratio of unsprung to sprung mass increases. For the locomotives in your example, traveling on a smooth rail this is farless of an issue.
One possiblity is placing the motor very near the wheel with a short drive shaft. Yes the complexity of the sytem increases, but it may still be better than the centrally located motor without the drawbacks of placing the mass outboard of the suspension.
Great tech for smooth highways or around a city with decent roads, but a concern I would like to see addressed is that the cables carrying all that power would get a real shake and vibe workout on many American streets/roads. Routing loops and special cables could possible help but piling up twist and bend cycles is an enemy of good electrical connection through copper wires.
We sometimes use ultra-fine high-flex wire to gain extra use where repetitive vibe and bending is unavoidable. However I've never used that method to carry power, just data. And we still see breakage given enough cycles.
Anyone have experience with power cables and high rate of flexure abuse?
Well said Bunter (Dennis), Unsprung weight is important (independently of what some guy at Lotus recently said)... But there are other things that need to be considered here. The matter of rotational mass (Polar moment of inertia) is one of them. Maybe the diameter of the motor assembly is small or the heaviest component is placed inside (either magnets or coil windings could be placed inside or outside depending on motor type selection, varying the rotational inertia).
In a perfectly flat road (never saw that where I live), placing the motors directly into the wheel is of little consecuence, but I guess that in a world full of huge potholes, the design of the tire will have to take into account a larger bump absorption capability than present day designs provide. Your suggestion about using a short shaft seems to me the best compromise perhaps. Amclaussen.
abq-engineer, thanks for that link. What fun! It sounds like a very similar design concept to the SIM-WIL. Of course, as the article points out, it weighed a lot because of the 1.8 tonnes (metric tons, or 1.984 US short tons) of batteries needed.
Ann, I have a feeling we'll look back at this period as an explosion of innovation in the auto industry. I would guess a lot of the technology that's getting developed to support hybrids and EVs will also be handy when used to meet the higher mpg standards in conventional autos.
The other potential issue, is synchronized control of the four motors ... if a failure occurs and one motor loses power, what does that do to control and handling (and tire wear). I would think that the AWD traction control systems would face similar problems, so perhaps this problem has been approached there - except that in those systems, you can default back to standard 2WD operation, which I see as less of a problem than inducing a sudden imbalance between the four drive wheels.
Computerized control of each wheel's torque for both driving and braking will eliminate any adverse effects on the controls and driving experience. Torque steer which I eperienced in my 200 Honda Accord under hard acceleration and a curve can be eliminated by appropriate algorithms in the cotrol system. The same control system can also compensate for loss of power or traction on any combination of wheels.
These systems will evolve and prices will come down once they enter mass production. The benefits of a computer controlled all electric wheel motor arre very compelling.
I remember the Tom Swift books where he built an atomic powered car with wheel motors. I think it could fly as well using the Coanda effect on some rotating cylinders near what would be the rocker panels.
Ivan, This is one thought I had; actually one question: How are the individual "motors" controlled and synchronized? It would have to be computer driven and would seem to need a sophisticated feedback system to maintain common RPM between wheels. I'm sure the technology is there. I feel the drive system AND composite materials provide an intriguing solution to mileage per charge. I do agree with one of the other comments in that it would seem to be a commuter car and not "interstate worthy".
There are several heavy construction machines that make use of wheel motors already. I assume they have computer control systems but I don't know for sure.
In controlling the wheel torque and speed it is not that hard a problem. All the wheels should be spinning at about the same speed with minor variations for turns creating a slight differential in rotational speed depending on the turn radius. The power applied to each wheel should probably be about the same so the motor generated torque output is the same on each wheel. Any wheel that spins too fast can be "throttled back" so as to stop it from spinning. The same would apply for braking torques. Electrical control would probably be faster than hydraulics and allow for more precise control of braking forces so as not to lock up the wheels and create an uncontrolled slide. The driver and computer could command maximum braking effort and by not locking up the wheels the car would remain steerable. No more brake pads adn shoes either. Maybe for the parking brake.
Advanced neodymium magnet materials are in the wheel motors as noted on the web site of the company. Another company, Protean I think is their name is entering volume production of wheel motors at their China plant and product will be available next year. I think everyone would be really impressed with the raw output torque from a modern advanced permanent magnet motor. I know the magnets are amazingly powerful. Pretty cheap too considering.
