Welcome to the TreeBella design process Instructable:
In this Instructable I will be documenting the process of designing a hammock/tent to hang in the tree. These are design criteria I will be striving to achieve:
Single Point Hanging Structure
Easy installation ( weekend camping trip capable )
Designed for Manufacturing ~$3,000 price point
Outdoor archival materials
Comfortable - Functional - Fits 3
Glowing night presence
I currently sketched through 2 different design approaches. One I refer to as the Camping Chair concept and the other as the Wedding Bell concept. I am currently investigating the 3rd distinct approach, the Tensegrity Concept.
This Instructable will act as a journal to document the process from beginning to end. Each step could represent either a progression in time, a splattering of images and information, a break through, or highlight a specific technique used in the exploration of form.
I have a company called O2 Treehouse. we build custom treehouses with a contemporary style. Our projects have ranged from tree decks to fully livable units. I started the company in 2006 after having the bug to see a sketch book idea realized full size. This idea was to create a geodesic sphere treehouse. Driven to see it realized I went through a long process of design, models and proposals to weary YMCA camps. Finally after evidence of my effort my dad offered me a shoe string budget to create the first full sized prototype. I installed the project in my Dad's front yard and I was off to the races.
This first structure started with a list of criteria set to innovate the category as a whole. This list included:
Fits in any tree
Recycled or recyclable materials
Flat pack ship-able
A pleasant open air tree experience
Room for 5 comfortably
Beginnings in the Tree World
After realizing the full size structure I was hooked. I didn't know it then but treehouses would become a life pursuit. Driven to explore this new concept using the poetry, simplicity and strength of the geodesic sphere. After building several variations on this original design in the Midwest among several different intermittent day jobs, my newly formed company brought me out to Los Angeles in 2009. I built for the rich and famous in the hills of LA for several years learning the ropes of owning a company and building custom architecture on the road ( aka out of my van ).
A journey I would not trade for anything I created lots of work and built a nice portfolio. Along the way I met many talented artist and builders. My dreams of selling a low cost flat pack geo treehouse to the masses was not realized nor the open source eco-village building system however along the way my company O2 Treehouse has received international recognition in both print, publication, and television. Open source geodesic treehouse hub systems for the eco-toursim camps of the world to harness among their trees... yet to come. Geo Treehouse kits flat pack and sold online is moving forward with our Sequoia and Tamarack models. The real juicy endevour however is the Treebella Project ( working title ) .
Treebella seeks to combine the sleek technical feel of climbing equipment and brands such as Petzl and Black Diamond with the natural and earthen materials. Grab your tree tent for the weekend and have a secluded leafy upper branch and moonlit getaway with your friends or lover. The design will nearly self assemble via its single point hang and tensegrity frame work. Loft the structure hovering just about the ground or send it sky high in a red wood.
Instructables AIR Program
My time at the Pier 9 Autodesk - Instructables Artist in Residency program will be the perfect time to develop this design which will require advanced manufacturing processes to perfect and form this piece into a stylish sexy upper canopy treehouse chuck of desire. I hope to achieve a price point affordable for many to enjoy.
Stick with me as I document this creative journey in the best creative development space in the San Francisco Bay Area.
Step 1: Sketch Process ( Archived From End )
Step 2: Preliminary Model 1/4 Scale
A rather sloppy model I must say, however this is not to bad for a 2 hour 1/4 scale model. This will function as a visual representation of the concept so that in the coming days we can refer to the model in our creative discussions.
Step 3: Model Making Round 2
Creating second model with cables to increase tension and test structure under pressure. Welding on turnbuckles to experiment different tensions & pressure on the tensegrity and how this affects spaces for further development and materials. First designs for the cable/pole connections.
- Materials Research
- Cable Pull Test to determine deflection acceptability on hammock cables
- Measure and test tension - convert into compression force within tensegrity - choose material size
Step 4: California College of the Arts - Materials Library
The last two weeks there has been steady progress on the Tree Tent. I've been concentrating on the design of the hubs and how this will integrate with the pop up/self assembly mechanisms. I've also been continuing the research on the materials front mainly for the canopy and hammock materials
Hubs - Narrowing Focus
The Hubs will be milled from 7075 alloy and will most-likely be a threaded plug. The piece will thread into the end of each of the aluminum compression struts. The hubs will support:
- A fixed end cable connection via a seat that will receive a button-swage swagged to the end of the 1/4" wire rope.
- Pulley mechanism to guide structural cable in and out of fully collapsed and open positions.
- Pulley mechanism to guide 3/32" tension spring loaded cable
- Rocker arm to 1. slip in 2. receive a mid line button swage and 3. lock and seat the swage
- Prototype 3 testing cable collapse-ability and open-ability, tension ability using a continuous cable and mid-line button swage conept.
- Speak with Shop manager about recommended alloys for hub component
- If Prototype 3 proves successful, next step will be to research tension springs and feasibility of the rocker arm mid-line capture and lock/unlock system.
