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I'm looking at adding a couple of electric motors to my 2017 Beetle. Some of what I am thinking so far:
-AWD rear suspension parts from a Golf, short custom CV joints, motors mounted near rear wheels.
-Some used Tesla battery modules mounted in the trunk, limited range. Use ICE alone after batteries are depleted.
-A suitable controller, wiring, etc.

I'm thinking of either having it be a completely independent system or having it add power while using the ICE. If independent, it would have its own accelerator control for the driver and the ICE could be left on and in neutral for accessories to function. Or could I do something to run the accessories without the ICE on? It already has electric PS, so basically just the AC and brakes would need some rotational energy/vacuum.

If tied together, I'm not sure how that would be accomplished. Could the motors/controller be set up to only add EV torque when accelerating, going up hills, etc?

Can anybody recommend a compact motor to fit in the small space? Perhaps with enough power to run the car if I later remove the ICE and replace with more battery?

Using two motors instead of a differential and one motor, will I have issues with differing motor speeds/power in turns?

Is it possible to tie the rear motors into the traction control somehow for better AWD?
 

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I'm thinking of either having it be a completely independent system or having it add power while using the ICE. If independent, it would have its own accelerator control for the driver ...
How would a separate accelerator be arranged, and be safe to use? If the car has an electronic throttle (I assume they all do now), why not use the same input to both drive systems, with a switch for modes (gas only, dual, electric only)?

... the ICE could be left on and in neutral for accessories to function.
I can't imagine how it could be efficient to run the engine just for accessories.

Or could I do something to run the accessories without the ICE on? It already has electric PS, so basically just the AC and brakes would need some rotational energy/vacuum.
Brakes would be like any full-electric vehicle (vacuum pump or whatever), and A/C would be like an EV or the hybrids which can maintain A/C operation when the engine is not running - that means replacing the mechanically-driven compressor with an electric one, or connecting the belt to an added electric motor instead of the engine. The 12V battery would be insufficient to run A/C, and with this through-the-road scheme the high-voltage (traction) battery may run down and require inefficient through-the-road charging, so it isn't ideal.

If tied together, I'm not sure how that would be accomplished. Could the motors/controller be set up to only add EV torque when accelerating, going up hills, etc?
That's how electric-assist bikes work. Yes, it is possible; that doesn't mean it would be easy.

Using two motors instead of a differential and one motor, will I have issues with differing motor speeds/power in turns?
Certainly coordination of the two motors is required. Although some motor types could be connected to a single controller, they won't share power and distribute torque ideally; in practice, separate controllers (inverters if AC) for the two motors, coordinated by one system, are required to do it right.

Is it possible to tie the rear motors into the traction control somehow for better AWD?
For the vehicle manufacturer, this is not just possible but required. For a DIY conversion, it would be a substantial challenge of integration with the original vehicle's systems.
 
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