Another thought about the speed needed to advance the screw using a 4x lobe wheel.
If you have one pin mounted on the motor, then the motor must do 4x revs to advance the wheel 1x revolution, but if you have 2x pins on the motor then the motor only does 2x revs to advance the wheel 1x revolution.
I found this video that might help explain what I'm talking about.
https://www.youtube.com/watch?v=cunj4O_03e4
I can't see why you couldn't have 4x pins acting on the wheel and thus saving time.

I tried to model it and I dont think 4 pins is possible due to the scallop cut away of the boss on the drive. This cut away boss keeps the wheel in it`s stopped position.
I do love mechanical devices and the Geneva is brilliant, i`m sure we could get this work as described with switches etc,
and a simple brain i wrote seemed to work ok (keyboard simuation mode)

Russ
The Gecko unit looks amazing, it would seem a hell of a waste to have most of it`s potential never used on my rig.

But have a look at this little beauty i found  https://www.youtube.com/watch?v=DYG8SlrwGHM
at around £30 looks like just the job. Direct drive - one rotation.

That's a handy little bugger wil, nice find !
Thanks for posting,
Russ

My only concern with using a device like that is the slight movement you get on powering up/down a stepper.
It wont affect my welding stage use for it as i could put a spring behind the weld electrode to take up any errors,
There is another axis on my machine i`m tempted to try use the same device, all it does it rotate from zero to 180 degrees
and back to zero again on command, but it must be in the correct place on machine start up.  easy enough with a homing sequence of a mach3 axis
but i`m not sure how to acheive that with the stepper movement driver device.
any thoughts ?