From reading elsewhere, I gather that the Volt will have a single large electrical engine with a transmission connecting to a "traditional" driveshaft. Does anyone have insights into why GM is doing this rather than using two (or four) in-hub motors?

I expect those will show up in later models, starting with high price / high performance models. The Lightning GT offers in-hub motors, but it costs $300K.

Hub motors are expensive. One motor, drive shafts and differential is cheaper.

I expect those will show up in later models, starting with high price / high performance models. The Lightning GT offers in-hub motors, but it costs $300K.

So if the in-hub motors cost so much $$$, why is the Mitsubishi iMiEV Sport (showcased in late 2007) listed on Wikipedia (http://en.wikipedia.org/wiki/MIEV#Mitsubishi_i_MiEV_Sport_.282007.29) as having "in-wheel motors for the front wheels, while a single motor powers the rears"?

I think the styling of the iMiEV Sport is rather horrible (http://www.autobloggreen.com/2008/02/09/mitsubishi-testing-upgraded-i-miev-in-japan/), but I imagine that it will be targeted for sale at the cheaper end of the spectrum.

David, you are going to have to trust the engineers to decide what is best in this case. They have to weigh many variables from cost to production issues. I'm sure GM has advanced programs on-going that are either designing wheel-hub motors or are dealing with venders that do. Wheel-hub motors are coming because they offer so many advantages from ease of maintenance to the ability to control each wheel in anyway the computer sees fit. I'm also looking forward to seeing them on my car in the near future. The possibilities are endless.

So if the in-hub motors cost so much $$$, why is the Mitsubishi iMiEV Sport (showcased in late 2007) listed on Wikipedia (http://en.wikipedia.org/wiki/MIEV#Mitsubishi_i_MiEV_Sport_.282007.29) as having "in-wheel motors for the front wheels, while a single motor powers the rears"?

I think the styling of the iMiEV Sport is rather horrible (http://www.autobloggreen.com/2008/02/09/mitsubishi-testing-upgraded-i-miev-in-japan/), but I imagine that it will be targeted for sale at the cheaper end of the spectrum.

Good question. I suspect that they were trying to eek as much mileage out of the NiMH batteries as possible, and need the regenerative braking capabilities of all 4 wheels. If they just switch to Li-Ion, they could dump the front wheel motors and have a much longer range vehicle at a much cheaper price.

Good question. I suspect that they were trying to eek as much mileage out of the NiMH batteries as possible, and need the regenerative braking capabilities of all 4 wheels. If they just switch to Li-Ion, they could dump the front wheel motors and have a much longer range vehicle at a much cheaper price.

Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.

Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.

Texas, you are right, if the RAV-4 had a 4WD transmission connecting all 4 wheels to one motor, that too would allow regenerative breaking, or 4 wheels to 2 motors, or 4 wheels to 4 motors. My only point was having all 4 wheels attached to motors to harvest energy from all brakes was probably the driving factor to include them in the RAV-4.

Sorry Jason, You missed my point. You could have one motor on one wheel and it will still absorb all the energy. Think of it like applying the brake to only one wheel in a car. It will stop right? If it can stop the car then it absorbed all the energy of the moving car. That is just the physics of the problem. Now if you are stopping hard or the surface is slippery then of course it is better to have four brakes with ABS or something even better, four-wheel computer controlled traction control. With four wheel-hub motors it will be possible to do all kinds of advanced things. You can apply a little more power to the front right wheel while stopping the spin on the back right wheel, etc. After a few years (decades?) of programming the cars will feel alive.

Jason wrote: I suspect that they were trying to eek as much mileage
out of the NiMH batteries as possible...

The Mitsu i-MiEV uses Li-ion battery pack developed by GS Yuasa.
It is said to have a nominal capacity of 16KWH (same as the volt).

The purpose of using smaller in-hub motors instead of one large
motor is, I think, to distribute the burden of high current when
starting from standstill. With a given voltage the current is highest
when the motor is not rotating. This could cause frying of the motor.
For example, Keio University's Eliica has 8 in-hub motors (it needs
8 wheels to avoid motor over-heat).

From the standpoint of driving dynamics the added unsprung
weight of in-hub motor is not desirable, though.

Texas, yes you can stop solely with breaking one wheel or two but not nearly as fast. If only the front wheels are used you could recover a significant amount of "recoverable" energy in real world driving but would still need 4 wheel breaking some of the time.

Hub motors will be slightly more efficient and allow better control of power to each wheel. But, they will always cost more, have unsprung weight issues, and most importantly reliability issue. Reliability issues stem from their position ahead of the suspension. They won't be cushioned from all of the potholes, curbs, rocks, etc that wheels get battered with.

Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.

The biggest advantage i can think of with wheel hub motors is the elimination of gears. Gears offer friction. Friction converts energy into waste heat, which ultimately uses more electicity and and produces less miles per kilowatt.

Motors are pretty heavy, and if they are in the Hub that would be unsprung weight. which is very bad for handling and stability of the vehicle.

Some smart engineer could probably come up with a way to use short driveshafts, so each motor could still be mounted inside the suspension but drives only one wheel.

As others have pointed out could lead to interesting traction control to be able to not only brake wheels individually but power them differently also.

Ah, I see some of you have not seen the following. Enjoy!

Mini Cooper - Wheel hub motors:
http://www.caranddriver.com/reviews/hot_lists/car_shopping/green_machines/pml_flightlink_electric_mini_cooper_car_news

PML Flightlink:
http://www.pmlflightlink.com/

“PML's specialty is flat "pancake" brushless electric motors it makes them for various military, marine, and construction applications and in the Mini these motors are entirely contained inside the 19-inch wheels. Each wheel contains an identical motor, each rated at 160 horsepower, which makes this an all-wheel-drive 640-horsepower Mini. Top speed is estimated to be in excess of 150 mph, with a 0-to-60 time of 4.5 seconds. The figures are estimated because, as this is written, the PML QED (for "quad electric drive") Mini has not run with electric power; its creators have been too busy drumming up interest at the British International Motor Show and the Electric Vehicle Symposium in Japan.

But the company is confident that it has a better solution amid the electric-and-hybrid-vehicle debate. Hub motors are not new, but PML claims its motors have the best power-to-weight ratio in the industry. PML's motor unit, including the miniature Hi-Pa drive inverter, weighs 53 pounds, and the complete wheel assembly, including the tire, is only 4.4 pounds heavier than a regular Mini's, so the effect on unsprung weight is small. “

For purposes of cabin design, performance and range, eventually, all cars will have 2 or 4 in-hub motors. Batteries, caps, fuel cells will be distributed throughout the floor of the vehicle for the same reason. Only an ICE generator (and passengers) will remain a large bulk item that will require it's own cubic volume.

Hey, if you use the word eventually then I would have to say that even the ICE will be gone. All that weight and complexity can be replaced with more nanotech batteries. ;)

I wonder if we will adopt a plan like Project Better Place anytime soon. The basic concept is that you need the charging infrastructure for fast recharge (or swap) before people can comfortably eliminate the range extender. When that happens we can forget about the gas, oil, maintenance, etc. that is associated with the ICE. I wonder how far we could get with 1.5 Trillion dollars worth of smart grid infrastructure. Probably a very good start. Hummm.

http://www.projectbetterplace.com/ I read that over 30 countries are trying to duplicate the model.

From the standpoint of driving dynamics the added unsprung weight of in-hub motor is not desirable, though.

I've read elsewhere that the additional weight is only about 35 kg (80 lbs.) per in-hub motor. Apparently the lower center of gravity (due to the battery pack) helps with various issues of having additional unsprung weight.

I've read elsewhere that the additional weight is only about 35 kg (80 lbs.) per in-hub motor. Apparently the lower center of gravity (due to the battery pack) helps with various issues of having additional unsprung weight.

If you read my previous post the additional weight is just 4.4 lbs. In addition, these are not even in mass production yet. Wait until all the major automotive companies and their vendors start optimizing the design. I predict that in 10 years 4-wheel-hub motor configurations will be standard on all cars and that their un-sprung wheel weight will be of no concern.

If you read my previous post the additional weight is just 4.4 lbs. In addition, these are not even in mass production yet. Wait until all the major automotive companies and their vendors start optimizing the design. I predict that in 10 years 4-wheel-hub motor configurations will be standard on all cars and that their un-sprung wheel weight will be of no concern.

I believe it will be a high percentage of vehicles, but there will be some who try 2 wheel and 4 wheel transmissions (unless companies overspec the 2 - 4 wheel motors to stay in maximum torque range at all speeds).

You are right, I should have said a majority of cars. There will always be manufacturers out there trying to solve engineering challenges in different ways. I'm really looking forward to seeing the development of the electric drivetrain.

You are right, I should have said a majority of cars. There will always be manufacturers out there trying to solve engineering challenges in different ways. I'm really looking forward to seeing the development of the electric drivetrain.

Amen brother.

If you read my previous post the additional weight is just 4.4 lbs.

