Originally Posted by
digits
OK, so that's going to be a pretty chunky main motor and drive - what's a ball park cost for a 7.5HP motor and vector drive?
Even if the 2nd motor is open circuit, it will still generate a large EMF when spun at turning speeds. You would have to be sure that this can't arc across your disconnection circuit, or reverse bias any semiconductors in the drive if you're disconnecting electronically. What circuit do you have in mind for swapping the motors over, and what happens if you hit e-stop or have a power failure under high-speed/high load operation? If your circuit disconnects a motor while it is still spinning, I would expect really, really bad things to happen to the driver board. Switching a multi-kilowatt inductive load is not trivial!
I'd also imagine that a 7.5HP spindle motor is going to have a shed load of rotational inertia - your indexing motor will have to overcome that if both motors are always physically coupled to the work. If your drive train uses gears, couldn't you just rotate one motor so that it comes out of mesh, or use a mechanical clutch? Similarly, a belt drive could move a motor pulley out of the way and push an idler up against the belt in its place to maintain the same tension?
Just my 2p's worth...