Every idea has merit and is worthy of consideration,you Guys keep throwing it out there,you might be suprised about some engineer scrooling through and in a “Gee Whiz”,"say,that might work!"Of course you wont get any credit for it,but ah,the satisfaction.I actually kept razzing a major manufacturer and offering ideas and finally most of them were implemented(they) didnt stop making mid size trucks after all.Coincidence?probaly ,but I have the satisfaction of knowing I tried.
Years ago when digital SLR’s first came out I posted on photo.net the suggestion that camera companies come out with a line of lenses designed for the sensors that are smaller than 35mm film.
Such lenses would be smaller, lighter & cheaper.
I got a lot of negative responses (who would invest in a crippled toy lens?), some pretty rude.
Soon after Canon came out with the EF-S line.
Coincidence?
Someone was paying attention.@ Circut.
There is a reason why the BMW i8 has a 2 speeds transmission for the electric motor.
The motor generates a reverse voltage (back emf) against the power source as it rotates. The voltage is generally proportional to the speed. Running at full speed unloaded, the back emf is almost equal to the source. Essentially, there’s only a few volts at the motor winding and the current through the motor is low. At low speed with full load, the back emf is quite low. In this operating condition, the power source pushes a high current through the motors winding and high current converts most of the electric power to heat rather than motion.
Now you may be tempted to say that adding reduction gears to a small motor would address the issue. But when you run a motor at high speed, you have a new source of power loss. The rotor doesn’t run in vacuum and you would have aerodynamic loss.
Like internal combustion engines, motors have a efficient operating range and some sees fit to add a multiple speeds transmission to keep it in that range
Four hub electric motor drives is being considered by many car makers. The motors could be used for braking as well as drive. The biggest problem is the energy required to drive them vs one motor. But, it is done now in a way with tractors and skidder said which use hydraulic motors at each wheel and a diesel running a pump. The high hydraulic pressures make transmissions easier to manage. They still aren’t as efficient as regular hybrids but the drivability is beyound belief with acceleration, cornering and braking all enhanced by four drive motors.cc
@dagosa In the scenario of separate drive motors on each wheel, isn’t that a safety issue if one wheel’s drive motor fails while the car is moving? Wouldn’t that affect safe handling?
There would be a failsafe mode Marnet,you are right the handling would certainly be different under power(I would imagine the computer would shut that end of the drive system down,cars typically only pull or push from one end anyway and there would have to be a “differential” action on the drive system anyway.
A good way to handle a motor failure is to have them fail open, or in neutral. That way it won’t inhibit movement and cause a skid or unplanned turn.
The big challenges with hub motors are:
unsprung weight
(salt)water intrusion
flexible high-voltage wires
That’s why I think inboard motors are the way to go; how it’s done on the Tesla.
Thats right Circuit,I would like 2 motors with halfshafts anytime you can keep a wire from flexing you are better off,CV joints are proven tech.
Seems like the base Tesla layout (1 motor and a diff, RWD) works pretty well. Why add more complexity?
@Marnet http://cleantechnica.com/2012/10/16/in-wheel-electric-drive-ftw/
There is no connection between the two primary moving parts.
If a motor fails and looses it’s power, I can see it effectively free wheeling. Then, the Moros that remain would affect handling no more then the drive going to just one wheel through an open differential. It’s really pretty fool proof. The braking action is as powerful as the driving force going in the opposite direction. I would anticipate regular brakes as back up but farthe inboard like tractor brakes.
Right now, the technology favoers inboard Motors. Hub motors are restricted to bikes. 
Thank you for all the replies to my question. After reading the article in link, now I have a further question, please. It mentions that the Protean system can be integrated with hybrid engines. But since hybrids run in part on gas IC engines, how does having electric motors on each wheel do away with all the driveshafts, etc needed to transfer power from an IC engine to drive wheels? (Please pardon if my terminology is lacking.)
I would assume that like a Highlander Hybrid rear motor, it would be where a differential would be with half shafts going to the wheels. There would only be shafts no different then those in AWD cars from the differentials. On a highlander, the engine only assists on the front wheels, not the rear. There is no drive shaft going to the rear, just control cable(s)
An agreeable setup on the Highlander.
diagosa: what happens when a motor fails depends on the failure type. There are many failure modes for electric motors. The most common is bearing failure, and this would be similar (in it’s effect on driveability) to a wheel bearing failure, ie, bad.
Other failure modes are shorted windings, open winding, broken case. I’m not clear as to how those affect the driveability of the car.
Then, the [motors] that remain would affect handling no more then the drive going to just one wheel through an open differential.An open differential allows traction either at both wheels or no wheels (neglecting traction control).