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Discussion Starter #1 (Edited)
I was just wondering how the volt's electric motor is going to handle sending the power to the wheels. Is there just going to be some sort of differential? Obviously a single motor driving 2 wheels needs something to allow a differential in rolling speed for turning and such and I was just curious how they were going to do it. I did a search and didn't find anything.

never mind I found posts already addressing this question
 

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With 2 (wheel) motors you wouldn't need any differential, steering gear or axle.

Varying the power to the motors would steer a vehicle! Differential steering.

More motors would definitely be less weight and complexity.
 

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Discussion Starter #4
huh

can't seem to find the posts at the moment, but there were 2 or 3 discussing this exclusively.


Differential steering sounds like a good way to ruin tires quickly and lower the volt's efficiency.
 

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can't seem to find the posts at the moment, but there were 2 or 3 discussing this exclusively.


Differential steering sounds like a good way to ruin tires quickly and lower the volt's efficiency.
Actually, it is a very good method of making tires last for a long time. Tires get their wear from turns because the inside tire scrubs away tread because the inside tire is forced to move faster than the outside tire (circumfrence of circle). With wheel motors, the outside tire can speed up, and the inside tire slow down when negotiating a turn. Tires last for ever. Also four wheel motors would give you really wonderful all wheel drive. And it would be cheap and simple. No fancy differentials for power transfer, etc..
 

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Actually, it is a very good method of making tires last for a long time. Tires get their wear from turns because the inside tire scrubs away tread because the inside tire is forced to move faster than the outside tire (circumfrence of circle). With wheel motors, the outside tire can speed up, and the inside tire slow down when negotiating a turn. Tires last for ever. Also four wheel motors would give you really wonderful all wheel drive. And it would be cheap and simple. No fancy differentials for power transfer, etc..
I agree you could get awesome traction control, more regen, small space savings and better efficiency. I don't agree with simple or cheap. Wheel motors are more complex than a differential and more expensive, especially since they will need some exotic materials to keep the wheels light enough to avoid unsprung weight issues. Most importantly, I just don't see how they can be made reliable enough for the abuse they will get from being in the wheel and below the suspension.
 

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Discussion Starter #7
Actually, it is a very good method of making tires last for a long time. Tires get their wear from turns because the inside tire scrubs away tread because the inside tire is forced to move faster than the outside tire (circumfrence of circle). With wheel motors, the outside tire can speed up, and the inside tire slow down when negotiating a turn. Tires last for ever. Also four wheel motors would give you really wonderful all wheel drive. And it would be cheap and simple. No fancy differentials for power transfer, etc..
I have to assume that you're talking about the differential steering being a supplement to conventional steering; because in that case I agree with you 100%. It reduces tire wear and increases handeling. It sounded like you were an advocate of nothing but differentials doing the steering; which works wonderfully for 2 wheeled vehicles but would be absolutely worthless on a 4 wheeled automobile.
 

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I agree you could get awesome traction control, more regen, small space savings and better efficiency. I don't agree with simple or cheap. Wheel motors are more complex than a differential and more expensive, especially since they will need some exotic materials to keep the wheels light enough to avoid unsprung weight issues. Most importantly, I just don't see how they can be made reliable enough for the abuse they will get from being in the wheel and below the suspension.
Chorus Motors are light enough & reliable enough for aircraft use! Cheap doesn't seem to be a problem for now. Look at the complexity & cost of a Prius.
 

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Chorus Motors are light enough & reliable enough for aircraft use! Cheap doesn't seem to be a problem for now. Look at the complexity & cost of a Prius.
Looks like a product in development for airplanes and not with years of service, but even then the 2 applications are not very similar. The demands on wheel motors for cars are significantly different from those for planes.
 

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Actually, it is a very good method of making tires last for a long time. Tires get their wear from turns because the inside tire scrubs away tread because the inside tire is forced to move faster than the outside tire (circumfrence of circle). With wheel motors, the outside tire can speed up, and the inside tire slow down when negotiating a turn. Tires last for ever. Also four wheel motors would give you really wonderful all wheel drive. And it would be cheap and simple. No fancy differentials for power transfer, etc..
Er, no. That's exactly what a mechanical differential does, lets the inside and outside wheel spin at different speeds while still applying power. Also one would need a steering gear to set up the geometry of the front wheels in a turn - the inside wheel needs to turn slightly more than the outside wheel because they are tracing different circles and the inside wheel is further along within its circle as well. Tire wear comes from the simple fact that they're rolling with a load, acceleration, braking, and from turns due to one side of the tread moving at a different speed relative to the road vs. the other side of the tread. This cannot be avoided.

