If you’ve followed any of our hot tub antics in the past, then you already know about the inflatable hot tub party on Ocean Beach in San Francisco. A few years ago we built a heat exchanger that would use a bonfire to heat up salty ocean water.

This winter I’m taking on a new project, following our work on Carbon Garden: to build a hot tub entirely out of carbon fiber.  Since fiberglass hot tubs are common, the same techniques should apply to building the carbon fiber tub.  Step one is to come up with a pleasing design, and for this I’m using Rhino, a CAD software tool.

The 3D shape is sliced into multiple flat pieces along the black lines, which are then cut out of 1/2″ plywood on a shopbot CNC router.  I’ve decided it will be easier to build the positive shape, so the mold will be more  of a hump than a dish.

Here’s a video of the shopbot going at it too

Next the mold stays are assembled by cutting correct length support pieces (according to the CAD model) and screwing the whole thing together. Here’s an image of the mold partially assembled.  In this shot the mold is upside down since it’s easier to put together that way.  Eventually it gets flipped over and it will look more like a hump.

Once the mold stays are assembled, I’ll lay sheets of paperboard across it to complete the bowl shape, then like drywall, apply plaster and sand it perfectly smooth (don’t want any bumps on the interior of the hot tub of course).  When the mold is complete it will be time to lay up the carbon fiber.  But that’s for another rainy winter day…

Here’s the layout for Carbon Garden as it will appear on the playa this year at Burning Man.  The four gates will be each have two flaming carbon fiber towers, and infrared sensors to trigger music and flame behaviors as people enter and exit.  We’ll be located 700 feet from the man along the invisible 4:30 line on your clock dial, pretty near to the Tea House, so it will indeed be quite a zen corner of the desert.

Oh, you’re the PDF type?

Check out the Hot Preview on KTVU.com about Fire Arts Festival. Some nice coverage of the event including Carbon Garden.

Video: http://www.ktvu.com/video/20046933/
Slideshow: http://www.ktvu.com/slideshow/entertainment/20046824/detail.html

Setup at Fire Arts Festival: KTVU Photo

While the blooms of Carbon Garden will be made from carbon fiber, we’ve decided to build the stems out of steel.  It’s so nice to get back to a material we understand!  Here’s a sketch by Eric Nguyen of a strategy for adding detail to the stems and a way to make wireframe leaves.

The red lines are the bent-steel tubing. The black ones are a thin material (copper piping? steel wire?) bent around and welded/brazed together to make more intricate, organic shapes around the fixed-diameter stem. The thin material can also be bent into leaf-shapes and can continue up the undersides of the petals.

Meanwhile Andy Lee drew up CAD models for a system to attach the petals together into a bloom and the flame effect to the stem.

We’re fully underway with carbon fiber flower petal production.  In addition we’ll start bending and hammering steel stems in the forge pretty soon, and we’ve got decent mechanical designs for the interfaces to hold petals, leaves and stems together.  On the flame effect side, our Flame Elements now have built in ultrasonic rangefinders that auto shutoff if people get too close.  The garden is laid out  to allow good participant flow but prevent cars from driving in there.

Here are some renderings by Andy Lee showing how a simple petal shape can be repeated and attached at different points to create a wide variety of flowers.

Any opinions or ideas you’d like to pass to us?  Also, if anyone knows people who are interested in learning how to lay up carbon fiber, we’re getting pretty good at it these days and always welcome visitors to the shop.  False Profit Labs workshop days are Wednesdays from 6-10pm and Saturdays from 1-5pm in San Francisco.  Early versions of Carbon Garden will appear at the American Steel opening party and Fire Arts Festival in July.  Email: brett at false dash profit dot com if you want to get involved.

Rendering of Carbon Garden at Burning Man by Erik Walker

When planning to fill a large enclosed chamber with hydrogen, oxygen and propane, and allow members of the public to voluntarily ignite the contents, we find it’s best to consider ways to decrease the likelihood of blasting out four foot by eight foot sheets of shattered polycarbonate at hundreds of feet per second. If you plan on igniting flammable gases for amazement and amusement (read: art), you really have to consider safety third, and certainly no lower than that.

