As has been widely reported, JB Straubel stated last October about the Model ☰: “We’re inventing a whole new platform: it’s a new battery architecture, it’s a new motor technology — brand new vehicle structure…so it’s a lot of work. This is something we started on even a few years ago. But it is a brand new vehicle — and it has to be.” -- http://evobsession.com/tesla-cto-jb-straubel-model-3-is-going-to-be-most...
Just as the Model S was a clean-sheet design, this implies that the Model ☰ may also be one. This makes sense because the design goals of the new platform are different than the design goals of the Model S platform. As many have opined over the past months, it will be difficult to cost-reduce the Model S enough to get the price down to $35,000. It would instead be better to design a new car from a clean sheet with the desired goals in mind.
In such a design, what would be some of the key elements? To answer that we need to look at the design goals that have been stated so far:
Base model price: $35,000
Size similar to Audi A4
Coeficient of Drag < 0.20
200+ mile "real world" range
Performance better than similarly-priced Audi and BMW competition
There are a lot of things outside of the powertrain which are implied by the above list (and many more goals that I've not mentioned), but let's look at these in terms of the battery and motor systems.
Tesla has spent the last 10 years producing cars using AC Induction motors. These motors have both pros and cons. Wally Rippel wrote on the Tesla Blog in 2007 (https://www.teslamotors.com/blog/induction-versus-dc-brushless-motors) that there's no one motor design that is "best". Recently, according to articles I've read, it seems Switched Reluctance motors are the new shiney item in motors. They tend to be slightly more efficient, have a broader range of speeds, can maintain high power at the higher speeds, and generate less rotor heat than induction motors. There are also hybrid permanent magnet/switched reluctance designs (I believe the BMW i3 uses one).
Within a motor, the power lost to internal resistance is given by I²R. When running two motors each at half the current, each motor wastes only 1/4 the amount that a single motor loses when running at the same overall power. Therefore, the system loses roughly half the power of the single-motor system. If you ran 4 motors, each at 1/4 the power, the loss-per-motor would be 1/16 for an overall system loss of 1/4. (Note, the power lost due to parasitic heat being talked about here is considering the DC resistance of the motor windings--not the AC reluctance of the system as a whole--that would be measuring the total power including the useful power output. The better formula for that is likely P=IE--current * voltage).
So...might we see:
quad motor design
switched reluctance and/or permanent magnet motors
true electronic traction control and torque vectoring
new battery chemistry
The Model S 60kWh base model was rated at 208 miles range. With a more efficient motor system, lower drag, smaller frontal cross section, and lighter weight, might we see a 50kWh battery on the base model and still reach 200+ miles per charge? Quad 100hp motors could be standard.
A performance version may increase the rear motors to 200hp and have a 70kWh battery.