All of the issues we have brought up here are in fact real and being addressed by the engineers working on the designs and manufacturing. As I noted earlier, the technology is improving steadily in many areas and the overall benefits are just too compelling not to be applied. There will be issues adn problems but with experience they will be resolved as necessary.
One issue not addressed is the possiblity to rethink the design of the wheel and tire given the advent of the iwheel motor. I suspect the days of the pneumatic tire are numbered and will be replaced with a system of flexible (albeit rather stiff) spokes as springs and a polyurethane tread. No more flat tires, better recyclability and more use of lightweight plastics.
Torque Steer is not a product of giroscopic forces, but the "torque-steer" you felt in the steering wheel of your Honda front wheel drive is a different phenomena, arising from manufacterer using different lenght (and mass) half shafts (unequal-lenght shafts).
Now, an electric motor installed completely inside the wheel will put a much heavier rotating mass than using a motor centrally or inside the car towards the chassis. Many unsuspecting owners have taken the absurd Too-Large wheel vogue, by going to 19", 20" or even larger aluminum wheels with correspondingly low tire profiles (not always keeping the external overall diameter). The deleterious effect on acceleration and fuel economy is not small. Even a few pounds of weight when located in the outer portion of the rotating assembly, will represent an unusual increase in rotating inertia, penalizing acceleration and braking more than other things, like unsprung weight, that mainly affects tire adhesion on uneven pavement. The only way to avoid a large penalty would be to keep rotating mass as lowest as possible, maybe by using advanced electric motor designs to keep inertial rotating mass and inertial moment to the minimum. In the old days, racers used to say that every pound added in a tire-wheel was "like adding ten or so pounds in car weight".
There are some articles on this subject, like SAE Paper Number: 900760. Amclaussen.
I have to disagree with the cause of the torque steer mentioned previously. Torque steer is an effect that arises from one wheel absorbing all the engine torque in a turn. This happens as a result of the differential putting all torque to the outer wheel. If the car had a posi-traction type differential that delivered equal torque to the driving wheels there would be no torque steer.
Presumably with a wheel motor on each of the 4 wheels the onboard computer would monitor relative rotation rates and torque demand from the driver to insure all wheels were optimally engaged in either breaking or accelerating.
The rotating mass of the wheel has little effect on the overall forces required to brake and accelerate. Rotational mass effects are small comared to the overall forces involved in accelerating and decelerating a 3500 lb car.
The unsprung mass of the wheel/motor/tire combination has the most effect on the suspension characteristics. A lower unsprung mass compared to the mass of the vehicle is desirable for smoothing the ride. In this respect, I believe the lower tire mass is intended to compensate for more wheel diameter. The overall effect should be to reduce the weight of the wheel and tire. Unfortunately as my new Hyundai Genesis demonstrates, the very low profile tires create a very stiff suspension overall since there is considerably less flex in the tires.
or purchase the SAE paper mentioned by me above. If you still disagree, maybe you are referring to another different thing. Otherwise, you'll have to go and tell a lot of SAE guys they were wrong for a lot of time! :)
(it could be that you are referring to a lack of centering of the steering wheel during a turn when accelerating at the same time, but that is certainly not called "torque-steer").
The "pull" to one side you feel at the steering wheel when accelerating hard is what is called "torque-steer". What you are probably referring with your Honda (a sensation when accelerating AND turning) is NOT universally recognized as "Torque-Steer".
What the car community calls "Torque-Steer" is felt mostly in higher powered Front Wheel Drive vehicles when acccelerating hard from standstill or low speeds. It's causes are not fully corrected by the differential type, but with a better designed transaxle and driveshafts set geometry, rigidity, and mass distribution. Not all front wheel drive cars use equal-lenght shafts and favorable geometry struts, and since it is most notable in higher powered cars with more torque at launching RPM's, and is often incorrectly attributted to a "powerful car" by car aficionados, it is not corrected in all models. Why don't you take a look under your Honda to asess if it has equal lenght shafts or not? Another big player in Torque-Steer is the Strut and Steering Knuckle geometry (a good introductory discussion to this is at http://www.caranddriver.com/features/ford-revoknuckle-and-gm-hiper-strut-explained-tech-dept article. Different left side wheel vs right side wheel "Scrub radius" often result from unequal lenght halfshafts car design.
