The motion was controlled by a 1.5 inch bore 11 inch stroke air cylinder. The structure was constructed out of "uni-strut" metal angle iron which has a series of holes in it that allow easy construction. The saucer itself was made of cardboard that was recycled from last years halloween decorations. The skin of the saucer was made using a series of mylar silver emergency blankets.
Here is a brief video of the saucer in action.
Here is a second video of a walk through of the whole haunt:
This is also my first instructable, so I hope you like it. Thanks. --Neil.
Step 1: Construct the base for the saucer
Fortunately the angle iron was available in 2 foot pre cut lengths, but it cuts easily with a hacksaw. A square of this angle iron was bolted together with 5/16in bolts that connect at the corners and to the base wood piece. A third vertical piece was connected to act as one bar of what will become a 4 bar mechanical linkage.
2 more 2 foot lengths were connected at an angle to stiffen the structure. They were bolted to the wood piece using short scrap lengths of angle iron as bracket.
A wider piece of angle iron was added horizontally to minimize twisting of the middle vertical piece. Twisting would become a problem later.
Two 4 foot lengths were bolted to the middle vertical piece with about 8 inch vertical separation. These will be the main lifting arms, and form 2 more links in the 4 bar linkage.
The linkage was completed by adding a vertical piece at the end of the 4 foot bar. The saucer will be attached to this piece.
For more information on the 4 bar linkage, a fundamental mechanical structure, you can read the article here http://en.wikipedia.org/wiki/Four_bar_linkage