At times one may want to control the transmission of rotational
motion by engaging or disengaging an axle from a motor. Such a
mechanism is called a clutch. LEGO has special parts that can be
used to make a clutch. However, these are relatively hard to
find, and take some force to engage or disengage. 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. I
was aiming to design a clutch that can engage or disengage with
very little force, while also being made of common parts. Below
is my most recent design which relies on the easy meshing
between two pin with towball pieces on the 24 tooth gear and the
Technic connector with axlehole on the central drive. The only
parts that are less common are the two Technic disks with
axlehole. These can probably be replaced with other parts.
Perhaps axles extending from the lever would work. Here are the
instructions in pdf form