And regarding limiting slip differentials, Car and Driver even critizised its use in FWD cars stating that "And when a limited-slip differential is employed in a front-driver, these effects are sometimes amplified as the diff decides which wheel to favor with power..." (http://www.caranddriver.com/columns/slowly-but-surely-horsepower-is-killing-front-drive ). This article mentions something about that sensation you probably felt and believed to be "torque-steer" when talking about the Dodge SRT-4 lack of steering wheel centering or more properly, Self-centering force when turning and applying a large torque at the same time during a turn. Please read more on this and we can discuss it better as long as all of us use the same term for the same concept. Respectfully, Amclaussen.
In straight line acceleration the Honda with 265 Hp does fine. I could not detect any problems with unequal torque being applied to the front drive wheels. The steering effort to keep it straight was negligible. The acceleration is very impressive in a relatively light car. I was referring to the Honda EX V6 with a 6 speed manual transmission, 2 dr coupe I bought new in 2005. In a turn and under hard acceleration the car would pull very strongly in the direction of the turn, so much so that an inexperienced driver could easily be overwhelmed and create an issue. It surprised me more than once and took some getting used to.
I am confident that the loss of self-centering (restoring) force on the steering wheel that you previously referred as "torque-steer" is a result of front wheel drive non-optimal geometry when subjected to simultaneous turning and large torque application. It is the same sensation referred in the Car and Driver article when describing the lack of return-to-center of the steering wheel in the powerful dodge SRT-4 that did not returned to center when accelerated. That the SRT-4 did NOT pull in the same direction of the turn means that in that respect, the overall steering design of the Dodge is better done than that V6 Honda, no doubt!
The sensation is VERY unpleasant, to say the least... specially when the lock to lock ratio has many turns in it. I clearly remember one of my first cars, a 2-door Valiant Duster (the mexican version of the Plymouth Duster) with the slant six 225 engine, manual steering with 24:1 ratio... in a slow turn, if I suddenly applied more than half accelerator without holding the steering wheel, the damn thing turned the steering into the turn until reaching the lock end! It turned out that that was a new model platform, and that the factory did a mistake and set the front suspension on entirely wrong settings. Once corrected camber/caster and toe (partially), that maddening tendency was subdued but not entirely fixed. Best Regards.
I remember the torque steer on the honda as being in effect in either direction of a turn. Left or right the car would pull significantly in the direction of the turn. I attributed this to the outside wheel receiving more if not all of the engine torque. Perhaps front wheel differentials are different than the rear wheel ones I used to deal with. the differentials I am familiar with only supply equal torque when the rotations of the output shafts are identical. If one wheel is rotating slower than the other in a turn then the torue is essentially applied to the faster wheel only.
Your explanation would indicate the torque from the engine is applied equally at least as far as the differential output shaft and varous other factors produce the torque steer effect.
I guess there are still some issues I don't quite follow regarding the front wheel differentials. the papers you referred to would seem to indicarte that torque steer is a usually subtle affect based on steering geometry and torsional stiffness of the drive train on each wheel. I thought it was a rather direct function of the differential.
With the amount of power they have at each wheel, it should work just fine as an AWD. After all, they have almost a Prius at each wheel! This could be a better than any other version of traction control because each wheel can be controlled independantly. Not something that you can do with 1 power plant and brakes.
I don't think unsprung weight will be much of an issue either. This is a commuter car not an entry into a F1 race.
Rob, I think you're right. Several automakers are introducing newer technologies, such as plastics and recycled materials, into their EV lines first. That appears to be partly to test out these technologies on lower-volume product runs to get the kinks out before committing to mass manufacturing, but also to help with the weight problem caused by batteries.
NOT a novel design approach...not even close!!! About 115 - 128 years off.
The first electric car hub motor was patented in 1884. In 1897 Ferdinand Porsche had an electric wheel hub motor "race car" that had a top speed over 65mph! There were over 300 of these fast electrics built and they were all sold to wealthy customers. The only novel approach I can see with this new electric car is that it is using a new type of plastic for the bobbin.
Below are some pretty interesting info:
In 1914 a Detroit Electric went 241 miles on a single charge setting a new record!
In the 1900's there were over 300 electric car companies with more than 30,000 electric cars on the road.
The first powered taxis in New York were all electric,.
The fastest race cars in the late 1890's were electric.
Jeff, you're right that the design approach isn't novel. However, as several commenters (including me) have pointed out below, those early cars with motors in their wheels weighed an insane amount due to battery size and weight, nearly two tons.
