Tuesday, October 18, 2011

Pneumatic Toe Pincher Coffin, Part 1

This year's challenge was for me to learn a bit about pneumatics and try to build a coffin that would automatically open when kids walk past it. Spooky skeleton inside, maybe some cool lighting and sound effects.

After reading Animatronics: Guide to Holiday Displays, I felt ready to begin this project.

First, I needed a "toe pincher" coffin plan. I searched the internet and found a few designs but they did not look quite right. I knew I was going to place a 4th quality bucky skeleton in the coffin, and that skeleton is 5'6" tall. Adding 3" all around for "padding" I knew approximately what the size of the coffin needed to be. I decided to write a little trigonometry program to solve for a set of measurements where the side panels would require no more precision than .25 inches.

The program produced 10 designs which I drew up and compared. I selected one design as most visually appealing. Click the image below to view the final design.
While all the panels are of easy-to-cut dimensions, the angles are not so straightforward. I decided to make angle templates (download: 48, 54, 76) to help align the miter saw. UPDATE 10/11/2021 the angle template links should be working now.
The only other dimension I needed to determine was the height, or depth of the coffin. That is, if the coffin is laying flat on the ground, how high it comes up from the ground. I decided on 11 inches.

Cutting and assembling the coffin is a 1-2 day project. The panels, base and lid are 1/2" birch plywood. I decided to use small 2" hinges with removable pins to connect all the panels together and to the base. That way I can take the pins out and break the coffin down into pieces for storage if space is tight.

After attaching the frame to the base and adding the lid, I painted the entire coffin black, inside and out. I then started to wipe down the sides with green fluorescent paint mixed with water. It is my hope that this will give the coffin a spooky antiqued look when lit with a blacklight.

Continue to: Pneumatic Toe Pincher Coffin, Part 2

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