I just recorded a video update of the motor, as it is, today.
hehe indeed, the backemf's were a problem from the start of this project, i found that after about 280volts, the transistors would simply blow, even though they are NTP rated. - but they are still a concern because of how old they are technologically. ... but i solved the offtime emf problems with a paralell capacitor across the motor, (see the MOT cap, in the video)
but after i achieved about 400volts, i noticed the rotation of the magnets were generating a voltage, that exceeded the input voltage, - which reduces the input current, but it also backfed the drain pin, and wouldnt allow the transistor too switch off properly., but some diodes fixed that (albeit slow ones)
and after i hit 500v, the collectors started too leak on the bottom end of the H Bridge., which is still a problem, - i had too remove darlington pairs at that point, and drive the FETS with seperate power supplies, - thats my biggest problem right now, - but running up too the max of my power supply right now, 740 volts, - . im about too replace the base drive transformers with some tiny SOC package dedicated dc-dc converters. - but i give that 50/50 change ... at best.
anyway when the big motor gets built next, i might consider just making my own base drivers with IR leds and solar cells. - either that or just bite the bullet and use a commutator