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The thing that separates this wheelchair from the others is the wheels: yes there's an outer arc between each of the 6-8 spokes and yes the arcs form a circle (ie: the tire), but the arcs can be folded 180deg inwards such that the wheel is now a 6-8 point star with the spoke tips exposed. Thus the operator
can climb stairs and negotiate icy walkways and ramps with ease.
coming soon: Segway Wheelchair.
Coming sooner than you think.
http://video.google...lchair&hl=en&emb=1#
Segway wheelchair. [2 fries shy of a happy meal, Jan 18 2009]
[link]
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It took the 3D modeller upstairs a couple of gos, but I think I've got it now. A picture might help though if you can run one off. An animated GIF all the better |
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What I get is: say there are 6 spokes, each spoke supports a 1/6th arc of the full circle. This arc is physically separate from its neighbour arcs, and the connection at its midpoint (to the spoke) is a pivot. |
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One brief point: this will need to be a lot sturdier than the bicycle style wheels on the average wheelchair. In those, the weight of the chair/bicycle (at the hub) is supported by the hanging tension of the spokes above it, and proportionally by all the other spokes, and from there transferred around the tensile outer wheel to the ground. |
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This allows a much lighter structure than yours - you'll have all the weight on a single spoke/pivot/foot assembly. So at a minimum, each assembly will need to be as strong - and probably heavier - than an entire bicycle wheel. |
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Still, [+]; given the right engineering, I reckon it oughta work as you describe. |
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Psst! [BunsenHoneydew], you typed [+], but you forgot to do [+]! |
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wow, I was gonna do <Segway link>, glad I didn't. |
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[BH] for silhouette illustration a foreshortened symmetrical oak leaf maybe. I don't see any change of tension distribution though. |
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Without a tensile and contiguous outer rim, this is a compressive structure with all weight supported on the bottom pedicule, and transferred by a single spoke from the hub - or in the best case, by at most two or three. Still, you would need to design the load factors to the single-spoke case. The other spokes can play no part in supporting the chair, as far as I can tell. |
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I did have an error in my visualisation. I saw each spoke/pedicule as a T-structure, with the arc of wheel as the top stroke of the T, a single piece that pivots, turning one end inwards and one end out. Re-reading the original post, I see //the wheel is now a 6-8 point star with the spoke tips exposed//, ie two pieces that both fold inwards either side of the spoke, forming a V. |
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I still think my point about weight loading applies, unless [FT] or someone else can explain how the load can be shared around a broken rim. |
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But the rim isn't broken. The spokes are still joined by the arcs, except they (the arcs) a're now concave instead of convex. |
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Though I do notice some trivial(?) angular loading on the hub I didn't see before. |
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I've trawled through Wikipedia to no avail, what is the class of geometric shapes produced, anybody ? |
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