Lots of visitors, lots of interest
Exhibiting the Sky Yurt at the Champlain Makers Faire was a wonderful experience. We were set up right next to the entrance to the Carriage Barn where all the indoor exhibits were housed. People stopped to read our text display, played with some of the models, and prowled around the Sky Yurt. Kids laid on the the grass and looked up at the sky through the ribs and cross stays. Lots of head scratching, Questions kept emerging. Then as some folks began to understand the design challenges, they began to share ideas. Some conceptual, some very concrete and practical. All thought provoking and useful.
Whirlwind getting ready for the Faire
The three broken ribs on the structure was really a set back for the team. I was able to replace one and then repair and sister the other two. I got an outer top cover finished, but didn’t have time to test it and the tie down system. So I just went with the framework. My engineer/artist buddy Andy Wekin and his crew Otis and Ezra worked with me to get the legs installed and reinforced. I replaced some broken connectors, made an exhibit poster, and we were ready to roll. It was a scramble to get the structure set up. We got a good start on Friday afternoon and evening. Darla – my main squeeze – pitched in on Saturday morning and just as the first of the crowd trickled in, we were up.
Where to take this project next?
I learned a lot from the ideas that visitors shared with me. I’ll post some of them in due time. But the big learnings for me are guiding to the next steps for the project.Time to go back to the drawing board and get a designer/engineer involved who knows tensile/tent structures and can do the math. The yurt structure could be so much lighter and much better engineered. My build/design process can only take me so far. Using off the shelf items, and build/designing as I go, has real limitations. I need to have someone on the team who can look at the whole system and come up with design parameters for the components. For instance, maybe properly sized tubing for the ribs and cross connectors with aluminum hubs. The whole frame structure could be lightweight and go up quickly. So I am putting the building to bed for the winter. When I start next summer, I hope to have a much improved and well thought out design to build from.
Yes! Just got the word that the Sky Yurt will be an exhibit at the Makers Faire at Shelburne Farms in Vermont September 28 and 29. Details at http://www.champlainmakerfaire.com/. I understand that there is lots of discussion in my little community of Essex as to “What is that space ship thing in the backyard?” I am working hard to get the prototype completed in time for set up on the Friday before the Faire. At first glance it doesn’t look like much has changed. But I am booming ahead in two important areas – getting the Yurt cover designed, laid out, cut and taped together. And building and painting the telescoping legs that will progressively lift the tramp frame to approx.10 feet off the ground.
Polytarp cut and tape sails
I am taking a page from the book of the folks who are using polytarp for sails to for small home-made boats. The word is that the sails out of this stuff will last for at least a couple of seasons. I am using Tyvek house wrap to make the roof and the side panels for the Sky Yurt. Why Tyvek? It is relatively easy to work with – it cuts with a scissors, can be marked on with a felt tip pen and the panels can be fastened with double-sided, fiberglass reinforced, indoor-outdoor carpet tape. I won’t be the final fabric that I chose for the cover, but it will work as I am experimenting with with the best way to shape and secure the panels.
Challenged to the core
Oh, I am so challenged making and fitting the test panels – which I will use for patterns for the other panels. I am rather dyslexic, always have had trouble with spelling and jig saw puzzles and scrabble and linear sequencing. And while the Tyvek is flat, the Sky Yurt roof and sides are curved. Yikes, I’ve been up and down the ladder too many times with my test panels, marking, measuring, cutting, taping,. Doing lots of head scratching. But I think I got it now. One more modification and then I can begin turning out panels and taping them together. Yahoo!
Sky Yurt as an exhibit at the Makers Faire in Vermont?
2013 Yurt structure
Now that I have the basic structure up, I felt confident enough to apply to the Makers Faire to exhibit the Sky Yurt in Shelburne, Vermont on the weekend of September 28-29. Here is some of the text from the application:
The Sky Yurt is the first prototype in a series of designs that provide working/ living structures for a nomadic community of artists/crafters/makers. The eight –sided Sky Yurt ‘s floor is 14 feet in diameter, with roof extending to almost 20 feet in diameter. The floor is perched 10 feet above the lower tent-canopied workspace which is an integral unit 32 feet in diameter and separate from the upper living space of the Sky Yurt. This lower space acts as the mother ship, and the upper living space structure actually “docks” to the trampoline frame at the center of the mother ship.
The prototype as as an on-going experiment
The prototype is a full scale working model which is allowing experimentation with design challenges inherent in two separate tent structures, the work structure on the ground and the yurt structure elevated 10 feet of the ground, combined with the need to make the combined structure portable. Structural materials, except for the laminated cedar beams, are readily available and easy to modify, including the trampoline frame, plywood, lumber, building wrap, epoxy, PVC pipe fittings, and fiberglass fence posts.
The design is “open sourced” and as the structure is modified and the engineering needs are better understood, future prototypes will utilize lightweight “engineered” materials and design features that improve portability.
