It's casual friday in the shop, and I'm working on a personal project after hours!
I was given a busted seat skeleton when I volunteered to help with CAB's Repair and Release, a service they provide to the community by fixing rusty old donated bikes and returning them to the city as "community bicycles" that anybody can use for transportation.
I have decided that today is the day to make a suitable saddle to go over the springs on the old seat, so here's what I did with a discarded aluminum bus-stop sign and a ball peen hammer. Enjoy the pics and videos.
These things are all basically the same thing: light, the energy that cooks food in microwaves, radio waves, x-ray radiation, and the infrared signal that comes out of your remote control. They are all part of the electromagnetic spectrum, a hierarchy of electromagnetic radiation divided into categories by wavelength.
So, our eyes are very good at detecting electromagnetic radiation in a certain spectrum of wavelengths: what we call visible light. Just slightly wider wavelengths produce a light that we cannot see: infrared light. That's the "light" given off by molecules when they vibrate. But you know this as heat. Here at the Discovery Center, we have a really nifty camera that detects heat, and displays it as a colorful image. By comparing the colors, you can determine what's hot, and what's not.
I fabricated a couple of interesting manipulatives for interacting with our heat vision camera.
The first is made out of acrylic sheet, the generic name for the brand Plexiglas®, which has some interesting properties. It transfers visible light, so you can see through it like glass. However, it absorbs the infrared spectrum. So, heat does not transfer through the sheet, at least not in the wavelengths we usually encounter with warm bodies and room temperature objects. So, an infrared camera cannot see through acrylic. Check out this video to see what I mean:
Now, the reason acrylic does not transmit infrared radiation is due to the arrangement of its molecules and the vibration of those molecules. It's interesting to think about a "clear" material absorbing infrared radiation, because that's exactly what happens in Earth's atmosphere. The sun casts its infrared radiation upon the land and oceans on Earth, and much of it is reflected back into space. But, not before being absorbed by the gasses in the atmosphere on the incoming and outgoing trip. This is what keeps the planet warm. However, the density of those atmospheric gasses is finely balanced. Nitrogen, for example, makes up most of the atmosphere, yet transmits heat without absorbing it. Humans are contributing more and more heat-absorbing carbon dioxide to the atmosphere by burning fossil fuels and forests. The result is a hotter land temperature, as those gasses radiate heat back toward us. That's global warming.
(Meanwhile, back at the museum...)
I put some text around the edge of this manipulative to help the visitors understand a little about why it works. I applied this text by tracing printed words onto the acrylic with an engraving tool. It was very time-consuming! It says "This material transmits visible light, but absorbs the infrared spectrum."
The other manipulative is a rectangular paddle with a unique material stretched across the interior.
This material blocks almost all visible light, so you cannot see through it at all. However, it is almost completely invisible in front of a heat-vision camera, because it transfers almost all infrared light without absorbing much at all. The thin, black, opaque material stretched across the open interior of the paddle is something you're very familiar with, but I bet you've never played with it in front of an infrared camera.
I'm not telling you what it is. You have to come down to the Discovery Center and see for yourself.
Our visitors were having problems with the Whisper Dishes. I'm talking about two huge, aluminum satellite dishes in our East exhibit gallery.
If you stand with your ear at the focal point of the paraboloid formed by the dish, you can hear a whisper from across the museum. It's really fantastic. The dishes even have a stainless steel attachment that helps our visitors know where the focal point is.
If you speak into this ring, the sound bounces off the dish and collects at the focal point of the other dish. This happens because a sound that originates at the focal point will bounce off the dish and travel perpendicular to the direction the dish is pointing, every time. This is why your paraboloid-shaped headlight reflectors cast a forward beam, and its this effect that allows a satellite dish to gather information beamed from space.
Ok, back to the problem with the Whisper Dishes. For a 12-foot dish like ours, the focal point is about 5 and a half feet off the ground. It's the perfect height if you happen to be a person around 6 feet tall, like me. Everybody else needs to get their mouth and ears a little higher or a little lower. Generally, children will grab a stool from nearby and stand on the stool to access the focal point. This is fine; we even have stools specifically designed for standing upon.
Now, it's much easier to climb atop a stool if you have something to hold on to. So, our visitors would grab on to the focal point ring to steady themselves. That's the problem.