- The struts will most likely be aluminum tubing. My instincts on the diameter of the tubing say 3" with a 3/16" side wall. Aluminum will allow us an anodized high value finish while staying well within the boundaries of recycleability as well as an infrastructure that supports it.
- Discovering the proper alloy. High strength is better.
- Thinking about using Aluminium 7075.
- "It is the highest strength bar typically stocked. When machined it produces curled or easily broken chips but results in a good surface finish. It displays high hardness and strength but poor weldability and corrosion resistance. It in commonly used in the aerospace industry and typically available in rounds and rectangles."
- This Alloy as stated does not weld well which is a concern as some of the mechanisms will require a welded tab or mounting bracket.
I've found the perfect material for the canopy. PTFE
Its chemically inert, recyclable, UV stable, and built for architectural applications. The current challege is to find it somewhere for less than $10 per square'. Besides its more practical qualities it also is semi translucent which will achieve one of the design requirements, the glow factor.
Among many fabric samples we have received in the mail this one is by far the most durable. The others are well suited but will not have the same archivability as they are mostly designed for tents which typically do not live outside on a full time basis.
There are several potentials for the flooring material. The best looking, performing, and cost effective is a woven polyester black material typically used for trampolines. It is super strong, light weight and also has a bit of a transparent quality to it.
Other materials also woven polyesters (pictured) come vinyl coated in white. These two types are incredibly durable, washable, 90 perpendicular patterning and if used would make a strong stylistic statement. The down side is that they are a PVC Polyester blend which I am sure is un-separable for any kind of post industrial processing.
Last and least from the main candidates category is woven polyester which gets the highest points for looks. Its round pattern makes it fit perfectly into the desirability and style that were going for however the weave under pressure and tension seams to deform a bit like a stretched out sweater. I'm still considering this beautiful and durable piece for the interior storage pocket material.
- Discover pricing for the prime candidates.
- Sewing Tests?
Step 5: Prototype 3 - Tensegrity Pole Slide Capability
The basis for the Treetent to collapse and pack into a slender long bag for easy car transport, storage and setup is the capability of the structure to transition from a taught tensegrity frame into a completely slack system. The success of the tree tent rests on the swiftness and ease of this transition for the user. The sharp angles of the prism tensegrity gives me a unique opportunity to make use of the trajectory of its force to trap the strut locations without having to use a fixed connection point. This in turn allows for a sliding connection point that will require no attention to the user during the setup process!
With the load bearing cables attached to the bottom of the structure and further assistance of gravity the tensegrity prism form will fall into form. With the potential additional action of bungee straps the tensegrity should self position after force is applied during the lifting process. This leaves the 2nd main step in setup simply tensioning the tensegrity.
The model exhibited in this step is a test of the sliding connection concept. This model proves that the strut under compression will be structurally sound using only a stopper along the cable or in this case a knot along the rope. In the case of this model I created a hole through the wood strut allowing the rope plenty of room to slide through the strut unobstructed. I intend in the full scale version to make a similar low friction pass through connection.
I would like the tensioning mechanism to be completely hidden giving the viewer no prominent visual clues as to how the system comes in and out of form. Traditionally the tensioning of cables in this context is performed by a simple turnbuckle however these are clunky and not designed for consistent tightening and loosening. Other options like a ratcheting mechanism would also be visually obtrusive and require potentially awkward positioning to bring the system to the required tension.
Step 6: Tension Test
An important aspect of the tree tent is its capability to expand and support a fully tensioned 3 person hammock space and all this from a single point. The tensegrity system needs to have the structural capability to not only expand and tension the hammock to a nearly flat surface but also sustain triple the weight of three potentially heavy people occupying the tent while sustaining a reasonable amount of cable deflection. By first deciding upon an occupancy weight limit and then testing this load on a pre-tensioned cable I could understand the total load happening upon my cable, cable connections, and compression members.
As important as understanding the loads I needed to feel out what amount of cable deflection would be comfortable as well as acceptably safe, ensuring that a user could not after loading the cable roll over the edge of the structure. Lets not forget that because of the tree tent's single point hanging capability it may often find itself hanging in very high situations.
To complete the load testing I needed to rent a special tool called a dynamometer which is used in scenarios like this where measuring the tension happening upon a cable. If your in the Bay Area and in need of one go to Cable Moore. They rent them for $136 per day tax included. Pictures above show me in the process of point loading and distributed loading of the cable to understand deflection and load. In the process I took reading of the dynamometer at differing starting tensions raising in increments of 10 lbs with a fixed load, myself plus some. I also measured the deflection for each increment as well.
I was able to determine that a starting load of 120 lbs gave me sufficient starting tension vs deflection improvement. After 120lbs starting load the deflection amount decreased in smaller increments. I now know the max tension the tensegrity system needs to support with safety factor and am able to run the test on the compression members through a computer simulation.
Step 7: Materials Sourcing & Costing
I was able to complete a considerable investigation of materials and connections through the design process.Below I've listed the most useful materials sources. Some of them are sources for material I will use in the final design and others are interesting sources for materials discovered along the way. Have a look!