Thinking about this, the idea of a plastic body for a car with hundreds of watt of energy flowing through it is very smart. I've shocked myself touching the body of a normal auto when static electricity had built up, and it was not fun. Amplify that by a factor of, oh, maybe 200 to 400, and wow! the advantage of using non-conductive parts begins to sound really intelligent. So I'm all in favor of it.
The unsprung weight of the car due to motors in the wheels would certainly reduce its handling capability. And I'd sure hate to hit a big pothole; you'd be out shopping for a new tire and wheel immediately, as soon as your teeth stopped rattling.
The range sounds almost too good- I wonder if it's anywhere near that far at freeway speeds.
But why do they insist on making these things look dorky? Did someone pass a law against making them look like a Tesla?
Chuck, that's a really good point about EVs. One of the reasons carbon composites are becoming popular in aircraft is their non-conductivity, which is useful for planes flying through electrical storms, for example. That does seem like an obvious benefit for EVs. Regarding what happens to the motors when they are impacted, good question. The company's description: http://www.sim-drive.com/english/technology/index.html#Shimizu_In_wheel_Motor-Drive sounds like the frame may have been made extra-rugged to accommodate this.
Ann, actually, the non-conductivity of composites is a huge problem for aircraft. Think about it: would you rather be flying along in a thunderstorm in a chair tied to an open board or would you rather be in an steel tube? Something about a Faraday Shield – you don't want the electric flowing through you but around you. They have known about composites for years but needed some way to make it a shield. It is done by burying metal screen in the layers of fiber. Point 2: forty years ago I saw a Honda "motorcycle" with the engine in the rear wheel. Not that new an idea. Point 3: big announcement about new crash testing http://money.cnn.com/2012/08/14/autos/luxury-cars-crash-test/index.html How do you think this car with lots of plastic will do on that test? And would you want to be riding in it during that test?
Whoa Ann...don't get carried away with the Carbon composites fad. Lightning strikes on composites don't always find a good ground return despite metallic mesh built into them. Experience with a flap having a composite leading edge grafted into an aluminum structure had a lightning strike spray across the composite and literally melt the aluminum spar as it went to ground...the mesh in the composite was "open circuit" and didn't do its job.
Composite helicopter rotor blades used to create miniature lightning strikes due to the build up of precipitation static in a faulty grounded rotor. All metal aircraft are continuously bleeding off static build up via the brushes systems fastened to various surfaces, so its not all good stuff where composites are concerned.
Carbon composites have been used in aircraft for decades, beginning with the military, and anything going into the construction of commercial aircraft has very strict specifications and requirements, including extensive testing on the ground and in the air. That's all fact. So is the conductivity of metals such as copper and aluminum. Carbon composites can be, and are being, designed with specific electrical properties to handle lightning strikes. Clearly, whether conductivity is a problem or not depends on how the materials and components are designed.
Unfortunately when it comes to putting things together on the shop floor or getting things from an outsourced location a whole lot of things can go wrong. Military aircraft and smaller aircraft built around composites are entirely different from commercial aircraft carrying a large number of passengers. Boeing's Dreamliner had its share of manufacturing problems significantly related to composite glitches and although most of them were dispositioned by the Liaison Engineers there are (inevitably) those which are still lurking in the aircraft...that's also a fact. Aluminum structure problems are generally self evident....composite problems are subtle but still there. My associates and I like composites....in their place...but there are things that do go wrong which don't cause grief in aluminum structures....just ask any stressman.
Ann, one of the major drawbacks of any EV is its less mileage. So any innovation, which can increase the mileage, may get more appreciated from both market and customer side. But am not getting how its possible to deploy one- one motor for each wheel
Motor in wheel is certainly an interesting idea (and an obvious one; it's been done before).
The statement "30 percent farther than other mass-produced EVs" is clearly not true. A cynic might say there isn't any such thing as a mass-produced EV, but if you assume that this means "not a concept car" and "not a limited production hand-built car" (like the Tesla Roadster) but rather something built in to a factory with the hope that it would sell in the thousands (like the Leaf) then clearly the Tesla model S qualifies, and that has a range around 300 miles.
I don't remember where I read it -- might have been Design News, or Aviation Week, but some years ago someone built a motor in nosewheel system to let airliners push back from the gate without needing a tug. As I recall, part of the puzzle there was to get enough torque and low enough RPM with reasonable drive electronics, and the answer to that involved having an unusually large number of poles.
