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?
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.
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.
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.
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.
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.
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.
Festo's BionicKangaroo combines pneumatic and electrical drive technology, plus very precise controls and condition monitoring. Like a real kangaroo, the BionicKangaroo robot harvests the kinetic energy of each takeoff and immediately uses it to power the next jump.
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