Separate wheel motors would be advantageous in getting rid of the differential, more efficient power transfer and better traction control that's it. You would still need a steering link system. Tire wear will not be affected.
 

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Product Development

Looks like a product in development for airplanes and not with years of service, but even then the 2 applications are not very similar. The demands on wheel motors for cars are significantly different from those for planes.
It is a product in development for airplanes as a whole new nosegear assembly is being designed and certified by the FAA, but the features of the motor are real and significant. Although the demo motor in their video shows it outside the gear, the commercial version to be delivered to Delta Airlines will be in the “WHEEL HUB” and not external. It will actually be a part of the wheel.

The size of plane wheels to the plane is much smaller than that of cars so it is at least possible that this is also doable with a Series Hybrid, although it may not be necessary or practical for sedans, but might be for trucks like garbage trucks or busses that shouldn’t expect much more than city conditions of lots of stops and startups on relatively smooth roads (with a few potholes).

So I would like to address your statement on the demands of wheel motors...

At present, the Volt is using a 3-phase AC electric motor and not a Permanent Magnet (PM) motor. A rugged 3-phase AC electric motor can be used for each wheel; although I’m suspect the Volt won’t for a couple of reasons.

The main reason the Volt is unlikely to have a motor directly power each wheel is that 3-phase AC motors are not particularly good at low speed/high torque applications; so the Volt would need to take gearing into consideration. PLUS the ‘burst’ requirements (i.e. going from a stop to entering the Highway) for vehicles are such that even when operating at 10%-35% of their standard maximum power, the 3-Phase AC electric motors will still need to be oversized such that much of each motors potential power is going unused: the motors will be greatly ‘overpowered/oversized’ for more than 99% of the conditions the vehicle will find itself in..

The hilarious thing about the Multi-phase Chorus Motor (and Drive/Inverter combo – called Chorus Meshcon) is that it’s ‘burst’ torque is not measure in the 10%-35% range that you would expect in an electric vehicle, but rather it the “10X” range (1,000%) for those 10-15 seconds that cars need the burst for whatever reason. This sudden acceleration at 10X the base torque means that the motors can be smaller and designed around their cruising speed and not designed around the more uncommon times that ‘burst’ is needed for only 10-15 seconds when the car is stopped and needs to get on the highway. At the very least, this ‘burst’ is what is going to make the consumer feel that the hybrid is going to have the same ‘performance’ as a standard gas vehicle.

This difference between a 3-Phase AC electric motor and Chorus Meshcon is HUGE, especially when it comes to providing one motor for each wheel. And since Chorus Meshcon can be both a low speed/high torque motor and a high speed motor, there would not need to be gearing from the motor to the wheel like you still need for a 3-phase AC electric motor driven Series Hybrid. The weight saving for eliminating or reducing gearing, and the weight savings for reducing the motor size/weight (to focus on the ‘cruising’ demands and not the peak torque demands) will save lots of money for the manufacturer. Simpler engineering and less weight represent real savings for vehicle production and better mileage.
 

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wheel motors poorly suited to street cars

Let me be clear about what I am and am not saying here. It sounds like the "chorus meshcon" is an interesting advancement in electric motors, and the motor technology might well be usefully applicable to the Volt and other EREV vehicles.

In-wheel motors, however, are not useful for street cars unless there's some order-of-magnitude weight reduction in electric motors. First off, at least for the foreseeable future I don't think you'll be able to completely discard mechanical brakes (in fact for a "parking brake" concept I think you'll be stuck with mechanical brakes for a long time.) Mechanical brakes are simple and reliable and allow you to maintain braking force without electrical power and complex controls. Brakes have mass. Tires and wheels have mass. Bearings and suspension components have mass. The more unsprung mass you have to deal with, the more difficult it is to control the ride quality and handling on roads that are less than perfectly smooth (which is to say most roads in the real world.) Adding electric motors to the wheel hubs is not going to be a positive change for ride and handling.

Aircraft taxiing around move fairly slowly, on very well-maintained surfaces. The ratio of the mass of large commercial aircraft to that of the nosewheel assembly is vastly greater than that of the mass of a normal car to its wheels. It's a very different application.
 

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convinced

Well, you've just convinced me that what they are doing for nosegear that they won't be doing the exact same thing for vehicles by putting it in the wheel up. ;-)
 

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I'm wondering about the trade-offs.

IF such a vehicle is much lighter, no internal combustion engine, or transmission, (although there is the weight of the batteries), the brakes wheels & tyres could be smaller & lighter. Thus maybe the unsprung weight gain would be mitigated. If regenerative braking proves possible, the brakes could again be lighter as their usage would be minimised.