It is good to see that automotive engineers no longer solving a hundred different structural problems and magically coming up with steel for every one of them. In the early days, cars used a wide range of the materials then available. For example doors might be made of thin aluminum over an oak frame, giving a very strong yet light result. The same for the body frame, except it was more often steel over wood. There were similar practices elsewhere in vehicles.
As for the lightning protection problem, I agree that a metal body would offer better protection, but how often is a car struck? And in those instance when it has happened, has it made a practical difference whether the top was metal or, say, canvas as has always been the case with convertibles? It seems we outht to concentrate on statistically significant events.
A radio antenna is happier with a ground plane, but again, is this a real problem? Even if it were, a few radial wires would be quite sufficient. Again, let's concentrate on real problems.
Rob, most all electric scooters have motors in the wheel hub and they work very well albeit at 500W maximum (in Canada). We're in the process of rigging such a system into a single seat three wheeler (2 in front and 1 behind...the powered one)
The scooters (and this 3 wheeler) have 20mph speed limits to legalize them as power assisted bicycles/tricycles and they're legal on bike trails...it's a fun way to travel and there's a lot of experience with hub drives in the scooters. The batteries are 48VDC Lead Acid (you can get Lithium Iron Phosphate for about 4x the cost of lead acid) up to 72VDC working through a controller.
We're great advocates of push technology...all of Mother Nature's designs for propulsion are push technology so (humour) where did this front wheel drive stuff come from?
Interesting, ScotCan. Are these vehicles legal on the road? On bike paths? I would think these would be ruled by state regulations, each of which would be different. I'll bet there is very little energy consumption with these vehicles.
In Quebec and Ontario they are regarded as power assisted bicycles limited to a maximum speed of 20mph and must have the pedals attached. The rider must wear a DOT approved helmet but there is no requirement for a vehicle licence, driver's licence or insurance. Since they are regarded as bicycles they can be driven anywhere a bicycle can be driven. Recharging a 48VDC system takes 11 cents of hydro and depending on use may take place every third day. They are ideal for shopping and general tootling around town.
Pkoning, am first time hearing about vehicle with motor on wheels and I don’t know how centralized control is possible for all independent motors. Any idea? Why you are telling that efficiency is not going to change-any particular reason.
I don't remember speaking of efficiency. But electric drive efficiency is pretty high; there's not much margin between today's numbers and 100%. The area for improvement is in batteries; the problem there is that it's not clear how.
As for control, what's the problem? For starters, each wheel wants to have torque delivered to it. Then you can look at traction control (anti-skid) which of course is inherently a per-wheel activity; conventional cars have to approximate that because they have centralized drive, and per-wheel drive makes it much easier.
If you're not doing traction control, the whole thing is trivial. Consider that electric trains (the motor car style) have had per-wheel drive for close to a century.
Was this article about the car or about Dupont plastics? I find it hard to believe that we got nothing about the battery or electronics on this car. So many new technologies and all we get is plastics talk.
Hmmm...looking at the website I'm getting the impression this is still pretty conceptual. The claimed weight on their pdf was 1580 kg (3483 lb), OK but not amazing and production vehicles rarely seem to make their projected weight.
With EVs I'm taking the stance that I'll believe their mileage claims when several independant testers confirm it and I'll believe their "price" when they can operate profitably at that number without external support.
Best of luck to them, but I'm not getting excited just yet.
I wonder how durable this system would be. Motors in the wheel where the magnets would also be exposed to all the road shock. I ahve worked with motors where the magnets came loose that were solid mounted with no shock to the motor. Also the cables, the iregular vibration that they would be exposed to going from the frame to the wheel would have to be considerred a harsh environment.
I would favor a mid mounted motor driving 2 wheels through more conventional half shafts. Fewer motors with the motors temselves being isolated from vibration and shock. Also would require few, albeit larger, motor controllers. From experience - the more complex the system, the more likeley it is to fail. More controllers, the more places to fail and the more likelyhood of a failure...
My opinion is that many of the current designs are made t do well in the JDPowers 1 year owner survey, but I would like to know how these designs will do in 5 and 10 years. For $32,000,00 US this car has to last a while to be able to justify the expenditure for all but the wealthy. Byut then, when folks will commit themselve to a $300,000+ house that they can't pay for I guess a $32,000 car they can't pay for seems like peanuts.
I think time will show that the idea of wheel motors is pretty compelling. Given the ability to control the torque at each wheel will improve handling. It is a tradeoff with the increased unsprung weight but eventually the wheel motors will be much lighter.
