I am thinking of implementing a ratchet action with a servo motor, implemented with a 24T clutch and a catchment mechanism.

Activating the servo at full power should give me 90 degrees of rotation on the 24T gear, 'clicking' through the catchment, and rotation on any meshed gears. If the catchment holds, then when the servo returns to its start position, the clutch should slip and not turn back when its axle turns, and any gears turned by the clutch gear should retain their new position and not return back? I think this would be a good way to transfer rotation to linear step motion, which I will need for a MOC I am thinking of.

thanks for comments

What about just using a PF standard motor and a gear rack?

For this particular MOC, I need to have a discrete step motion - a PF standard motor would be difficult to control to give specific amount of rotation. The servo motor will give about 90 degrees rotation on every actuation, which after some gearing and maybe a linear actuator, will result in a known distance of travel of a particular component. A gear rack or two may be involved at some point rather than an LA, still pondering this aspect.

I am looking to build a rig for focus-stepping in the vertical direction, with steps in the micron range, the stage only needs to travel 1-2 millimeters; however, the focus steps need to be highly repeatable as this is a requirement for the software used to integrate the stack of images. I have seen this done, with LEGO of course, for focus-steppers in a horizontal direction, with micron-level travel steps.