I worked out a deal with my neighbors Bev and Brian to set up the Sky yurt in their big backyard in exchange for doing their lawn. I just have one more set of cross struts to add to the lower structure, and then I can begin building the fabric covers for the tent structures. I will also start to deploy my anchoring system. I am moving into new territory with this prototype. I see the Faire as an opportunity to engage makers, elicit design ideas and move the open sourcing of the project ahead.
Docking to the “mother ship”
Prototype 2 – Lower hub support
It was important to me to keep the lower tent-canopied workspace as an integral unit, separate from the upper living space of the Sky Yurt. This lower space would act as the mother ship, and the upper living space structure would actually “dock” to the trampoline frame at the center of the mother ship. But docking the Sky yurt structure by resting the lower beams on the trampoline frame created an additional bending stress on those beams.Maybe I could carry the weight of the Sky Yurt structure on the lower hub.
I realized that the circular trampoline frame was incredibly strong in compression. I could use cables from the frame to support a separate central lower hub that would support the Sky Yurt hub and provide a platform for a pillar that could be used to support the center of the floor as well. I used a bicycle wheel rim with drilled eye bolts for this lower support hub in the next prototype. If I could use the trampoline frame to carry the floor and support the weight of the Sky Yurt by the lower hub, then the Sky yurt tent frame could be light and airy. It only had to support its own weight and the force of the wind on the tent fabric.
Adjusting the tension in the Sky Yurt tent
As I worked to solve one set of design challenges, I kept learning that based on the new concepts, new challenges always emerged. If I was going the support the Sky Yurt tent upper structure on its bottom hub and just let it kiss the trampoline frame, then I needed to be able to move the bottom hub up and down, to get the right clearance from the beams to the tramp frame. All this started to come together when I began to build the second prototype in the summer of 2012.
“I’ll huff, and I’ll puff….”
As I was working on my build/design project with the Sky Yurt, one big issue kept churning around in my mind – the power of the wind. I knew from sailing just how powerful the wind can be. On a sail, as the speed of the wind increases, the force on the sail increases exponentially.That’s why almost all boats have sails can be reefed and the sails have lines (sheets) so they can be depowered and lines (halyards) so they can be dropped completely. I began to look on the web for tent structures similar to the Sky Yurt – I wanted to see how professionally engineered structures dealt with wind forces on a large expanse of fabric. There are some huge fabric structures – most of these are tied to steel masts set in concrete and looked beefy enough to dock the Von Hindenburg zepplin. Way out of my league.
Gone with the Wind
One big concern was the fact that I really couldn’t find any-tent like structures that were set up like the Sky Yurt – none at all. I found tree houses well-secured to trees and structures built on slopes with some space underneath, but nothing that was trying to combine a large umbrella like work space with a living quarters above. It just might be that if similar structures were built, they were impossible to secure against strong winds, and blew way or were quickly abandoned. Working on dealing with wind forces was going to be a major challenge – and maybe would scuttle the whole project.
Crash and burn
I also knew that tent structures could be hot. Fabric can trap solar energy and hold on to it. We had an old army tent as kids and it could be stifling in the summer. I had to make sure the whole structure wouldn’t blow away, but also make sure that the air could escape from the workspace without congregating in the upper yurt. I also wanted decent airflow in the yurt itself. I had a sense that if I could design the shelter to be secure in strong winds, that solutions to the ventilation issues would suggest themselves. I started to look on-line for earth anchors and tie down straps, the kind they use to keep small planes from blowing away when parked on the ground. The project was getting more complex, more challenging and more exciting.
Prototype hub – PVC
My first goal in building a full scale prototype was to see if the basic engineering for the Sky Yurt tension structure would work. The PVC pipe was 2″ in diameter, dirt cheap (I did have to wash it all) and under tension I could get it to bend. I built two plywood hubs, about 2 feet in diameter with slots for the PVC beams made out of 2×4’s sandwiched between the top and bottom plywood circles. On the ends of the PVC beams I added end caps with eye bolts to catch the stainless steel cable. I had a primitive system to tension the outside cable. The structure went up with a minimum of hassle. It nestied inside the 14 foot diameter trampoline frame Andy and I bolted together.
Checking out the forces on the structure
As I increased the tension on the Sky Yurt structure the PVC beams wanted to move closer together. They began to bend in a sweet curve vertically, but they also wanted to begin to bend horizontally. Also they wanted to rotate the hubs so that the beams could begin to “pass” each other. Another problem – the lower beams were resting on the trampoline frame; they were carrying the weight of the whole Sky Yurt structure, and were beginning to bend upward. I experimented with adding struts – 1/1/2″ PVC pipe – between the upper and lower beams. It was fun using the chop saw that Andy lent me to cut PVC fittings at the angles I needed to connect the struts with the beams.
Structural lesson learned
Prototype 1 – struts
The struts, by tying together the upper and and lower beams, added lots of rigidity to the beams, but I wanted a structure that could be tensioned, so it needed to be strong, but flexible. I didn’t want to make the lower beams beefier than the upper beams. I would be screwing around with the symmetry, making the structure more complicated, and even more difficult for me to get my head around. One thing that was clear was that I would need beams that had a rectangular cross-section or a built-in vertical curve to minimize sideways bending under tension. I was also going to need some cross bracing between the beams to provide support for the cover and to stiffen up the beams. I did end up with a pretty elegant set of solutions to these issues that were incorporated in the second prototype.
