Following the info from the Geneva Mechanism previous post, found its true origin. Another blog also with some more interesting topics about LEGO TECHNIC.
It calls BrickEngineer (from Kevin Knuth) and I want to highlight today a design for an interesting smooth clutch.
A clutch is a mechanism which allows to engage or disengage an axle from a motor, when we want to control the transmission of a rotational motion.
Many clutch designs simply move gears back and forth across one another, but this causes the gears to grind and eventually wears down the parts. In these systems, the clutch does not engage smoothly.Below a few animations that show a possible solution made of common parts and requiring little force for engage/disengage (see the author page linked above, for instructions and LDraw files).
On the right, the details from coupling mechanism (bottom view).
Below also a few images from other clutch mechanism implementation ideas, found at Brickshelf (click to enlarge and see more details).
Learn more about, how clutches work, here.