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Well I just went looking around for half an hour reading about 996 AWD, disassembled Tesla units, and lightweight batteries. And this thread is 18 months old. Try not to necropost please :)
-Isaac
 

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Sorry, I didn't see the date on the post before. Jan 10 2019 is 18 months ago, and since then the OP has been gone. In my experience necroposting usually means replying to an old thread, I didn't exactly look up the definition before using the word (probably a mistake of mine, not the first one).
I'd really appreciate if you wouldn't go calling people little kids though :)

BTW, to answer your question, as long as there's a direct connection (gearbox or otherwise) between electric motor and wheels there is no problem with motor RPM synchronization.
A Tesla motor is especially painless, since it's induction rather than PMAC (no back EMF problems when unpowered) and it's torque controlled rather than speed controlled.
If you want a cheap SDU controller take a look at openinverter, for 300 euros (maker is in Germany) you can get a replacement logic board which will get tons of power out of the SDU (though maybe not matching the efficiency of the Tesla logic board.) There is also a forum with lots of bleeding edge development, mostly in repurposing OEM motors and inverters.
-Isaac
 

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Thank you for the information Brian but I guess I’m just especially dense on this topic. Do I have the below written correctly?

If a rear engine car had an independent electric axle upfront, it would be considered a Parallel hybrid. Because the motors are disconnected from one another and paralleled through the road.

And remain a parallel hybrid when under braking or zero throttle the electric axle regenerates power back into the e-axle driving battery pack.

but the minute the regen is activated while the car is being powered by the gasoline rwd engine it becomes an inefficient series hybrid, because you are using rear mounted gas engine to power up the battery of the front e-axle.
Yes, it would be a parallel hybrid, of the 'through-the-road' type as Brian said (I hadn't seen that term before, thanks for the new word!).
It's not a series hybrid - in a series hybrid, there is a completely separate generator and the engine is not connected to the wheels directly.

As a matter of fact, the front axle is a better spot for regen anyways (front axle braking is preferable). But when charging via regen you're putting extra load on the drivetrain, on the tires and on the original engine -- more wear everywhere, and probably losing at least 10% of the power (plus inefficiencies in the electric motor).
For pure track use, this is probably fine, and does allow you to reduce costs.

BTW if an onboard charger is an issue, it's very possible to add CHAdeMO DC charging, which minimizes the extra onboard weight and allows much higher charge rates. OpenInverter people (myself included) are working on a very simple setup which will enable that.

-Isaac
 

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For a more efficient drivetrain, how about the Tesla SDU up front and then a smaller generator connected to the transmission's front wheel output shaft? Well that's more weight and more complexity... Hybrids are hard. But it would still offer better generation capabilities, although the ideal is connection directly to the flywheel (allows generation while idling/at any speed/in neutral).
 

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Isaac97's idea of using the now unused output shaft of the AWD transmission is a good one if a generator can be appropriately sized for the RPM range. I'm not sure on the SW controls the cars have regarding torque split between the rear diff and front diff... i assume some custom ECU work would be required to determine the right amount of torque split to the generator based on the state of charge of the battery.
The 996 has no torque split controller -- it's just a viscous coupler to the front end. Some versions have stability control (keeps the car pointing straight), others have traction control (anti-wheelspin). Traction control is rear-only, it's a virtual LSD using the brakes. But there are no electronics controlling the torque split, only the viscous clutch/coupler - someone quoted 15% torque normally, up to 45% after extended rear slippage.

EDIT Looks like we've got the same ideas here.
 

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A few minutes of Wikipedia checks (might be wrong) tells me that 996 and 997 have viscous clutches, no data on 991 (generation after).

EDIT 993 (1995-1999) had viscous too, generation before that had a real differential.
 
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