Rotating Ballnut - design ideas

[Kitwn]

Yes, 32mm pitch with 2:1 ratio will give the same linear torque as 16mm pitch 1:1 so torque is canceled by pitch difference like you say.
However, when I say Torque is doubled so the smaller motor can be used, what I'm referring to is that if 1:1 the 32mm pitch would require a larger motor to give the same linear force as 16mm pitch. So the ratio doubles the torque and allows the smaller motor to have the same linear force as 16mm pitch.

Aha! The point I had missed is that your 'smaller motor' required to drive a 32mm pitch screw with 2:1 pulleys is NOT smaller than the motor required to directly drive the 16mm pitch screw. In fact it may well be the same motor, which is at the heart of what I was trying to say. Thanks for clearing that up.

Is there a case for using the direct driven screw with a bigger motor? You are saving the cost and complexity of the 2:1 drive and halving the speed required from the motor, so running it in it's higher torque region anyway?

Kit

[JAZZCNC]

Is there a case for using the direct driven screw with a bigger motor? You are saving the cost and complexity of the 2:1 drive and halving the speed required from the motor, so running it in it's higher torque region anyway?

Kit

Can do either but using a larger motor usually doesn't cost less because requires larger drive and often more volts so larger PSU.
However, on long machines rotating nut wins hands down and requires a belt connection, so the ratio is no extra cost. Rotating the screw on the long machine means much larger ballscrew is required and this really starts to ramp up the costs because everything scales up with it, Bearings, couplers, motors, drives, PSU
Even then a rotating the screw system cannot achieve the feeds a rotating nut can.