X Y balanced drive motors.

[JAZZCNC]

That answer makes me wonder - given that ballscrews have such low friction and a lead that means that a carriage could drive the screw, what happens to the Z axis when the power goes off the stepper and it loses almost all holding torque? With a heavy spindle plus Z mounting plate, etc., I could imagine the spindle dropping under its own weight. Does this happen in practice? Or does, say, a 1605 ballscrew in conjunction with the permanent magnetism in the stepper manage to stay put when power goes off?

Just curious!

Often they stay put but if heavy then yes they can and do drop when powers off.