The design benefits should not be overlooked in terms of reducing the amount of space taken up by the motor, transmission and other drivetrain components. Moving all this outboard to the wheel provides more room in the chassis for batteries.
The use of plastics is very significant in that reducing weight of the vehicle is the only first order variable in miles per gallon or in this case range of the vehicle.
I 'm looking for a small two seat commuter car much like this one. I drive less than 75 miles per day on my daily commute and can park the car in the garage and connect it to a 240 volt charger for an overnight charge. Five days a week, 50 weeks a year. My big crew cab pickup with a V8 getting 17 miles per gallon will be relegated to weekend duties around town and long distance trips. I figure the savings in gas expenditures will pay for a good piece of the new car payments.
I am glad to see companies attempting new ideas. This idea isn't exactly new, (http://www.treehugger.com/cars/electric-mini-0-60-in-4-seconds-it-has-motors-in-its-wheels.html) but who really cares unless there is IP involved. I hope their efforts bear fruit for others to take it further. The tough parts to this solution will be the control software (traction control, stability control, failure modes) and managing the effects to the passenger's ride experience from the extra unsprung weight in the wheels. I'm not a tire expert, but I bet it will take special small tires to handle the extra stresses as they will undoubtedly rely on the tires to absorb some of the energy from bumps.
It seems like it would be great in town or for low speed commuting, but highway speeds would require overcoming some large gyroscopic effects. I'd like to see some specs on the steering control system.
I think that was the main problem in the original design of 100 years ago wasn't it?
I suspect you're right, tkhorton. These are the kinds of innovations that Tesla will need to come to fruition (that is, assuming the costs are reasonable) if the industry is going to turn Musk's prediction into a reality.
Hub motor because they have no gearing advantage of a diff must be the gearing x HP more in size or the vehicle can't start up a hill, the actual design point for useful car drives.
Since they have to be 4x's as large just to get the vehicle started, hub motor vehicles will always be more costly though once going, the do kick azz.
The problem is the RPM is so low and since a PM field gives up the 3x's more torque advantage of a series motor is why 350hp of wheel motors are needed along with controllers, etc.
Hub unsprung weight might not be such a problem since the EV has so much weight in batteries to get it's range. In lighter vehicles like my EV trike clearly show how bad too much unsprung weight of my motor/axle/diff/wheels can be.
All this adds up to why you don't see hub motor EV cars for sale.
Now on bikes, MC's they/HMotors can be far lighter, lower power as the rider can push off to help a hard start up a hill with their legs, cutting size needed by 2/3's.
I'm not sure why the weight of the vehicle has anything to do with the unsprung weight of the wheel. Doesn't unsprung weight become a problem on normal roads with bumps and potholes because the wheel can't "follow" the profile of the pothole/bump? If you had a 10 ton truck the wheels still have to follow the surface of the road.
The wheel motor is quite amenable to the use of a planetary gear set if necessary. A planetary gearset gives very high reduction ratios adn is quite compact to incorporate in the design of a wheel motor.
It is the ratio of the unsprung wheel weight to vehicle weight that forms the basis of the calculations for spring rates and dampening that are part of the equations for suspension design. The goal has always been to minimize the wheel weight in order to create a smoother ride.
Follow this link and more to the Protean information on their wheel motor.
I would suggest that four motors are better. Four motors offer redundancy, better traction control. The more used allow for smaller motors. I would expect the car to be drivable on one motor but perhaps not so much acceleration available if the other three motors were inoperable for some reason.
Technically you could probably design the car with only one wheel motor but four or at least one per wheel seems more logical. And it makes them all interchangable.
As others have said, a non conductive body is not a good idea as it eliminates the Faraday shield that can protect a motorist from a lightning strike. Furthermore, it prevents vehicle whip antennas from having a proper ground plane with which to function. The best way to eliminate dry weather finger tip ESD is to design low ESD materials into vehicle seats and carpeting.
Vehicle electical systems often use the metallic frame as the return path for their energy supply. With a non metallic vehicle one would have to beef up the ground return wiring which would add weight back into the equation and increase the risk of an electrical fire to boot.
As for unsprung weight, axle mounted motors will have to be made of state of the art magnetic materials with highest flux density per kilogram and operated at higher voltages so that copper windings can be a bit thinner but with higher performance insulation, thus lowering the motor mass.
