I was
hoping that I would have most of the RPM range at 72 volts, since the motor itself doesn't need to be running any faster than it does no-load at 72v. And I figured that getting the amps in to it might be easier, since the armature-alone resistances is less than the combined armature + field resistance of a series-wound motor.
I can't really verify it without driving it longer than the half a block I have to work with. And I dare not try that without brakes!
Others have made "city" EVs on 72v. I'm hoping to be able to boot around the city in seconds gear without shifting at 72v. It might do it with more field current. Won't know until I try.
I guess I will service up the brakes next. That sounds like fun. Assuming that doesn't help enough, then it's on to adding a vacuum pump. Then, finally, I can take it for a couple of km drive. That will tell me a lot.