Summary

This is a simple lever and fulcrum that, combined with LEGO minifigures and children, turns into a catapult. Inspired by the "Made by Joel" website. http://madebyjoel.com/2012/05/small-catapult-toy.html

Also, an opportunity to experiment with laser-cut parts in OpenSCAD, and to test laser-cutter offsets for press-fit peg-joints.

Instructions

First laser-cut wasn't a success. Perfect tolerance in OpenSCAD creates a too-loose fit with the laser-cutter. Needed to add some xy-plane thickness to the pegs to account for material removed by the laser.

Used minkowski() on the pegs to make them thicker:
-- 0.125mm recommended offset was too loose, needed glue.
-- 0.375mm appears to be a perfect press-fit offset (no hammering, no glue)
-- 0.5mm too-tight press-fit offset (had to hammer together, stripping a layer of laminate)

Idea and initial offset dimensions from http://www.thingiverse.com/thing:27736

Research suggests the laser cuts a v-shaped notch, widest closest to the cutting surface. Width and depth of the notch are presumably functions of the power and speed settings.
A 0.375mm offset worked best with 4.75mm (3/16") baltic birch plywood. Epilog 36-EXT, laser setting was SPEED=08, POWER=85 and FREQ=450.

OpenSCAD code has lots of comments and test-modules.

LEGO launcher in OpenSCAD