Strong but not heavy
Sky Yurt – model #3
To hold the Sky Yurt up in the air, and to attach the awning for the workspace I was going to need a strong core structure. But the Sky Yurt itself could be made of much lighter structural materials. It only had to hold itself together, like a pop-up camping tent. I was driving into Willsboro one afternoon and saw a backyard trampoline with a kids low play tent stretched over tramp. I knew about trampolines from my trimaran sailing. A few people jumping on a trampoline generate a strong downward force that needs to be resisted by the frame. So trampoline frames are built to be very strong. .But they are also portable and are pretty light for the stresses they have to deal with.
Using the trampoline frame to hold up the Sky Yurt
For the next model I went hunting for circular rings. Found what I was looking for in a craft shop – those hardwood rings that are used for needlepoint work. I made a new balsa wood and plastic straw model, and I really liked the look and feel of it. I was ready to build my first prototype. Now I was getting into the real building project. My scare-level increased to the point where I thought I might need to start wearing a metaphorical diaper. I asked my friend Andy Wekin – he was an artist who had gone back to school to be an engineer and he came with his partners Otis and Ezra (more on this team later) – to be the consulting engineer.
Beginning to build the first prototype
Sky Yurt – PVC prototype
I found a trampoline frame on Craig’s List and hauled it home. They are really available, sort of like old hot tubs and spas. They are in those class of things that at the time seem like a good idea, but they stop being used (you don’t want your kid to break her neck) and they take up space a lot of space in the outdoors. My friend Robin runs a preschool at a farm. They had a lot of PVC pipe that had been used in an irrigation project, and for a small donation I had my beams. I made hubs out of plywood and scrounged for PVC connectors that I could cut up and experiment with. I had SS wire from some of my old sailing rigs. Mostly I wanted to learn from this first structure -see if the basic engineering would work, where I would need extra support and how the Sky Yurt structure would interface with the trampoline frame. And it started out looking pretty promising.
Sky Yurt drawing #1
I started making very rough sketches years ago. I wanted an open, circular, covered workspace on ground-level. The living space needed to be elevated, so you could almost walk underneath it, or at least see through it. I flattened out the tall tipi shape to make it more like a diamond, like in my early dowel and wire model. I decided the yurt would set on vertical uprights, doubled under each set of beams. The workspace tent structure would then radiate out from the eight-sided elevated yurt-like living space. The fabric cover on the workspace would need to be adjustable, so one side could be tucked down to block the wind, while the opposite side might want to be open wide and high to let in the warm early morning sun..
Sky Yurt Concept #2
I made a painstaking model out of dimensional balsa wood -held together with pins and light wire. That got lost in the shuffle over the years. The next model used clear straws for beams and joists, pipe cleaners at the outer ends of the beams, and cardboard and hot glue for the center hubs. I really liked the look of the design but some real concerns began to emerge.
I was still stuck on using vertical posts to hold the yurt off the ground. The whole structure was looking less like a tension structure. Those posts were going to need to be heavy and I was thinking that the whole structure was going to need to be pretty beefy to match it. And hell, this needed to be nomadic – meaning light and strong.
I ain’t no designer
You need to know as I walk you through this process, if you haven’t figured it out already, that my skills as a designer are severely limited. I can’t draw worth a hill of beans. I am dyslexic and have trouble with sequencing. I can get an idea, walk around thinking about it almost all the time – but I have to build the damn thing so I can begin to figure out if my “design” idea will really work. My neighbor Bruce, who has watch my “follies” emerge in the backyard laughed the other day, “I have heard of design/build, but I think what you do is build/design”. And he hit the nail on the head. That my process – build/design. It ain’t pretty, won’t work for a brick and mortar house, but with my Sky Yurt, I can take it apart, fix what doesn’t work and give it another shot.
How could I put a tipi-like structure up in the air?
Sky Yurt structure
I began to make some models and do some rough drawings. I was influenced by Bucky Fuller who said that structures should have an integrity that didn’t depend on gravity. I think he called that “tensegrity”. If the house I live in now, a Greek Revival built in the 1860’s, were pushed off into space, the components would begin to come apart. A tensegrity structure would hold together, like a bicycle wheel. It wouldn’t depend on the forces of gravity.
Long ago I built an eight-sided model out of dowels, eye screws and wire. I was impressed with how stiff the structure was and how strong it it felt. I carried that model through all my life changes and moves. I hung it up in a prominent place in my office or living space so I wouldn’t forget the concept.
An amazingly strong structure
Strength testing the basic structure
The strength in the structure comes from the compression ring around the outside diameter – much like a yurt. I added the tension wire in the middle, but was sure that I wanted a design that would be completely open inside. I would need to create another way of tensioning the yurt.
Today, I went ahead and strength-tested the structure to see if it was really as strong as i imagined. Amazingly, it held my weight (200 lbs.). In the current prototype of the Sky Yurt the downward tension comes from fabric cover.