Hi George

As you stated induction motors are heavy (not good on a z axis) and I believe are difficult to control the speed. :nope:

The idea of using a 3 phase motor and Variable Frequency Drive (VFD) is that you feed it 240v AC at a set current and control the speed by "varing" the frequency of the AC supply. Therefore you get full (ish) power over the whole speed range. not to mention over speeding the motor to way beyond its rated speed if you dare........

I'm by no means an expert on this so I plan to post a separate question on motors later if your interested?