When i first saw this my Initial reaction was that that was simply not possible. The pancake style DC motors are not light, and the tire, and rim still need to be there. How could that not just be added weight.

However i followed the link and saw that they removed the rotor and brake calipers. Using the motor to regen brake. In light of that, and a light (read $$$) DC motor and rim, i could see such a small increase in unsprung wieght.

A little tangental, in the performance crowd an extra 5 lbs per tire is a very significant increase. But that could probably be forgiven when the power and torque curves were looked at. As well as the dynamic power and braking algorithms that could be applied to a truly independant 4 wheel drive system.

One note from the article is that they mentioned not currently having a manual back up brake system. Maybe someone who knows more about DC motors could tell me what the failure mode is with regards to regen braking? IE. if the motor loses connection with the rest of the car will it apply full brake, or will it spin freely? I realize it might depend on the DC motor but if you know i'd be interested.

I have been thinking about a back-up brake system and the thought of fly-by-wire braking made me a bit uneasy. Sure we have fly-by-wire airplanes and they work just fine but NO physical brakes? Burrrrr.

So, I was thinking how can we have a back-up system that will make everyone feel safe and not add much weight. Remember, we are counting on the removal of the disk brake assemblies to make the wheel-hub motors light enough. Since the unlikely failure of the fly-by-wire braking system would result in the vehicle being transported back to the shop for extensive repairs I recommend a one-use emergency braking system. I'm thinking along the lines of the new table saws that stop the blade if you accidentally touch your skin to it. These brake systems disintegrate and have to be replaced if used. I think this type of disintegrating system would be a perfect match. It only has to be used to stop the car once and would have to be replaced along with the other major components, should the fly-by-wire brake system fail. Very light, probably inexpensive and makes everyone feel all warm and fuzzy. Nothing like that feeling when you try to stop your car and the brake pedal goes directly to the floor and you remember that your emergency brake has been frozen with rust for the past 5 years! ;)

If you read my previous post the additional weight is just 4.4 lbs. In addition, these are not even in mass production yet. Wait until all the major automotive companies and their vendors start optimizing the design. I predict that in 10 years 4-wheel-hub motor configurations will be standard on all cars and that their un-sprung wheel weight will be of no concern.

I read your post after submitting my post ... :o The article that I was mentioning was based on an analysis of Mitsubishi's iMIEV Colt EV from 2005. (I don't recall the source.) Quoting from an article on Wikipedia: MIEV motors are constructed using an in-wheel motor rotor, an in-wheel motor stator, a rotor bracket, stator bracket and inverter directly behind the brakes. (Source: http://en.wikipedia.org/wiki/MIEV)

Images of the MIEV motor show that it is much more bulky than PML's "pancake" brushless electric motors used in the Mini EV prototype. However, the Mitsubishi motor includes the required rotor, brakes, etc. that the Mini EV does not include.

According to the following article, the 2005 Mitsubishi Lancer Evolution IX "has a top speed of 111 mph and weighs 1,590 kg, just 120 kg more than the standard Evo IX". (Source: http://www.carpages.ca/go/conceptcars/2005_mitsubishi_lancer_evo_ix_miev_concept.aspx)

Obviously, the weight difference between ICE and EV is decreasing ... perhaps someday the EV will weigh less!

Since the unlikely failure of the fly-by-wire braking system would result in the vehicle being transported back to the shop for extensive repairs I recommend a one-use emergency braking system. I'm thinking along the lines of the new table saws that stop the blade if you accidentally touch your skin to it. These brake systems disintegrate and have to be replaced if used. I think this type of disintegrating system would be a perfect match. It only has to be used to stop the car once and would have to be replaced along with the other major components, should the fly-by-wire brake system fail.

Sounds like a great idea - hopefully it can get past the various transportation regulators ...

I'm thinking along the lines of the new table saws that stop the blade if you accidentally touch your skin to it. These brake systems disintegrate and have to be replaced if used. I think this type of disintegrating system would be a perfect match.


What i would worry about with the system described above is that, unlike the table saw, ti would be undesirable to lock up the wheel in the even of a brake failure. some progressive application of the brake would be needed.

I agree that the emergency brake system should be compact and light weight. It should also be a completely independant from the primary brake system.

So i was thinking about it. The DC motor sits on a shaft and is bolted to the rim. It spins around the shaft and that moves the wheel.
if the inside face of the DC motor had a thin steel plate attached to it. a friction brake could be used. Obviosly this would be a system thatt would not hold up to heavy use but should be able to stop a car one time and allow for gradual application/reapplication of the braking force.

