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
Step 2: Add the pneumatic saucer lifter and control solenoid
Note that the cylinder will have to be able to pivot at the base as it extends and retracts, so a rigid mount wont allow the linkage to move.
You can see 1/8 inch pipe thread to 1/4 inch OD quick connect pipe fittings mounted to the air cylinder. 1/4 inch tubing connects the air cylinder to a solenoid control valve, a 5 port 4 way valve is used to control the double acting air cylinder.
The solenoid valve is connected like this:
Feed port: connected to a length of tubing that has a quick connect "I" type fitting to mate to the air compressor hose. There is a "Tee" fitting in this line to route air up to the second penumatic lifter used to lift the passenger alien out of the saucer later.
Normally on (this would be the N.C. port on an electric switch) port: is connected to the lower port of the air cylinder, so the saucer will be in the raised position.
Normally off port (the N.O. port on an electric switch) is connected to the upper port of the air cylinder, so that when the solenoid is activated, the saucer descends.
The 2 exhaust ports of the solenoid valve are connected to flow regulators to regulate the speed at which the saucer raises and lowers. Once the solenoid is triggered by 12V in this case, the air supply is connected to the upper port on the cylinder, but for the cylinder to retract the air from the other side has to be vented (exhausted). By controlling the the rate at which this happens the rate at which the saucer moves can be controlled.
Step 3: Make the core tube of the saucer & alien lifter
The diameter of the octagon is about 17 inches. The height is 30 inches to mate to the vertical metal bar from the linkage. A flat strip of the same angle iron was added on the inside to act as a surface to hold a bolt.
Inside the cardboard tube an additional air cylinder of 3/4 inch diameter and 13 inch stroke was mounted as shown, An additional solenoid was added to control this cylinder. The connections are similar to the first cylinder.
Step 4: Cut a template for the saucer section
The printouts of the spine were glued to sheet of masonite, and cut out with a jigsaw.
To save cardboard and weight on the final structure only half of the fin was drawn on a template, but the bottom half is symmetrical so 16 of the fin piece are needed.
The second arc template piece will glue to the outer edge of the fin pieces to hold them apart. This is hard to visualize, but will be clear in a later step hopefully
The grey highlighted parts of the template are used as a gluing surface.
Step 5: Assemble the flying saucer fins to the central tube
Then the lower fin pieces were glued to the bottom edge ot the tube.
The arc pieces were then glued up. A second pair of hands provided by my friend Matt was invaluable.
Step 6: Finish the skeleton of the saucer part
8 mylar emergency blankets purchased from the local surplus store were hot melt glued to the skeleton, this made a big difference in the appearance but was pretty quick work.
Step 7: Finishing touches and wrap up.
A few notes that I noticed did not get into the main instructable are collected here, and they may not necessarily apply to your particular flying saucer (actual space mileage may vary consult dealer for details.....)
First, I noticed that due to wind on the particular night, and the need to keep the saucer well balanced, it was necessary to add 4 flat metal straps from the long arm to the edge of the frame (I will try to get a clean picture of this). This "wishbone" or pair of them prevented the saucer from twisting dangerously even in the 20 + mph gusts of wind we had on 10/31/2008 in Mountain View, CA.
Secondly, I added ring of fast blinking X-mas lights around the edge to add effect. My wonderful and creative wife made a soundtrack of songs with space, aliens etc.. which were played out of an MP3 player and a set of amplified speakers. wwas used to
Thirdly, A fog machine on a remote trigger was placed below the saucer to hide the mechanism.
A remote control from surpluscenter.com was used to control the effect: http://www.surpluscenter.com/item.asp?UID=2008110215190946&item=11-2495-3&catname=
That one was out of stock at present, (I bought mine a year or so ago), but a 2 channel one is in stock:
The remote control receive side has a relay closure outputs which are normally open, and can route 12V to the output when a button on the remote transmitter which looks like an older car keyless entry remote is pressed. One channel goes to the solenoid valves that control the pneumatics, the other goes to a solid state relay that switches the fog machine on.
If I was starting over at this point, I might use square tube for the vertical middle piece of the frame, to minimize twisting, but that is harder to work with and more expensive then the reinforcing straps I added as mentioned above. I had considered automating the control of the saucer, pop-up alien and fog machine with a PC and a parallel port IO connected relays, as described in the Make: Halloween special issue, (or a USB IO interface), but ran out of time to construct that, and I do like the ability to time the effect manually so that the saucer starts to move as a trick or treater gets close to it.