DNA Fountain
Motivation
Caltech has a tradition of a series of parties called "Little I". These seven Interhouse parties are hosted separately throughout the year by each of the seven houses. "Big I" is hosted once every few years, and every house throws a party in their own courtyard at the same time. In Blacker house, we are renowned for construction-intensive themes. My contribution for the 2011 theme, "Eccentric Millionaire Mansion", was the DNA fountain.
Concept
I wanted to make a sculpture using metal as my main medium. Turning it into a fountain seemed to be the next logical step! A double helix fit the theme and suited the general geekyness of the people attending. It was also an interesting design challenge, as I wanted a fairly large scale model with smooth, uniform curves. I ended up using 22 gauge sheet metal for the backbone, cut to the right width on a table shear and welded to length. The nice curve was produced by laying the structure out like a ladder with the base pairs as rungs and running a rod up the center. The joints between the base pairs and the center rod and backbone were free to spin, so as I twisted the backbone around the center rod, the spacing of the base pairs naturally produced the double helix.
Construction
Each of the five base pairs was made from solid acrylic rod. They were each turned on a lathe to narrow one end slightly so it would slip into the steel tubes welded to the backbone. The faces were sanded down to improve the light diffusion later on, while the ends were polished with a flame. The other end was drilled to slip over the connectors on the center rods. These connectors were made by welding two steel rods around the circumference of a short steel tube and adding a setscrew, to secure the assembly in place on the center rod. The base, some 3/4" steel bars, was welded onto the center rod. The waterworks were made with some large transparent tubing connected to a pump and a nozzle, and wound around the center rod. The design was not very effective, so it was later modified into a horizontal pvc tube with a bunch of holes. It sounded much more pleasant!
Electronics
Yes, the LEDs were controlled by an Arduino. It was a last minute thing trying to get all the lighting together, so printing out a board and doing something more integrated were out of the question. Even so, despite some small connectivity issues, it worked pretty well. Four different colours of high power LEDs were used for each of the base pairs. Each set of five was driven by one KSP2222 transistor and some supporting resistors on a common variable power supply. Nothing fancy, but it worked. To draw the heat away from the transistors, I made a completely overkill heat sink with a milled groove and interlocking holes for each transistor. The heat sinks for the LEDs were also overkill - solid aluminum rods with a recessed disk turned into one end for the LED, and a threaded hole on the other to lock into the backbone. A bit of thermal paste in all the joints, and nothing burned out.
Final Effect
Future Plans
Unfortunately, my paint job was not perfect. The backbone experienced some severe rusting along the edges, and had to be scrapped as we cleaned out our courtyard. If I make another, more permanent version, I plan on making a thicker center rod and adding more welded supports for stability. The water nozzle could also be improved into a spinning rod to create another double helix out of the streams. I could also make the center rod into a tube to run all the water up to the top without the ugly acrylic hose.
Unfortunately, my paint job was not perfect. The backbone experienced some severe rusting along the edges, and had to be scrapped as we cleaned out our courtyard. If I make another, more permanent version, I plan on making a thicker center rod and adding more welded supports for stability. The water nozzle could also be improved into a spinning rod to create another double helix out of the streams. I could also make the center rod into a tube to run all the water up to the top without the ugly acrylic hose.