A 737 has a front wheel size of 15 inches?, Similar to a European mid sized vehicle. In those rims will fit 2 motors capable of moving a 300,000lb plane. How small / light would the Chorus Motors be for a car weighing one 60th of that?

Is additional unsprung weight actually an issue here?

Minimising the mechanicals maximises the usable cabin space. Smaller & lighter yet just as roomy.
 

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I'm wondering about the trade-offs.

IF such a vehicle is much lighter, no internal combustion engine, or transmission, (although there is the weight of the batteries), the brakes wheels & tyres could be smaller & lighter. Thus maybe the unsprung weight gain would be mitigated. If regenerative braking proves possible, the brakes could again be lighter as their usage would be minimised.

A 737 has a front wheel size of 15 inches?, Similar to a European mid sized vehicle. In those rims will fit 2 motors capable of moving a 300,000lb plane. How small / light would the Chorus Motors be for a car weighing one 60th of that?

Is additional unsprung weight actually an issue here?

Minimising the mechanicals maximises the usable cabin space. Smaller & lighter yet just as roomy.
Not to ignore the amount of torque that's required to move a loaded 737, the WheelTug isn't moving aircraft down the highway for long periods at high speed. WheelTug's site indicates that the system is capable of moving the aircraft from 1 mph to 20 mph "depending on available power." The demonstration motor shown on their site indicates significant reduction from motor RPM to wheel RPM, so we're not looking at a direct-drive situation.

If you build an extremely light car, you'll have an even greater effect from the same mass of unsprung weight, since there's a relationship to the ratio of the sprung mass and the unsprung mass. "Adding lightness" (as Colin Chapman put it) does indeed make for a more fun and efficient car, check out the Lotus Elise, the car that donates its basic architecture for the Tesla. There are limits, though, and neither the Elise nor the Tesla have hub motors to add unsprung mass. I think that motor or motors mounted low and near the center of the car with appropriate, minimal gearing is the way to go with current technology, even with the magical Meshcon. Unsprung weight really is a big deal, just ask anyone who's ridden in a stupid hoopty with heavy, tacky 22" rims.
 

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I agree you could get awesome traction control, more regen, small space savings and better efficiency. I don't agree with simple or cheap. Wheel motors are more complex than a differential and more expensive, especially since they will need some exotic materials to keep the wheels light enough to avoid unsprung weight issues. Most importantly, I just don't see how they can be made reliable enough for the abuse they will get from being in the wheel and below the suspension.
I do not claim expertise on the internals of electric motors. I do know that Mits (iMev) is using them, and, IIRC, Michelin is making them. They unsprung weight issue is demonstrably a non-issue. I've read (from Mits) that cost is comparable to any other electric motor (copper is copper). Sorry I don't have cites for most of this.
 

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I'm not sure how we got to wheel motors. I don't like them personally, and I can't see how the benefit that outweighs the risk. I like the idea of one motor per wheel, but that doesn't have to be a wheel motor. Just two simple transverse motor housings with two motors each (one for each wheel). Couple it to the tire with a small drive shaft and be done with it. It is safer (pot holes) on the street, and if you're off road fording a stream with a wheel motor can be problematical. Still get all the advantages of perfect four wheel drive, steering via wheel speed (ala tracked vehicles), etc..
 

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A Wheel motor design could be just 2.

The Chorus Motor doesn't appear to be inherently expensive to manufacture. In fact it's likely to be cheaper, production for comparable production. Smaller & less Power Electronics // No PMs.

It is capable of being robust enough for aircraft use. As far as I can see, there aren't any specific issues relating to a Chorus Motor construction that wouldn't similarly apply to a regular motor.

Wheel motors were a point of discussion I introduced... It is just such an elegant, simple, design concept. It would be a big plus if all gearing could be eliminated. Other than the fuel tank & battery there would be almost nothing large to take up space in the cabin. Easy on maintenance too. Differential steering is another simplicity I like.

Maybe just a simplistic dream. The less the less the merrier.
 

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Oh - I agree with you. I love simple also. But there are costs and risks associated with any design choice. Tradeoffs happen. For a normal around town car, wheel motors might make sense. The problem is when you hit a large pot hole, you could be in for some serious damages. In addition, my understanding is that wheel motors are pretty limited in torque and horsepower. This can be gotten around by having four of them. And, last but not least, all wheel drive is a plus especially if you live in places where you get bad driving conditions. With a off road capable vehicle, you don't want them at all. I'm sure somebody will try it, so we will certainly see how it works in the real world.
 
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