With each chin-up, the apparatus becomes more and more bent. Eventually, one of them broke. I welded it back together, but it broke elsewhere. So, my goal was to develop an alternative method for visitors to access the focal point.
At first, the exhibit team thought about building a standing platform with a hand rail. I studied our visitors habits and found some interesting design roadblocks to the platform theory:
The focal point needed to be accessed by people of all heights; toddlers, children, and adults. A standing platform for children would be as tall as a stool, but adults using a platform that tall would be required to lower themselves to the focal point by stooping or kneeling.
The focal point was frequently shared by more than one visitor. We witnessed school children in groups of two and three standing on stools and competing for the focal point. A standing platform would need to accommodate several people, otherwise it would be used unsafely. This meant the platform would need to be, well, pretty wide and deep.
A handrail around the platform would need to surround all sides of it, otherwise it is a fall hazard.
Pre-school children on platforms are usually accompanied by an adult at arms' length away, because the potential for falling off the platform makes parents anxious. A platform of sufficient size to accommodate several children, and deep enough to not be a fall hazard, will be too deep for a parent to stand at arms' length, unless they, too, stand on the platform.
A platform will require stairs, which can be climbed by crawling infants. And crawling infants can fall down stairs. So, I will need to invent some clever anti-baby stairs.
My study revealed another visitor phenomenon: many people faced the wrong direction when using the dishes! Without any kind of cue to face toward the dish (and away from your partner across the room), many people turned inward and found that the dishes did not work. So, I began to think about ways to get people to understand how to face the right way, without explicitly saying so with a graphic element of some sort.
This thought experiment prompted me to begin a series of drawings for investigation. Working out some design elements with drawing would ultimately determined the overall form of the prototype.
I began thinking about using bicycle handlebars as an attractive and recognizable place for hands to rest, therefore showing the visitor which way to face.
Next, I realized it could be possible to move the visitor's mouth or ear away from the focal point with some sort of sound tube. Physical prototyping began, and the result was a PVC device and the coining of a new word: the "audio-periscope."
Ultimately, I decided the PVC pipe had good sound quality and made it possible for a standing child to use the whisper dish without climbing anything. Now there is no risk of falling! I also discovered this allowed the user to change the direction of their voice, enabling the user to face the other dish and see their partner(s) across the room.
After that, it was simply a matter of choosing prototype materials that were visitor-friendly and putting it all together. Here's the working prototype, and it has survived a lot of abuse in the last two months!
My museum owns an exhibit from the Exploratorium called "Bubble Suspension."
You can read all about it here, but the exhibit is basically a chamber filled with relatively dense carbon dioxide gas. Blowing a bubble into the chamber results in the bubble hovering on top of this invisible gas layer for a long time, suspended in mid air. The carbon dioxide is provided by dry ice.
Beautiful! This is one of my personal favorites, really. It's a well-designed exhibit, and I know our visitors like it, too. So it came as a real surprise when I heard that a weekend visitor had fallen into the exhibit and turned blue! An unattended child had used a stool to reach the top of Bubble Suspension, and fell into the chamber. There is no oxygen in there, mind you. The child was fine because he was pulled out quickly, but a lung full of CO2 is enough to make you turn blue. He went to the hospital and checked out just fine, and there were no side effects. Still, it could have been worse. So I was given the task of preventing that from happening while maintaining the exhibit's function.
I ordered a custom acrylic dome to match the diameter of the opening in the top. After about 6 weeks, it arrived. This picture shows it already attached, with a hole in the front for blowing bubbles into the exhibit.
Now we needed to attach it to the top of the exhibit, but make sure it's easy to remove for cleaning. I fabricated three custom pocket lockers and attached aluminum tabs to the dome that could lock it into the top of the exhibit with a twist.
While the exhibit was being refurbished, I decided to replace the well-used plastic bubble wand with something a little more durable. I'm not exactly sure what kind of bubble wand was originally shipped with the exhibit, but the wand attached to the exhibit at that time was a real veteran of many visitor experiences.
Here's the prototype. Who knew there was so much usable stainless steel in the office kitchen?
The Delrin washers are grooved to provide an abundance of surface area for bubble solution to cling to. I hand made these from a 3/4 inch diameter Delrin rod.
And here's the final update. Bubbles are blown into the chamber through a 6-inch hole cut in the face of the acrylic dome.
