Three-phase motors with VFD’s (Variable-Frequency Drives) are indeed relatively inexpensive and quite reliable these days. But they can’t completely replace a multi-ratio mechanical transmission. With VFD’s, the motor power necessarily falls off at lower speeds. To compensate, you would have to use a considerably larger motor.P89DC wrote:Over on OWWM.org it's very common to use a three phase motor and electronic controller to run off of 1ph power. It allows variable speed control. I've been looking at converting my JET 16.5" drill press to this set up. It wouldn't be much of a stretch to use a 3 phase motor in a Shopsmith power head with a controller outside the head. I'm pretty sure they're calling this kind of setup "DVR". The only issues are mounting the motor on the power head, setting up pulleys and mounting the controller. Cost of motor and controller is ~$150.
3 phase motors with digital control have replaced mechanical transmissions in most high and medium level washing machines. The technology is very reliable.
With a mechanical transmission, as the speed is decreased, the output torque increases proportionally. So full output power is available at all speeds.
A good hybrid solution is to have two or three mechanical transmission ratios to chose from, and then use a VFD to vary the speed within each speed range. That way, the motor can generally be operated in its full-power speed range. A 10ER, with its three belt-drive ratios, would be a great application for this. And as you can buy Frame 56 3-phase motors, mounting the motor would be trivial.