Sprung weight includes the battery pack(s). Use more of them to achieve greater mass and run time and make use of electrodynamic braking to cycle more of that additional moving mass (dynamic energy) back into stored electrical energy (potential energy).
If one had the room, a gimballed flywheel motor generator might be a more efficient way to recycle braking energy back into movement and at the same time impart stability control to the vehicle.
It would be my guess that the car does not get the 218 miles per charge at 100MPH, nor doing 0-60 in 6 seconds. Four wheel drive in a car may make it possible to have decent handling dispite all the ubsprung weight in the wheels. The big challenge would definitely be in providing decent handling characteristics.
Keeping the motors running at the same speed is not that complex, no microcontoller is needed. The asme for the ABS function, just monitor wheell speed and reduce the torque of wheels that slow to much, or that spin to fast durring acceleration.
Flexing of the power wires is not a problem, just consider the cables on a robotic arc welder robot. They flex a lot more than an auto suspension does.
One other problem that I can see will be heat, since the brakes on the wheels will be next to the motors, and even with regenerative braking, motors still heat up. In fact, regenerative braking can be far more demanding on a motor than other useage.
Still, it will be interesting to see how the car does in the market, if the materials for those high energy magnets remain available.
Why would there be any need for brakes? Other than a parking brake the motor should be able to perform all necessary torque requirements. Think about it. If the motor can spin the wheels or has enough power to do so then it can also provide that much torque as resistance. Eliminating any kind of hardware and associated weight for a braking system other than the torque control in the motor would be another benefit.
There is an additional benefit of course in being able to recover the energy normally lost to friction as usable energy for the battery. Apprpriate ducting can channel air flow to the wheel motor and keep it cool. I would suspect there will be temperatur monitoring of each wheel motor by the onboard computer as well. Unless air flow is blocked the control system could direct less current to a wheel in distress until temperatures returned to normal or maintenance could be performed.
Also keep in mind the advent of self driving cars that are in development. This wheel motor technology will play into that nicely with such fine grained control of the torque at each wheel.
You need 4 motors so each one can be smaller, thus lighter, cutting unsprung weight by 75% vs 1.
While controllers can go very low regen or even lock up it makes a much more costly controller plus relying on electronics for braking only is not good enough safety wise. Plus this causes the motor to heat up even more which in turn means a bigger motor.
While gearing either planetray or rim adds as much weight as a bigger motor would. They have been used especially in electric trucks 1900-1930's but they were slow speed, under 20mph.
I've looked deeply into hub motors looking to produce them for my EV but whatever way you look at it they are 2-3x's as expensive as regular EV drive with differential. I'm going with trailing arm suspension with the motor shaft at the pivot point and toothed belt reduction drive for my lightweight EV's.
You can't use regenerative braking all the way to a full stop, and it does not do very well at holding a position, either. One other thing is that no electrical drive system will ever be so reliable that an alternative means of stopping is required. Consider what would happen if there were a "primary fuse" failure towards the end of that 0 to 110 MPH acceleration?
The regenerative braking in all other cars is always backed up by mechanicl brakes of some kind, because, in addition to being speed dependant, regenerative braking may not have adequate capability. IT is entirely possible to absorb anough energy during a panic stop to destroy the motor or the battery. That is the third limitation, that the battery can only absorb power as charge at some maximum rate, after that you are just raising the temperature or creaing steam.
One more thing is the question of keeping the car in place while it is parked. Regenerative braking can't do that. Active position control can, but that burns a lot of battery staying still.
And all of those systems are controlled by the processor, which is VERY subject to failure.
In addition, in most sensible places, it is not legal to drive a car on the streets that does not have brakes.
Wow! Everything about this prototype sounds great – thanks for sharing, Ann Thryft! The motors in this EV's wheel are no doubt an exciting development, but it's the use of lightweight plastics that really give the extended drive range of this vehicle a serious boost. And because plastics are also known for their strength, we can expect this automobile to be safe in addition to fast and efficient. Can't wait to see this one in production in 2014! PS College for Creative Studies (CCS) students in Detroit have for years been "dreaming" fly by wire technology like this for the wheels! Here you've found it in reality and shared it with us. We will share it with them!!!
RobKrebs, thanks for the enthusiastic response. And the reminder that the point of the article wasn't EV design but the range extension made possible at least in part by plastics. OTOH, you might want to let those automotive design students know about the history of the motors-in-the-wheels idea, which can be found sprinkled throughout these comments.
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