Does anyone know what this kind of motor is called (where the rod runs all the way through the motor)? Also, are they available in the US?
Just googled "non-captive stepper motor" and sure enough! That's what they're called. This is exactly the kind of motion I'm looking for! Where the motor propels itself along the threaded rod. Thank you so much for your help Rick!
They have a good selection of these at http://www.omc-stepperonline.com/ I've been thinking one of these would make for a nice compact Z axis drive.