As a side note. I wonder if ABS would be easier or harder to implement with a regen system.

As a side note. I wonder if ABS would be easier or harder to implement with a regen system.

I can't say this for certain, but it seems to me that an ABS brake could only be pulsed dozens of times a second, whereas a motor could be pulsed many, many times that, or it might be able to apply a continuous rolling drag with no pulsing at all.

Yes! The use of motors and controllers gives you basically robotic control over the wheels. They can be pulsed, slowed, reversed, sped up, made to keep from skidding right down to the smallest degree. Four wheel-hub motor control will be an amazing advance. After the software goes though a few generations people will be amazed with the amount of control. Like a modern day fighter jet. The computers make adjustments so fast that without them a human cannot fly it. I would like to call this four wheel-hub control, "Wheels alive". :)

Regen braking only on the front wheels will still recover most braking energy. As your auto mechanic will attest by the relative wear of your brake pads, your front brakes do about 75% of the braking. This is because the vehicle's weight shifts forward during deceleration, giving the front tires way more traction. That's why ABS, when it kicks in, usually has to back off the rear brakes, as they can't do much braking without locking up the rear wheels.

Regen braking only on the front wheels will still recover most braking energy. As your auto mechanic will attest by the relative wear of your brake pads, your front brakes do about 75% of the braking. This is because the vehicle's weight shifts forward during deceleration, giving the front tires way more traction. That's why ABS, when it kicks in, usually has to back off the rear brakes, as they can't do much braking without locking up the rear wheels.

Well, if you have the wheel-hub motors on all corners then you might as well use them. Why use brake pads in the back and waste that energy? Are you suggesting just using two wheel-hub motors? If so for cost? Having complete control over all four wheels gives you all kinds of options for safety and performance. You can also have smaller motors in each hub. If you only have two hub motors they will need to be twice as powerful and thus more massive. I think having four wheel hub motors is the way to go to for safety, redundancy, performance, etc. Of course the cost could be an issue but inexpensive cars will probably just have one central motor anyway. We will just have to wait and see what the engineers come up with. Can't wait to see them on the show room floor! The thought of making a very light rail car using production wheel-hub motors and a powerful nanotechnology lithium-ion (or other technology) battery keeps me smiling. Probably the kid in me.

The 2008 Volvo ReCharge concept, a flexfuel plug-in serial hybrid with individual electric wheel motors and batteries
that can be recharged via a regular electrical outlet, is slated to go into production in 2010.
This vehicle is even more ambitious than the Volt...should be interesting to see what becomes of it.
Check it out:
http://www.conceptcarz.com/vehicle/z14099/Volvo_ReCharge_Concept.aspx

http://www.popsci.com/files/imagecache/article_image_large/files/articles/hiw_hybrid_infog_485.jpg

Yes, this will be an excellent competitor to the Volt - it will be interesting to see how expensive it is.

...is slated to go into production in 2010.


Guy, I love this concept and have been following it for a while but can you please give us the reference to where you heard that the project is a go? I'm pretty sure it's still at concept status but I really hope I'm wrong! An advanced hybrid with 4 wheel-hub motors is top on my list, even at a steep premium.

Buying this Volvo is buying a Ford but I don't think the ReCharge is the big secret project at Ford. For one...

"According to people close to Mulally, he is looking at selling Volvo despite Ford's repeated statements that it intends to hang on to the brand. He also hopes to kill off the ailing Mercury brand."

http://www.theaustralian.news.com.au/story/0,25197,23588928-36375,00.html

Secondly, I feel the the secret project going on at Ford (My belief) will be much more radical in terms of light weight, aerodynamic body design. Think stealthy fighter jet (Saab like perhaps - ironically Saab is owned by GM). The ex-Boeing CEO will probably take the automobile in that direction. He has more belief than any automobile company CEO on the planet on the virtues of light weight, aerodynamic design. I'm waiting for big news from Ford, I just don't think the Volvo ReCharge is it.

Please do tell when the first hub motors are announced for a production vehicle. I need to know when to implement my hub motor replacement stand idea (Easy-hub) :D

Please do tell when the first hub motors are announced for a production vehicle. I need to know when to implement my hub motor replacement stand idea (Easy-hub) :D

Sounds like Midas will have a new service to provide to replace oil change and brakes - motor maintainance, be it in-hub or otherwise.

Sounds like Midas will have a new service to provide to replace oil change and brakes - motor maintainance, be it in-hub or otherwise.


Damn!!! Gonna have to buy Midas stock instead. There will be a lot needing replacement. :rolleyes: