1. get DC series motor, max of ~25HP or so. Obviously not gonna cut it for powering the car, it's just to produce average power for range extending.
2. replace/mod brush setup into slip-rings. The rotor will be continuous DC field, adjustable strength via sliprings to control voltage/curent output. Just like a big alternator.
3. profit! not yet. Separate the outer windings and pump them into a bridge rectifier.
So I'm thinking of trying this. Hopefully the commutator I can just lathe in half then split up the brushes into 2 groups. Field control will be a fairly simple chopper ckt to limit voltage and current, both to maximums and to a few inputs from the BMS and the gasser powering it (like stall prevention).
If it works then I may be tempted to convert it to brushless.
It's either this or just slap a rectifier to a BLDC and deal with purely RPM based output control. The main things on my mind about this are cost, power density, and long term magnet demagnetization.
also I found this:
If they aren't horrifically overpriced I'd be tempted to go there. I've been looking for a cute little 3-cyl diesel!