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.
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 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.
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.
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.
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?
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.
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".
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?
Although plastics make up only about 11% of all US municipal solid waste, many are actually more energy-dense than coal. Converting these non-recycled plastics into energy with existing technologies could reduce US coal consumption, as well as boost domestic energy reserves, says a new study.
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