If it was me, I'd go for direct drive coupling to the lead screw...forget about gearing unless the motors are just way undersized.
As for the arrangement, I'd keep the X and Y motors the same, and put the oddball on the Z axis, perhaps with a finer pitch screw, to compensate for the lack of resolution you'll be getting with the 7.5 deg stepper.
As for the relationship is gearing, 2:1 means that for every 2 revolutions of 1 shaft, 1 revolution happens on the other one. Depending on which way you're going, it means your assembly would deliver double the torque at half the speed, or vice versa.
-- Chuck Knight |