We’ve taken a number of measures to reduce the risk of life and limb, the most important of which is the hydrogen chamber itself. There’s a lot less chance of someone burning their hand, face, neck, neck, chest or faux fur costume if they are physically separated from the fire by a plastic barrier.

But again we come back to the question: How do we avoid blowing up the chamber? The key is to understand what the maximal flow rate in cubic feet per minute (cfm) is of our bubble blowing devices, and the flash point of hydrogen. Hydrogen becomes flammable in air at concentrations of just 4%. So we built an air blower and duct system that creates positive pressure inside the chamber at roughly 50-100 times our hydrogen usage. In our case, our bubble machines will consume 3-4cfm of hydrogen. Therefore we have installed a blower system that will push around 400cfm of air into the chamber. This reduces the maximum hydrogen concentration in the chamber to less than 2%. In addition, we’ve mounted many nichrome ignitors (see Ben’s last post) to ignite any small pockets of hydrogen, either contained by or not contained by bubbles, before they can collect into a dangerous situation.

How would we know if a dangerous situation occurs before the gigantic explosion? We mount a detector on the wall of our chamber, at a level where we would want to shut down the project if gas somehow pooled from the ceiling down to the detector mount point. If the detector goes off, the project is shut down until the chamber returns to safe levels.

A couple of weeks ago, Erik did some great drawings of the hydrogen chamber in Rhino. Since then, we’ve been working to refine the design (uhh, we forgot a door… can we add one?) and build out the first level.  It was also cool to have Erik show us how he works in Rhino. The software combines the manipulation and viewing power of a 3d modeler like Maya with the accuracy and dimensioning capabilities of a CAD program. Perfect combination for this kind of work.

So far, first the six steel frames are welded, the aluminum for the surrounds is cut and drilled, and yesterday I got about half of the brackets welded on. It’s cool to see our physical work starting to look like the 3d model!

We’ve begun work on the PyroCardium sculpture, making a 6-foot-tall version with 1 Watt red LEDs to appear at False Profit Alchemy on April 26 at Cell Space. On the virtual side, the sculpture truss and helix is all modeled up in 3D using Rhino. On the physical side, the TIG welder is out, as is the metal bender, and the smaller truss is coming together.

Probably the most challenging aspect of building a swirly sculpture (aside from the dancing fire) is bending thick pieces of aluminum on all 3 axes. Dyche has come up with a pretty ingenious method. Our first helix will be comprised of seven semi-circles, of successively smaller diameter. Each piece of aluminum stock is placed in the metal roller at angle, so it gets bent in a semi-circle in one dimension, and pulled upward out of the circle’s plane as well. When these pieces connect together, the decreasing diameter is what gives the sculpture its skewed shape.

False Profit Labs is happy to announce that we will be making appearances around the Bay Area in the coming months. First, on April 12 you can come out to NASA Ames at Moffett Field and enjoy our fire art out on the tarmac in celebration of Yuri’s Night. Check out their website here: www.ynba.org.Then on May 3 & 4 we bring more explosions to Maker Faire at the San Mateo Fairgrounds. More on this at: www.makerfaire.com.We’ll publish more details as we get them, but for now here’s an appetizing 3d model that Brendan Colloran made in Matlab(!) for the PyroCardium scultpure. Now it’s just a matter of building it.

They’re in.  And here they are so you can see not only what we’re up to this year for Burning Man, but also so you can get involved.  There are at least a dozen sub-projects related to The Hydrogen Economy and PyroCardium.  Maybe you want to help with construction of a double-helix sculpture, or you’re good at machining small plastic and metal parts.  Maybe you have no skills at all but are full of enthusiasm.  Perfect.  Post a comment with your contact info and we’ll find a way to plug you into the mix.The 2008 False Profit Labs Burning Man Proposals:

The Hydrogen Economy

PyroCardium