Aaron Cantrell
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Portfolio Piece: Corner Sitter

During my Design for the Greater Good class, one of the projects was to design a 'corner sitter' chair for an orthotist who does work in orphanages with the Healing Hands for Haiti, a non-profit. A corner sitter is a medical device that is used as part of basic physical therapy for people with cerebral palsy. A currently produced corner sitter can be viewed at http://www.adaptivemall.com/ricoflsi.html. The orthotist needed the sitter to be extremely durable, inexpensive to produce, readily assemble-able, provide lateral support and to be easily packed within the FAA baggage restrictions. I decided to focus on the structure of the chair first as I saw that padding and straps could be added easily so long as the core structure would accommodate them. After working through a few renditions and initially working with a group of people interested in using cardboard as the primary material, I decided that cardboard might not be the best route to go and started working individually.

I moved on to developing a system of lugs (think like lugs on a bike frame but allowing different material thicknesses) that could be used in conjunction with any sort of round and straight material such as bamboo, PVC, branches, etc to create a frame and then have a fabric seat stretched over the frame. After starting to make the first lug out of steel tubing and clamps, I realized the amount of work that milling slots to accommodate a range of material sizes, mitering all the pieces and welding them together was fairly production intensive and wouldn't be very cheap to produce. After thinking for a while, the idea outline below came to mind. This was a design that could be made out of a variety of materials, could be disassembled and easily transported, and produced by a CNC cutter meaning little to no production costs would be involved.

My current iteration of the design forms a rigid structure out of a series of pieces that fit together like a three dimensional puzzle. Part of allowing the design to be made out of a variety of materials would necessitate changing dimensions and notch thicknesses depending on the material thickness. I opted to create a model in SolidWorks and use all the equations I had developed to calculate the notch thicknesses where two pieces meet in a non-perpendicular configuration to create a dynamic model. With this model, I can put in a material thickness and angle for the side pieces and then it runs through all my equations and updates the model and changes my dimensioned drawings. Ultimately what this means is that no redesign work needs to be done if the chair were produced out of a different material thickness.

The current prototype is made out of 3/4" plywood and once assembled forms a rigid structure; assembly only takes a couple of minutes. This is only the structure of the chair and padding still needs to be developed. Additionally it will need to be tested and all dimensions tweaked after doing a series of tests. This prototype took seven hours to layout on the plywood from full-scale drawings and 11 hours to cut all pieces using a table-saw, scroll-saw, jigsaw and drill. Using a CNC cutter, a full chair could be fabricated in approximately one hour. I plan on continuing to work with this design and work towards a final product, but chose to include this as part of my portfolio as I feel it is a good representation of how I go about designing a functional piece and an example of the type of projects I would like to pursue in the future.

Medium: Currently Plywood, but can be made out of a wide range.

Fabrication Method: Hand Cut (Production is Intended to use a CNC Cutter).

Design and Engineering Methods: SolidWorks Modeling, Hand Calculations and Sktechs.

Physical Dimensions: Width: 29", Length: 24", Height: 26".

Year: 2009 - ongoing.

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Assembly

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