Introduction: Giant Pot of Gold
A foam pot of gold used to cover a radio controlled confetti cannon robot driven by a clown surrounded by leprechauns at a St. Patrick's Day rave.
A majority of the work for this prop was in design and planning. The pot had to be built to fit snugly around a robot that was only partially complete. The pot would be driven on a mobility scooter through crowds so durability had to be considered. The entire robot would tilt 45 degrees to shoot confetti so consideration of range of travel and robust mounting points were required. It also had to be easy to transport, assemble and disassemble.
Total cost was ~$400 with $220 of that being the pink foam board. That may sound pricey, but keep in mind your time is valuable too. I was able to do this in a week and a half outside of the 9-5 workday.
Step 1: Design and Planning
The pot is based on a stacked ring design. Actual pieces were done in half-circles to minimize material waste.
Achieving the proper fit required a couple dozen measurements. To calculate the proper interior radius, the width/length of the box had to be measured at key heights.
Then use your 6th grad trigonometry skills to calculate A squared plus B squared equals C squared.
Radius = sqrt[(0.5xlength)^2+(0.5xwidth)^2]
I went with pink foam board available at any home improvement store. It is ~$20 per 8'x4'x2" sheet. It had the advantage of being strong enough to stand up to 30,000 kids dancing against it and an accidental run into a wall. Paper Mache wouldn't have lasted 10 minutes.
The pot was 52" x 40" not including the 40" hat and sheets of gold coins. I needed to be able to deliver it easily in my Volvo station wagon. The pot was therefore constructed in quarters (lower front/back, upper front/back). The hat was not glued to the brim so that it could lay flat in transport.
I love zip ties! Eyebolts were inserted into the foam with a coating of gorilla glue. Zip ties would then be run through each set to cinch the pieces together. The interior radius was not cut out of 2 layers in the middle of the pot. These "shelves" would rest on top of a bracket on the robot. Rods of PEX tubing were run between the top and bottom layers to maintain flush alignment.
Step 2: Cutting and Stacking Rings
First: Build a giant compass to draw your radius lines. I took a wooden yard stick, added a finish nail in the tip and drilled holes at 2" increments down the length.
Second: I'd recommend building a version of my makeshift foam scroll saw. I took the wire from an old hair drier, wrapped the ends around eye bolts and attached an automotive battery trickle charger (2-6A). It was then mounted using a lab glassware stand.
SAFETY: Always wear a dust mask when sanding foam. Wear a high quality respirator in a well ventilated area if you're going to use hot wire melting tools.
Do a test stack of the pieces to confirm everything has gone to plan. Then apply 3M 77 spray adhesive to each surface in addition to a drizzle of Gorilla Glue. Apply weight to achieve a clamping effect and allow to dry completely.
I highly recommend the long box cutters that can be found cheap at most dollar stores (Dollar Tree). Other tools can include a wire brush attachment on a drill, Surform foam shapers (Amazon), or pro hot wire foam tools if you have the budget. Start with tools that leave foam pieces as large as possible to minimize dusty mess.
Step 3: Painting
Spray paint can NOT be used directly on the pink foam. The surface must first be sealed. I used latex house paint through a Wagner Powershot sprayer.
Step 4: Hat, Gold and Clovers
The hat and fold pieces were made from cross-linked polyethylene foam rubber. Pieces are glued together using contact cement. The foam is very porous so it needs to be sealed first or paint will continually soak in. PlastiDip is the most recommended product, but latex paint would also work.
Step 5: Final Product
Here is the final product. If you have any questions, don't hesitate to ask.