Summary

This Crossbow shoots marshmallows and is powered by large #64 rubber bands. It requires about 10 inches of 1/4 inch dowel and 2 12" x 24" sheets of 1/4 inch plywood, about four feet of string, and a 6"x"6 inch piece of 1/8 inch vaneer plywood (often sold as door skins) for the marshmallow cup.
The colors are just to help keep the pieces separate during design.
I was inspired by the decor at Disneyland's Tomorrowland, very retro 1950's sci-fi.

Instructions

First you will need to Laser cut the pieces from 1/4 inch plywood ( actual thickness was 0.18 inches)

Assemble the stock pieces with glue.
Assemble the arms of the bow with the spaces between, spiral to the center of the bow, and tri-lobed end toward the outside. The rubber bands will eventually be looped over these protrusions.
Assemble the trigger with parts spaced on either side of the trigger guard. You will need a small piece of 1/4 inch dowel as a holder for the marshmallow cup.
Attach the top and bottom to the stock, with the spacers at the front to keep them apart and stable. These spacers are where the other end of the rubber band will attach when assembled.
Assemble the cup (made of 1/8 in vaneer) with the hook (made of 1/4 inch plywood) out the back
Attach the bow arms with 1/4 inch dowel and keep in place with the small arrowhead shaped pieces.
Cut two strings long enough to span the bow. About 24 inches each.
Run string through the holes in the cup and tie them off on either side of the bow arms.
Attach rubber bands from the front spacers to the arm spaces. I used 3 #64 sized bands on each arm.
Attach a smaller rubber band from the back of the trigger through the stock and back tot he trigger. Tie it off so that the trigger returns after pulled.
Load marshmallow, fire at unobservant people. 8)

TomorrowLand Marshmallow Crossbow