Outdoor Performance Fabrics
Tensegrity Compression Members
Pressure fit bearings for threaded rod fixed turnpoint connection:
Step 8: Scale Prototype - Hole Locations ( Radially Accurate Cable Trajectories )
Conceptual design rounds
Tensegrity form design iterations
Deflection & load tests
Researching durable outdoor UV fabrics
Tension mechanism research
Flat CNC cut connections
Canopy tension spring
I am now ready for a scale prototype reflecting actual materials and mechanics. I've sourced the proper scale aluminum tubing and captured all of the hole locations for the model. I've laid out all of the proper tools needed in the image attached. The following process is a good way to create a tensegrity model in so your cable trajectories exit from each strut at the proper angles. Should you be starting with a computer model and are able to measure the radial angle hole locations this is a good starting point:
- First cut all of the struts to equal length.
- Lay out the radial hole location angles on a board with a hole at the diameter of my struts at the angle origin.
- Using a caliper mark the distance from the end of the strut to the location of the hole.
- With a sharp point scribe mark a cross hair on each of the hole locations using the wood jig.
- Using a metal vice with a horizontal notch in it to clamp and position the scribe cross-hair facing directly up.
- With the calipers measure the size of the cable and choose a drill bit size that will be sufficiently over-sized.
- Use a center punch to create a small indent in the metal allowing the drill bit to center directly over the whole.
- Drill all holes repeating these steps.
- To mark the other side of the strut in so that the holes are radially equivalent you will need special clamp tooling. I did not have the clamp centering tools so I was able to improvise using a notched straight edge. Any other accurately manufactured object/device containing a similar notch will work. Press the strut into the notch as to square it to the edge of the notch in so that the tube lies flat in the notch. Rotate the tube until the original hole is centered over the notch edge. Follow the notch edge to the other side of the tube. Mark the location using the scribe.
- Continue drilling holes on the other side of the tube in the same manor.
I was able to find a smaller aluminum tubing that would nearly fit the ID of my strut material but not quite fit. This part is required for the telescoping mechanism that will bring tension into the tensegrity system. A long piece of threaded rod will turn through a nut affixed to the end of the telescoping aluminum short strut. The end of the threaded rod will have a pressure fit bearing which will be affixed to a mid point in the full length strut.
I have not yet sourced the ID material for this telescoping piece for the full size version. In order to keep costs low I will need to find this crucial piece with a small enough tolerance to allow for a slide fit, machining will not be in the budget at full scale. For the small scale version I was able to drill out the large strut, increasing the ID and creating a beautiful slide fit. Attached is an illustration of a previous version of this mechanism with a side turn geared down mechanical advantage. After further investigation I realized the pressure required would allow for a 1 x 1 direct force option with the proper sized turn arm also moving the turn location to the end of the strut.
Step 9: Scale Model - Exact Fabric Templates
Considering the scale the fabric sections for the canopy required exact fabric templates with proper seam allowances. I cut templates on the laser cutter with seam allowances built in and pencil guides to ensure exact edges were marked for cutting. I would have cut the material directly in the laser bud however the type of polymer was not on the allowed cut list for the mahcines at Pier 9.
Attached are step by step instructions using the sketch tools in Fusion 360. I created my model originally in Sketch Up and exported the the fabric canopy panels as a .dxf file. I then imported this geometry into Fusion 360. I had to retrace the geometry as it did not convert as actual paths in 360.
Once I had the paths redrawn I exported as .dxf once again out of Fusion and imported into Illustrator where I was able to then cut the files.
Step 10: Scale Model - Cut, Glue, Sew
Prior to sewing the actual rip stop out door fabric I created first a linen prototype to ensure that the seam allowances were created accurately and provided sufficient room to create a strong seam.
Once the prototype was completed and was functioning properly I moved on to the cutting of the actual fabrics for the prototype which is also the same fabric that I will use in the full scale version. After cutting the woven nylon pieces I glued the edges of the fabric as the weave was likely to come undone during the hemming and sewing process. The gluing proved to be sufficient even after using the hot iron to press a fold to set the hem locations.
The sewing proved to be laborious as the way in which I cut and assembled the individual pieces as well as the hem style is accurate to the final product. The left many edges in need of gluing, trimming and general care and accuracy for each stitch on the Juke Industrial Sewing Machine. I also made sure that all of the loose threads received a touch of glue to ensure nothing would come unraveled.
The sewn floor section in the model will receive considerable tension as the tensegrity structure cables will have proportionate tension as to the full scale version. The floor section has radial cables which run through a tubular hem towards the center of the hammock space. Here the cables tie into a triangular tension ring. This triangular tension ring will provide holding power both for the occupants as well as the potentially long rope ladder or multiple guest using a single line ascension method to enter the tree tent.
The hems proved to be quite tight and were tricky to thread the cable through the hems after the sewing and gluing was completed. I was able to use my super strong model glue with catalyst to glue the actual cable onto the but end of a slim piece of welding wire. From this point I was able to force the cable through the sewing and thread the cable through the hems.
Once the cables were all properly threaded I was able to make the end loops using the farrells.
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